Despite the effective use of antiepileptic drugs (AEDs) for epilepsy, therapeutic failure occurs in 30% of patients. <em>N</em>ovel approaches are targeting the inhibition of epileptogenesis. <em>N</em>-<em>acetyl</em>-<em>5</em>-<em>methoxytryptamine</em> (melatonin) is an indoleamine produced mainly by the pineal gland, and has been observed to exhibit antiepileptic and neuroprotective effects in experimental and clinical investigations. In the present study, the underlying protective mechanism of melatonin on neonatal seizure-induced long-term excitotoxicity was examined in the hippocampus of rats, predominantly on the metabolism-associated genes. Sprague Dawley rats (6-day-old; P6) were randomly divided into four groups, the control (Cont), melatonin-treated control (Mel), recurrent neonatal seizure (RS) and treatment with melatonin and RS combined (Mel+RS). At P3<em>5</em>, mossy fiber sprouting and changes in gene expression in hippocampus were assessed using Timm staining, reverse transcription-quantitative polymerase chain reaction and use of the 2(-ΔCT) methods, respectively. The aberrant mossy fiber sprouting in the supra granular region of the dentate gyrus and CA3 subfield of the hippocampus was suppressed by pretreatment with melatonin. In addition, among the nineteen genes identified, four energy metabolism-associated genes (Kcnj11, leptin receptor, dopamine receptor D2 and melanocortin 4 receptor), four lipid metabolism-associated genes (apolipoprotein A-I, opioid receptor κ 1, pyruvate dehydrogenase kinase, isozyme 4 and cytochrome P4<em>5</em>0, family 46, subfamily a, polypeptide 1) and zinc transporter 1 (ZnT1), sphingomyelinase (nSMase) and Cathepsin-E, were markedly downregulated by melatonin treatment in the Mel group or in the developmental seizure RS and Mel + RS groups, compared with that in the Cont group. Furthermore, the melatonin-pretreated seizure rats (Mel + RS) exhibited a significantly upregulated expression of calcium/calmodulin-dependent protein kinase II α (CaMKIIα), <em>acetyl</em>-Coenzyme A <em>acetyl</em>transferase 1 (ACAT1), ZnT-1, metallothionein 1 (MT-1), nSMase and Cathepsin-E, compared with the RS rats. Thus, the present study investigated changes in the expression of metabolic genes in the hippocampus following pretreatment with melatonin. Fluorthyl-induced decreases in the expression levels of ACAT1/nSMase/Cathepsin-E, ZnT-1/MT-1 and CaMKIIα in the hippocampus, and the reversal by melatonin may be associated with a decrease in neonatal seizure-induced aberrant mossy fiber sprouting, which requires further investigation.

Melatonin (<em>N</em>-<em>acetyl</em>-<em>5</em>-<em>methoxytryptamine</em>), which is primarily synthesized in and secreted from the pineal gland, plays a pivotal role in cell proliferation as well as in the regulation of cell metastasis and cell survival in a diverse range of cells. The aim of this study is to investigate protection effect of melatonin on H2O2-induced cell damage and the mechanisms of melatonin in human keratinocytes. Hydrogen peroxide dose-dependently induced cell damages in human keratinocytes and co-treatment of melatonin protected the keratinocytes against H2O2-induced cell damage. Melatonin treatment activated the autophagy flux signals, which were identified by the decreased levels of p62 protein. Inhibition of autophagy flux via an autophagy inhibitor and ATG<em>5</em> siR<em>N</em>A technique blocked the protective effects of melatonin against H2O2-induced cell death in human keratinocytes. And we found the inhibition of sirt1 using sirtinol and sirt1 siR<em>N</em>A reversed the protective effects of melatonin and induces the autophagy process in H2O2-treated cells. This is the first report demonstrating that autophagy flux activated by melatonin protects human keratinocytes through sirt1 pathway against hydrogen peroxide-induced damages. And this study also suggest that melatonin could potentially be utilized as a therapeutic agent in skin disease.

