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Melatonin for Prevention and Treatment of Complications Associated with Chemotherapy and Radiotherapy: Implications for Cancer Stem Cell Differentiation
Published in Paloma Tejero, Hernán Pinto, Aesthetic Treatments for the Oncology Patient, 2020
Germaine Escames, Ana Guerra-Librero, Dario Acuña-Castroviejo, Javier Florido, Laura Martinez-Ruiz, Cesar Rodríguez-Santana, Beatriz I Fernandez-Gil, Iryna Russanova
The synthesis of melatonin begins with the hydroxylation of tryptophan to 5-hydroxy-tryptophan (5HTP) by tryptophan-5-hydroxylase (TPOH). This product is subsequently decarboxylated to 5-hydroxy-L-tryptamine (serotonin or 5-HT) under the catalytic action of aromatic amino acid decarboxylase (AADC). Serotonin is then acetylated to N-acetylserotonin by arylalkylamine N-acetyltransferase (AANAT). Finally, N-acetylserotonin is methylated to melatonin by hydroxyindole-O-methyl transferase (HIOMT), now known as N-acetyl-serotonin methyltransferase (ASMT) [43], which is a melatonin synthesis rate-limiting enzyme inhibited by light [44]. Therefore, melatonin concentrations in serum, mainly originating from the pineal gland, follow a circadian pattern.
Roles of Melatonin in Maintaining Mitochondrial Welfare
Published in Shamim I. Ahmad, Handbook of Mitochondrial Dysfunction, 2019
Feres José Mocayar Marón, Emiliano Diez, Russel J. Reiter, Walter Manucha
Melatonin synthesis and secretion were initially described in the pineal gland; its synthesis is regulated by the environmental light/dark cycle via the suprachiasmatic nucleus. The pineal gland is part of the photoneuroendocrine system, and acts as a transducer, converting afferent neurally-coded photic information into melatonin, the chemical expression of darkness5. The precursors of melatonin are the aromatic amino acid tryptophan and serotonin. The pineal parenchyma captures tryptophan; then it is hydroxylated and decarboxylated to serotonin. Serotonin is then N-acetylated by the enzyme aralkylamine N-acetyltransferase (AANAT), and finally, the product is converted into melatonin by the N-Acetylserotonin-O-methyltransferase (ASMT), also known as hydroxyindole-O-methyltransferase (HIOMT)6. Melatonin is not stored within the gland but quickly diffuses into the bloodstream and cerebrospinal fluid7.
Introduction to substance use and misuse
Published in G. Hussein Rassool, Alcohol and Drug Misuse, 2017
The main problem of drugs at the global level continues to be cannabis, while amphetamines remain the second most commonly used drug. However, the use of opiates and prescription opioids is less common, but opioids, mainly heroin, remain one of the major drugs of public health concern with potential harm and health consequences (UNDOC 2016). It is reported that cocaine consumption increased significantly mainly because of an increase in cocaine use in South America and there appears to be some stability in the use of amphetamines (UNDOC 2016). It is estimated that “excluding alcohol, tobacco and caffeine products the top 10 drugs used across the world were: cannabis, MDMA, cocaine, amphetamines, LSD, magic mushrooms, prescribed and non-prescribed opioid medication, nitrous oxide, ketamine and poppers” (Global Drug Survey 2016). The Novel Psychoactive Substances (NPS), marketed as Spice, bath salts and herbal incense continue to be characterised by the large number of new substances being reported. By modifying the chemical compounds of the drugs, the new synthetic drugs on the market are circumventing existing laws. Most of the psychoactive substances in this category include cannabinoids, cathinones, opioids, phenethylamines, tryptamines, benzodiazepines and arylalkylamines (EMCDDA 2015; UNDOC 2016). However, there is limited information of the dangers and toxicity of most of the novel synthetic psychoactive drugs.
