Back عامل إطلاق مونوامين Arabic Agente liberador de monoamina Spanish Agente de liberação de monoamina Portuguese Агент, высвобождающий моноамин Russian Agens otpuštanja Serbo-Croatian Releaser SIMPLE Agens otpuštanja Serbian 單胺釋放劑 Chinese
A monoamine releasing agent (MRA), or simply monoamine releaser, is a drug that induces the release of one or more monoamine neurotransmitters from the presynaptic neuron into the synapse, leading to an increase in the extracellular concentrations of the neurotransmitters and hence enhanced signaling by those neurotransmitters.[2][3][4][1][5] The monoamine neurotransmitters include serotonin, norepinephrine, and dopamine; MRAs can induce the release of one or more of these neurotransmitters.[2][3][4][1][5]
MRAs work by reversing the direction of the monoamine transporters (MATs), including the serotonin transporter (SERT), norepinephrine transporter (NET), and/or dopamine transporter (DAT), causing them to promote efflux of non-vesicular cytoplasmic monoamine neurotransmitter rather than reuptake of synaptic monoamine neurotransmitter.[5][6][1][7] Many, but not all MRAs, also reverse the direction of the vesicular monoamine transporter 2 (VMAT2), thereby additionally resulting in efflux of vesicular monoamine neurotransmitter into the cytoplasm.[5]
A variety of different classes of drugs induce their effects in the body and/or brain via the release of monoamine neurotransmitters.[2][3] These include psychostimulants and appetite suppressants acting as dopamine and norepinephrine releasers like amphetamine, methamphetamine, and phentermine; sympathomimetic agents acting as norepinephrine releasers like ephedrine and pseudoephedrine; non-stimulant appetite suppressants acting as serotonin releasers like fenfluramine and chlorphentermine; and entactogens acting as releasers of serotonin and/or other monoamines like MDMA.[2][3] Trace amines like phenethylamine and tryptamine, as well as the monoamine neurotransmitters themselves, are endogenous MRAs.[2][3][4] It is thought that monoamine release by endogenous mediators may play some physiological regulatory role.[4]
MRAs must be distinguished from monoamine reuptake inhibitors (MRIs) and monoaminergic activity enhancers (MAEs), which similarly increase synaptic monoamine neurotransmitter levels and enhance monoaminergic signaling but work via distinct mechanisms.[5][1][8][9]
- ^ a b c d e Heal DJ, Smith SL, Gosden J, Nutt DJ (June 2013). "Amphetamine, past and present--a pharmacological and clinical perspective". Journal of Psychopharmacology. 27 (6): 479–496. doi:10.1177/0269881113482532. PMC 3666194. PMID 23539642.
Although the pharmacological effect of amphetamine is predominantly mediated by monoamine release, this mechanism is complemented by reuptake inhibition [...] that combine additively or synergistically to augment synaptic monoamine concentrations. The description of amphetamine as a 'monoamine reuptake inhibitor' often causes some confusion, and the difference between the mechanisms of amphetamine, which is a competitive reuptake transport substrate, and classical reuptake inhibitors is illustrated in Figure 3. [...] d-Amphetamine is generally accepted to be a weak dopamine reuptake inhibitor with a Ki value of ~100 nM, a moderately potent inhibitor of noradrenaline reuptake (Ki = 40–50 nM) and a very weak inhibitor of 5-HT reuptake (Ki = 1.4-3.8 µM). [...] the efficacy of amphetamine relative to other indirect monoamine agonists, for example classical reuptake inhibitors, can only be estimated from in vivo experiments. [...] [d- and l-Amphetamine] dose-dependently increased the extracellular concentrations of noradrenaline in the prefrontal cortex (PFC) and dopamine in the striatum. The pharmacodynamics of their effects are typical of those reported for monoamine releasing agents, i.e. a fast onset of action with peak increases of noradrenaline and dopamine efflux occurring at 30–45 min, large effects (400–450% of baseline for noradrenaline and 700–1500% of baseline for dopamine), with a relatively rapid decline after the maximum (Figure 4). [...] the magnitude of the increases produced by amphetamine's isomers are greater than those reported for classical reuptake inhibitors such as atomoxetine or bupropion, and there is no dose-effect ceiling to amphetamine's actions [...] The primary action of amphetamine is to increase synaptic concentrations of monoamine neurotransmitters, thereby indirectly enhancing noradrenergic, dopaminergic neurotransmission in the CNS.
- ^ a b c d e Rothman RB, Baumann MH (October 2003). "Monoamine transporters and psychostimulant drugs". European Journal of Pharmacology. 479 (1–3): 23–40. doi:10.1016/j.ejphar.2003.08.054. PMID 14612135.
- ^ a b c d e Rothman RB, Baumann MH (2006). "Therapeutic potential of monoamine transporter substrates". Current Topics in Medicinal Chemistry. 6 (17): 1845–1859. doi:10.2174/156802606778249766. PMID 17017961.
- ^ a b c d Blough B (July 2008). "Dopamine-releasing agents" (PDF). In Trudell ML, Izenwasser S (eds.). Dopamine Transporters: Chemistry, Biology and Pharmacology. Hoboken [NJ]: Wiley. pp. 305–320. ISBN 978-0-470-11790-3. OCLC 181862653. OL 18589888W.
- ^ a b c d e Reith ME, Blough BE, Hong WC, Jones KT, Schmitt KC, Baumann MH, et al. (February 2015). "Behavioral, biological, and chemical perspectives on atypical agents targeting the dopamine transporter". Drug and Alcohol Dependence. 147: 1–19. doi:10.1016/j.drugalcdep.2014.12.005. PMC 4297708. PMID 25548026.
Converging lines of evidence have solidified the notion that DA releasers are substrates of the transporter and once translocated, they reverse the normal direction of transporter flux to evoke release of endogenous neurotransmitters. The nature of this reversal is not well understood, but the entire process is primarily transporter-dependent and requires elevated intracellular sodium concentrations, phosphorylation of DAT, and possible involvement of transporter oligomers (Khoshbouei et al., 2003, 2004; Sitte and Freissmuth, 2010). [...] A library of approximately 1400 phenethylamine compounds (PAL compounds) has been screened using these protocols. Among the active compounds,the smaller DAT ligands were found to be DA releasers while the sterically larger compounds were DAT uptake inhibitors. [...] Generic pharmacophore for biogenic amine transporter ligands. Note that transportable substrate ligands exhibit size constraints defined by the red circle. Functional groups attached to the nitrogen, α-carbon or phenyl ring that extend beyond the "edge" of the pharmacophore will generate partial substrates, transporter blockers or be inactive. [...] phenmetrazine was found to be completely inactive at VMAT2 indicating that a direct interaction of the releaser with VMAT2 is not required for inducing neurotransmitter efflux into the extracellular space (Partilla et al., 2006). Phentermine and benzylpiperazine were also found in the same study to lack VMAT2 activity (Table 5).
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