InTechOpen uses cookies to offer you the best online experience. By continuing to use our site, you agree to our Privacy Policy.

Medicine » Mental and Behavioural Disorders and Diseases of the Nervous System » "A Synopsis of Parkinson's Disease", book edited by Abdul Qayyum Rana, ISBN 978-953-51-1229-7, Published: March 26, 2014 under CC BY 3.0 license. © The Author(s).

Chapter 3

Melatonin in Parkinson’s Disease

By Alessia Carocci, Maria Stefania Sinicropi, Alessia Catalano, Graziantonio Lauria and Giuseppe Genchi
DOI: 10.5772/57352

Article top


Toxins in experimental PD models.
Figure 1. Toxins in experimental PD models.
Biosynthetic pathway of melatonin.
Figure 2. Biosynthetic pathway of melatonin.
Melatonin oxidation.
Figure 3. Melatonin oxidation.

Melatonin in Parkinson’s Disease

Alessia Carocci1, Maria Stefania Sinicropi2, Alessia Catalano1, Graziantonio Lauria2 and Giuseppe Genchi2

1. Introduction

Parkinson’s disease (PD) is characterized by the progressive depletion of pigmented neurons containing dopamine (DA) in the region known as substantia nigra pars compacta (SNpc) and by the presence of intraneuronal aggregates called Lewy bodies, which are enriched in filamentous α-synuclein and other proteins, that are often ubiquitinated before being destroyed [1]. The locus coeruleus, the dorsal motor nucleus, the autonomic nervous system and the cerebral cortex are additional neuronal fields and neurotransmitter systems involved in PD with consequent loss of noradrenergic, serotonergic and cholinergic neurons. These neuronal changes led to progressive non-motor symptoms like sleep abnormalities, depression and cognitive decline in the later stages of PD [2].

Currently, levodopa is widely prescribed for the treatment of PD. Although it is highly effective as a symptomatic treatment, levodopa is incapable of providing the long-term protection that is needed to impair the onset or progress of the disease [3]. In fact, in addition to a few specific mutations, oxidative stress and generation of free radicals from both mitochondrial impairment and DA metabolism play critical and important roles in PD etiology. Deficits in mitochondrial functions, oxidative and nitrosative stress, accumulation of aberrant and misfolded proteins, and ubiquitin-proteasome system dysfunction can represent the main molecular pathways that trigger the pathogenesis of sporadic and familiar forms of PD [4].

It is known that about 15% of PD patients has a family background of the disease and few specific mutations have been identified to be responsible for rare familial forms of the pathology: α-synuclein, parkin, UCH-L1, DJ-1, and PINK1 are genes found to be related to PD [5]. These genetic defects seem to affect a common molecular pathway related to the ubiquitin-proteasome system with exception of PINK1, which is related to mitochondrial metabolism [6]. Some, if not all, of these mutations are partially related to free-radical generation. High levels of free-radical, reactive oxygen species (ROS) and reactive nitrogen species (RNS) damage not only phospholipids and polyunsaturated fatty acids of mitochondrial bilayers but also mitochondrial DNA (mtDNA) and mitochondrial proteins [7]. Uncontrolled increase in these metabolites lead to free radical-mediated chain reactions which indiscriminately target proteins, lipids and DNA resulting in cell death [8], producing neurodegeneration, at least in part, through the mitochondrial apoptotic pathway [9]. Several experimentally PD models are used to study the pathogenesis of the disease. 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) is a neurotoxin able to produce experimentally Parkinson’s disease in humans and monkeys (Figure 1). When administered to animals, MPTP readily crosses the blood-brain barrier (BBB), where it selectively destroys DA neurons in the substantia nigra (SN). Once MPTP crosses the BBB, it enters astrocytes, where it is converted into the active metabolite 1-methyl-4-phenylpyridinium (MPP+) by the action of the enzyme monoamine oxidase B (MAO B) [10]. MPP+ leaves the astrocytes and via the DA transporter enters the dopaminergic neurons. First of all, MPP+ accumulates into mitochondrial matrix, where it inhibits the Krebs cycle enzyme α-ketoglutarate dehydrogenase [11]. In addition, this metabolite inhibits complex I of the electron transport chain (ETC), causing increased generation of ROS, decreased adenosine triphosphate (ATP) production and nigral cell death [12,13]. MPP+, by inducing nitric oxide synthase (NOS) expression in SNpc, has been shown to produce large amounts of nitric oxide (NO) that, reacting with O2 generates the highly toxic peroxynitrite (ONOO), a molecule that impairs mitochondrial functions causing irreversible inhibition of all ETC complexes [14] and neuronal cell death [15].

Together with MPTP, other toxin-based models frequently used to induce dopaminergic neurodegeneration include the neurotoxin 6-hydroxydopamine (6-OHDA), the herbicides paraquat (N,N′-dimethyl-4,4′-bipyridinium dichloride) and rotenone, and the fungicide maneb (Figure 1). They are capable of inducing the pathological hallmark of PD, the neuronal cell loss in the SN. The main contributing factor to this cell loss is mitochondrial dysfunction by inhibiting complex I, resulting in oxidative stress and eventually cell death [16]. In particular, neurotoxin 6-OHDA induces reduction of the antioxidant glutathione (GSH) and antioxidant enzyme superoxide dismutase (SOD) [17], increase of iron levels in SN [18] and inhibition of complexes I and IV in mitochondria [19] which lead to further oxidative stress. The herbicide paraquat having a structural similarity to MPP+ directly inhibits complex I [20] and produces oxidative stress through redox cycling. The herbicide rotenone, extracted from tropical plants, easily crosses the BBB and accumulates inside the mitochondrial dopaminergic neuron, where it inhibits complex I. Maneb, on the other hand, induces the nigrostriatal dopaminergic neurodegeneration by inhibiting complex III [16].

Actually, considering that the existence of mitochondrial damage, due to oxidative stress, is the base of the disease which may lead to a decrease in the activities of mitochondrial complexes and ATP production, and as a consequence, a further increase in free radical generation, with the final consequence being cell death by necrosis or apoptosis, the use of antioxidants as an important co-treatment with traditional therapies has been suggested.

There are several agents that are currently under investigation for their potential neuroprotective effects based on their capacity to modify mitochondrial dysfunction. These include creatine, melatonin (MLT), nicotine, nicotinamide, lipoic acid, acetyl-L-carnitine, resveratrol etc. (Table 1) [21]. Among these compounds, melatonin has shown to be effective in preventing neuronal cell death and ameliorating PD symptoms in several in vivo and in vitro PD models.

MLT is a natural hormone secreted by the pineal gland that easily crosses BBB. This hormone regulates and modulates a wide variety of physiological functions. Besides the well-known chronobiotic and sleep inducing properties [22], many other physiological effects have been ascribed to MLT, such as the modulation of cardiovascular [23] and immune [24] systems and the influence on hormone secretion and metabolism [25]. Other effects of MLT described in the literature include antitumor [26,27], anti-inflammatory [28], pain modulator [29], neuroprotective [30,31], and antioxidant [32] activities.


Figure 1.

Toxins in experimental PD models.

Many in vitro and in vivo experimental models have contributed to demonstrate the role of MLT as an efficient radical scavenger against several reactive oxygen species (ROS), for example, the hydroxyl radical, the peroxynitrite anion, the superoxide anion, and singlet oxygen [33]. MLT has also been shown to enhance the production and the activity of several antioxidant enzymes, including superoxide dismutase (SOD), glutathione peroxidase (GPx), glutathione reductase (GRd), catalase, and glucose-6-phosphate dehydrogenase [34,35]. Furthermore, in vivo observations on the protective role of MLT in ischemic brain injury [36] or in animal models of PD [37] emphasize the therapeutic potential of this compound as a neuroprotective agent [38]. Moreover, MLT increases the efficiency of the electron transport chain thereby limiting electron integrity of the mitochondria and helps to maintain cell functions and survival [39]. Treatment with MLT counteracts the effects of MPTP in brain nuclei, increasing complex I activity, and the effects of MPTP on lipid peroxidation and nitrite levels in the cytosol and in the mitochondria of mice brain [40]. There is growing evidence that MLT antiapoptotic effects play an important role in neurodegeneration as well [41].

Agent Structure
(acetylsalicylic acid)
(–)-Epigallocatechin gallate
(R)-Lipoic acid

Table 1.

Neuroprotective agents in PD models.

2. Neuroprotective agents for Parkinson’s disease

Relevant preclinical studies have identified several compounds such as MLT, estrogen, nicotine, caffeine, riluzole, curcumin, aspirin, epigallocatechin-3-gallate (EGCG) and resveratrol, as neuroprotective agents in PD [42] (Table 1). Various prospective studies have suggested a strong association between tobacco smoking and a decreased risk of PD. Nicotine is one of the main constituents of tobacco and is known for its pharmacological effects, exerted by interaction with cholinergic nicotinic receptors in both central and peripheral nervous systems [43]. A recent clinical trial among six male PD patients demonstrated that chronic high doses of nicotine improved motor scores, reduced dopaminergic treatment and had a potential beneficial effect on striatal dopamine transporter density [44]. Chronic nicotine treatment partly protects against the MPTP-induced degeneration of nigrostriatal dopamine neurons in the black mouse, counteracts the disappearance of tyrosine-hydroxylase-immunoreactive nerve cell bodies, dendrites and terminals in the mesostriatal dopamine system and prevent striatal dopamine loss provoked by 6-OHDA administration in the substantia nigra [45-47].

