1521-009X/44/3/445–452$25.00 http://dx.doi.org/10.1124/dmd.115.067413 DRUG METABOLISM AND DISPOSITION Drug Metab Dispos 44:445–452, March 2016 Copyright ª 2016 by The American Society for Pharmacology and Experimental Therapeutics Melatonin Supports CYP2D-Mediated Serotonin Synthesis in the Brain Anna Haduch, Ewa Bromek, Jacek Wójcikowski, Krystyna Gołembiowska, and Władysława A. Daniel Institute of Pharmacology, Polish Academy of Sciences, Krakow, Poland Received September 25, 2015; accepted January 7, 2016 ABSTRACT Melatonin is used in the therapy of sleep and mood disorders and as (a monoaminoxidase inhibitor), the effect of melatonin was not a neuroprotective agent. The aim of our study was to demonstrate visible in the majority of the brain structures studied but could be that melatonin supported (via its deacetylation to 5-methoxytrypt- seen in all of them in 5,7-dihydroxytryptamine–lesioned animals Downloaded from amine) CYP2D-mediated synthesis of serotonin from 5-methoxy- when serotonin storage and synthesis via a classic tryptophan tryptamine. We measured serotonin tissue content in some brain pathway was diminished. Melatonin alone did not significantly regions (the cortex, hippocampus, nucleus accumbens, striatum, increase extracellular serotonin concentration in the striatum of thalamus, hypothalamus, brain stem, medulla oblongata, and cere- naïve rats but raised its content in pargyline-pretreated animals bellum) (model A), as well as its extracellular concentration in the (model B). The CYP2D inhibitor propafenone given intrastructurally striatum using an in vivo microdialysis (model B) after melatonin prevented the melatonin-induced increase in striatal serotonin in dmd.aspetjournals.org injection (100 mg/kg i.p.) to male Wistar rats. Melatonin increased those animals. The obtained results indicate that melatonin supports the tissue concentration of serotonin in the brain structures stud- CYP2D-catalyzed serotonin synthesis from 5-methoxytryptamine in ied of naïve, sham-operated, or serotonergic neurotoxin the brain in vivo, which closes the serotonin-melatonin-serotonin (5,7-dihydroxytryptamine)–lesioned rats (model A). Intracerebroven- biochemical cycle. The metabolism of exogenous melatonin to the tricular quinine (a CYP2D inhibitor) prevented the melatonin-induced neurotransmitter serotonin may be regarded as a newly recognized increase in serotonin concentration. In the presence of pargyline additional component of its pharmacological action. at ASPET Journals on September 28, 2021 Introduction melatonin synthesis in them. Extrapineal melatonin seems not to be Melatonin is used in the treatment of some sleep disorders, including engaged in the regulation of the photoperiod (Acuña-Castroviejo et al., concurrent sleep disturbances in the course of different psychiatric 2014); however, together with pineal melatonin, extrapineal melatonin diseases such as schizophrenia and major depressive and seasonal protects cells against damage from oxidative stress due to its antioxidant affective disorders (Dolberg et al., 1998; Dalton et al., 2000; Shamir and anti-inflammatory activity. Moreover, melatonin exerts an anti- et al., 2000; Singh and Jadhav, 2014). Moreover, high doses of excitotoxic effect in the brain by reducing glutamate activity and melatonin are recommended for neuroprotection (Venegas et al., increasing that of GABA and it stimulates neurogenesis (Pandi-Perumal 2012; Acuña-Castroviejo et al., 2014). et al., 2008; Acuña-Castroviejo et al., 2014; Singh and Jadhav, 2014). The synthesis of endogenous melatonin in the pineal gland is Being an amphiphilic substance, peripheral melatonin easily crosses the – governed by the light/dark cycle, which controls circadian and blood brain barrier (Green et al., 1975). Circulating melatonin is circannual rhythms. However, melatonin can also be produced in a metabolized mainly in the liver by cytochrome P450 isoforms of the substantial amount in extrapineal organs, including the gastrointestinal CYP1A subfamily (CYP1A1/A2/B1) to form 6-hydroxymelatonin and tract (in enterochromaffin cells), where it is not controlled by the then 6-sulfatoxymelatonin (Ma et al., 2005; Hardeland, 2010), but it can photoperiod (Pandi-Perumal et al., 2008; Venegas et al., 2012; Acuña- also be deacetylated to 5-methoxytryptamine (5-MT) (Rogawski et al., Castroviejo et al., 2014). The synthesis of melatonin from tryptophan 1979; Beck and Jonsson, 1981). via serotonin is catalyzed by N-acetyltransferase and hydroxyindole-O- In the brain, melatonin deacetylation to 5-MT seems to be of minor methyltransferase, these two enzymes being present in a variety of importance; both melatonin and 5-MT are formed mainly in the pineal organs/tissues such as the heart, liver, leukocytes, or