Melatonin (<em>N</em>-<em>acetyl</em>-<em>5</em>-<em>methoxytryptamine</em>)/MT2 receptor-dependent epigenetic modification represents a novel pathway in the treatment of neuropathic pain. Because spinal ten-eleven translocation methylcytosine dioxygenase 1 (Tet1)-dependent epigenetic demethylation has recently been linked to pain hypersensitivity, we hypothesized that melatonin/MT2-dependent analgesia involves spinal Tet1-dependent demethylation. Here, we showed that spinal Tet1 gene transfer by intrathecal delivery of Tet1-encoding vectors to naïve rats produced profound and long-lasting nociceptive hypersensitivity. In addition, enhanced Tet1 expression, Tet1-metabotropic glutamate receptor subtype <em>5</em> (mGluR<em>5</em>) promoter coupling, demethylation at the mGluR<em>5</em> promoter, and mGluR<em>5</em> expression in dorsal horn neurons were observed. Rats subjected to spinal nerve ligation and intraplantar complete Freund's adjuvant injection displayed tactile allodynia and behavioral hyperalgesia associated with similar changes in the dorsal horn. <em>N</em>otably, intrathecal melatonin injection reversed the protein expression, protein-promoter coupling, promoter demethylation, and pain hypersensitivity induced by Tet1 gene transfer, spinal nerve ligation, and intraplantar complete Freund's adjuvant injection. All the effects caused by melatonin were blocked by pretreatment with a MT2 receptor-selective antagonist. In conclusion, melatonin relieves pain by impeding Tet1-dependent demethylation of mGluR<em>5</em> in dorsal horn neurons through the MT2 receptor. Our findings link melatonin/MT2 signaling to Tet1-dependent epigenetic demethylation of nociceptive genes for the first time and suggest melatonin as a promising therapy for the treatment of pain.

Melatonin (<em>N</em>-<em>acetyl</em>-<em>5</em>-<em>methoxytryptamine</em>) is an important regulator of circadian rhythms and immunity in animals. However, the diurnal changes of endogenous melatonin and melatonin-mediated diurnal change of downstream responses remain unclear in Arabidopsis. Using the publicly available microarray data, we found that the transcript levels of two melatonin synthesis genes (serotonin <em>N</em>-<em>acetyl</em>transferase (S<em>N</em>AT) and caffeate O-methyltransferase (COMT)) and endogenous melatonin level were regulated by diurnal cycles, with different magnitudes of change. Moreover, the transcripts of C-repeat-binding factors (CBFs)/Drought response element Binding 1 factors (DREB1s) were co-regulated by exogenous melatonin and diurnal changes, indicating the possible correlation among clock, endogenous melatonin level and AtCBFs expressions. Interestingly, diurnal change of plant immunity against Pst DC3000 and CIRCADIA<em>N</em>CLOCK ASSOCIATED 1 (CCA1) expression were largely lost in AtCBFs knockdown line-amiR-1. Taken together, this study identifies the molecular pathway underlying the diurnal changes of immunity in Arabidopsis. <em>N</em>otably, the diurnal changes of endogenous melatonin may regulate corresponding changes of AtCBF/DREB1s expression and their underlying diurnal cycle of plant immunity and AtCCA1.

Melatonin (<em>N</em>-<em>acetyl</em>-<em>5</em>-<em>methoxytryptamine</em>) is a naturally synthesized hormone secreted from the pineal gland in a variety of animals and is primarily involved in the regulation of the circadian rhythm, which is the natural cycle controlling sleep in organisms. Melatonin acts on specific receptors and has an important role in overall energy metabolism. This review encompasses several aspects of melatonin activity, such as synthesis, source, structure, distribution, function, signaling and its role in normal physiology. The review highlights the cellular signaling and messenger systems involved in melatonin's action on the body and their wider implications, the distribution and diverse action of different melatonin receptors in specific areas of the brain, and the pharmacological agonists and antagonists that have specific action on these melatonin receptors. This review also incorporates the antitumor effects of melatonin in considerable detail, emphasizing on melatonin's role as an adjuvant therapeutic agent in glioma treatment. We conclude that the diminishing levels of melatonin have significant debilitating effects on normal physiology and can also be associated with malignant conditions such as glioma. Based on the review of the available evidence, our study provides a broad platform for a better understanding of the specific roles of melatonin and serves as a starting point for further investigation into the therapeutic effect of melatonin in glioma as an adjuvant therapeutic agent.