17β-estradiol (E2) is a predominant sex hormone that acts on the whole body. Since several epidemiological studies have shown a greater incidence of PD in men than women, extensive research have investigated the possible neuroprotective effects of E2 in MPTP mice models and in 6-OHDA-injury model [48,49]. Estrogens alters MPTP-induced neurotoxicity in female mice with effects on striatal DA concentrations and release [50]. E2 prevents loss of dopamine transporter (DAT) and vesicular monoamine transporter (VMAT2) in substantia nigra, induces regulation of striatal preproenkephalin mPRNA levels in MPTP-lesioned mice, protects the SNpc of female rats from lesion induced by 6-OHDA and interacts with the insulin-like growth factor-1 (IGF-1) system to protect nigrostriatal dopamine and maintain motoric behavior after 6-OHDA lesions [51-53].

Caffeine is the most widely used psychoactive substance in the world due to its presence in coffee and other beverages. Several epidemiological studies have linked coffee intake with a lower incidence of PD, suggesting neuroprotective properties for caffeine and demonstrating its strong neuroprotective role in rodents for various injury models [54,55]. In particular, Chen and co-authors found that caffeine (10 mg/kg) was neuroprotective when administered 10 min prior to four injections of MPTP [56], attenuating the depletions in striatal DA, 3,4-dihydroxyphenylacetic acid (DOPAC) and DAT-binding sites. The same effects were also established in a 6-OHDA model [57]. Several epidemiological studies suggested an interaction between estrogen and caffeine. It has been reported that caffeine attenuated the toxic effects of MPTP in male mice in a dose-dependent manner. In contrast, this results was not found in female mice and estrogen treatment also prevented this effect in young male mice [58].

Riluzole is a selective Na+-channel blocker and some researchers have demonstrated its neuroprotective effects in rodents and in a primate model. Boireau and co-authors reported that riluzole neuroprotection in combination with MPTP was due to interference with MPP+ production by MAO-B inhibition. The protective effect was confirmed in MPTP- treated mice, partially due to astrocyte activation [59].

Many evidences reported that an important risk factor for the disease is aging [60]. It contributes to PD progression because of accumulative oxidative damage and decrease of antioxidant capacity. Genetic studies have also revealed that aging can be controlled by changes in intracellular NAD/NADH ratio regulating sirtuins, a group of proteins linked to aging, metabolism and stress tolerance in several organisms. Consistently, the neuroprotective roles of dietary antioxidants including for example, acetyl-L-carnitine, curcumin, epigallocatechin-3-gallate (EGCG), carnosine, resveratrol, etc. have been demonstrated through the activation of these redox-sensitive intracellular pathways.

In particular, acetyl-L-carnitine has been proposed to have beneficial effects in preventing the loss of brain function which typically occurs during aging and neurodegenerative disorders [21]. In fact, acetyl-L-carnitine treatment has been shown to prevent age-related changes in mitochondrial respiration and decrease oxidative stress biomarkers through the up-regulation of HO-1 (heme oxygenase-1), Hsp70 (heat shock protein 70) and superoxide dismutase-2 in senescent rats [61]. Acetyl-L-carnitine has shown to be neuroprotective through a variety of other effects such as the increase in protein kinase C (PKC) activity [62]. Moreover acetyl-L-carnitine has also been reported to attenuate the occurrence of parkinsonian symptoms associated with MPTP in vivo, and protects in vitro against the toxicity of neurotoxic MPP+ [63].

Curcumin is an active polyphenolic compound of Turmeric (Curcuma longa), which is extensively used as dietary spice in Indian food. Curcumin is used as a food additive because of its yellow colouring properties and presents anti-inflammatory and antioxidant properties. Recent studies demonstrated the neuroprotective effects of pretreatment with curcumin in the 6-OHDA model in rats. Both motor deficits and neuronal damage were prevented by curcumin and by one of its main metabolites, tetrahydrocurcumin, which also had beneficial effects on the antioxidant status, with increasing GSH levels and activity of antioxidant enzymes. Curcumin inhibited, in fact, MAO-B activity which prevents the conversion of MPTP to its toxic metabolite MPP+ [64].

EGCG is a catechin ubiquitously found in plants and is an important substance in green tea. Interestingly, there are several epidemiological studies that investigated an association between tea and PD. Among tea drinkers, the risk of developing PD was lower than in non-tea drinkers [65]. This effect was thought to be especially influenced by EGCG, to which has been ascribed a wide range of therapeutic properties, including neuroprotection. In fact, green tea and EGCG prevented MPTP-induced neuron loss and inhibited the upregulation of striatal SOD and catalase enzymes [66].

Inflammation is believed to be one of the important factors in the pathogenesis of PD. Moreover, it had been demonstrated that the enzyme cyclooxygenase (COX) and other inflammatory proteins are elevated in PD. Therefore, there is a significant interest in non-steroidal anti-inflammatory drugs (NSAIDs), especially aspirin [42]. The aspirin has an additional free radical scavenging property in addition to COX2 inhibition. In a study reported by Marahaj and co-authors, aspirin (100 mg/kg) and paracetamol (100 mg/kg) prevented KCN-induced superoxide generation and lipid peroxidation. While paracetamol was a more effective antioxidant, aspirin completely blocked the debilitating effects of MPP+ on striatal DA in rats, whereas paracetamol was only able to partially block this effect [67].

Also resveratrol, a polyphenol compound, found in grapes and in red wine, has shown anti-inflammatory, anti-oxidant, and neuroprotective properties. The effects of resveratrol on the 6-OHDA injury in rats were studied by Khan and colleagues [68]. They have demonstrated that resveratrol was not only capable to protect neurons, but also to increase the activity of antioxidant enzymes and decrease the levels of thiobarbituric acid reactive substances (TBARS), protein carbonyl (PC), and phospholipase A2 (PA2), providing evidence for a possible antioxidant property. Then, pretreatment with resveratrol (50 and 100 mg/kg) prevented neuronal cell loss in the SN and striatal DA depletion, in 6-OHDA-injury model in rats it was neuroprotective and it has been shown to decrease mRNA and protein levels of TNF-α in COX2, suggesting that an anti-inflammatory mechanism underlies the protective effects of this polyphenol [69,70].

3. Melatonin

Melatonin (N-acetyl-5-methoxy triptamine, MLT), a triptophan derivative, is a highly conservative naturally occurring molecule present in a wide spectrum of organisms, including bacteria, fungi, plants, protozoa, invertebrates [71] and vertebrates. In vertebrates, MLT is primarily produced by the pineal gland with a marked circadian rhythm that is governed by the central circadian pacemaker in the suprachiasmatic nuclei (SCN) of the hypothalamus, the highest levels occurring during the period of darkness [72]. Extrapineal sites of MLT production include retina, Harderian gland, gut, bone marrow [74], platelets, and skin [75]. However, with the exception of retina, the physiological significance of these extrapineal sites is still a matter of debate. MLT was first isolated and identified in the bovine pineal gland by Lerner and coworkers in 1958 [76].

MLT acts as time-giver (Zeitgeber) in the regulation of circadian rhythms [77,78] and in synchronizing the reproductive cycle with the appropriate season of the year in photoperiodic species [8]. In non-photoperiodic species such as humans, MLT actions consist in consolidation of sleep and regulation of the circadian rhythm [9]. MLT actions, however, are not restricted to its role in the neuroendocrine physiology. Many other physiological effects have been ascribed to MLT, such as the modulation of cardiovascular [23] and immune [24] systems and the influence on hormone secretion and metabolism [25]. Other effects of MLT described in the literature include antitumor [26, 27], anti-inflammatory [28], pain modulator [29], neuroprotective [30, 31] and antioxidant [32] properties. MLT have also been associated with the cellular antioxidant defence since it is a powerful free radical scavenger, and it is able to induce the expression and/or the activity of the main antioxidant enzymes [79].

MLT exerts its actions by multiple mechanisms. Many of its physiological actions are mediated through activation of distinct MLT receptors expressed in a wide variety of tissues. Cloning studies have revealed at least three MLT receptor subtypes, two of which (MT1 and MT2) have been found in mammals and are localized in different areas of the central nervous system (CNS) as well as in peripheral tissues [80]. Moreover, a non-mammalian MLT binding site with a lower affinity profile (MT3) has been found in hamster brain and characterized as a MLT-sensitive form of the human enzyme quinine reductase 2 [81]. MLT is also a ligand for retinoid orphan nuclear hormone receptors referred to as RZRα and RZRβ at concentrations in the low nanomolar range. Both receptors are present in the central and peripheral nervous system and have been associated with cell differentiation and immune response regulation [82,83]. The melatonin MT1 receptor is coupled to different G proteins that mediate the inhibition of adenylyl cyclase and the activation of phospholipase C [84], while the MT2 receptor is coupled to a number of signal transduction mechanisms, among them phosphoinositide production, inhibition of adenylyl cyclase and guanylyl cyclase [80].

Tryptophan serves as the precursor for the biosynthesis of MLT (Figure 2). It is converted into serotonin via 5-hydroxytryptophan. Serotonin is then acetylated to form N-acetylserotonin by arylalkylamine N-acetyltransferase (AANAT or NAT), one of the key enzyme in MLT synthesis. N-acetylserotonin is then converted to MLT by hydroxyindole-O-methyltransferase (HIOMT) which has been identified as the rate-limiting enzyme in the biosynthesis of pineal MLT [85]. In all mammals pineal MLT biosynthesis is synchronized to light/dark cycle by the SCN, which receives its input from the retinohypothalamic tract. Special photoreceptive retinal ganglion cells containing melanopsin as a photopigment are involved in the projection from retina [86]. Fibers from the SCN pass through a circuitous route involving the paraventricular nucleus of the hypothalamus and then proceed to innervate pineal gland as postganglionic sympathetic fibers. Norepinephrine released from these fibers binds to postsynaptic adrenoceptors whose activation induces an increase in cyclic adenosine-3′,5′-monophosphate (cyclic AMP) accumulation and a subsequent activation of NAT [87].

