Serotonergic neurotoxicity of methylenedioxyamphetamine and methylenedioxymetamphetamine

Psychedelics in Psychiatry: Neuroplastic, Immunomodulatory, and Neurotransmitter Mechanisms

Mounting evidence suggests safety and efficacy of psychedelic compounds as potential novel therapeutics in psychiatry. Ketamine has been approved by the Food and Drug Administration in a new class of antidepressants, and 3,4-methylenedioxymethamphetamine (MDMA) is undergoing phase III clinical trials for post-traumatic stress disorder. Psilocybin and lysergic acid diethylamide (LSD) are being investigated in several phase II and phase I clinical trials. Hence, the concept of psychedelics as therapeutics may be incorporated into modern society. Here, we discuss the main known neurobiological therapeutic mechanisms of psychedelics, which are thought to be mediated by the effects of these compounds on the serotonergic (via 5-HT_2A and 5-HT_1A receptors) and glutamatergic [via N-methyl-d-aspartate (NMDA) and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors] systems. We focus on 1) neuroplasticity mediated by the modulation of mammalian target of rapamycin-, brain-derived neurotrophic factor-, and early growth response-related pathways; 2) immunomodulation via effects on the hypothalamic-pituitary-adrenal axis, nuclear factor ĸB, and cytokines such as tumor necrosis factor-α and interleukin 1, 6, and 10 production and release; and 3) modulation of serotonergic, dopaminergic, glutamatergic, GABAergic, and norepinephrinergic receptors, transporters, and turnover systems. We discuss arising concerns and ways to assess potential neurobiological changes, dependence, and immunosuppression. Although larger cohorts are required to corroborate preliminary findings, the results obtained so far are promising and represent a critical opportunity for improvement of pharmacotherapies in psychiatry, an area that has seen limited therapeutic advancement in the last 20 years. Studies are underway that are trying to decouple the psychedelic effects from the therapeutic effects of these compounds. SIGNIFICANCE STATEMENT: Psychedelic compounds are emerging as potential novel therapeutics in psychiatry. However, understanding of molecular mechanisms mediating improvement remains limited. This paper reviews the available evidence concerning the effects of psychedelic compounds on pathways that modulate neuroplasticity, immunity, and neurotransmitter systems. This work aims to be a reference for psychiatrists who may soon be faced with the possibility of prescribing psychedelic compounds as medications, helping them assess which compound(s) and regimen could be most useful for decreasing specific psychiatric symptoms.

Caffeine promotes hyperthermia and serotonergic loss following co-administration of the substituted amphetamines, MDMA (“Ecstasy”) and MDA (“Love”)

The present study determined the effect of caffeine co-administration on the core body temperature response and long-term serotonin (5-HT) loss induced by methylenedioxymethamphetamine (MDMA; "Ecstasy") and its metabolite methylenedioxyamphetamine (MDA; "Love") to rats. In group-housed animals, caffeine (10 mg/kg) enhanced the acute toxicity of MDMA (15 mg/kg) and MDA (7.5 mg/kg), resulting in an exaggerated hyperthermic response (+2 degrees C for 5 h following MDMA and +1.5 degrees C for 3 h following MDA) when compared to MDMA (+1 degree C for 3 h) and MDA (+1 degree C for 1 h) alone. Co-administration of caffeine with MDMA or MDA was also associated with increased lethality. To reduce the risk of lethality, doses of MDMA and MDA were reduced in further experiments and the animals were housed individually. To examine the effects of repeated administration, animals received MDMA (10 mg/kg) or MDA (5 mg/kg) with or without caffeine (10 mg/kg) twice daily for 4 consecutive days. MDMA and MDA alone induced hypothermia (fall of 1 to 2 degrees C) over the 4 treatment days. Co-administration of caffeine with MDMA or MDA resulted in hyperthermia (increase of up to 2.5 degrees C) following acute administration compared to animals treated with caffeine or MDMA/MDA alone. This hyperthermic response to caffeine and MDMA was not observed with repeated administration, unlike caffeine + MDA, where hyperthermia was obtained over the 4 day treatment period. In addition, 4 weeks after the last treatment, co-administration of caffeine with MDA (but not MDMA) induced a reduction in 5-HT and 5-hydroxyindole acetic acid (5-HIAA) concentrations in frontal cortex (to 61% and 58% of control, respectively), hippocampus (48% and 60%), striatum (79% and 64%) and amygdala (63% and 37%). However, when caffeine (10 mg/kg) and MDMA (2.5 mg/kg) were co-administered four times daily for 2 days to group-housed animals, both hyperthermia and hippocampal 5-HT loss were observed (reduced to 68% of control). Neither MDMA nor MDA alone induced a significant reduction in regional 5-HT or 5-HIAA concentrations following repeated administration. In conclusion, caffeine promotes the acute and long-term toxicity associated with MDMA and MDA. This is a serious drug interaction, which could have important acute and long-term health consequences for recreational drug users.