Melatonin (<em>N</em>-<em>acetyl</em>-<em>5</em>-<em>methoxytryptamine</em>) has differentiated the effects on apoptosis in normal and cancer cells. The mechanisms that account for the opposite effects on these cells are not adequately understood. In this study, we investigated the combined effect of melatonin and thapsigargin (TG) on apoptosis of renal cancer cells. Cotreatment with melatonin (1mm) and TG (<em>5</em>0nm) induced approximately 10-fold expression levels of CCAAT-enhancer-binding proteins homologous protein (CHOP) compared with that of TG (<em>5</em>0nm) alone. Downregulation of CHOP expression using small interfering R<em>N</em>As markedly attenuated melatonin plus TG-mediated apoptosis. In addition, cotreatment with TG- and melatonin-induced CHOP upregulation likely relates to melatonin's antioxidant capacity because we proved that this CHOP upregulation is melatonin receptor independent. Our results collectively demonstrate that the upregulation of CHOP contributes to the enhancing effect of melatonin plus TG on apoptosis in cancer cells.

OBJECTIVE

We studied the effect of melatonin (MLT) (<em>N</em>-<em>acetyl</em> <em>5</em>-<em>methoxytryptamine</em>) on the growth rate of normal skin fibroblasts and of fibroblasts from involved and apparently uninvolved skin of patients affected by systemic sclerosis (SSc).

METHODS

The growth rate was evaluated on the basis of growth curves and a 3H-thymidine incorporation assay.

RESULTS

Our results demonstrate that a dose of 200 micrograms/ml of MLT inhibits >> 80%) both control and SSc fibroblasts. Inhibition was dose-dependent and was greater than 70% for MLT concentrations of 100 micrograms/ml, 200 micrograms/ml and 400 micrograms/ml. 3H-thymidine incorporation was correlated with the effect on the growth curves (81% at 200 micrograms/ml of MLT). In contrast, at a low dosage of 6 micrograms/ml, MLT exerted a stimulatory effect on cell proliferation in all the cell lines analyzed. Cell viability was not affected by MLT at any of the concentrations tested. A recovery study indicated that replacement of MLT-containing medium with MLT-free medium resulted in a re-establishment of cell growth.

CONCLUSIONS

These results suggest that MLT, at higher dosages, is a potent inhibitor of the proliferation of fibroblasts derived from the skin of healthy and SSc patients.

Action of melatonin (<em>N</em>-<em>acetyl</em>-<em>5</em>-<em>methoxytryptamine</em>; MEL) on guinea pig hippocampal cells (CA3 neurons and dentate granule cells) were studied in vitro using both extra- and intracellular recording. MEL (1-10 mmol/1) had the following effects: Response to repetitive synaptic stimulation was changed drastically: Double shock facilitation (20 ms interval) turned into depression and stimulus trains of a frequency as low as 1 Hz led to a drastic reduction of the response. Membrane potential was hyperpolarized. Duration of action potential was strongly increased. Threshold for the triggering of action potentials was shifted to more positive levels. IPSPs were prolonged and their shunting power enhanced. Repetitive spiking elicited by the application of bicuculline was reversibly abolished. All these effects had in common that cell excitability was lowered. It is concluded that MEL might influence epileptic seizure activity and should be further investigated as potential anticonvulsant.

Melatonin and resistance exercise alone have been shown to increase the levels of growth hormone (GH). The purpose of this study was to determine the effects of ingestion of a single dose of melatonin and heavy resistance exercise on serum GH, somatostatin (SST), and other hormones of the GH/insulin-like growth factor 1 (IGF-1) axis. Physically active males (n = 30) and females (n = 30) were randomly assigned to ingest either a melatonin supplement at 0.5 mg or 5.0 mg, or 1.0 mg of dextrose placebo. After a baseline blood sample, participants ingested the supplement and underwent blood sampling every 15 min for 60 min, at which point they underwent a single bout of resistance exercise with the leg press for 7 sets of 7 reps at 85% 1-RM. After exercise, participants provided additional blood samples every 15 min for a total of 120 min. Serum free GH, SST, IGF-1, IGFBP-1, and IGFBP-3 were determined with ELISA. Data were evaluated as the peak pre- and post-exercise values subtracted from baseline and the delta values analyzed with separate three-way ANOVA (p < 0.05). In males, when compared to placebo, 5.0 mg melatonin caused GH to increase (p = 0.017) and SST to decrease prior to exercise (p = 0.031), whereas both 0.5 and 5.0 mg melatonin were greater than placebo after exercise (p = 0.045) and less than placebo for SST. No significant differences occurred for IGF-1; however, males were shown to have higher levels of IGFBP-1 independent of supplementation (p = 0.004). The 5.0 mg melatonin dose resulted in higher IGFBP-3 in males (p = 0.017). In conclusion, for males 5.0 mg melatonin appears to increase serum GH while concomitantly lowering SST levels; however, when combined with resistance exercise both melatonin doses positively impacts GH levels in a manner not entirely dependent on SST.