MLT has two important functional groups which determine its specificity and amphiphilicity: the 5-methoxy group and the N-acetyl side chain. Due to its lipophilic nature and pKa, MLT readily crosses the BBB. Once formed within the pineal gland, the majority of MLT diffuses directly towards the cerebrospinal fluid of the brain's third ventricle, while another fraction is released into the blood stream where it is distributed to all tissues. The brain has much higher concentrations of MLT than any other tissue in the body [88].

Circulating MLT is partially bound to albumin and can also binds to hemoglobin [89,90]. MLT is mainly metabolized in the liver via hydroxylation reaction by cytochrome P450 mono-oxygenases. This reaction is followed by conjugation with sulfuric or glucuronic acid, to produce the principal urinary metabolite, 6-sulfatoxymelatonin. Conjugated MLT and minute quantities of unmetabolized MLT are eliminated through the kidney. In addition to hepatic metabolism, oxidative pyrrole-ring cleavage appears to be the major metabolic pathway in other tissues, including CNS [91].


Figure 2.

Biosynthetic pathway of melatonin.

MLT seems to function via a number of means to reduce oxidative stress. It can develop its action at two levels: as a direct antioxidant, due its ability to act as a free radical scavenger, and as an indirect antioxidant, since it is able to induce the expression and/or the activity of the main antioxidant enzymes.

MLT is a powerful free radical scavenger since it is able to remove H2O2, OH, peroxinitrite anion (ONOO), singlet oxygen (1O2), O2•– and peroxyl radical (LOO). MLT, as an electron-rich molecule, is able to interact with free radicals through consecutive reactions giving rise to many stable compounds that can be excreted by urine. In fact, the MLT antioxidant mechanism implied a free radical scavengers cascade, since secondary, and even tertiary metabolites are also efficient free radicals scavengers, like N-acetyl-N-formyl-5-methoxykynuramine (AFMK) and N-acetyl-methoxykynuramine (AMK) (Figure 3) [92,93]. The formation of such metabolites from MLT implies that, unlike classic antioxidants, melatonin does not produce prooxidant reactions and, even more, AMK and AFMK, in all the mitochondrial studies where comparisons were made, were more potent than MLT itself [94].

The large subcellular distribution of MLT allows its interaction with almost any kind of molecule, diminishing oxidative damage in both lipid and aqueous environments. This is supported experimentally by numerous data that show that MLT is able to protect lipids in the cellular membranes, proteins in the cytosol and DNA in the nucleus from free radical damage [95]. MLT gets free access to all cell components especially in the nucleus [96] and mitochondria [97], where it seems to accumulate in high concentration. In addition, MLT interacts with lipid bilayers of mitochondria, stabilizing its inner membrane [98], an effect that improves ETC activity [99].

Apart from its direct scavenging activity, MLT confers indirect protection against oxygen species through its capability to increase the gene expression and/or activities of antioxidant enzymes. This regulatory role is also mediated by the metabolites of MLT [34,35]. The expression of enzymes, such as GPx, GRd and SOD, related to the endogenous antioxidant system of the cells and the mitochondria, are under genomic regulation of MLT [100,101]. Some antioxidant properties of MLT are attributable to a genomic effect in the regulation of the activities of other antioxidant enzymes such as inducible (iNOS) and mitochondrial (mtNOS) isoforms of nitric oxide synthase [102]. MLT also inhibits neuronal nitric oxide synthase (nNOS) activity because of its binding to the calcium-calmodulin complex [103].

The pineal production of MLT exhibits an unambiguous circadian rhythm with its peak near the middle of scotophase and basal levels during the photophase. The amount of MLT produced by the pineal gland of mammals changes as animals age. The tendency is that pineal MLT production wanes with advanced age. In humans, MLT production not only decreases in the aged but also is significantly lower in many age-related diseases as Alzheimer’s, Parkinson’s and Huntington’s disease [104,105] and cardiovascular disease [106,107].


Figure 3.

Melatonin oxidation.

4. Mitochondria and melatonin

Mitochondria are organelles found almost ubiquitously in eukaryotes, that play a central role in the cell physiology; in fact, besides their classic function of energy metabolism, these organelles perform many other functions including the distribution of energy through the cells, energy/heat modulation, ROS regulation, calcium homeostasis, and apoptosis control. In mitochondria important metabolic pathways take place including fatty acids β-oxidation, pyruvate oxidation, Krebs cycle, lipids and cholesterol biosynthesis. Many of these processes are functions required for the wellbeing of the cells and of the human beings. The inner mitochondrial membrane is rich in proteins, half of which are involved in oxidation-reduction reactions with transport of electrons and in oxidative phosphorylation (OXPHOS). The oxidative phosphorylation, coupled to electron transport chain (ETC), allows the synthesis of adenosine triphosphate (ATP), a molecule rich in energy, via the enzyme complex ATP synthase.

Human mitochondria contain their own genome (mitochondrial DNA, mtDNA), a circular double stranded-molecule. The human mitochondrial chromosome contains 37 genes (16,569 base pairs), including 13 that encode subunits of respiratory chain/oxidative phosphorylation proteins; the remaining genes code for rRNA and tRNA molecules necessary to the protein-synthesizing complex of mitochondria. About 99% of the mitochondrial proteins are encoded by nuclear DNA (nDNA); so these proteins have to be imported into mitochondria. Mitochondrial proteins synthesized in the cytosol possess mitochondrial targeting signals that direct them to the appropriate compartment (outer or inner membranes, intermembranes space and matrix) within the organelle. Transport across outer and inner membranes needs a complex machinery including the presence of ATP, docking proteins, chaperonins and proteases, and it involves unfolding and refolding of the proteins to be translocated.

NADH produced in the cytosol by glycolysis and in the mitochondria by oxidation of pyruvate, fatty acids β-oxidation, and Krebs cycle, are oxidized by respiratory chain transferring electrons to O2, that is converted to water. The primary function of mitochondria is to generate ATP (from ADP and phosphate by adenin nucleotide and phosphate translocators and FoF1 ATP synthase) through the ETC resulting in OXPHOS. The ETC, located in the inner mitochondrial membrane, comprises a series of electron carriers grouped into four enzyme complexes: complex I or NADH ubiquinone reductase, complex II or succinate ubiquinone reductase, complex III or ubiquinol cytochrome c reductase, and complex IV or cytochrome c oxidase. The end product of the respiratory chain is water generated after reduction of O2 by mitochondrial complex IV; this process needs the addition of four electrons to each oxygen molecule. However, about 5-10% of the oxygen is involved in production of hydrogen peroxide (H2O2), superoxide anion radical (O2•–), and the extremely reactive hydroxyl radical (OH) [108]. These three molecules are ROS and represent endogenous oxidotoxins. The mitochondria for action of the enzyme nitric oxide synthase (mtNOS) can also produce nitric oxide (NO) from L-arginine [109], which can be converted into various reactive nitrogen species (RNS), such as nitrosonium cation (NO+), nitroxyl anion (NO) and peroxynitrite (ONOO) [110]. These free radicals are detoxified or their peroxidation products are decomposed by the natural antioxidant defense system as SOD, glutathione redox cycle, catalase and coenzyme Q. Mitochondria not only generate ROS/RNS, but are also the main target of their actions [111]. Small fluctuations in the steady-state concentration of ROS/RNS may play a role in intracellular signaling [112]. Several mechanisms take part in the control of ROS/RNS production. Among these the enzyme SOD, localized in the inner side of the inner mitochondrial membrane, remove O2•– [113]. When formed, O2•– is immediately dismutated to H2O2 by cytosolic or mitochondrial superoxide dismutase. As H2O2 is the precursor of the highly damaging OH, it is imperative that H2O2 is removed very quickly.

The enzyme GPx metabolizes H2O2 to water and O2; GPx in this reaction also converts reduced GSH to its oxidized form (GSSG). In turn, GSSG is reduced to GSH by the action of the enzyme glutathione reductase (GRd) in the presence of NADPH [114,115]. These enzymes form part of the endogenous antioxidant defense system suppressing ROS/RNS levels both in the cells and in the mitochondria. Under normal conditions, MLT reduces mitochondrial hydroperoxide levels and stimulates the activity of GPx and GRd, enzymes involved in the GSH-GSSG balance [116]. The indoleamine MLT is also able to neutralize the oxidative stress induced by high doses of t-butyl hydroperoxide, restoring GSH levels and GPx and GRd activities. However, vitamins C and E have no such effect under the same conditions [116].

Other antioxidants such as ascorbate, ubiquinone and α-tocopherol can participate in the mitochondrial antioxidative defense system, but without to be able to convert O2•– to O2. However, uncontrolled increase in these metabolites leads to a series of reactions which target proteins, lipids and DNA resulting in cell death by necrosis or apoptosis. In recent years, several findings support the antioxidant effect of MLT in mitochondrial homeostasis [99,117,118].