Human pharmacology of MDMA: pharmacokinetics, metabolism, and disposition

MDMA (3,4-methylenedioxymethamphetamine, ecstasy) is a widely misused psychostimulant drug abused among large segments of the young population. Pharmacologically it displays effects related to amphetamine-type drugs and a set of distinctive effects (closeness to others, facilitation to interpersonal relationship, and empathy) that have been named by some authors "entactogen" properties. MDMA is a potent releaser and/or reuptake inhibitor of presynaptic serotonin (5-HT), dopamine (DA), and norepinephrine (NE). These actions result from the interaction of MDMA with the membrane transporters involved in neurotransmitter reuptake and vesicular storage systems. The most frequent effects after MDMA/ecstasy administration are euphoria, well-being, happiness, stimulation, increased energy, extroversion, feeling close to others, increased empathy, increased sociability, enhanced mood, mild perceptual disturbances, changed perception of colors and sounds, somatic symptoms related to its cardiovascular and autonomic effects (blood pressure and heart rate increase, mydriasis), and moderate derealization but not hallucinations. Acute toxic effects are related to its pharmacologic actions. The serotonin syndrome (increased muscle rigidity, hyperreflexia, and hyperthermia), among others, is characteristic of acute toxicity episodes. MDMA metabolism is rather complex and includes 2 main metabolic pathways: (1) O-demethylenation followed by catechol-O-methyltransferase (COMT)-catalyzed methylation and/or glucuronide/sulfate conjugation; and (2) N-dealkylation, deamination, and oxidation to the corresponding benzoic acid derivatives conjugated with glycine. The fact that the polymorphic enzyme CYP2D6 partially regulates the O-demethylenation pathway prompted some expectations that subjects displaying the poor metabolizer phenotype may be at higher risk of acute toxicity episodes. In this metabolic pathway a mechanism-based inhibition of the enzyme operates because the formation of an enzyme-metabolite complex that renders all subjects, independently of genotype, phenotypically poor metabolizers after the administration of 2 consecutive doses. Therefore, the impact of CYP2D6 pharmacogenetics on acute toxicity is limited. One of the interesting features of MDMA metabolism is its potential involvement in the development of mid- to long-term neurotoxic effects as a result of progressive neurodegeneration of the serotonergic neurotransmission system.

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.

Methylenendioxyamphetamine produces serotonin nerve terminal loss and diminished behavioural and neurochemical responses to the antidepressant fluoxetine

The effect of prior exposure to methylenedioxyamphetamine (MDA) on behavioural and neurochemical responses to fluoxetine were assessed in a rat model of antidepressant action. MDA (7.5 mg/kg, i.p.) was administered to rats twice daily for 4 consecutive days, and 4 weeks later the behavioural effect of fluoxetine (5 or 20 mg/kg; i.p. x 3) was examined in the modified rat forced-swimming test. In addition, the ability of fluoxetine to reduce serotonin (5-HT) metabolism was measured as an index of its efficacy in inhibiting 5-HT reuptake in vivo. In vehicle-treated rats, fluoxetine (5 and 20 mg/kg) produced a characteristic increase in swimming behaviour in the forced-swimming test. In contrast, fluoxetine-induced swimming was markedly attenuated in MDA-treated rats. MDA pretreatment resulted in 5-HT nerve terminal degeneration, indicated by reduced 5-HT and 5-HIAA concentrations in the frontal cortex, amygdala and hippocampus, and reduced [3H]paroxetine binding in the frontal cortex. In vehicle-treated rats, fluoxetine (5 and 20 mg/kg) decreased 5-HT metabolism (5-HIAA : 5-HT ratio) in the frontal cortex, amygdala and hippocampus. MDA pretreatment attenuated the ability of fluoxetine to reduce 5-HT metabolism in all brain regions examined. These findings are the first to demonstrate that prior exposure to the methylenedioxy-substituted amphetamine MDA results in diminished responsiveness to the antidepressant fluoxetine.