Melatonin (<em>N</em>-<em>acetyl</em>-<em>5</em>-<em>methoxytryptamine</em>) is a biogenic indoleamine structurally related with other important substances such as tryptophan, serotonin, indole-3-acetic acid (IAA). In mammals, birds, reptiles and fish melatonin is a biological modulator of several timing (circadian) processes such as mood, sleep, sexual behavior, immunological status, etc. Since its discovery in plants in 199<em>5</em> several physiological roles, including a possible role in flowering, circadian rhythms and photoperiodicity and as growth-regulator have been postulated. Recently, a possible role in rhizogenesis in lupin has also been proposed. Here, these actions of melatonin in plant development are commented on and some other interesting recent data concerning melatonin in plants are also discussed. The need for more investigation into melatonin and plants is presented as an obvious conclusion.

The present study used male Sprague-Dawley rats to investigate changes in glutathione [reduced (GSH) and oxidized GSH (GSSG)]. lipid peroxidation (as indicated by tissue levels of malonaldehyde and 4-hydroxyalkenals), and the activity of the antioxidant enzyme glutathione peroxidase after a bout of swimming (30 min.) with or without melatonin (<em>N</em>-<em>acetyl</em>-<em>5</em>-<em>methoxytryptamine</em>) treatment. In muscle, the concentration of GSH and the GSH/GSSG ratio were decreased following 30 min. of swimming: these changes are indicative of enhanced oxidative stress. Pretreatment with melatonin prevented these effects. In liver, swimming increased significantly both GSH and GSSG, and decreased the GSH/GSSG ratio. When animals were treated with melatonin, concentrations of GSH and GSSG were also increased after swimming: however, the reduction in the GSH/GSSG ratio was prevented by melatonin. Brain GSH/GSSG ratio was not affected by exercise or by melatonin. Swimming enhanced the levels of lipid peroxidation products is muscle: this was prevented in animals treated with melatonin. Glutathione peroxidase activity was significantly elevated after swimming in both liver and brain with the change not being influenced by concurrent melatonin treatment. It is concluded that swimming imposes an oxidative stress on liver and skeletal muscle and the results show that melatonin confers partial protection against oxidative toxicity, especially in muscle.

The aim of this study was to establish whether the nocturnal peak concentrations of circulating melatonin are affected by a single dose of 7,12-dimethylbenz[a]anthracene (DMBA) in female Sprague-Dawley rats as used for mammary tumor induction. Prior to this, the circadian rhythms of melatonin (<em>N</em>-<em>acetyl</em>-<em>5</em>-<em>methoxytryptamine</em>) and 6-sulfatoxymelatonin, the main metabolic product of melatonin, were determined in female Sprague-Dawley rats. The cosinor analysis revealed significant circadian rhythms with very similar acrophases around 1.00 a.m. for both substances. To enable explanations for possible changes in plasma melatonin after DMBA treatment, the biosynthesis in the pineal and the major metabolic product in the liver, 6-sulfatoxymelatonin, were measured 2 and 7 days after DMBA. Plasma melatonin was depressed by 31-37% (p less than 0.0<em>5</em>) 2 and 7 days after DMBA but the pineal melatonin content remained unchanged. 2 days after DMBA, pineal serotonin and <em>N</em>-<em>acetyl</em>serotonin showed a transient elevation of 3<em>5</em>% (p less than 0.02<em>5</em>) and 2<em>5</em>% (p less than 0.0<em>5</em>), respectively. The plasma concentrations of 6-sulfatoxymelatonin were the same in DMBA- and vehicle-treated animals. An elevation of the 6-sulfatoxymelatonin/melatonin ratio indicated a relative increase in the metabolism of melatonin due to DMBA. The absence of an absolute increase in 6-sulfatoxymelatonin after DMBA could be caused by an additional shift within the spectrum of different metabolic products of melatonin due to the carcinogen. Possible mechanisms are discussed.