Apoptosis and necrosis are two types of cell death occurring in neurodegeneration. Apoptosis (programmed cell death) occurs naturally under normal physiological conditions; on the contrary, necrosis is caused by external factors such as toxins, infections and trauma. Apoptosis is characterized by cell shrinkage, cytoplasm contraction, nuclear fragmentation, chromatin condensation, and chromosomal DNA fragmentation, plasma membrane bleb formation and apoptotic body formation [119]. Many of these changes are activated by a family of caspases, i.e. proteases that in their active site possess a cysteine and cleaves the substrates after aspartate residues. Apoptotic cells are rapidly sequestered by phagocytosis before they can lyse and cause an inflammatory process [120]. Necrosis does not involve any DNA or protein degradation and is accompanied by swelling of the cytoplasm and of the mitochondria with membrane ruptures. Both apoptosis and necrosis involve a change in mitochondrial membrane permeabilization (MMP) [121].

MMP causes the opening of a nonspecific pore in the mitochondrial membranes, known as the mitochondrial transition pore (MTP), that allows the passage of any molecules of >1500 Da across this membrane. This pore can be rapidly closed by chelation of calcium ion. Because MTP allows also rapid passage of protons (H+), its opening causes depolarization of mitochondria and uncoupling of oxidative phosphorylation without synthesis of ATP. If the MTP remains open, ATP levels can be totally depleted; on the contrary, transient opening of the MTP can be involved in the mitochondrial-mediated apoptosis through the proteins released from mitochondria. Among these apoptogenic proteins we know cytochrome c [122], the serine protease HtrA2/Omi [123], and endonuclease G [124].

Permeabilization events, which occur at points where outer and inner mitochondrial membranes are in contact, involve association of several proteins from different districts of the cell and the mitochondria [125]: cytosol (hexokinase), outer mitochondrial membrane (peripheral benzodiazepine receptor and voltage dependent anion channel or VDAC), mitochondrial inner membrane space (creatine kinase), inner mitochondrial membrane (adenine nucleotide translocator or ANT) and mitochondrial matrix (cyclophilin D).

Two main considerations suggest a role for MLT in mitochondrial homeostasis. As it is known, mitochondria produce high amounts of ROS and RNS. Besides, mitochondria depend on the GSH uptake from the cytosol, even if they have GPx and GRd to maintain redox cycling. Thus, the anti-oxidant effect of melatonin and its ability to increase the levels of GSH may be of great importance for mitochondrial physiology [126]. The fact that the inhibition of CN on complex IV of the mitochondrial ETC is removed by MLT, also supports its intramitochondrial role [127]. A protective effect of MLT against MPP+-induced inhibition of complex I of ETC has been also shown [128].

The effects of MLT on mitochondrial ETC have been also studied on submitochondrial particles from rat liver and brain mitochondria [129]. MLT at 1 nM concentration significantly increased the activity of the complexes I and IV of ETC in rat liver submitochondrial particles, whereas 10-100 nM MLT stimulated the activity of the same complexes but in brain submitochondrial particles. The indoleamine counteracted CN-induced inhibition of complex IV, restoring the levels of Cyt aa3. This effect was of physiological significance, since the MLT increased the ETC and OXPHOS activities with a consequent increase of ATP synthesis [129]. In addition, due the high redox potential of MLT (-0.98 V), this molecule can donate directly electrons to complex I of the ETC [130].

The effect of MLT (10 mg/kg) on ETC complexes from rat liver and brain mitochondria has been also studied in vivo. Martin et al. [116] have found that MLT increases the activity of the respiratory chain complexes I and IV and ATP synthesis in a time-dependent manner after mitochondrial damage induced by ruthenium red [116].

Recently, the role of MLT on cardiolipin and mitochondrial biogenesis was studied [131]. Cardiolipin, a phospholipid located in inner mitochondrial membrane, is required for several mitochondrial bioenergetic processes as well as for the activity of transport proteins. Alterations in cardiolipin structure and acyl chain composition have been associated with mitochondrial dysfunction under a variety of pathological dysfunctions. The authors [131] reported that MLT protects the mitochondrial membranes from oxidation-reduction damage by preventing cardiolipin oxidation.

5. Melatonin and Parkinson’s

In the last decade, many research findings provide scientific evidence for the protective role of MLT in a number of oxidative stress related diseases, especially Alzheimer’s [132] and Parkinson’s diseases [133], being the protective actions of the indoleamine attributable to its direct and indirect antioxidative properties. The first evidence of a significant relationship between Parkinson's disease and MLT derived from the evidence of a reduction in the concentration of circulating MLT in PD patients as a consequence of a decreased activity of the pineal gland [134]. After its antioxidant properties were uncovered, melatonin has been successfully tested in several in vivo and in vitro PD models.

MLT was found to inhibit in vitro the prooxidant effects of dopamine and L-dopa [135] and to be more effective than the vitamin E analog, trolox, in preventing dopamine autooxidation [136]. Melatonin was also reported to prevent in the MPTP model the rise in lipid peroxidation products in the substantia nigra (SN) of MPP+-treated rats and, additionally, to preserve tyrosine hydroxylase (TH) activity, which is normally decreased after toxin treatment [69].

When the 6-OHDA model was used instead of MPTP ones to induce dopaminergic degeneration, MLT administration restored the motor deficits elicited by apomorphine co-treatment with 6-OHDA [137] and also completely prevented the rise in neural lipid peroxidation products and partially rescued striatal dopaminergic levels after lesioning with 6-OHDA [138]. The protective action of MLT against dopaminergic neuronal degeneration was also expressed by reduction of the DNA fragmentation induced by MTPT [139] and of mitochondrial complex I deficiency observed after 6-OHDA administration [140]. MLT also counters MPTP-induced c-Jun-N-terminal kinase and caspase-dependent signaling leading to the dopaminergic neurodegeneration [141]. It has been reported that MLT partially preserves the GSH concentrations in SN of MPTP-treated rats [142,143]. The antioxidant activity of MLT was supposed to be the major mechanism underlying MLT’s protection in these PD models. The protective function of MLT also include its antiapoptotic effects. MLT has been reported to rescue dopamine neurons from spontaneous cell death in low-density seeding culture [144].

PD epidemiological studies have suggested an association with the environmental toxin rotenone, a mitochondrial complex I inhibitor. In recent years, Drosophila melanogaster has been used as a model for several neurodegenerative diseases, including PD. Coulom and Birman studied for several days the neurodegenerative effects of a chronic exposure to rotenone in Drosophila melanogaster. After several days of treatment, flies presented characteristic locomotor impairments that increased with the dose of herbicide. Immunocytochemistry analysis demonstrated a dramatic and selective loss of dopaminergic neurons in the brain of all treated flies. The addition of L-dopa into the feeding medium rescued the behavioral deficits but not neuronal death, as is the case in human PD patients. On the contrary, the antioxidant MLT alleviated both symptomatic impairment and neuronal loss, supporting the idea that this agent may be beneficial in the treatment of parkinsonism [145].

MLT has been shown to protects PC12 cells from both apoptosis and necrosis induced by high doses of 6-OHDA [146,147]. Since 6-OHDA induced cellular toxicity is mediated by increased free-radical generation, the antioxidant properties of MLT presumably account for its ability to suppress both necrosis and apoptosis. Numerous data suggest a role for MLT in mitochondrial homeostasis [148]. It has been reported that MLT increases the activities of respiratory complexes I and IV in a time-dependent manner after in vivo administration to rats [129] and maintains GSH homeostasis in the mitochondrial matrix under increased oxidative stress; these actions are not shared by either vitamin C or vitamin E [117]. Mitochondria in the cell are the major source of ROS, owing to the leakage of electrons through the electron transport chain. Due the critical role of mitochondria in programmed cell death and PD, it is conceivable that actions at the mitochondrial level mediate at least some of MLT apoptotic effects. It has been reported that MLT induces ATP production, increasing the activity of the mitochondrial oxidative phosphorylation (OXPHOS) enzymes [129]. The indoleamine also protects mitochondrial DNA, which is particularly vulnerable to oxidative damage, thus indirectly helping to preserve mitochondrial metabolism.

Since mitochondria play a critical role in the pathogenesis of PD, it is conceivably that actions at mitochondria level mediate some of MLT antiapoptotic effects. The beneficial actions of MLT in PD has been widely investigated not only on the basis of its neuroprotective efficacy assessment but also because of the down regulation of MLT receptors in the nigrostriatal region of PD brain [149]. There is growing evidence of sleep–wake boundary dysfunction in PD. REM sleep behavior disorder (RBD) which is characterized by loss of normal skeletal muscle tone with prominent motor activity and dreaming, has been associated with PD and/or other forms of dementia, with a tendency for RBD to precede the onset of parkinsonism. There is some clinical evidence that MLT can be a useful add-on therapy for RBD in PD [150].

6. Conclusions

PD is a highly debilitating condition that concerns thousands of family in the world and annually cost millions of euro for treatment. This disease has occasionally a genetic basis, but the signs of PD develop after free-radical damage to the substantia nigra pars compacta. Moreover, neuroinflammation and mitochondrial dysfunction participate in the ethiology of this neurodegenerative disorder and contribute to the increase of oxidative damage to the dopaminergic neurons.

The mitochondria in cells play a myriad of different and important functions, so any alteration in these organelles could have a considerable impact on the functionality of the cells and also the entire body. Mitochondria are also the site of generation of reactive oxygen and nitrogen species (ROS/RNS) and the subsequent widespread deleterious effects (oxidation and/or nitrosylation of mtDNA, oxidation of phospholipids and proteins) of these intermediates. These effects lead also to the opening of the mitochondrial transition pore, release of Cyt c and the activation of the events that culminate in apoptosis.

