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(Redirected from Alpha-Methyldopamine)
Chemical compound
Pharmaceutical compound
Interest in α-methyldopamine lies in the fact that 3,4-methylenedioxyamphetamine (MDA) and 3,4-methylenedioxy-N-methylamphetamine (MDMA) may not themselves be responsible for their serotonergicneurotoxicity, as an intracerebroventricular injection does not appear to cause neurotoxicity. While many studies suggest excitotoxicity or oxidative stress as likely mechanisms, which may be an effect of MDMA itself, this has led to the search for other mechanisms for the observed toxicity of serotonin axons and subsequent reduction in serotonin (5-HT) and 5-HIAA (its major metabolite in the body) in vivo following administration. A common theory follows that a metabolite of MDA and MDMA in the periphery must be responsible, and several have been cited as responsible. Although α-methyldopamine is widely cited as the source of this neurotoxicity in a number of lay sources, McCann, et al. (1991), demonstrated that the major metabolites α-methyldopamine and 3-O-methyl-α-methyldopamine (3-O-Me-α-MeDA or HMA) did not produce neurotoxicity.
It was first demonstrated, in 1978, by Conway et al. and possibly others that, while α-methyldopamine caused acute decreases in the levels of neuronaldopamine, in some areas of the brain in excess of 75%, levels returned to baseline within 12 hours, indicating that α-methyldopamine could not be responsible for the toxic effects observed.
However, the story complicates as α-methyldopamine readily oxidizes to the o-quinone and reacts with endogenousantioxidants in the body, such as glutathione (GSH). It was demonstrated by Miller et al. (1997), that 5-(glutathion-S-yl)-α-methyldopamine and 5-(N-acetylcystein-S-yl)-α-methyldopamine produced similar effects to the parent compound, but did not induce neurotoxicity when injected intracerebroventricularly. However, the derivative metabolite 2,5-bis-(glutathion-S-yl)-α-methyldopamine (injected at ~1.5 times the usual per-kg MDMA dose) did in fact induce neurotoxicity, providing initial evidence that this metabolite may be the source of neuronal toxicity following the administration of MDA and MDMA, and the subsequent reduction in serotonergic axons.
In spite of the above, there is also evidence that metabolites may not be involved in the neurotoxicity of MDMA or related drugs and that the neurotoxicity is intrinsic to their mechanism of action, specifically simultaneous induction of serotonin and dopamine release. Accordingly, while single injections of MDMA directly into the brain have not been found to produce neurotoxicity, slow infusions of MDMA into the brain over 1 hour do result in signs of neurotoxicity.
^ Monks TJ, Jones DC, Bai F, Lau SS (April 2004). "The role of metabolism in 3,4-(+)-methylenedioxyamphetamine and 3,4-(+)-methylenedioxymethamphetamine (ecstasy) toxicity". Ther Drug Monit. 26 (2): 132–136. doi:10.1097/00007691-200404000-00008. PMID15228153.
Conway EL, Louis WJ, Jarrott B (December 1978). "Acute and chronic administration of alpha-methyldopa: regional levels of endogenous and alpha-methylated catecholamines in rat brain". European Journal of Pharmacology. 52 (3–4): 271–280. doi:10.1016/0014-2999(78)90279-0. PMID729639.
Miller RT, Lau SS, Monks TJ (April 1997). "2,5-Bis-(glutathion-S-yl)-alpha-methyldopamine, a putative metabolite of (+/-)-3,4-methylenedioxyamphetamine, decreases brain serotonin concentrations". European Journal of Pharmacology. 323 (2–3): 173–180. doi:10.1016/S0014-2999(97)00044-7. PMID9128836.
^ Baggott, Matthew; Mendelson, John (2001). "Does MDMA Cause Brain Damage?". In Holland, J. (ed.). Ecstasy: The Complete Guide: A Comprehensive Look at the Risks and Benefits of MDMA. Inner Traditions/Bear. pp. 110–145, 396–404. ISBN978-0-89281-857-0. Retrieved 24 November 2024. While a single injection of MDMA into the brain (intracerebroventricularly) had no effect on TPH activity, slow infusion of 1 mg/kg MDMA into the brain over 1 hr produced enough oxidative stress to acutely reduce TPH activity (Schmidt and Taylor 1988). The acute decrease in TPH activity is an early effect of MDMA and can be measured at post 15 min (Stone et al. 1989b). TPH inactivation can also be produced by non-neurotoxic MDMA doses (Schmidt and Taylor 1988; Stone et al. 1989a; Stone et al. 1989b). It therefore appears that MDMA rapidly induces oxidative stress but only produces neurotoxicity when endogenous free radical scavenging systems are overwhelmed.