High-affi<em>n</em>ity bi<em>n</em>di<em>n</em>g of melato<em>n</em>i<em>n</em> to crude membra<em>n</em>e preparatio<em>n</em>s of bovi<em>n</em>e pi<em>n</em>eal gla<em>n</em>d was exami<em>n</em>ed by a rapid filtratio<em>n</em> procedure through Whatma<em>n</em> GFB paper. Maximal melato<em>n</em>i<em>n</em> bi<em>n</em>di<em>n</em>g was attai<em>n</em>ed i<em>n</em> 60 mi<em>n</em> at 37 degrees C, i<em>n</em> 2 h at 2<em>5</em> degrees C a<em>n</em>d i<em>n</em> <em>5</em> h at 0 degree C; at 2<em>5</em> a<em>n</em>d 37 degrees C it was 36 a<em>n</em>d 42% of that at 0 degree C. Specific bi<em>n</em>di<em>n</em>g was thermolabile a<em>n</em>d decreased followi<em>n</em>g i<em>n</em>cubatio<em>n</em> with trypsi<em>n</em>; it was also pH depe<em>n</em>de<em>n</em>t, the maximum bei<em>n</em>g observed at physiological pH. Melato<em>n</em>i<em>n</em> bi<em>n</em>di<em>n</em>g was i<em>n</em>hibited by the additio<em>n</em> of mo<em>n</em>ovale<em>n</em>t or divale<em>n</em>t io<em>n</em>s to the i<em>n</em>cubatio<em>n</em> buffer. Subcellular fractio<em>n</em>atio<em>n</em> studies i<em>n</em>dicated that 39 a<em>n</em>d <em>5</em>0% of bi<em>n</em>di<em>n</em>g was located i<em>n</em> the pellets at 900 a<em>n</em>d 27,000 g whereas 11% was detected i<em>n</em> the microsomal pellet. Scatchard a<em>n</em>alysis revealed a si<em>n</em>gle populatio<em>n</em> of bi<em>n</em>di<em>n</em>g sites with Kd = (7.0 +/- 1.<em>5</em>) 10(-7) M (mea<em>n</em> +/- SEM, <em>n</em> = 4); bi<em>n</em>di<em>n</em>g site co<em>n</em>ce<em>n</em>tratio<em>n</em> ra<em>n</em>ged from 18<em>5</em> to 3<em>5</em>6 fmol/mg of protei<em>n</em>. Whe<em>n</em> various melato<em>n</em>i<em>n</em> a<em>n</em>alogues were tested for their ability to i<em>n</em>hibit (3H)-melato<em>n</em>i<em>n</em> bi<em>n</em>di<em>n</em>g, the followi<em>n</em>g Ki values (10(-7) M), were obtai<em>n</em>ed: <em>N</em>-<em>acetyl</em>-seroto<em>n</em>i<em>n</em> 120, seroto<em>n</em>i<em>n</em> 130, 2-methyl i<em>n</em>dole 1<em>5</em>4, <em>5</em>-hydroxytryptophol 218, <em>5</em>-<em>methoxytryptamine</em> 266, <em>5</em>-methoxytryptophol 660, tryptami<em>n</em>e 1,740, <em>5</em>-hydroxyi<em>n</em>dole acetic acid 3,4<em>5</em><em>5</em>, <em>5</em>-methoxyi<em>n</em>dole acetic acid 12,690, <em>5</em>-hydroxytryptopha<em>n</em> 13,600, a<em>n</em>d 6-hydroxymelato<em>n</em>i<em>n</em> <em>5</em><em>5</em>,<em>5</em><em>5</em>0. Those results suggest that melato<em>n</em>i<em>n</em> receptors may be prese<em>n</em>t i<em>n</em> the pi<em>n</em>eal gla<em>n</em>d.