Abnormal mitochondrial functions (decreased respiratory complexes activities, increased electron leakage, opening of the mitochondrial transition pore) have all been shown to play a role in the pathophysiology of neurodegenerative disorders such as PD, AD and HD. Mitochondrial involvement in PD is revealed by deficiency of mitochondrial complexes I and IV, decreased ATP production with a parallel reduction in GSH levels.

Among the substances involved in maintaining mitochondrial biogenetics, a number of in vivo and in vitro studies indicate that MLT may emerge as a major therapeutic candidate to preserve bioenergetic function of mitochondria.

MLT is a molecule present in all creatures from prokaryotes to human beings. It is an antioxidant that protected organisms from oxidative stresses and apoptosis and mediates seasonal physiological functions, is a signal of dark/light promoting also sleep, modulates the immune system, and inhibits the growth of several cancer. Indoleamine is an antioxidant that directly scavenges ROS/RNS produced during the normal metabolism of mitochondria and it indirectly promotes the activity of the antioxidant enzymes including SOD, catalase, GPx and GRd.

It has also been documented that the ability of MLT to quell the oxidation-reduction processes, with the formation of free radicals, is due to its conversion to metabolites, such as cyclic 3-OHM, AFMK and AMK. Considering the cascade of reactions that include AFMK and AMK, a MLT can scavenge about ten ROS/RNS. MLT increases the activity of ETC and the ATP synthesis, reducing at the same time the oxygen consumption; then, it avoids an excess of ROS/RNS, preventing PTP opening and apoptosis.

Considering that this hormone is an endogenous, nontoxic, antioxidant molecule without known side-effects, it should be considered as a useful agent in PD patients as a treatment with other conventional therapies. Although MLT is an important molecule and possibly has a great future in PD research, it should be extensively tested across multiple populations for efficacy and real effects along with the side effects at the efficacious doses. Future therapeutic strategies could be directed at identifying and developing MLT analogues as drugs with more powerful inhibitory effects on the mitochondrial cell death pathway, slowing the progression of neurodegenerative diseases.


