Serotonergic neurotoxicity of 3,4-(+/-)-methylenedioxyamphetamine and 3,4-(+/-)-methylendioxymethamphetamine (ecstasy) is potentiated by inhibition of gamma-glutamyl transpeptidase

Psychedelic Therapy: A Primer for Primary Care Clinicians-3,4-Methylenedioxy-methamphetamine (MDMA)

BACKGROUND

After becoming notorious for its use as a party drug in the 1980s, 3,4-methylenedioxy-methampetamine (MDMA), also known by its street names "molly" and "ecstasy," has emerged as a powerful treatment for post-traumatic stress disorder (PTSD).

AREAS OF UNCERTAINTY

There are extensive data about the risk profile of MDMA. However, the literature is significantly biased. Animal models demonstrating neurotoxic or adverse effects used doses well beyond the range that would be expected in humans (up to 40 mg/kg in rats compared with roughly 1-2 mg/kg in humans). Furthermore, human samples often comprise recreational users who took other substances in addition to MDMA, in uncontrolled settings.

THERAPEUTIC ADVANCES

Phase III clinical trials led by the Multidisciplinary Association for Psychedelic Studies (MAPS) have shown that MDMA-assisted psychotherapy has an effect size of d = 0.7-0.91, up to 2-3 times higher than the effect sizes of existing antidepressant treatments. 67%-71% of patients who undergo MDMA-assisted psychotherapy no longer meet the diagnostic criteria for PTSD within 18 weeks. We also describe other promising applications of MDMA-assisted psychotherapy for treating alcohol use disorder, social anxiety, and other psychiatric conditions.

LIMITATIONS

Thus far, almost all clinical trials on MDMA have been sponsored by a single organization, MAPS. More work is needed to determine whether MDMA-assisted therapy is more effective than existing nonpharmacological treatments such as cognitive behavioral therapy.

CONCLUSIONS

Phase III trials suggest that MDMA is superior to antidepressant medications for treating PTSD. Now that MAPS has officially requested the Food and Drug Administration to approve MDMA as a treatment for PTSD, legal MDMA-assisted therapy may become available as soon as 2024.

Locomotor effects of 3,4-methylenedioxymethamphetamine (MDMA) and its deuterated form in mice: psychostimulant effects, stereotypy, and sensitization

RATIONALE

There is a renewed interest in the use of 3,4-methylenedioxymethamphetamine (MDMA) for treating psychiatric conditions. Although MDMA has entered phase II clinical trials and shows promise as an adjunct treatment, there is an extensive literature detailing the potential neurotoxicity and adverse neurobehavioral effects associated with MDMA use. Previous research indicates that the adverse effects of MDMA may be due to its metabolism into reactive catechols that can enter the brain and serve directly as neurotoxicants. One approach to mitigate MDMA's potential for adverse effects is to reduce O-demethylation by deuterating the methylenedioxy ring of MDMA. There are no studies that have evaluated the effects of deuterating MDMA on behavioral outcomes.

OBJECTIVES

The purpose of the present study was to assess the motor-stimulant effects of deuterated MDMA (d2-MDMA) and compare them to MDMA in male mice.

METHODS

Two experiments were performed to quantify mouse locomotor activity and to vary the drug administration regimen (single bolus administration or cumulative administration).

RESULTS

The results of Experiments 1 and 2 indicate that d2-MDMA is less effective at eliciting horizontal locomotion than MDMA; however, the differences between the compounds diminish as the number of cumulative administrations increase. Both d2-MDMA and MDMA can elicit sensitized responses, and these effects cross-sensitize to the prototypical drug of abuse methamphetamine. Thus, d2-MDMA functions as a locomotor stimulant similar to MDMA, but, depending on the dosing regimen, may be less susceptible to inducing sensitization to stereotyped movements.

CONCLUSIONS

These findings indicate that d2-MDMA is behaviorally active and produces locomotor effects that are similar to MDMA, which warrant additional assessments of d2-MDMA's behavioral and physiological effects to determine the conditions under which this compound may serve as a relatively safer alternative to MDMA for clinical use.

Amphetamine-related drugs neurotoxicity in humans and in experimental animals: Main mechanisms

Amphetamine-related drugs, such as 3,4-methylenedioxymethamphetamine (MDMA) and methamphetamine (METH), are popular recreational psychostimulants. Several preclinical studies have demonstrated that, besides having the potential for abuse, amphetamine-related drugs may also elicit neurotoxic and neuroinflammatory effects. The neurotoxic potentials of MDMA and METH to dopaminergic and serotonergic neurons have been clearly demonstrated in both rodents and non-human primates. This review summarizes the species-specific cellular and molecular mechanisms involved in MDMA and METH-mediated neurotoxic and neuroinflammatory effects, along with the most important behavioral changes elicited by these substances in experimental animals and humans. Emphasis is placed on the neuropsychological and neurological consequences associated with the neuronal damage. Moreover, we point out the gap in our knowledge and the need for developing appropriate therapeutic strategies to manage the neurological problems associated with amphetamine-related drug abuse.

The mixture of "ecstasy" and its metabolites impairs mitochondrial fusion/fission equilibrium and trafficking in hippocampal neurons, at in vivo relevant concentrations

3,4-Methylenedioxymethamphetamine (MDMA; "ecstasy") is a potentially neurotoxic recreational drug of abuse. Though the mechanisms involved are still not completely understood, formation of reactive metabolites and mitochondrial dysfunction contribute to MDMA-related neurotoxicity. Neuronal mitochondrial trafficking, and their targeting to synapses, is essential for proper neuronal function and survival, rendering neurons particularly vulnerable to mitochondrial dysfunction. Indeed, MDMA-associated disruption of Ca(2+) homeostasis and ATP depletion have been described in neurons, thus suggesting possible MDMA interference on mitochondrial dynamics. In this study, we performed real-time functional experiments of mitochondrial trafficking to explore the role of in situ mitochondrial dysfunction in MDMA's neurotoxic actions. We show that the mixture of MDMA and six of its major in vivo metabolites, each compound at 10μM, impaired mitochondrial trafficking and increased the fragmentation of axonal mitochondria in cultured hippocampal neurons. Furthermore, the overexpression of mitofusin 2 (Mfn2) or dynamin-related protein 1 (Drp1) K38A constructs almost completely rescued the trafficking deficits caused by this mixture. Finally, in hippocampal neurons overexpressing a Mfn2 mutant, Mfn2 R94Q, with impaired fusion and transport properties, it was confirmed that a dysregulation of mitochondrial fission/fusion events greatly contributed to the reported trafficking phenotype. In conclusion, our study demonstrated, for the first time, that the mixture of MDMA and its metabolites, at concentrations relevant to the in vivo scenario, impaired mitochondrial trafficking and increased mitochondrial fragmentation in hippocampal neurons, thus providing a new insight in the context of "ecstasy"-induced neuronal injury.

Catechol-o-methyltransferase and 3,4-({+/-})-methylenedioxymethamphetamine toxicity

Metabolism of 3,4-(±)-methylenedioxymethamphetamine (MDMA) is necessary to elicit its neurotoxic effects. Perturbations in phase I and phase II hepatic enzymes can alter the neurotoxic profile of systemically administered MDMA. In particular, catechol-O-methyltransferase (COMT) plays a critical role in determining the fraction of MDMA that is converted to potentially neurotoxic metabolites. Thus, cytochrome P450 mediated demethylenation of MDMA, or its N-demethylated metabolite, 3,4-(±)-methylenedioxyamphetamine, give rise to the catechols, N-methyl-α-methyldopamine and α-methyldopamine, respectively. Methylation of these catechols by COMT limits their oxidation and conjugation to glutathione, a process that ultimately gives rise to neurotoxic metabolites. We therefore determined the effects of modulating COMT, a critical enzyme involved in determining the fraction of MDMA that is converted to potentially neurotoxic metabolites, on MDMA-induced toxicity. Pharmacological inhibition of COMT in the rat potentiated MDMA-induced serotonin deficits and exacerbated the acute MDMA-induced hyperthermic response. Using a genetic mouse model of COMT deficiency, in which mice lack a functional COMT gene, such mice displayed greater reductions in dopamine concentrations relative to their wild-type (WT) counterparts. Neither WT nor COMT deficient mice were susceptible to MDMA-induced decreases in serotonin concentrations. Interestingly, mice devoid of COMT were far more susceptible to the acute hyperthermic effects of MDMA, exhibiting greater increases in body temperature that ultimately resulted in death. Our findings support the view that COMT plays a pivotal role in determining the toxic response to MDMA.