Hematopoietic protection and mechanisms of ferrostatin-1 on hematopoietic acute radiation syndrome of mice
Published in International Journal of Radiation Biology, 2021
Xiaohong Zhang, Mengxin Tian, Xin Li, Chunyan Zheng, Ailian Wang, Jundong Feng, Xiaodan Hu, Shuquan Chang, Haiqian Zhang
Ferroptosis is a form of regulated cell death characterized by the iron-dependent accumulation of lipid reactive oxygen species (ROS), the inactivation or depletion of glutathione peroxidase 4 (GPX4), and the exhaustion of glutathione, which was first reported in cultured cancer cells (Dixon et al. 2012). It has since been associated with cell death in vivo following acute tissue injuries, such as cerebral injuries (Li et al. 2017), and kidney or heart ischemia/reperfusion (Friedmann Angeli et al. 2014; Fang et al. 2019). Therefore, the regulation of ferroptosis has proved to be a new therapeutic strategy in the treatment of cancers and ferroptosis-related diseases. Ferrostatin-1, a radical-trapping agent containing an arylalkylamine group (Skouta et al. 2014), which prevents lipid peroxidation to membrane lipids, had been identified as a ferroptosis inhibitor (Dixon et al. 2012), and is used to rescue ferroptosis-related diseases (Li et al. 2017).
Ocular and systemic melatonin and the influence of light exposure
Published in Clinical and Experimental Optometry, 2019
Melatonin (N‐acetyl‐5‐methoxytryptamine), an indolamine, is synthesised from the precursor tryptophan, which is converted to 5‐hydroxytryptophan and serotonin by tryptophan 5‐hydroxylase and L‐amino acid decarboxylase,1999 and then to N‐acetylserotonin and melatonin by hydroxyindole‐0‐methyltransferase (HIOMT) and arylalkylamine N‐acetyltransferase (AANAT).1967 AANAT and HIOMT are critical enzymatic mediators of melatonin synthesis, with AANAT being a major rate‐limiting step. Circulating melatonin is degraded through several pathways involving multiple enzymatic steps, being primarily metabolised in the liver, kidney, and central nervous system.2010 In humans, melatonin is rapidly metabolised in the liver by hepatic cytochrome P450,2001 with a half‐life of approximately 45–60-minutes,2005 allowing measures of circulating melatonin in plasma to accurately reflect its synthesis. Melatonin is soluble in lipids and transported in the blood via albumin binding.1981
Mitochondrial dysfunction in age-related macular degeneration: melatonin as a potential treatment
Published in Expert Opinion on Therapeutic Targets, 2020
Saeed Mehrzadi, Karim Hemati, Russel J. Reiter, Azam Hosseinzadeh
Melatonin is synthesized from the amino acid L-tryptophan in four consecutive enzymatic steps. (I) L-tryptophan is hydroxylated by tryptophan hydroxylase to form 5-hydroxytryptophan. (II) 5-hydroxytryptophan is decarboxylated by l-aromatic amino acid decarboxylase to form 5-hydroxytryptamine (5-HT, also called serotonin). (III) arylalkylamine N-acetyltransferase/serotonin N-acetyltransferase (AANAT/SNAT) acetylates serotonin to form N-acetyl-5-hydroxytryptamine (N-acetylserotonin, AANAT). (IV) N-acetylserotonin is converted to melatonin (N‐acetyl‐5‐methoxytryptamine) by N‐acetylserotonin‐O‐methyltransferase (ASMT); AANAT is considered as the rate-limiting step in the biosynthesis of melatonin [24]. In addition to this classic melatonin synthetic pathway, new evidence indicates the existence of an alternative pathway for the biosynthesis of melatonin, in which melatonin is produced from N-acetylation of 5-methoxytryptamine generated from the O-methylation of serotonin. This alternative pathway may be prominent in certain organisms and under some conditions [25]. Once produced, melatonin is immediately released into the blood or into the cerebrospinal fluid [26]. Melatonin functions may be mediated through receptor-dependent or receptor-independent mechanisms. The receptor-independent actions of melatonin relate to melatonin’s ability to scavenge free radicals and receptor-dependent actions result from binding to cytosolic molecules, e.g., calmodulin and to membrane receptors including MT1 and MT2 receptors or nuclear receptors including RAR-related orphan receptors (RORs) and the retinoid Z receptors (RZRs) [27].