1 - Lee VM, Trojanowsky JQ. Mechanisms of Parkinson’s disease linked to pathological alpha-synuclein: new targets for drug discovery. Neuron 2006;52(1): 33-38.
2 - Braak H, Del Tredici K, Rub U, de Vos RA, Jansen Steur EN, Braak E. Staging of brain pathology related to sporadic Parkinson’s disease. Neurobiology of Aging 2003;24(2): 197-211.
3 - Yacoubian TA, Standaert DG. Targets for neuroprotection in Parkinson’s disease 2009;1792(7): 676-687.
4 - Schapira AHV. Mitochondria in the aetiology and pathogenesis of Parkinson’s disease. The Lancet Neurology 2008;7(1): 97-109.
5 - Huang Y, Cheung L, Rowe D, Halliday G. Genetic contributions to Parkinson's disease. Brain Research Brain Research Reviews 2004;46(1): 44-70.
6 - Vila M, Przedborski S. Genetic clues to the pathogenesis of Parkinson's disease. Nature Medicine 2004;10(7s): S58-S62.
7 - Dexter DT, Holley AE, Flitter WD, Slater TF, Wells FR, Daniel SE, Lees AJ, Jenner P, Marsden CD. Increased levels of lipid hydroperoxides in the Parkinsonian substantia nigra: an HPLC and ESR study. Movement Disorders 1994;9(1): 92-97.
8 - Fleury C, Mignotte B, Vayssiere JL. Mitochondrial reactive oxygen species in cell death signaling. Biochimie 2002;84(2-3): 131-141.
9 - Vila M, Przedborski S. Targeting programmed cell death in neurodegenerative diseases. Nature Reviews Neuroscience 2003;4(5): 365-375.
10 - Javitch JA, D'Amato RJ, Strittmatter SM, Snyder SH. Parkinsonism-inducing neurotoxin, N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine: uptake of the metabolite N-methyl-4-phenylpyridine by dopamine neurons explains selective toxicity. Proceedings of the National Academy of Sciences of the United States of America 1985;82(7): 2173-2177.
11 - Mizuno Y, Saitoh T, Sone N. Inhibition of mitochondrial alpha-ketoglutarate dehydrogenase by 1-methyl-4-phenylpyridinium ion. Biochemical and Biophysical Research Communications 1987;143(3): 971-976.
12 - Schober A. Classic toxin-induced animal models of Parkinson’s disease: 6-OHDA and MPTP. Cell and Tissue Research 2004;318(1): 215-224.
13 - Terzioglu M, Galter D. Parkinson’s disease: genetic versus toxin-induced rodent models. The FEBS Journal 2008; 275(7): 1384-1391.
14 - Brown GC, Borutaite, V. Inhibition of mitochondrial respiratory complex I by nitric oxide, peroxynitrite and S-nitrosothiols. Biochimica et Biophysica Acta (BBA) - Bioenergetics 2004;1658(1-2): 44-49.
15 - Zhang L, Dawson VL, Dawson TM. Role of nitric oxide in Parkinson’s disease. Pharmacological Therapy 2006;109(1-2): 33-41.
16 - Duty S, Jenner P. Animal models of Parkinson’s disease: a source of novel treatments and clues to the cause of the disease. British Journal of Pharmacology 2011;164(4): 1357-1391.
17 - Perumal AS, Gopal VB, Tordzro WK, Copper TB, Cadet JL. Vitamine E attenuates the toxic effects of 6-hydroxydopamine on free radical scavenging systems in rat brain. Brain Research Bulletin 1992;29(5): 699-701.
18 - Oestreicher E, Sengstock GJ, Riederer P, Olanow CW, Dunn AJ, Arendash GW. Degeneration of nigostriatal dopaminergic neurons increases within the substantia nigra: a histochemical and neurochemical study. Brain Research 1994;660(1): 8-18.
19 - Glinka Y, Gassen M, Youdim MB. Mechanism of 6-hydroxydopamine neurotoxicity. Journal of Neural Transmission. Supplementa 1997;50: 55-56.
20 - Miller GW. Paraquat: the red herring of Parkinson’s disease research. Toxicological Sciences 2007; 100(1): 1-2.
21 - Sinicropi M.S., Rovito N., Carocci A., Genchi G. Acetyl-L-carnitine in Parkinson’s disease. In: Dushanova J. (ed.) Mechanisms in Parkinson's Disease - Models and Treatments. Rijeka: Intech; 2011. p367-392.
22 - Pevet P, Bothorel B, Slotten H, Saboureau M. The chronobiotic properties of melatonin. Cell Tissue Research 2002;309(1): 183-191.
23 - Sewerynek E. Melatonin and the cardiovascular system. Neuroendocrinology Letters 2002;23(Suppl 1): 79-83.
24 - Carillo-Vico A, Reiter RJ, Lardone PJ, Herrera JL, Fernandez-Montesinos R. Guerrero JM, Pozo D. The modulatory role of melatonin on immune responsiveness. Current Opinion in Investigational Drugs 2006;7(5): 423-431.
25 - Barrenetxe J, Delagrange P, Martinez JA. Physiological and metabolic functions of melatonin. Journal of Physiological Biochemistry 2004;60(1): 61-72.
26 - Blask DE, Sauer LA, Dauchy RT. Melatonin as a chronobiotic/anticancer agent: cellular, biochemical, and molecular mechanisms of action and their implications for circadian-based cancer therapy. Current Topics in Medicinal Chemistry 2002;2(2): 113–132
27 - Millis E, Wu P, Seely D, Guyatt G. Melatonin in the treatment of cancer: a systematic review of randomized controlled trials and meta-analysis. Journal of Pineal Research 2005;39(4): 360-366.
28 - Genovese E, Mazzon C, Muia P, Bramanti P, De Sarro A, Cuzzocrea S. Attenuation in the evolution of experimental spinal cord trauma by treatment with melatonin. Journal of Pineal Research 2005;38(3): 198-208.
29 - Peres MFP. Melatonin, the pineal gland and their implications for headache disorders. Cephalalgia 2005;25(6): 403-411.
30 - Srinivasan V, Pandi-Perumal SR, Cardinali DP, Poeggeler B, Hardeland R. Melatonin in Alzheimer's disease and other neurodegenerative disorders. Behavioral and Brain Functions 2006;2: 15.
31 - Medeiros CA, Carvalhedo de Bruin PF, Lopes LA, Megalhães MC, de Lourdes Seabra M, de Bruin VM. Effect of exogenous melatonin on sleep and motor dysfunction in Parkinson's disease. A randomized, double blind, placebo-controlled study Journal of Neurology 2007;254(4): 459-464.
32 - Sofic E, Rimpapa Z, Kundurovic Z, Sapcanin A, Tahirovic I, Rustencbegovic A, Cao G. Antioxidant capacity of the neurohormone melatonin. Journal of Neural Transmission 2005;112(3): 349-358.
33 - Reiter RJ. Oxidative damage in the central nervous system: protection by melatonin. Progess in Neurobiology 1998,56(3): 359-384.
34 - Rodriguez C, Mayo JC, Sainz RM, Antolín I, Herrera F, Martín V, Reiter RJ. Regulation of antioxidant enzymes: a significant role for melatonin. Journal of Pineal Research 2004;36(1): 1-9.
35 - Tomas-Zapico C, Coto-Montes A. A proposed mechanism to explain the stimulatory effect of melatonin on antioxidative enzymes. Journal of Pineal Research 2005; 39(2): 99-104.
36 - Cuzzocrea S, Costantino C, Gitto E, Mazzon E, Fulia F, Serraino I, Cordaro S, Barberi I, De Sarro A, Caputi AP. Protective effects of melatonin in ischemic brain injury. Journal of Pineal Research 2000; 29(4): 217-227.
37 - Mayo JC, Sainz RM, Tan DX, Antolín I, Rodríguez C, Reiter RJ. Melatonin and Parkinson’s disease. Endocrine 2005;27(2):169–178.
38 - Savaskan, E. Melatonin in aging and neurodegeneration. Drug Development Research 2002;56(3): 482-490.
39 - Leon J, Acuña-Castroviejo D, Sainz RM, Mayo JC, Tan DX, Reiter RJ. Melatonin and mitochondrial function. Life Sciences 2004;75(7): 765-790.
40 - Tapias V, Escames G, López LC, López A, Camacho E, Carrión MD, Entrena A, Gallo MA, Espinosa A, Acuña-Castroviejo D. Melatonin and its brain metabolite N1-acetyl-5-methoxykynuramine prevent mitochondrial nitric oxide synthase induction in parkinsonian mice. Journal of Neuroscience Research 2009;87(13): 3002-3010.
41 - Wang X. The antiapoptotic activity of melatonin in neurodegenerative disease. CNS Neuroscience & Therapeutics 2009;5(4): 345-357.
42 - Douna H, Bavelaar BM, Pellikaan H, Olivier B, Pieters T. Neuroprotection in Parkinson’s disease: a systematic review of the preclinical data. The Open Pharmacology Journal 2012;6: 12-26.
43 - Allam MF, Campbell MJ, Hofman A, Del Castillo AS, Fernàndez-Crehuet Navajas R. Smoking and Parkinson’s disease: systematic review of prospective studies. Movement Disorders 2004;19(6): 614-621.
44 - Itti E, Villafane G, Malek Z, Brugières P, Capacchione D, Itti L, Maison P, Cesaro P, Meignan M. Dopamine transporter imaging under high-dose transdermal nicotine therapy in Parkinson’s disease: an observational study. Nuclear Medicine Communications 2009;30(7): 513-518.
45 - Janson AM, Fuxe K, Agnati LF, Kitayama I, Härfstrand A, Andersson K, Goldstein M. Chronic nicotine treatment counteracts the disappearance of tyrosine-hydroxylase-immunoreactive nerve cell bodies, dendrites and terminals in the mesostriatal dopamine system of the male after partial hemitransection. Brain Research 1988;455(2): 332-345.
46 - Costa G, Abin-Carriquiry JA, Dajas F. Nicotine prevents striatal dopamine loss produced by 6-hydroxydopamine lesion in the substantia nigra. Brain Research 2001;888(2): 336-342.
47 - Abin-Carriquiry JA, McGregor-Armas R, Costa G, Urbanavicius J, Dajas F. Presynaptic involvement in the nicotine prevention of the dopamine loss provoked by 6-OHDA administration in the substantia nigra. Neurotoxicity Research 2002;4(2): 133-139.
48 - Taylor KSM, Cook JA, Counsell CE. Heterogeneity in male to female risk for Parkinson’s disease. Journal of Neurology, Neurosurgery & Psychiatry 2007;78: 905-906.
49 - Murray HE, Pillai AV, McArthur SR, Razvi N, Datla KP, Dexter DT, Gillies GE. Dose and sex-dependent effects of the neurotoxin 6-hydroxydopamine on the nigrostriatal dopaminegic pathway of adult rats: differential actions of estrogen in males and females. Neuroscience 2003;116(1): 213-222.
50 - Dluzen DE, McDermott JL, Liu B. Estrogen alters MPTP-induced neurotoxicity in female mice: effects on striatal dopamine concentrations and release. Journal of Neurochemistry 1996;66(2): 658-666.
51 - Quesada A, Micevych PE. Estrogen interacts with the IGF-1 system to protect nigrostriatal dopamine and maintain motoric behavior after 6-hydroxdopamine lesions. Journal of Neuroscience Research 2004;75(1): 200-205.
52 - D’Astous M, Morisette M, Callier S, Di Paolo T. Regulation of striatal preproenkephalin mRNA levels in MPTP-lesioned mice treated with estradiol. Journal of Neuroscience Research 2005;80(1): 138-144.
53 - Jourdain S, Morissette M, Morin N, Di Paolo T. Oestrogens prevent loss of dopamine transporter (DAT) and vesicular monoamine transporter (VMAT2) in substantia nigra of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine mice. Journal of Neuroendocrinology 2005;17(8): 509-517.