Psychostimulants and brain dysfunction: a review of the relevant neurotoxic effects

Psychostimulants abuse is a major public concern because is associated with serious health complications, including devastating consequences on the central nervous system (CNS). The neurotoxic effects of these drugs have been extensively studied. Nevertheless, numerous questions and uncertainties remain in our understanding of these toxic events. Thus, the purpose of the present manuscript is to review cellular and molecular mechanisms that might be responsible for brain dysfunction induced by psychostimulants. Topics reviewed include some classical aspects of neurotoxicity, such as monoaminergic system and mitochondrial dysfunction, oxidative stress, excitotoxicity and hyperthermia. Moreover, recent literature has suggested new phenomena regarding the toxic effects of psychostimulants. Thus, we also reviewed the impact of these drugs on neuroinflammatory response, blood-brain barrier (BBB) function and neurogenesis. Assessing the relative importance of these mechanisms on psychostimulants-induced brain dysfunction presents an exciting challenge for future research efforts. This article is part of the Special Issue entitled 'CNS Stimulants'.

Glial cell response to 3,4-(+/-)-methylenedioxymethamphetamine and its metabolites

3,4-(±)-Methylenedioxymethamphetamine (MDMA) and 3,4-(±)-methylenedioxyamphetamine (MDA), a primary metabolite of MDMA, are phenylethylamine derivatives that cause serotonergic neurotoxicity. Although several phenylethylamine derivatives activate microglia, little is known about the effects of MDMA on glial cells, and evidence of MDMA-induced microglial activation remains ambiguous. We initially determined microglial occupancy status of the parietal cortex in rats at various time points following a single neurotoxic dose of MDMA (20mg/kg, SC). A biphasic microglial response to MDMA was observed, with peak microglial occupancy occurring 12- and 72-h post-MDMA administration. Because direct injection of MDMA into the brain does not produce neurotoxicity, the glial response to MDMA metabolites was subsequently examined in vivo and in vitro. Rats were treated with MDA (20mg/kg, SC) followed by ex vivo biopsy culture to determine the activation of quiescent microglia. A reactive microglial response was observed 72 h after MDA administration that subsided by 7 days. In contrast, intracerebroventricular (ICV) administration of MDA failed to produce a microglial response. However, thioether metabolites of MDA derived from α-methyldopamine (α-MeDA) elicited a robust microglial response following icv injection. We subsequently determined the direct effects of various MDMA metabolites on primary cultures of E18 hippocampal mixed glial and neuronal cells. 5-(Glutathion-S-yl)-α-MeDA, 2,5-bis-(glutathion-S-yl)-α-MeDA, and 5-(N-acetylcystein-S-yl)-α-MeDA all stimulated the proliferation of glial fibrillary acidic protein-positive astrocytes at a dose of 10 µM. The findings indicate that glial cells are activated in response to MDMA/MDA and support a role for thioether metabolites of α-MeDA in the neurotoxicity.

"Ecstasy"-induced toxicity in SH-SY5Y differentiated cells: role of hyperthermia and metabolites

3,4-Methylenedioxymethamphetamine (MDMA; "ecstasy") is a recreational hallucinogenic drug of abuse known to elicit neurotoxic properties. Hepatic formation of neurotoxic metabolites is thought to play a major role in MDMA-related neurotoxicity, though the mechanisms involved are still unclear. Here, we studied the neurotoxicity mechanisms and stability of MDMA and 6 of its major human metabolites, namely α-methyldopamine (α-MeDA) and N-methyl-α-methyldopamine (N-Me-α-MeDA) and their correspondent glutathione (GSH) and N-acetyl-cysteine (NAC) conjugates, under normothermic (37 °C) or hyperthermic conditions (40 °C), using cultured SH-SY5Y differentiated cells. We showed that MDMA metabolites exhibited toxicity to SH-SY5Y differentiated cells, being the GSH and NAC conjugates more toxic than their catecholic precursors and MDMA. Furthermore, whereas the toxicity of the catechol metabolites was potentiated by hyperthermia, NAC-conjugated metabolites revealed higher toxicity under normothermia and GSH-conjugated metabolites-induced toxicity was temperature-independent. Moreover, a time-dependent decrease in extracellular concentration of MDMA metabolites was observed, which was potentiated by hyperthermia. The antioxidant NAC significantly protected against the neurotoxic effects of MDMA metabolites. MDMA metabolites increased intracellular glutathione levels, though depletion in thiol content was observed in MDMA-exposed cells. Finally, the neurotoxic effects induced by the MDMA metabolite N-Me-α-MeDA involved caspase 3 activation. In conclusion, this study evaluated the stability of MDMA metabolites in vitro, and demonstrated that the catechol MDMA metabolites and their GSH and NAC conjugates, rather than MDMA itself, exhibited neurotoxic actions in SH-SY5Y differentiated cells, which were differently affected by hyperthermia, thus highlighting a major role for reactive metabolites and hyperthermia in MDMA's neurotoxicity.

Lost in translation: preclinical studies on 3,4-methylenedioxymethamphetamine provide information on mechanisms of action, but do not allow accurate prediction of adverse events in humans

3,4-Methylenedioxymethamphetamine (MDMA) induces both acute adverse effects and long-term neurotoxic loss of brain 5-HT neurones in laboratory animals. However, when choosing doses, most preclinical studies have paid little attention to the pharmacokinetics of the drug in humans or animals. The recreational use of MDMA and current clinical investigations of the drug for therapeutic purposes demand better translational pharmacology to allow accurate risk assessment of its ability to induce adverse events. Recent pharmacokinetic studies on MDMA in animals and humans are reviewed and indicate that the risks following MDMA ingestion should be re-evaluated. Acute behavioural and body temperature changes result from rapid MDMA-induced monoamine release, whereas long-term neurotoxicity is primarily caused by metabolites of the drug. Therefore acute physiological changes in humans are fairly accurately mimicked in animals by appropriate dosing, although allometric dosing calculations have little value. Long-term changes require MDMA to be metabolized in a similar manner in experimental animals and humans. However, the rate of metabolism of MDMA and its major metabolites is slower in humans than rats or monkeys, potentially allowing endogenous neuroprotective mechanisms to function in a species specific manner. Furthermore acute hyperthermia in humans probably limits the chance of recreational users ingesting sufficient MDMA to produce neurotoxicity, unlike in the rat. MDMA also inhibits the major enzyme responsible for its metabolism in humans thereby also assisting in preventing neurotoxicity. These observations question whether MDMA alone produces long-term 5-HT neurotoxicity in human brain, although when taken in combination with other recreational drugs it may induce neurotoxicity.

Pro-oxidant effects of Ecstasy and its metabolites in mouse brain synaptosomes

BACKGROUND AND PURPOSE

3,4-Methylenedioxymethamphetamine (MDMA or 'Ecstasy') is a worldwide major drug of abuse known to elicit neurotoxic effects. The mechanisms underlying the neurotoxic effects of MDMA are not clear at present, but the metabolism of dopamine and 5-HT by monoamine oxidase (MAO), as well as the hepatic biotransformation of MDMA into pro-oxidant reactive metabolites is thought to contribute to its adverse effects.