the brain (e.g., the gland from which they are released to the circulation or to the third cerebral cortex and striatum), which also suggests the occurrence of ventricle. However, 5-MT formed from gut-derived melatonin in the liver crosses the blood–brain barrier (Beck and Jonsson, 1981; Acuña- Castroviejo et al., 2014) and, together with the brain-derived 5-MT, This research was supported by the European Union and the Polish Ministry of provides a direct substrate for CYP2D to form serotonin. Thus, the gut- Science and Higher Education [Grant DeMeTer POIG.01.01.02-12-004/09] and by derived or the exogenously supplied melatonin that provides most of the Polish Academy of Sciences Institute of Pharmacology [Statutory Funds]. the 5-MT for the organism may support serotonin formation by a dx.doi.org/10.1124/dmd.115.067413. CYP2D-mediated alternative pathway in vivo. ABBREVIATIONS: 5,7-DHT, 5,7-dihydroxytryptamine; 5-HIAA, 5-hydroxyindoleacetic acid; 5-HT, serotonin; 5-MT, 5-methoxytryptamine; aCSF, artificial cerebrospinal fluid; DA, dopamine; DMSO, dimethylsulfoxide; DRN, dorsal raphe nuclei; HPLC, high-performance liquid chromatography; MAO, monoaminoxidase; MRN, median raphe nuclei; NA, noradrenaline. 445 446 Haduch et al. Recent studies have shown that, apart from the classic pathway of Materials and Methods serotonin formation from L-5-hydroxytryptophan, serotonin may also Chemicals be synthesized via CYP2D-catalyzed O-demethylation of 5-MT. Melatonin (hydrochloride), pargyline (hydrochloride), quinine (hydrochlo- Such a way of serotonin synthesis has been demonstrated for human ride), propafenone (hydrochloride), serotonin (5-hydroxytryptamine or 5-HT; and rat cDNA-expressed CYP2D isoforms, as well as for brain hydrochloride) and its metabolite 5-hydroxyindoleacetic acid (5-HIAA), dopa- microsomes (Yu et al., 2003; Haduch et al., 2013). Moreover, using a mine (DA), noradrenaline (NA), 5,7-DHT (a creatinine sulfate salt), and ascorbic microdialysis model, the formation of serotonin via this alternative acid were purchased from Sigma-Aldrich (St. Louis, MO). Ketamine hydro- pathway has recently been shown to function in the brain in vivo chloride (Ketamine) and xylazine hydrochloride (Sedazin) came from Biowet (Haduch et al., 2015). (Puławy, Poland). All organic reagents were of high-performance liquid The aim of this study was to demonstrate that exogenous melatonin chromatography (HPLC) grade and were supplied by Merck (Darmstadt, supported (via deacetylation to 5-MT) CYP2D-mediated serotonin Germany). synthesis from 5-MT in the rat brain in vivo (Fig. 1) by measuring tissue or extracellular serotonin concentration after intraperitoneal Animals melatonin injection. Serotonin tissue content was measured in brain All experimental procedures were carried out in accordance with the National regions containing CYP2D and serotonergic innervation (model A). Institutes of Health Guide for the Care and Use of Laboratory Animals and were The experiment was carried out with naïve and 5,7-dihydroxytryptamine approved by the Bioethics Commission at the Polish Academy of Sciences (5,7-DHT)–pretreated animals in the absence/presence of the mono- Institute of Pharmacology, as compliant with the Polish law. The study was Downloaded from amine oxidase (MAO) inhibitor pargyline. Intraperitoneal pargyline conducted on male Wistar-Han rats (Charles River Laboratories, Sulzfeld, – was applied to prevent 5-MT (successively formed from melatonin Germany) weighing 300 325 g. The animals were housed in rooms with a controlled temperature and humidity on a 12-hour light/dark cycle and had free in the liver) and serotonin (formed from 5-MT in the brain) from access to tap water and standard laboratory food during the study. theoxidationbyMAOandthustopotentiate the effect of melatonin on the serotonin level in the brain (Prozialek and Vogel, 1978; The Tissue Levels of Serotonin in the Brain after Intraperitoneal Suzuki et al., 1981; Galzin and Langer, 1986; Raynaud and Pévet, Melatonin Administration (Ex Vivo Measurement, Model A) dmd.aspetjournals.org 1991). Intracerebral 5,7-DHT (a neurotoxin specific to serotonergic neurons) was used to decrease the production of serotonin via a To study the supportive effect of exogenous melatonin on the alternative classic pathway from tryptophan and serotonin storage in neuronal pathway of serotonin synthesis from 5-MT in a brain tissue, melatonin was injected intraperitoneally (100 mg/kg i.p.) to naïve and 5,7-DHT–lesioned rats. terminals of the brain (Rogawski et al., 1979; Beck and Jonsson, The rats were anesthetized with ketamine HCl (75 mg/kg i.p.) and xylazine 1981) and, consequently, to enhance serotonin derived from the HCl (10 mg/kg i.p.) and were then placed in stereotaxic apparatus (David