54 - Kachroo A, Irizarry MC, Schwarzschild MA. Caffeine protects against combined paraquat and maneb-induced dopaminergic neuron degeneration. Experimental Neurology 2010;223(2): 657-661.
55 - Xu K, Xu Y-H, Chen J-F, Schwarzschild MA. Neuroprotection by caffeine: time course and role of its metabolites in the MPTP model of Parkinson’s disease. Neuroscience 2010;167(2): 475-481.
56 - Chen JF, Xu K, Petzer JP, Staal R, Xu YJ, Beilstein M, Sonsalla PK, Castagnoli K, Castagnoli N, Schwarzschild MA. Neuroprotection by caffeine and A(2A) adenosine receptor inactivation in a model of Parkinson’s disease. The Journal of Neuroscience 2001;21(10) RC143.
57 - Joghataie MT, Roghani M, Negahdar F, Hashemi L. Protective effect of caffeine against neurodegeneration in a model of Parkinson’s disease in rat: behavioral and histochemical evidence. Parkinsonism & Related Disorders 2004;10(8): 657-661.
58 - Xu K, Xu Y, Brown-Jermyn D, Chen J-F, Ascherio A, Dluzen DE, Schwarzschild MA. Estrogen prevents neuroprotection by caffeine in the mouse 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine model of Parkinson’s disease. The Journal of Neuroscience 2006;26(2): 535-541.
59 - Boireau A, Bubedat P, Bordier F, Imperato A, Moussaoui S. The protective effect of riluzole in the MPTP model of Parkinson’s disease in mice is not due to a decrease in MPP+ accumulation. Neuropharmacology 2000;39(6): 1016-1020.
60 - Parris MK. Parkinson’s disease as multifactorial oxidative neurodegeneration: implications for integrative management. Alternative Medicine Review 2000;5(6): 502-545.
61 - Calabrese V, Colombrita C, Sultana R, Scapagnani G, Calvani M, Butterfield DA, Giuffrida Stella AM. Redox modulation of heat shock protein expression by acetylcarnitine in aging brain: relationship to antioxidant status and mitochondrial function. Antioxidants and Redox Signaling 2006;8(3-4): 404-416.
62 - McDaniel MA, Maier SF, Einstein GO. “Brain-specific” nutrients: a memory cure? Nutrition 2003;19(11-12): 957-975.
63 - Hongyu Z, Haiqun J, Jianghai L. Ni A, Bing Y, Weili S, Xuemin W, Xin L, Cheng L, Jiankang L. Combined R-α-lipoic acid and acetyl-L-carnitine exerts efficient preventative effects in a cellular model of Parkinson’s disease. Journal of Cellular and Molecular Medicine 2010;14(1-2): 215-225.
64 - Rajeswari A, Sabesan M. Inhibition of monamine oxidase-B by the polyphenolic compound, curcumin and its metabolite tetrahydrocurcumine, in a model of Parkinson’s disease induced by MPTP neurodegeneration in mice. Inflammopharmacology 2008;16(2): 96-99.
65 - Hu G, Bidel S, Jousilahti P, Antikainen R, Tuomilehto J. Coffee and tea consumption and the risk of Parkinson’s disease. Movement Disorders 2007;22(1): 2242-2248.
66 - Levites Y, Weinreb O, Maor G, Youdim MB, Mandel S. Green tea polyphenol (-) epigallocatechin-3-gallate prevents N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced dopaminergic neurodegeneration. Journal of Neurochemistry 2001;78(5): 1073-1082.
67 - Maharaj DS, Saravanan KS, Maharaj H, Mohanakumar KP, Daya S. Acetaminophen and aspirin inhibit superoxide anion generation and lipid peroxidation, and protect against 1-methyl-4-phenyl pyridinium-induced dopaminergic neurotoxicity in rats. Neurochemistry International 2004;44(5): 355-360.
68 - Khan M, Ahmad A, Ishrat T, Khan MB, Hoda MN, Khuwaja G, Raza SS, Khan A, Javed H, Vaibhav K, Islam F. Resveratrol attenuates 6-hydroxydopamine-induced oxidative damage and dopamine depletion in rat model of Parkinson’s disease. Brain Research 2010;1328(139-151): 139-151.
69 - Jin BK, Shin DY, Jeong MY, Gwag MR, Baik HW, Yoon KS, Cho YH, Joo WS, Kim YS, Baik HH. Melatonin protects nigral dopaminergic neurons from 1-methyl-4-phenylpyridinium (MPP+) neurotoxicity in rats. Neuroscience Letters 1998;245(2): 61-64.
70 - Blanchet J, Longpré F, Bureau G, Morisette M, Di Paolo T, Bronchti G, Martinoli MG. Resveratrol, a red wine polyphenol, protects dopaminergic neurons in MPTP-treated mice. Progress in Neuropsychopharmacology and Biological Psychiatry 2008;32(5): 1243-1250.
71 - Hardeland R, Coto-Montes A, Poeggeler B. Circadian rhythms, oxidative stress and antioxidative defense mechanisms. Chronobiology International 2003;20(6): 921-962.
72 - Berson DM, Dunn FA, Takao M. Phototransduction by retinal ganglion cells that set the circadian clock. Science 2002;295(5557): 1070-1073.
73 - Iuvone PM, Tosini G, Pozdeyev N, Haque R, Klein DC, Chaurasia SS. Circadian clocks, clock networks, arylalkylamine N acetyltransferase, and melatonin in the retina. Progress in Retinal and Eye Research 2005; 24(4): 433-456.
74 - Conti A, Conconi S, Hertens E, Skwarlo-Sonta K, Markowska M, Maestroni JM. Evidence for melatonin synthesis in mouse and human bone marrow cells. Journal of Pineal Research 2000;28(4): 193-202.
75 - Slominski A, Tobin DJ, Zmijewski MA, Wortsman J, Paus R. Melatonin in the skin: synthesis, metabolism and functions. Trends Endocrinolology & Metabolism 2007;19(1) 17-24.
76 - Lerner AB, Case JD, Takahashi Y, Lee TH, Mori W. Isolation of melatonin, the pineal gland factor that lightens melanocytes. Journal of the American Chemical Society 1958;80(10): 2587-2587.
77 - Reiter RJ. Melatonin: the chemical expression of darkness. Molecular and Cellular Endocrinology 1991;79(1-3): C153-C158.
78 - Reiter RJ. The melatonin rhythm: both a clock and a calendar. Experientia 1993;49(8) 654-664.
79 - Tomas-Zapico C, Coto-Montes A. Melatonina as antioxidant under pathological processes. Recent Patents on Endocrine, Metabolic & Immune Drug Discovery 2007;1: 63-82
80 - Dubocovich ML, Delagrange P, Krause DN, Sugden D, Cardinali DP, Olcese J. International union of basic and clinical pharmacology. LXXV. Nomenclature, classification, and pharmacology of G protein-coupled melatonin receptors. Pharmacological Reviews 2010; 62: 343-380.
81 - Nosjean O, Ferro M, Coge F, Beauverger P, Henlin JM, Lefoulon F, Fauchere JL, Delagrange P, Canet E, Boutin JA. Identification of the melatonin-binding site MT as the quinone reductase 2, Journal of Biological Chemistry 2000;275(40): 31311-31317.
82 - Wiesenberg I, Missbach M, Kahlen JP, Schrader M, Carlberg C. Transcriptional activation of the nuclear receptor RZRα by the pineal gland hormone melatonin and identification of CGP 52608 as a synthetic ligand. Nucleic Acids Research 1995;23(3): 327-333.
83 - Smirnov AN. Nuclear melatonin receptors. Biochemistry 2001;66(1): 19-26.
84 - Dubocovich ML, Delagrange P, Krause DN, Sugden D, Cardinali DP, Olcese J. International union of basic and clinical pharmacology. LXXV. Nomenclature, classification, and pharmacology of G protein-coupled melatonin receptors. Pharmacological Reviews 2010;62(3): 343-380.
85 - Liu T, Borjigin J. N-acetyltransferase is not the ratelimiting enzyme of melatonin synthesis at night. Journal of Pineal Research 2005;39(1): 91-96.
86 - Berson, DM, Dunn FA, Takao M. Phototransduction by retinal ganglion cells that set the circadian clock. Science 2002;295: 1070-1073.
87 - Sugden D. Melatonin biosynthesis in the mammalian pineal gland. Experientia 1989;45(10): 922-932.
88 - Tan DX, Manchester LC, Sanchez-Barcelo E, Mediavilla MD, Reiter RJ. Significance of high levels of endogenous melatonin in mammalian cerebrospinal fluid and in the central nervous system. Current Neuropharmacology 2010;8(3): 162-167.
89 - Cardinali DP, Lynch HJ, Wurtman RJ. Binding of melatonin to human and rat plasma proteins. Endocrinology 1972;91(5): 1213-1218.
90 - Gilad E, Zisapel N. High-affinity binding of melatonin to hemoglobin. Biochemical and Molecular Medicine 1995;56(2): 115-120.
91 - Hirata F, Hayaishi O, Tokuyama T, Senoh S. In vitro and in vitro formation of two new metabolites of melatonin. Journal of Biological Chemistry 1974;249(4):1311-1313.
92 - Tan DX, Manchester LC, Burkhardt S, Sainz RM, Mayo JC, Kohen R, Shohami E, Huo Y-S, Hardeland R, Reiter RJ. N1-acetyl-N2- formyl-5-methoxykynuramine, a biogenic amine and melatonin metabolite, functions as a potent antioxidant. The FASEB Journal 2001; 15(12): 2294-2296.
93 - Ressmeyer AR, Mayo JC, Zelosko V, et al. Antioxidant properties of the melatonin metabolite N1-acetyl-5-methoxykynuramine (AMK): scavenging of free radicals and prevention of protein destruction. Redox Report 2003; 8(4): 205-213.
94 - Acuña-Castroviejo D, Escames G, Leon J, Carazo A, Khaldy H. Mitochondrial regulation by melatonin and its metabolites. Advances in Experimetal Medicine and Biology 2003; 527: 549-557.
95 - Reiter RJ, Tan DX, Gitto E, Sainz RM, Mayo JC, Leon J, Manchester LC, Vijayalaxmi, Kilic E, Kilic U. Pharmacological utility of melatonin in reducing oxidative cellular and molecular damage. Polish Journal of Pharmacology 2004; 56(2): 159-170.
96 - Menendez-Pelaez A, Poeggeler B, Reiter RJ, Barlow-Walden L, Pablos MI, Tan DX. Nuclear localization of melatonin in different mammalian tissues: immunocytochemical and radioimmunoassay evidence. Journal of Cellular Biochemistry 1993;53: 373-382.
97 - Escames G, López A, García JA, García L, Acuña-Castroviejo D, García JJ, López LC. The role of mitochondria in brain aging and the effects of melatonin. Current Neuropharmacology 2010;8(3): 182-193.
98 - García JJ, Reiter RJ, Pié J, Ortiz GG, Cabrera J, Sáinz RM, Acuña-Castroviejo D. Role of pinoline and melatonin in stabilizing hepatic microsomal membranes against oxidative stress. Journal of Bioenergetics and Biomembranes 1999;31(6): 609-616.
99 - Acuña-Castroviejo D, Martin M, Macias M, Escames G, Leon J, Khaldy H, Reiter RJ. Melatonin, mitochondria, and cellular bioenergetics. Journal of Pineal Research 2001;30(2): 65-74.
100 - Antolín I, Rodríguez C, Saínz RM, Mayo JC, Uría H, Kotler ML, Rodríguez-Colunga MJ, Tolivia D, Menéndez-Peláez A. Neurohormone melatonin prevents cell damage: effect on gene expression for antioxidant enzymes. The FASEB Journal 1996;10(8): 882-890.