EXPERIMENTAL APPROACH

Using mouse brain synaptosomes, we evaluated the pro-oxidant effects of MDMA and its metabolites, α-methyldopamine (α-MeDA), N-methyl-α-methyldopamine (N-Me-α-MeDA) and 5-(glutathion-S-yl)-α-methyldopamine [5-(GSH)-α-MeDA], as well as those of 5-HT, dopamine, l-DOPA and 3,4-dihydroxyphenylacetic acid (DOPAC).

KEY RESULTS

5-HT, dopamine, l-DOPA, DOPAC and MDMA metabolites α-MeDA, N-Me-α-MeDA and 5-(GSH)-α-MeDA, concentration- and time-dependently increased H(2) O(2 ) production, which was significantly reduced by the antioxidants N-acetyl-l-cysteine (NAC), ascorbic acid and melatonin. From experiments with MAO inhibitors, it was observed that H(2) O(2) generation induced by 5-HT was totally dependent on MAO-related metabolism, while for dopamine, it was a minor pathway. The MDMA metabolites, dopamine, l-DOPA and DOPAC concentration-dependently increased quinoproteins formation and, like 5-HT, altered the synaptosomal glutathione status. Finally, none of the compounds modified the number of polarized mitochondria in the synaptosomal preparations, and the compounds' pro-oxidant effects were unaffected by prior mitochondrial depolarization, excluding a significant role for mitochondrial-dependent mechanisms of toxicity in this experimental model.

CONCLUSIONS AND IMPLICATIONS

MDMA metabolites along with high levels of monoamine neurotransmitters can be major effectors of neurotoxicity induced by Ecstasy.

Inhibition of 3,4-methylenedioxymethamphetamine metabolism leads to marked decrease in 3,4-dihydroxymethamphetamine formation but no change in serotonin neurotoxicity: implications for mechanisms of neurotoxicity

3,4-Methylenedioxymethamphetamine (MDMA)'s O-demethylenated metabolite, 3,4-dihydroxymethamphetamine (HHMA), has been hypothesized to serve as a precursor for the formation of toxic catechol-thioether metabolites (e.g., 5-N-acetylcystein-S-yl-HHMA) that mediate MDMA neurotoxicity. To further test this hypothesis, HHMA formation was blocked with dextromethorphan (DXM), which competitively inhibits cytochrome P450 enzyme-mediated O-demethylenation of MDMA to HHMA. In particular, rats were randomly assigned to one of four treatment groups (n = 9-12 per group): (1) Saline/MDMA; (2) DXM/MDMA; (3) DXM/Saline; (4) Saline/Saline. During drug exposure, time-concentration profiles of MDMA and its metabolites were determined, along with body temperature. One week later, brain serotonin (5-HT) neuronal markers were measured in the same animals. DXM did not significantly alter core temperature in MDMA-treated animals. A large (greater than 70%) decrease in HHMA formation had no effect on the magnitude of MDMA neurotoxicity. These results cast doubt on the role of HHMA-derived catechol-thioether metabolites in the mechanism of MDMA neurotoxicity.

Gamma-glutamyl compounds: substrate specificity of gamma-glutamyl transpeptidase enzymes

Gamma-glutamyl compounds include antioxidants, inflammatory molecules, drug metabolites, and neuroactive compounds. Two cell surface enzymes that metabolize gamma-glutamyl compounds have been identified: gamma-glutamyl transpeptidase (GGT1) and gamma-glutamyl leukotrienase (GGT5). There is controversy in the literature regarding the substrate specificity of these enzymes. To address this issue, we have developed a method for comprehensive kinetic analysis of compounds as substrates for GGT enzymes. Our assay is sensitive, quantitative, and conducted at physiological pH. We evaluated a series of gamma-glutamyl compounds as substrates for human GGT1 and human GGT5. The K(m) value for reduced glutathione was 11μM for both GGT1 and GGT5. However, the K(m) values for oxidized glutathione were 9μM for GGT1 and 43μM for GGT5. Our data show that the K(m) values for leukotriene C(4) are equivalent for GGT1 and GGT5 at 10.8 and 10.2μM, respectively. This assay was also used to evaluate serine-borate, a well-known inhibitor of GGT1, which was 8-fold more potent in inhibiting GGT1 than in inhibiting GGT5. These data provide essential information regarding the target enzymes for developing treatments for inflammatory diseases such as asthma and cardiovascular disease in humans. This assay is invaluable for studies of oxidative stress, drug metabolism, and other pathways that involve gamma-glutamyl compounds.

Mechanisms of MDMA (ecstasy)-induced oxidative stress, mitochondrial dysfunction, and organ damage

Despite numerous reports about the acute and sub-chronic toxicities caused by MDMA (3,4-methylenedioxymethamphetamine, ecstasy), the underlying mechanism of organ damage is poorly understood. The aim of this review is to present an update of the mechanistic studies on MDMA-mediated organ damage partly caused by increased oxidative/nitrosative stress. Because of the extensive reviews on MDMA-mediated oxidative stress and tissue damage, we specifically focus on the mechanisms and consequences of oxidative-modifications of mitochondrial proteins, leading to mitochondrial dysfunction. We briefly describe a method to systematically identify oxidatively-modified mitochondrial proteins in control and MDMA-exposed rats by using biotin-N-maleimide (biotin-NM) as a sensitive probe for oxidized proteins. We also describe various applications and advantages of this Cys-targeted proteomics method and alternative approaches to overcome potential limitations of this method in studying oxidized proteins from MDMA-exposed tissues. Finally we discuss the mechanism of synergistic drug-interaction between MDMA and other abused substances including alcohol (ethanol) as well as application of this redox-based proteomics method in translational studies for developing effective preventive and therapeutic agents against MDMA-induced organ damage.

Neurotoxic thioether adducts of 3,4-methylenedioxymethamphetamine identified in human urine after ecstasy ingestion

3,4-Methylenedioxymethamphetamine (MDMA, Ecstasy) is a widely misused synthetic amphetamine derivative and a serotonergic neurotoxicant in animal models and possibly humans. The underlying mechanism of neurotoxicity involves the formation of reactive oxygen species although their source remains unclear. It has been postulated that MDMA-induced neurotoxicity is mediated via the formation of bioreactive metabolites. In particular, the primary catechol metabolites, 3,4-dihydroxymethamphetamine (HHMA) and 3,4-dihydroxyamphetamine (HHA), subsequently cause the formation of glutathione and N-acetylcysteine conjugates, which retain the ability to redox cycle and are serotonergic neurotoxicants in rats. Although the presence of such metabolites has been recently demonstrated in rat brain microdialysate, their formation in humans has not been reported. The present study describes the detection of 5-(N-acetylcystein-S-yl)-3,4-dihydroxymethamphetamine (N-Ac-5-Cys-HHMA) and 5-(N-acetylcystein-S-yl)-3,4-dihydroxyamphetamine (N-Ac-5-Cys-HHA) in human urine of 15 recreational users of MDMA (1.5 mg/kg) in a controlled setting. The results reveal that in the first 4 h after MDMA ingestion approximately 0.002% of the administered dose was recovered as thioether adducts. Genetic polymorphisms in CYP2D6 and catechol-O-methyltransferase expression, the combination of which are major determinants of steady-state levels of HHMA and 4-hydroxy-3-methoxyamphetamine, probably explain the interindividual variability seen in the recovery of N-Ac-5-Cys-HHMA and N-Ac-5-Cys-HHA. In summary, the formation of neurotoxic thioether adducts of MDMA has been demonstrated for the first time in humans. The findings lend weight to the hypothesis that the bioactivation of MDMA to neurotoxic metabolites is a relevant pathway to neurotoxicity in humans.

