Article

Melatonin and synthetic melatonergic agonists: actions and metabolism in the central nervous system.

Johann Friedrich Blumenbach Institute of Zoology and Anthropology, University of Goettingen, Goettingen, Germany.
Central Nervous System Agents in Medicinal Chemistry(Formerly Current Medicinal Chemistry - Central Nervous System Agents) 05/2012; 12(3):189-216.
Source: PubMed

ABSTRACT The CNS is both source and target of melatonin. This methoxyindole formed in the pineal gland is also produced in other CNS regions and additionally enters the brain by uptake from the circulation as well as via the pineal recess. The mammalian circadian pacemaker, the suprachiasmatic nucleus (SCN), not only controls the pineal, but also receives a feedback information on darkness. Two G protein-coupled melatonin receptors, MT1 and MT2, are responsible for the transduction of many melatonergic actions. High receptor densities are especially found in the SCN, but their presence at lower expression levels in other areas is functionally important. Various metabolites and analogs are formed in the CNS, such as N-acetylserotonin, 5-methoxytryptamine, 5-methoxytryptophol, 5-methoxylated kynuramines, and even 6-sulfatoxymelatonin. The chronobiological effects of melatonin go beyond the resetting of a single circadian oscillator. They contribute to phase relationships between oscillatory subsets and are required for robust rhythm amplitudes. CNS effects of melatonin comprise sleep initiation, antiexcitatory, antiepileptic, antinociceptive, anxiolytic, proneurotrophic, antiinflammatory, antioxidant and other neuroprotective actions. The role as a sleep-promoting compound, which is limited by its short half-life in the circulation, has led to the development of controlled-release formulations and of various synthetic agonists, such as ramelteon, agomelatine, tasimelteon, TIK-301, UCM765 and UCM924. Their differences concerning receptor affinities, preferences for receptor subtypes, and pharmacokinetics are discussed, as well as additional antidepressive actions of agomelatine and TIK-301 based on properties as antagonists of the serotonergic 5-HT2C receptor. Indirect antidepressive effects by melatonergic drugs are largely explained by circadian readjustments.

0 Bookmarks
 · 
126 Views
  • [Show abstract] [Hide abstract]
    ABSTRACT: Tasimelteon (HETLIOZ™) is an orally bioavailable agonist of the melatonin MT1 and MT2 receptors that has been approved in the US for the treatment of non-24-hour sleep-wake disorder. It is the first US FDA-approved medication for this orphan indication. Melatonin is thought to play a role in governing the body's natural sleep-wake cycle through physiological processes regulated in the suprachiasmatic nucleus of the hypothalamus. The hormone is secreted by the pineal gland, with onset typically occurring when daylight begins to dim. In healthy, sighted individuals, the endogenous circadian period is a little over 24 hours, but is entrained to the 24-hour day through exposure to environmental cues, such as light and darkness. In the absence of these cues, synchronisation is lost and the circadian rhythm follows the intrinsic non-24-hour clock, resulting in disorders like non-24-hour sleep-wake disorder. Because the rhythm of endogenous melatonin is considered to be a measure of the human circadian phase, the carefully timed administration of melatonin analogues, such as tasimelteon, can potentially promote circadian readjustment. This article summarizes the milestones in the development of tasimelteon leading to this first approval for the treatment of non-24-hour sleep-wake disorder.
    Drugs 03/2014; · 4.13 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Endogenous melatonin is synthesized from tryptophan via 5-hydroxytryptamine. It is considered an indoleamine from a biochemical point of view because the melatonin molecule contains a substituted indolic ring with an amino group. The circadian production of melatonin by the pineal gland explains its chronobiotic influence on organismal activity, including the endocrine and non-endocrine rhythms. Other functions of melatonin, including its antioxidant and anti-inflammatory properties, its genomic effects, and its capacity to modulate mitochondrial homeostasis, are linked to the redox status of cells and tissues. With the aid of specific melatonin antibodies, the presence of melatonin has been detected in multiple extrapineal tissues including the brain, retina, lens, cochlea, Harderian gland, airway epithelium, skin, gastrointestinal tract, liver, kidney, thyroid, pancreas, thymus, spleen, immune system cells, carotid body, reproductive tract, and endothelial cells. In most of these tissues, the melatonin-synthesizing enzymes have been identified. Melatonin is present in essentially all biological fluids including cerebrospinal fluid, saliva, bile, synovial fluid, amniotic fluid, and breast milk. In several of these fluids, melatonin concentrations exceed those in the blood. The importance of the continual availability of melatonin at the cellular level is important for its physiological regulation of cell homeostasis, and may be relevant to its therapeutic applications. Because of this, it is essential to compile information related to its peripheral production and regulation of this ubiquitously acting indoleamine. Thus, this review emphasizes the presence of melatonin in extrapineal organs, tissues, and fluids of mammals including humans.
    Cellular and Molecular Life Sciences CMLS 02/2014; · 5.62 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Huntington's disease (HD), a devastating neurodegenerative disorder, is characterized by progressive motor dysfunction, emotional disturbances, dementia, weight loss, depression. Melatonin receptors are widely expressed in the central nervous system. Vanilloids are also valuable as pharmacological tools for investigating neurobiology. This study investigates the utility of agomelatine, a dual agonist of MT1 and MT2 melatonin receptor as well as vanillin, a selective agonist of TRPV1 (vanilloid receptor) in 3-nitropropionic acid (3-NPA) induced experimental HD in rats. Locomotor activity (Actophotometer), motor coordination (Rota rod) and learning-memory (Morris water maze) were assessed. Brain striatum oxidative stress (lipid peroxidation-MDA, glutathione-GSH, superoxide dismutase-SOD and catalase-CAT), nitrosative stress (nitrite/nitrate) and mitochondrial enzyme complexes (I, II and IV) were also assessed. 3-NPA has induced weight loss, impaired locomotion, motor coordination as well as learning and memory. It has induced brain striatum oxidative as well as nitrosative stress, cholinergic dysfunction and impaired mitochondrial enzyme complexes (I, II and IV). Tetrabenazine (TBZ) was used as positive control. Treatment with agomelatine and vanillin and TBZ has significantly attenuated 3-NPA induced weight loss, impaired locomotion, motor coordination and learning-memory as well as biochemical impairments. Thus, agomelatine and vanillin exhibit protective effect against 3- NPA induced HD. It may be concluded that agomelatine and vanillin may provide benefits in HD.
    Pharmacology Biochemistry and Behavior 03/2014; · 2.61 Impact Factor

Full-text

View
132 Downloads
Available from
Jun 3, 2014