101 - Crespo E, Macias M, Pozo D, Escames G, Martin M, Vives F, Guerrero JM, Acuña-Castroviejo D. Melatonin inhibits expression of the inducible NO synthase II in liver and lung and prevents endotoxemia in lipopolysaccharide-induced multiple organ dysfunction syndrome in rats. The FASEB Journal. 1999;13(12): 1537-1546.
102 - Escames G, Leon J, Macias M, Khaldy H, Acuña-Castroviejo D. Melatonin counteracts lipopolysaccharide-induced expression and activity of mitochondrial nitric oxide synthase in rats. The FASEB Journal 2003;17(8): 932–934.
103 - León J, Macías M, Escames G, Camacho E, Khaldy H, Martín M, Espinosa A, Gallo MA, Acuña-Castroviejo D. Structure-related inhibition of calmodulin-dependent neuronal nitric-oxide synthase activity by melatonin and synthetic kynurenines. Molecular Pharmacology 2000;58(5): 967-975.
104 - Liu RY, Zhou JN, van Heerikhuize J, Hofman MA, Swaab DF. Decreased melatonin levels in postmortem cerebrospinal fluid in relation to aging, Alzheimer's disease, and apolipoprotein E-epsilon4/4 genotype. The Journal of Clinical Endocrinology & Metabolism 1999;84(1): 323-327.
105 - SrinivasanV, Spence DW, Pandi-Perumal SR, Brown GM, Cardinali DP. Melatonin in mitochondrial dysfunction and related disorders. International Journal of Alzheimer’s Disease 2011: 1-16.
106 - Domínguez-Rodríguez A, Abreu-González P, García MJ, Sanchez J, Marrero F, de Armas-Trujillo D. Decreased nocturnal melatonin levels during acute myocardial infarction. Journal of Pineal Research 2002;33(4): 248-252.
107 - Yaprak M, Altun A, Vardar A, Aktoz M, Ciftci S, Ozbay G. Decreased nocturnal synthesis of melatonin in patients with coronary artery disease. International Journal of Cardiology 2003;89(1): 103-107.
108 - Lenaz G. The mitochondrial production of reactive oxygen species: mechanisms and implications in human pathology. IUBMB Life 2001;52(3-5): 159-164.
109 - Giulivi C, Poderoso JJ, Boveris A. Production of nitric oxide by mitochondria. The Journal of Biological Chemistry 1998;273(18): 11038-11043.
110 - Stamler JS, Singel DJ, Loscalzo, J. Biochemistry of nitric oxide and its redox-activated forms. Science 1992;258(5090): 1898-1902.
111 - Raha S, Robinson BH. Mitochondria, oxygen free radicals, disease and ageing. Trends in Biochemical Sciences 2000;25(10): 502-508.
112 - Droge W. Free radicals in the physiological control of cell function. Physiological Reviews 2002;82(1): 47-95.
113 - Liochev SI, Fridovich I. Mechanism of the peroxidase activity of Cu, Zn superoxide dismutase. Free Radical Biology and Medicine 2010;48(12): 1565-1569.
114 - Chance B, Sies H, Boveris A. Hydroperoxide metabolism in mammalian organs. Physiological Reviews 1979;59(3): 527-605.
115 - Fernandez-Checa JC, Kaplowski N. Hepatic mitochondrial glutathione: transport and role in disease and toxicity. Toxicology and Applied Pharmacology 2005;204(3): 263-273.
116 - Martín M, Macías M, Escames G, Leon J, Acuña-Castroviejo D. Melatonin but not vitamins C and E maintains glutathione homeostasis in t-butyl hydroperoxide-induced mitochondrial oxidative stress. The FASEB Journal 2000;14(12): 1677-1679.
117 - Martín M, Macías M, Escames G, Reiter RJ, Agapito MT, Ortiz GG, Acuña-Castroviejo D. Melatonin-induced increased activity of the respiratory chain complexes I and IV can prevent mitochondrial damage induced by ruthenium red in vivo. Journal of Pineal Research 2000;28(4): 242-248.
118 - Acuña-Castroviejo D, Escames G, Carazo A, Leon J, Khaldy H, Reiter RJ. Melatonin, mitochondrial homeostasis and mitochondrial-related diseases. Current Topics in Medicinal Chemistry 2002;2(2): 133-151.
119 - Kerr J.F.R., Harmon B.V. Definition and incidence of apoptosis: an historical perspective. In: Tomei L.D., Cope F.O. (ed.) Apoptosis: the Molecular Basis of Cell Death. Cold Spring Harbor Laboratory Press, Cold Spring Harbor, NY, 1991. p5-29.
120 - Ren Y, Savill J. Apoptosis: the importance of being eaten. Cell Death & Differentiation; 1998;5(7): 563-568.
121 - Kroemer G, Dallaporta B, Resche-Rigon M. The mitochondrial death/life regulator in apoptosis and necrosis. Annual Review of Physiology 1998;60: 619-642.
122 - Yang J, Liu X, Bhalla K, Kim CN, Ibrado AM, Cai J, Peng TI, Jones DP, Wang X. Prevention of apoptosis by Bcl-2: release of cytochrome c from mitochondria blocked. Science 1997;275(5303): 1129-1132.
123 - Suzuki Y, Imai Y, Nakayama H, Takahashi K, Takio K, Takahashi R. A serine protease, HtrA2, is released from the mitochondria and interacts with XIAP, inducing cell death. Molecular Cell 2001;8(3): 613-621.
124 - Li LY, Luo X, Wang X. Endonuclease G is an apoptotic DNase when released from mitochondria. Nature 2001;412(6842): 95-99.
125 - Halestrap AP, Mcstay GP, Clarke SJ. The permeability transition pore complex: another view. Biochimie 2002;84(2-3): 153-166.
126 - Urata Y, Honma S, Goto S, Todoriki S, Ueda T, Cho S, Honma K, Kondo T. Melatonin induces-glutamylcysteine synthase mediated by activator protein-1 in human vascular endothelial cells. Free Radical Biology & Medicine 1999;27(7-8): 838-847.
127 - Yamamoto HA, Tang HW. Preventive effects of melatonin against cyanide-induced seizures and lipid peroxidation in mice. Neuroscience Letters 1996;207(2): 89-92.
128 - Absi E, Ayala A, Machado A, Parrado J. Protective effect of melatonin against the 1-methyl-4-phenylpyridinium-induced inhibition of Complex I of the mitochondrial respiratory chain. Journal of Pineal Research 2000;29(1): 40-47.
129 - Martín M, Macías M, León J, Escames G, Khaldy H, Acuña-Castroviejo D. Melatonin increases the activity of the oxidative phosphorylation enzymes and the production of ATP in rat brain and liver mitochondria. The International Journal of Biochemistry & Cell Biology 2002;34(4): 348-357.
130 - Reiter RJ, Tan DX, Qi, W, Manchester LC, Karbownik M, Calvo JR. Pharmacology and physiology of melatonin in the reduction of oxidative stress in vivo. Biological Signals and Receptors 2000;9(3-4): 160-171.
131 - Paradies G, Petrosillo G, Paradies V, Reiter RJ, Ruggiero FM. Melatonin, cardiolipin and mitochondrial bioenergetics in health and disease. Journal of Pineal Research 2010;48(4): 297-310.
132 - Pappolla MA, Simovich MJ, Bryant-Thomas T, Chyan Y-J, Poeggeler B, Dubocovich M, Bick R, Perry G, Cruz-Sanchez F, Smith MA. The neuroprotective activities of melatonin against the Alzheimer β-protein are not mediated by melatonin membrane receptors. Journal of Pineal Research 2002;32(3): 135-142.
133 - Antolín I, Mayo JC, Sainz RM, de los Angeles del Brío M, Herrera F, Martín V, Rodríguez C. Protective effect of melatonin in a chronic experimental model of Parkinson’s disease. Brain Research 2002;943(2): 163-173.
134 - Sandik R. Pineal melatonin functions: possible relevance to Parkinson's disease. International Journal of Neuroscience 1990;50(1-2): 37-53.
135 - Miller JW, Selhub J, Joseph JA. Oxidative damage caused by free radicals produced during catecholamine autoxidation: protective effects of O-methylation and melatonin. Free Radical Biology & Medicine 1996;21(2): 241-249.
136 - Khaldy H, Escames G, Leon J, Vives F, Luna JD, Acuna-Castroviejo D. Comparative effects of melatonin, L-deprenyl, Trolox and ascorbate in the suppression of hydroxyl radical formation during dopamine autoxidation in vitro. Journal of Pineal Research 2000;29(2): 100-107.
137 - Kim YS, Joo WS, Jin BK, Cho YH, Baik HH, Park CW. Melatonin protects 6-OHDA-induced neuronal death of nigrostriatal dopaminergic system. Neuroreport 1998;9(10): 2387-2390.
138 - Joo WS, Jin BK, Park CW, Maeng SH, Kim YS. Melatonin increases striatal dopaminergic function in 6-OHDA-lesioned rats. NeuroReport 1998;9: 4123-4126.
139 - Ortiz GG, Crespo-Lopez ME, Moran-Moguel C, Garcia JJ, Reiter RJ, Acuna-Castroviejo D. Protective role of melatonin against MPTP-induced mouse brain cell DNA fragmentation and apoptosis in vivo. Neuroendocrinology Letters 2001;22(2): 101-108.
140 - Dabbeni-Sala F, Di Santo S, Franceschini D, Skaper SD, Giusti P. Melatonin protects against 6-OHDA-induced neurotoxicity in rats: a role for mitochondrial complex I activity. The FASEB Journal 2001;15(1): 164-170.
141 - Chetsawang J, Govitrapong P, Chetsawang B. Melatonin inhibits MPP+-induced caspase-mediated death pathway and DNA fragmentation factor-45 cleavage in SK-N-SH cultured cells. Journal of Pineal Research 207;43(2): 115-120.
142 - Khaldy H, Escames G, Leon J, Bikjdaouene L, Acuna-Castroviejo D. Synergistic effects of melatonin and deprenyl against MPTP-induced mitochondrial damage and DA depletion. Neurobiology of Aging 2003;24(3): 491-500.
143 - Chen ST, Chuang JI, Hong MH, Li EI. Melatonin attenuates MPP+-induced neurodegeneration and glutathione impairment in the nigrostriatal dopaminergic pathway. Journal of Pineal Research 2002;32(4): 262-269.
144 - Stull ND, Polan DP, Iacovitti L. Antioxidant compounds protect dopamine neurons from death due to oxidative stress in vitro. Brain Research 2002;931(2): 181-185.
145 - Coulom H, Birman S. Chronic exposure to rotenone models sporadic Parkinson's disease in Drosophila melanogaster. Journal of Neuroscience 2004;24(48):10993-10998.
146 - Mayo JC, Sainz RM, Uria H, Antolin I, Esteban MM, Rodriguez C. Melatonin prevents apoptosis induced by 6-hydroxydopamine in neuronal cells: implications for Parkinson's disease. Journal of Pineal Research 1998; 24(3): 179-192.
147 - Mayo JC, Sainz RM, Antolin I, Rodriguez C. Ultrastructural confirmation of neuronal protection by melatonin against the neurotoxin 6-hydroxydopamine cell damage. Brain Research 1999;818(2): 221-227.
148 - León J, Acuña-Castroviejo D, Escames G, Tan DX, Reiter RJ. Melatonin mitigates mitochondrial malfunction. Journal of Pineal Research 2005;38(1): 1-9.
149 - Adi N, Mash DC, Ali Y, Singer C, Shehadeh L, Papapetropoulos S. Melatonin MT1 and MT2 receptor expression in Parkinson’s disease. Medical Science Monitor 2010;16(2): BR61-BR67.
150 - Aurora RN, Zak RS, Maganti RK, Auerbach SH, Casey KR, Chowdhuri S, Karippot A, Ramar K, Kristo DA, Morgenthaler TI. Best practice guide for the treatment of REM sleep behavior disorder (RBD). Journal of Clinical Sleep Medicine 2010;6(1): 85-95.