A novel, species-specific class of uncompetitive inhibitors of gamma-glutamyl transpeptidase

Expression of gamma-glutamyl transpeptidase (GGT) in tumors contributes to resistance to radiation and chemotherapy. GGT is inhibited by glutamine analogues that compete with the substrate for the gamma-glutamyl binding site. However, the glutamine analogues that have been evaluated in clinical trials are too toxic for use in humans. We have used high throughput screening to evaluate small molecules for their ability to inhibit GGT and have identified a novel class of inhibitors that are not glutamine analogues. These compounds are uncompetitive inhibitors, binding the gamma-glutamyl enzyme complex. OU749, the lead compound, has an intrinsic K(i) of 17.6 microm. It is a competitive inhibitor of the acceptor glycyl-glycine, which indicates that OU749 occupies the acceptor site while binding to the gamma-glutamyl substrate complex. OU749 is more than 150-fold less toxic than the GGT inhibitor acivicin toward dividing cells. Inhibition of GGT by OU749 is species-specific, inhibiting GGT isolated from human kidney with 7-10-fold greater potency than GGT isolated from rat or mouse kidney. OU749 does not inhibit GGT from pig cells. Human GGT expressed in mouse fibroblasts is inhibited by OU749 similarly to GGT from human cells, which indicates that the species specificity is determined by differences in the primary structure of the protein rather than species-specific, post-translational modifications. These studies have identified a novel class of inhibitors of GGT, providing the basis for further development of a new group of therapeutics that inhibit GGT by a mechanism distinct from the toxic glutamine analogues.

The relationship between core body temperature and 3,4-methylenedioxymethamphetamine metabolism in rats: implications for neurotoxicity

RATIONALE

A close relationship appears to exist between 3,4-methylenedioxymethamphetamine (MDMA)-induced changes in core body temperature and long-term serotonin (5-HT) loss.

OBJECTIVE

We investigated whether changes in core body temperature affect MDMA metabolism.

MATERIALS AND METHODS

Male Wistar rats were treated with MDMA at ambient temperatures of 15, 21.5, or 30 degrees C to prevent or exacerbate MDMA-induced hyperthermia. Plasma concentrations of MDMA and its main metabolites were determined for 6 h. Seven days later, animals were killed and brain indole content was measured.

RESULTS

The administration of MDMA at 15 degrees C blocked the hyperthermic response and long-term 5-HT depletion found in rats treated at 21.5 degrees C. At 15 degrees C, plasma concentrations of MDMA were significantly increased, whereas those of three of its main metabolites were reduced when compared to rats treated at 21.5 degrees C. By contrast, hyperthermia and indole deficits were exacerbated in rats treated at 30 degrees C. Noteworthy, plasma concentrations of MDMA metabolites were greatly enhanced in these animals. Instrastriatal perfusion of MDMA (100 microM for 5 h at 21 degrees C) did not potentiate the long-term depletion of 5-HT after systemic MDMA. Furthermore, interfering in MDMA metabolism using the catechol-O-methyltransferase inhibitor entacapone potentiated the neurotoxicity of MDMA, indicating that metabolites that are substrates for this enzyme may contribute to neurotoxicity.

CONCLUSIONS

This is the first report showing a direct relationship between core body temperature and MDMA metabolism. This finding has implications on both the temperature dependence of the mechanism of MDMA neurotoxicity and human use, as hyperthermia is often associated with MDMA use in humans.

On the role of tyrosine and peripheral metabolism in 3,4-methylenedioxymethamphetamine-induced serotonin neurotoxicity in rats

The mechanisms underlying 3,4-methylenedioxymethamphetamine (MDMA)-induced serotonergic (5-HT) toxicity remain unclear. It has been suggested that MDMA depletes 5-HT by increasing brain tyrosine levels, which via non-enzymatic hydroxylation leads to DA-derived free radical formation. Because this hypothesis assumes the pre-existence of hydroxyl radicals, we hypothesized that MDMA metabolism into pro-oxidant compounds is the limiting step in this process. Acute hyperthermia, plasma tyrosine levels and concentrations of MDMA and its main metabolites were higher after a toxic (15 mg/kg i.p.) vs. a non-toxic dose of MDMA (7.5mg/kg i.p.). The administration of a non-toxic dose of MDMA in combination with l-tyrosine (0.2 mmol/kg i.p.) produced a similar increase in serum tyrosine levels to those found after a toxic dose of MDMA; however, brain 5-HT content remained unchanged. The non-toxic dose of MDMA combined with a high dose of tyrosine (0.5 mmol/kg i.p.), caused long-term 5-HT depletions in rats treated at 21.5 degrees C but not in those treated at 15 degrees C, conditions known to decrease MDMA metabolism. Furthermore, striatal perfusion of MDMA (100 microM for 5h) combined with tyrosine (0.5 mmol/kg i.p.) in hyperthermic rats did not cause 5-HT depletions. By contrast, rats treated with the non-toxic dose of MDMA under heating conditions or combined with entacapone or acivicin, which interfere with MDMA metabolism or increase brain MDMA metabolite availability respectively, showed significant reductions of brain 5-HT content. Altogether, these data indicate that although tyrosine may contribute to MDMA-induced toxicity, MDMA metabolism appears to be the limiting step.

Modulation of human multidrug resistance protein (MRP) 1 (ABCC1) and MRP2 (ABCC2) transport activities by endogenous and exogenous glutathione-conjugated catechol metabolites

Members of the multidrug resistance protein (MRP/ABCC) subfamily of ATP-binding cassette proteins transport a wide array of anionic compounds, including sulfate, glucuronide, and glutathione (GSH) conjugates. The present study tested the ATP-dependent vesicular transport of leukotriene C(4) and 17beta-estradiol 17-(beta-d-glucuronide) (E(2)17betaG) mediated by the MRP1 and MRP2 transporters in the presence of six potential modulators from three different classes of GSH-conjugated catechol metabolites: the ecstasy metabolite 5-(glutathion-S-yl)-N-methyl-alpha-methyldopamine (5-GS-N-Me-alpha-MeDA), the caffeic acid metabolite 2-(glutathion-S-yl)-caffeic acid (2-GS-CA), and four GSH conjugates of 2-hydroxy (OH) and 4-OH estrogens (GS estrogens). MRP1-mediated E(2)17betaG transport was inhibited in a competitive manner with a relative order of potency of GS estrogens (IC(50) <1 microM) > 2-GS-CA (IC(50) 3 microM) > 5-GS-N-Me-alpha-MeDA (IC(50) 31 microM). MRP2-mediated transport was inhibited with a similar order of potency, except the 2-hydroxy-4-(glutathion-S-yl)-estradiol and 4-hydroxy-2-(glutathion-S-yl)-estradiol conjugates were approximately 50- and 300-fold less potent, respectively. Transport activity was unaffected by N-acetylcysteine conjugates of N-Me-alpha-MeDA and CA. The position of GSH conjugation appears important as all four GS estrogen conjugates tested were potent inhibitors of MRP1 transport, but only the 2-hydroxy-1-(glutathion-S-yl)-estradiol and 2-hydroxy-1-(glutathion-S-yl)-estrone conjugates were potent inhibitors of MRP2-mediated transport. In conclusion, we have identified three new classes of MRP1 and MRP2 modulators and demonstrated that one of these, the estrogen conjugates, shows unanticipated differences in their interactions with the two transporters.

Accumulation of Neurotoxic Thioether Metabolites of 3,4-(±)-Methylenedioxymethamphetamine in Rat Brain

The serotonergic neurotoxicity of 3,4-(+/-)-methylenedioxymethamphetamine (MDMA) appears dependent upon systemic metabolism because direct injection of MDMA into the brain fails to reproduce the neurotoxicity. MDMA is demethylenated to the catechol metabolite N-methyl-alpha-methyldopamine (N-Me-alpha-MeDA). Thioether (glutathione and N-acetylcysteine) metabolites of N-Me-alpha-MeDA are neurotoxic and are present in rat brain following s.c. injection of MDMA. Because multidose administration of MDMA is typical of drug intake during rave parties, the present study was designed to determine the effects of multiple doses of MDMA on the concentration of neurotoxic thioether metabolites in rat brain. Administration of MDMA (20 mg/kg s.c.) at 12-h intervals for a total of four injections led to a significant accumulation of the N-Me-alpha-MeDA thioether metabolites in striatal dialysate. The area under the curve (AUC)(0-300 min) for 5-(glutathion-S-yl)-N-Me-alpha-MeDA increased 33% between the first and fourth injections and essentially doubled for 2,5-bis-(glutathion-S-yl)-N-Me-alpha-MeDA. Likewise, accumulation of the mercapturic acid metabolites was reflected by increases in the AUC(0-300 min) for both 5-(N-acetylcystein-S-yl)-N-Me-alpha-MeDA (35%) and 2,5-bis-(N-acetylcystein-S-yl)-N-Me-alpha-MeDA (85%), probably because processes for their elimination become saturated. Indeed, the elimination half-life of 5-(N-acetylcystein-S-yl)-N-Me-alpha-MeDA and 2,5-bis-(N-acetylcystein-S-yl)-N-Me-alpha-MeDA increased by 53 and 28%, respectively, between the first and third doses. Finally, although the C(max) values for the monothioether conjugates were essentially unchanged after each injection, the values increased by 38 and approximately 50% for 2,5-bis-(glutathion-S-yl)-N-Me-alpha-MeDA and 2,5-bis-(N-acetylcystein-S-yl)-N-Me-alpha-MeDA, respectively, between the first and fourth injections. The data indicate that neurotoxic metabolites of MDMA may accumulate in brain after multiple dosing.

3,4-Methylenedioxymethamphetamine (MDMA) neurotoxicity in rats: a reappraisal of past and present findings

RATIONALE

3,4-Methylenedioxymethamphetamine (MDMA) is a widely abused illicit drug. In animals, high-dose administration of MDMA produces deficits in serotonin (5-HT) neurons (e.g., depletion of forebrain 5-HT) that have been interpreted as neurotoxicity. Whether such 5-HT deficits reflect neuronal damage is a matter of ongoing debate.

OBJECTIVE

The present paper reviews four specific issues related to the hypothesis of MDMA neurotoxicity in rats: (1) the effects of MDMA on monoamine neurons, (2) the use of "interspecies scaling" to adjust MDMA doses across species, (3) the effects of MDMA on established markers of neuronal damage, and (4) functional impairments associated with MDMA-induced 5-HT depletions.

RESULTS

MDMA is a substrate for monoamine transporters, and stimulated release of 5-HT, NE, and DA mediates effects of the drug. MDMA produces neurochemical, endocrine, and behavioral actions in rats and humans at equivalent doses (e.g., 1-2 mg/kg), suggesting that there is no reason to adjust doses between these species. Typical doses of MDMA causing long-term 5-HT depletions in rats (e.g., 10-20 mg/kg) do not reliably increase markers of neurotoxic damage such as cell death, silver staining, or reactive gliosis. MDMA-induced 5-HT depletions are accompanied by a number of functional consequences including reductions in evoked 5-HT release and changes in hormone secretion. Perhaps more importantly, administration of MDMA to rats induces persistent anxiety-like behaviors in the absence of measurable 5-HT deficits.

CONCLUSIONS

MDMA-induced 5-HT depletions are not necessarily synonymous with neurotoxic damage. However, doses of MDMA which do not cause long-term 5-HT depletions can have protracted effects on behavior, suggesting even moderate doses of the drug may pose risks.

Causes and consequences of methamphetamine and MDMA toxicity

Methamphetamine (METH) and its derivative 3,4-methylenedioxymethamphetamine (MDMA; ecstasy) are 2 substituted amphetamines with very high abuse liability in the United States. These amphetamine-like stimulants have been associated with loss of multiple markers for dopaminergic and serotonergic terminals in the brain. Among other causes, oxidative stress, excitotoxicity and mitochondrial dysfunction appear to play a major role in the neurotoxicity produced by the substituted amphetamines. The present review will focus on these events and how they interact and converge to produce the monoaminergic depletions that are typically observed after METH or MDMA administration. In addition, more recently identified consequences of METH or MDMA-induced oxidative stress, excitotoxicity, and mitochondrial dysfunction are described in relation to the classical markers of METH-induced damage to dopamine terminals.

Ecstasy: are animal data consistent between species and can they translate to humans?

The number of 3,4-methylenedioxymethamphetamine (ecstasy or MDMA) animal research articles is rapidly increasing and yet studies which place emphasis on the clinical significance are limited due to a lack of reliable human data. MDMA produces an acute, rapid release of brain serotonin and dopamine in experimental animals and in the rat this is associated with increased locomotor activity and the serotonin behavioural syndrome in rats. MDMA causes dose-dependent hyperthermia, which is potentially fatal, in humans, primates and rodents. Subsequent serotonergic neurotoxicity has been demonstrated by biochemical and histological studies and is reported to last for months in rats and years in non-human primates. Relating human data to findings in animals is complicated by reports that MDMA exposure in mice produces selective long-term dopaminergic impairment with no effect on serotonin. This review compares data obtained from animal and human studies and examines the acute physiological, behavioural and biochemical effects of MDMA as well as the long-term behavioural effects together with serotonergic and dopaminergic impairments. Consideration is also given to the role of neurotoxic metabolites and the influence of age, sex and user groups on the long-term actions of MDMA.

(±)-3,4-Methylenedioxymethamphetamine Administration to Rats Does Not Decrease Levels of the Serotonin Transporter Protein or Alter Its Distribution between Endosomes and the Plasma Membrane

We showed that the serotonin (5-HT) neurotoxin 5,7-dihydroxytryptamine (5,7-DHT) reduces brain tissue 5-HT, decreases expression of 5-HT transporter (SERT) protein, and increases expression of glial fibrillary acidic protein (GFAP). In contrast, doses of (+/-)-3,4-methylenedioxymethamphetamine (MDMA) that decrease brain tissue 5-HT fail to alter expression of SERT or GFAP. Using a new and highly sensitive anti-SERT antibody, we determined whether MDMA alters the subcellular distribution of SERT protein by measuring SERT expression in endosomes and plasma membranes 2 weeks after MDMA administration. Rat brain tissues (caudate, cortex, and hippocampus) were collected 3 days and 2 weeks after MDMA (7.5 mg/kg i.p., every 2 h x 3 doses) or 5,7-DHT (150 microg/rat i.c.v.) administration. Representative results from cortex are as follows. At both 3 days and 2 weeks postinjection, MDMA decreased tissue 5-HT (65%) and had no effect on GFAP expression. MDMA increased heat shock protein 32 (HSP32; a marker for microglial activation) expression (30%) at 3 days, but not 2 weeks. MDMA did not alter SERT expression at either time point and did not alter SERT levels in either endosomes or plasma membranes (2 weeks). 5,7-DHT decreased tissue 5-HT (80%), increased HSP32 expression at both time points (about 50%), and increased GFAP expression at 2 weeks (40%). 5,7-DHT decreased SERT expression (33%) at 2 weeks, but not at 3 days. These findings indicate that a dosing regimen of MDMA that depletes brain 5-HT does not alter SERT protein expression or the distribution of SERT between endosomes and the plasma membrane and does not produce detectable evidence for neurotoxicity.

Metabolism is required for the expression of ecstasy-induced cardiotoxicity in vitro

Cardiovascular complications associated with 3,4-methylenedioxymethamphetamine (MDMA, ecstasy) abuse have increasingly been reported. The indirect effect of MDMA mediated by a sustained high level of circulating biogenic amines may contribute to the cardiotoxic effects, but other factors, like the direct toxic effects of MDMA and its metabolites in cardiac cells, remain to be investigated. Thus, the objective of the present in vitro study was to evaluate the potential cardiotoxic effects of MDMA and its major metabolites 3,4-methylenedioxyamphetamine (MDA), N-methyl-alpha-methyldopamine (N-Me-alpha-MeDA), and alpha-methyldopamine (alpha-MeDA) using freshly isolated adult rat cardiomyocytes. The cell suspensions were incubated with these compounds in the final concentrations of 0.1, 0.2, 0.4, 0.8, and 1.6 mM for 4 h. alpha-MeDA, N-Me-alpha-MeDA, and their respective aminochromes (oxidation products) were quantified in cell suspensions by HPLC-DAD. The toxic effects were evaluated at hourly intervals for 4 h by measuring the percentage of cells with normal morphology, glutathione (GSH), and glutathione disulfide (GSSG); intracellular Ca(2+), ATP, and ADP; and the cellular activities of glutathione peroxidase, glutathione reductase, and glutathione-S-transferase. No toxic effects were found after exposure of rat cardiomyocytes to MDMA or MDA at any of the tested concentrations for 4 h. In contrast, their catechol metabolites N-Me-alpha-MeDA and alpha-MeDA induced significant toxicity in rat cardiomyocytes. The toxic effects were characterized by a loss of normal cell morphology, which was preceded by a loss of GSH homeostasis due to conjugation of GSH with N-Me-alpha-MeDA and alpha-MeDA, sustained increase of intracellular Ca(2+) levels, ATP depletion, and decreases in the antioxidant enzyme activities. The oxidation of N-Me-alpha-MeDA and alpha-MeDA into the toxic compounds N-methyl-alpha-methyldopaminochrome and alpha-methyldopaminochrome, respectively, was also verified in cell suspensions incubated with these MDMA metabolites. The results obtained in this study provide evidence that the metabolism of MDMA into N-Me-alpha-MeDA and alpha-MeDA is required for the expression of MDMA-induced cardiotoxicity in vitro, being N-Me-alpha-MeDA the most toxic of the studied metabolites.

Serotonergic Neurotoxic Metabolites of Ecstasy Identified in Rat Brain

The selective serotonergic neurotoxicity of 3,4-methylenedioxyamphetamine (MDA) and 3,4-methylenedioxymethamphetamine (MDMA, ecstasy) depends on their systemic metabolism. We have recently shown that inhibition of brain endothelial cell gamma-glutamyl transpeptidase (gamma-GT) potentiates the neurotoxicity of both MDMA and MDA, indicating that metabolites that are substrates for this enzyme contribute to the neurotoxicity. Consistent with this view, glutathione (GSH) and N-acetylcysteine conjugates of alpha-methyl dopamine (alpha-MeDA) are selective neurotoxicants. However, neurotoxic metabolites of MDMA or MDA have yet to be identified in brain. Using in vivo microdialysis coupled to liquid chromatography-tandem mass spectroscopy and a high-performance liquid chromatography-coulometric electrode array system, we now show that GSH and N-acetylcysteine conjugates of N-methyl-alpha-MeDA are present in the striatum of rats administered MDMA by subcutaneous injection. Moreover, inhibition of gamma-GT with acivicin increases the concentration of GSH and N-acetylcysteine conjugates of N-methyl-alpha-MeDA in brain dialysate, and there is a direct correlation between the concentrations of metabolites in dialysate and the extent of neurotoxicity, measured by decreases in serotonin (5-HT) and 5-hydroxyindole acetic (5-HIAA) levels. Importantly, the effects of acivicin are independent of MDMA-induced hyperthermia, since acivicin-mediated potentiation of MDMA neurotoxicity occurs in the context of acivicin-mediated decreases in body temperature. Finally, we have synthesized 5-(N-acetylcystein-S-yl)-N-methyl-alpha-MeDA and established that it is a relatively potent serotonergic neurotoxicant. Together, the data support the contention that MDMA-mediated serotonergic neurotoxicity is mediated by the systemic formation of GSH and N-acetylcysteine conjugates of N-methyl-alpha-MeDA (and alpha-MeDA). The mechanisms by which such metabolites access the brain and produce selective serotonergic neurotoxicity remain to be determined.

Neurotoxicity of MDMA (ecstasy): the limitations of scaling from animals to humans

Several studies suggest that MDMA-induced acute toxicity and long-term neurotoxicity is dependent on the metabolic disposition of MDMA. Differences in MDMA metabolism among animal species might therefore account for different sensitivities to its neurotoxic effects. The kinetic parameters of enzymes that regulate the formation of neurotoxic metabolites of MDMA differ among species, as does the ability of MDMA to self-inhibit these enzymes and the degree of genetic polymorphisms exhibited by these enzymes. Such features limit allometric scaling across animal models.

Thioether metabolites of 3,4-methylenedioxyamphetamine and 3,4-methylenedioxymethamphetamine inhibit human serotonin transporter (hSERT) function and simultaneously stimulate dopamine uptake into hSERT-expressing SK-N-MC cells

3,4-Methylenedioxyamphetamine (MDA) and 3,4-methyl-enedioxymethamphetamine (MDMA, ecstasy) are widely abused amphetamine derivatives that target the serotonin system. The serotonergic neurotoxicity of MDA and MDMA seems dependent on their systemic metabolism. 5-(Glutathion-S-yl)-alpha-methyldopamine [5-(GSyl)-alpha-MeDA] and 2,5-bis(glutathion-S-yl)-alpha-methyldopamine [2,5-bis(GSyl)-alpha-MeDA], metabolites of MDA and MDMA, are also selective serotonergic neurotoxicants and produce behavioral and neurochemical changes similar to those seen with MDA and MDMA. We now show that 5-(GSyl)-alpha-MeDA and 2,5-bis(GSyl)-alpha-MeDA are more potent than MDA and MDMA (K(i) = 69, 50, 107, and 102 microM, respectively) at inhibiting 5-hy-droxytryptamine (serotonin) transport into SK-N-MC cells transiently transfected with the human serotonin transporter (hSERT). Moreover, 5-(GSyl)-alpha-MeDA and 2,5-bis(GSyl)-alpha-MeDA simultaneously stimulated dopamine (DA) transport into the hSERT-expressing cells, an effect attenuated by fluoxetine, indicating that stimulated DA transport was hSERT-dependent. Finally, 5-(GSyl)-alpha-MeDA and 2,5-bis(GSyl)-alpha-MeDA, and to a lesser extent MDA and MDMA, induced a concentration and time-dependent increase in reactive oxygen species (ROS) in both hSERT and human dopamine transporter-transfected cells. Fluoxetine attenuated the increase in ROS generation in hSERT-expressing cells. The results are consistent with the view that the serotonergic neurotoxicity of MDA and MDMA may be mediated by the metabolism-dependent stimulation of DA transport into hSERT-expressing cells and ROS generation by redox active catechol-thioether metabolites and DA.

Acute and long-term effects of MDMA on cerebral dopamine biochemistry and function

RATIONALE AND OBJECTIVES

The majority of experimental and clinical studies on the pharmacology of 3,4-methylenedioxymethamphetamine (MDMA, ecstasy) tend to focus on its action on 5-HT biochemistry and function. However, there is considerable evidence for MDMA having marked acute effects on dopamine release. Furthermore, while MDMA produces long-term effects on 5-HT neurones in most species examined, in mice its long-term effects appear to be restricted to the dopamine system. The objective of this review is to examine the actions of MDMA on dopamine biochemistry and function in mice, rats, guinea pigs, monkeys and humans.

RESULTS AND DISCUSSION

MDMA appears to produce a major release of dopamine from its nerve endings in all species investigated. This release plays a significant role in the expression of many of the behaviours that occur, including behavioural changes, alterations of the mental state in humans and the potentially life-threatening hyperthermia that can occur. While MDMA appears to be a selective 5-HT neurotoxin in most species examined (rats, guinea pigs and primates), it is a selective dopamine neurotoxin in mice. Selectivity may be a consequence of what neurotoxic metabolites are produced (which may depend on dosing schedules), their selectivity for monoamine nerve endings, or the endogenous free radical trapping ability of specific nerve endings, or both. We suggest more focus be made on the actions of MDMA on dopamine neurochemistry and function to provide a better understanding of the acute and long-term consequences of using this popular recreational drug.

The Role of Metabolism in 3,4-(±)-Methylenedioxyamphetamine and 3,4-(±)-Methylenedioxymethamphetamine (Ecstasy) toxicity

3,4-Methylenedioxyamphetamine (MDA) and 3,4-methylenedioxymethamphetamine (MDMA, ecstasy) are ring-substituted amphetamine derivatives with stimulant and hallucinogenic properties. The recreational use of these amphetamines, especially MDMA, is prevalent despite warnings of irreversible damage to the central nervous system. MDA and MDMA are primarily serotonergic neurotoxicants. Because (1) neither MDA nor MDMA produces neurotoxicity when injected directly into brain, (2) intracerebroventricular (i.c.v.) administration of some major metabolites of MDA and MDMA fails to reproduce their neurotoxicity, (3) alpha-methyldopamine (alpha-MeDA) and N-methyl-alpha-MeDA are metabolites of both MDA and MDMA, (4) alpha-MeDA and N-methyl-alpha-MeDA are readily oxidized to the corresponding ortho-quinones, which can undergo conjugation with glutathione (GSH), and (5) quinone thioethers exhibit a variety of toxicologic activities, we initiated studies on the potential role of thioether metabolites of alpha-MeDA and N-methyl-alpha-MeDA in the neurotoxicity of MDA and MDMA. Our studies have revealed that the thioether conjugates stimulate the acute release of serotonin, dopamine, and norepinephrine and produce a behavioral response commensurate with the "serotonin syndrome." Direct injection of the conjugates into rat brain also produces long-term depletions in serotonin (5-HT) concentrations, elevations in GFAP expression, and activation of microglial cells. The data are consistent with the view that thioether metabolites of alpha-MeDA and N-methyl-alpha-MeDA contribute to the neurotoxicity of the parent amphetamines.

3,4-methylenedioxymethamphetamine (MDMA) administration to rats decreases brain tissue serotonin but not serotonin transporter protein and glial fibrillary acidic protein

Previous experiments conducted in this laboratory showed that administration of high-dose D-fenfluramine (D-FEN) and p-chloroamphetamine (PCA) decreased 5-HT transporter (SERT) binding and tissue 5-HT by 30-60% in caudate and whole brain tissue 2 days and 2 weeks after drug administration. However, protein expression as determined by Western blot analysis did not change in either tissue or time point, except for a 30% decrease in the caudate 2 days after PCA administration. In the present study, we studied the effect of MDMA and 5,7-dihydroxytryptamine (5,7-DHT) on tissue 5-HT levels and the protein expression level of SERT and glial fibrillary acidic protein (GFAP), a validated neurotoxicity marker.

HYPOTHESIS

MDMA administration decreases SERT expression.

METHODS

Two weeks after MDMA administration (7.5 mg/kg i.p., q 2 h x 3 doses) or 2 weeks after i.c.v. administration of 5,7,-DHT (150 microg/rat), male Sprague-Dawley rats were sacrificed and the caudate, cortex, and hippocampal tissue collected. Western blots for SERT and GFAP were generated using published methods. Tissue 5-HT levels were determined by HPLC coupled to electrochemical detection.

RESULTS

MDMA treatment decreased tissue 5-HT in cortex, hippocampus, and caudate by about 50%. However, MDMA treatment had no significant effect on expression level of SERT and GFAP in any brain region. In contrast, 5,7-DHT reduced tissue 5-HT by more than 90%, decreased SERT protein expression by 20-35%, and increased GFAP by 30-39%.

CONCLUSION

These data suggest the MDMA treatment regimen used here does not cause degeneration of 5-HT nerve terminals. Viewed collectively with our previous results and other published data, these data indicate that MDMA-induced persistent 5-HT depletion may occur in the absence of axotomy.

Serotonin neurotoxins--past and present

Autoxidation pathways and redox reactions of dihydroxytryptamines (5,6- and 5,7-DHT) and of 6-hydroxydopamine (6-OH-DA) are illustrated, and their potential role in aminergic neurotoxicity is discussed. It is proposed that certain aspects of the cytotoxicity of 6-OH-DA and of the DHTs, namely redox cycling of their quinone- and quinoneimine-intermediates as a source of free radicals, may also apply to quinoidal reactive intermediates and to glutathionyl- or cysteinyl conjugates ("thioether adducts") of o-dihydroxylated (catechol-like) metabolites of certain substituted amphetamines (of methylenedioxymethamphetamine (MDMA) and of methylenedioxyamphetamine (MDA)). Despite similarities in their primary interaction with the plasmalemmal (serotonergic transporter/dopamine transporter, SERT/DAT) and vesicular monoamine transporters (VMAT2), MDMA and fenfluramine (N-ethyl-meta-trifluoromethamphetamine, Fen) differ substantially in many aspects of their metabolism, pharmacokinetics, pharmacology, and neurotoxicology profile; the consequences of these differences for neuronal response patterns and long-term survival prospects are not yet fully understood. However, sustained hyperthermia appears to be a critical factor in these differences. Methodological requirements for adequate detection and description of pre- and postsynaptic forms of drug-induced neurotoxicity are exemplified using recently published accounts. The inclusion of microglial markers into research strategies has widened contemporary pathogenetic concepts on methamphetamine (MA)-induced neurotoxicity as an example of inflammatory neurodegeneration, thus complementing the traditional ROS and RNS-dependent stress models. Amphetamine-type neurotoxicity studies may assist in elaborating of preventive strategies for human neurodegenerative disorders.

Synthesis, in vitro formation, and behavioural effects of glutathione regioisomers of alpha-methyldopamine with relevance to MDA and MDMA (ecstasy)

Administration of 3,4-methylenedioxymethamphetamine (MDMA) or 3,4-methylenedioxyamphetamine (MDA) to rats produces serotonergic nerve terminal degeneration. However, they are not neurotoxic when injected directly into the brain, suggesting the requirement for peripheral metabolism of MDMA to a neurotoxic metabolite. Alpha-methyldopamine (alpha-MeDA) is a major metabolite of MDA. There are indications that a glutathione metabolite of alpha-MeDA and/or 3,4-dihydroxymethamphetamine may be responsible for the neurotoxicity and some of the behavioural effects produced by MDMA and/or MDA. The present study details the synthesis, purification and separation of the 5-(glutathion-S-yl)-alpha-MeDA and 6-(glutathion-S-yl)-alpha-MeDA regioisomers of alpha-MeDA. Incubation of MDA with human liver microsomes demonstrated that production of both glutathione adducts are related to cytochrome P450 2D6 isoform activity. Following intracerebroventricular administration (180 nmol) of either GSH adduct into Dark Agouti or Sprague-Dawley rats only 5-(glutathion-S-yl)-alpha-MeDA produced behavioural effects characterised by hyperactivity, teeth chattering, tremor/trembling, head weaving, splayed posture, clonus and wet dog shakes. Pre-treatment with a dopamine receptor antagonist (haloperidol, 0.25 mg/kg; i.p.) attenuated hyperactivity, teeth chattering, low posture and clonus and potentiated splayed postural effects. These results indicate that MDA can be converted into two glutathione regioisomers by human liver microsomes, but only the 5-(glutathion-S-yl)-alpha-MeDA adduct is behaviourally active in the rat.

The pharmacology and clinical pharmacology of 3,4-methylenedioxymethamphetamine (MDMA, "ecstasy")

The amphetamine derivative (+/-)-3,4-methylenedioxymethamphetamine (MDMA, ecstasy) is a popular recreational drug among young people, particularly those involved in the dance culture. MDMA produces an acute, rapid enhancement in the release of both serotonin (5-HT) and dopamine from nerve endings in the brains of experimental animals. It produces increased locomotor activity and the serotonin behavioral syndrome in rats. Crucially, it produces dose-dependent hyperthermia that is potentially fatal in rodents, primates, and humans. Some recovery of 5-HT stores can be seen within 24 h of MDMA administration. However, cerebral 5-HT concentrations then decline due to specific neurotoxic damage to 5-HT nerve endings in the forebrain. This neurodegeneration, which has been demonstrated both biochemically and histologically, lasts for months in rats and years in primates. In general, other neurotransmitters appear unaffected. In contrast, MDMA produces a selective long-term loss of dopamine nerve endings in mice. Studies on the mechanisms involved in the neurotoxicity in both rats and mice implicate the formation of tissue-damaging free radicals. Increased free radical formation may result from the further breakdown of MDMA metabolic products. Evidence for the occurrence of MDMA-induced neurotoxic damage in human users remains equivocal, although some biochemical and functional data suggest that damage may occur in the brains of heavy users. There is also some evidence for long-term physiological and psychological changes occurring in human recreational users. However, such evidence is complicated by the lack of knowledge of doses ingested and the fact that many subjects studied are or have been poly-drug users.

Analysis of ecstasy (MDMA)-induced transcriptional responses in the rat cortex

3,4-methylenedioxymethamphetamine (MDMA, ecstasy) is a popular drug of abuse. MDMA is pharmacologically classified as an entactogen because of its affinities to classical hallucinogens and stimulants. Oral ingestion of a single dose of the drug is associated with euphoria, elevated self-confidence, and heightened sensory awareness in humans. Evidence for neurotoxicity in the human serotonin (5-HT) system has been provided. In rats, a single injection of MDMA induces hyperthermia and formation of reactive oxygen species. These effects may cause MDMA-associated, long-term 5-HT depletion, with the cortex being quite sensitive to the biochemical effects of MDMA. It has been suggested that these MDMA effects may be associated with molecular changes in this brain region. To test these ideas, we have made use of the cDNA array analysis, which can provide a more global view of the molecular changes secondary to MDMA injections. Our results show that the genes regulated by MDMA encode proteins that belong to signaling pathways, transcription regulators, or xenobiotic metabolism. Our observations indicate that cortical cells respond to the acute administration of MDMA by modulating transcription of several genes that might lead to long-term changes in the brain.

A review of the common properties of drugs with idiosyncratic hepatotoxicity and the "multiple determinant hypothesis" for the manifestation of idiosyncratic drug toxicity

Idiosyncratic drug toxicity is generally believed to be a phenomenon that cannot be readily evaluated experimentally. Reasons for this difficulty include the following: 1. It is a rare event (<1/5,000) and therefore impossible to be studied in clinical trials; 2. It is a human-specific event not detectable in experimental animals. To aid the understanding of idiosyncratic toxicity and to develop an experimental strategy for this phenomenon, a hypothesis is proposed. The hypothesis states that the low frequency of idiosyncratic drug toxicity is due to the requirements for the occurrence of multiple critical and discrete events, with the probability for the occurrence of idiosyncratic drug toxicity as a product of the probabilities of each event. The key determinants of these critical events are proposed to be: 1. Chemical properties; 2. exposure; 3. environmental factors; and 4. genetic factors. Based on this hypothesis, idiosyncratic drug toxicity can be evaluated experimentally via studying these key determinants. The chemical properties critical to idiosyncratic drug toxicity are identified via a review of the common properties of drugs that cause idiosyncratic liver toxicity. These properties include: 1. Formation of reactive metabolites. 2. Metabolism by P450 isoforms. 3. Preponderance of P450 inducers, and 4. Occurrence of clinically significant pharmacokinetic interactions with co-administered drugs. Based on this review, it is proposed that these common properties may be useful experimental endpoints for the prediction and therefore avoidance of the selection of drug candidates with idiosyncratic drug toxicity for further development.

Protection against 3,4-methylenedioxymethamphetamine-induced neurodegeneration produced by glutathione depletion in rats is mediated by attenuation of hyperthermia

3,4-Methylenedioxymethamphetamine (MDMA) administration produces neurotoxic degeneration of serotonin terminals in rat brain. These effects occur only after systemic administration and not after central injection, suggesting that peripheral metabolism, possibly hepatic, is required for toxicity. Glutathione is one of the principal cellular defence mechanisms, but conjugation with glutathione can, on some occasions, increase the reactivity of certain molecules. Previous studies have shown that central administration of glutathione adducts of a MDMA metabolite produces a neurotoxicity profile similar to that of systemic MDMA. In the present study, depletion of peripheral (hepatic) glutathione by 43% with dl-buthionine-(S,R)-sulfoximine (an inhibitor of glutathione synthesis) did not attenuate MDMA-induced neurotoxicity as indicated by the 34% loss of [(3) H]paroxetine binding to the serotonin uptake sites in Dark Agouti rats treated with the inhibitor. However, a more profound depletion (92%) of glutathione by diethylmaleate (direct conjugation) administration significantly reduced the serotonergic neurotoxicity produced by MDMA. This depletion protocol also attenuated the hyperthermic response to MDMA. A combination protocol utilising both buthionine-(S,R)-sulfoximine and diethylmaleate that did not alter the hyperthermic response of the rats given MDMA also failed to attenuate the neurotoxicity. These findings indicate that glutathione depletion does not offer specific protection against MDMA-induced serotonin neurotoxicity in Dark Agouti rats.

In vitro neuronal and vascular responses to 5-HT in rats chronically exposed to MDMA

1. This study examined the effects of chronic exposure of rats to 3,4-methylenedioxymethamphetamine (MDMA) on [(3)H]5-hydroxytryptamine ([(3)H]5-HT) re-uptake into purified rat brain synaptosomes, 5-HT-induced isometric contraction of aortic rings and [(3)H]5-HT re-uptake into rat aorta. 2. Rats were administered MDMA (20 mg kg(-1) i.p.) twice daily over 4 days. One, 7, 14 or 21 days post treatment, whole brain synaptosomes and descending thoracic aortic rings were prepared for investigation. 3. Chronic MDMA treatment significantly reduced the maximum rate (V(max)) of specific high-affinity [(3)H]5-HT re-uptake 1 day after treatment and for up to 21 days post-final administration of MDMA. Direct application of MDMA (100 microM) abolished synaptosomal re-uptake of [(3)H]5-HT in vitro. 4. Chronic MDMA administration significantly reduced the maximum contraction (E(max)) to 5-HT at 1 and 7 days after treatment, but not at 14 or 21 days. 5. Chronic MDMA administration had no effect on sodium-dependent [(3)H]5-HT re-uptake into aorta 1 day after treatment, nor did 100 microM MDMA have any direct effect on [(3)H]5-HT uptake into aortic rings in vitro. 6. These results show, for the first time, an altered responsiveness of vascular tissue to MDMA after chronic administration. In addition, they demonstrate a difference in the sensitivity of central and peripheral 5-HT uptake systems to chronic MDMA exposure, and suggest that the action of MDMA in the cardiovascular system does not arise from a direct effect of MDMA on peripheral 5-HT transport.