A simple, sensitive and specific high throughput radioimmunoassay (RIA) for the quantitative determination of total melatonin (<em>N</em>-<em>acetyl</em>-<em>5</em>-<em>methoxytryptamine</em>) was developed. This method allows the analysis of melatonin in different biological fluids with small sample volumes (e.g. mice and rats), and wide working range. With the preparation of matrix-specific calibrators called "Equalizing Reagent" the influence of results due to different composition between standards and sample matrix was reduced. This reagent is produced by use of the respective biological liquid. Endogenous melatonin is removed by adsorption to activated charcoal. The melatonin-free biological liquid is then used to equalize the assay matrix of standards and untreated samples. Finally, all samples including the standards are digested by use of a protease to reduce non-specific binding, for example to albumin or albumin-like molecules. High-affinity specific antibodies were produced by immunization of rabbits with <em>5</em>-<em>methoxytryptamine</em>-bovine serum albumin. The review of cross reactions to ten structurally similar compounds showed that the antibody has a high specificity for melatonin. This direct RIA uses a [(12<em>5</em>)I]-melatonin tracer for the determination of melatonin. <em>5</em>-<em>methoxytryptamine</em> was synthesized by direct iodination with [(12<em>5</em>)I]-Bolton-Hunter-Reagent. The required acceptance criteria for validation parameters were fulfilled. The flexible standards cover a working range from 12 to 4000 pg/mL with a sample volume of <em>5</em>0 microL (e.g. working range from 3 to 1000 pg/mL with a sample volume of 200 microL). The limit of detection in mouse serum and mouse plasma was 9 pg/mL and 7 pg/mL, respectively. The recovery of melatonin in mouse serum was 108% and in mouse plasma 99%. The variation coefficients of the assay, within and between runs, ranged between 7 and 13% in mouse serum and between <em>5</em> and 8% in mouse plasma. Based on the determination of a 24-h profile of melatonin in mouse samples a characteristic diurnal rhythm of melatonin was observed. The wide working range makes it possible to analyse low and high melatonin concentrations. The validated direct RIA was compared with established sample preparation methods such as liquid-liquid- and solid-phase-extraction followed by RIA. The correlation for methanol extraction is y=1.1x-0.9, R(2)=0.98, P<0.001 and C(18)-extraction y=0.8x-0.03, R(2)=0.99, P<0.001. The distinct advantage of the direct assay of melatonin is that complicated extraction steps can be avoided. The realized advantages of the direct RIA when compared to a commercially available melatonin RIA are its low sample volume and ease of implementation. Exemplary, plasma melatonin was determined at C3H, C<em>5</em>7BL, wild-type and melatonin receptor (MT1-/- and MT2-/-) knockout mice kept under L:D=12:12 cycles. The results have indicated that at all mouse strains have plasma melatonin content, with higher levels during the night and lower levels during the day. Because of different melatonin concentrations the direct RIA convince by its low detection limit and wide working range. The determination of serum and plasma melatonin in mice by ELISA or HPLC-technique previously failed due to the required use of a high sample volume and the low sensitivity. In summary, it can be concluded that the developed and validated direct RIA meets the requirements for the determination of melatonin and is especially suitable for the analysis of melatonin in different mouse strains.

Melatonin (<em>N</em>-<em>acetyl</em>-<em>5</em>-<em>methoxytryptamine</em>) is a chemical mediator produced in the pineal gland and other sites in the body. The melatonin found in the blood is derived almost exclusively from the pineal gland. Since the pineal synthesizes melatonin primarily at night, blood levels of the indole are also higher at night (<em>5</em>-1<em>5</em> fold) than during the day. Some individuals on a nightly basis produce twice as much melatonin as others of the same age. Throughout life, the melatonin rhythm gradually wanes such that, in advanced age, melatonin production is usually at a minimum. Melatonin was recently found to be a free radical scavenger and antioxidant. It has been shown, in the experimental setting, to protect against both free radical induced D<em>N</em>A damage and oxidative stress-mediated lipid peroxidation. Pharmacologically, melatonin has been shown to reduce oxidative damage caused by such toxins as the chemical carcinogen safrole, carbon tetrachloride, paraquat, bacterial lipopolysaccharide, kainic acid, δ-aminolevulinic and amyloid β peptide of Alzheimer's disease as well as a model of Parkinson's disease involving the drug 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Additionally, the oxidative damage caused by agents such as ionizing radiation and excessive exercise is reduced by melatonin. Since free radical-induced molecular injury may play a significant role in aging, melatonin's ability to protect against it suggests a potential function of melatonin in deferring aging and age-related, free radical-based diseases. Besides its ability to abate oxidative damage, other beneficial features of melatonin may be important in combating the signs of aging; these include melatonin's immune-stimulating function, its sleep-promoting ability, its function as an anti-viral agent, and general protective actions at the cellular level. Definitive tests of the specific functions of physiological levels of melatonin in processes of aging are currently being conducted.

OBJECTIVE

We tested the ability of melatonin (<em>N</em>-<em>acetyl</em>-<em>5</em> <em>methoxytryptamine</em>), a highly effective radical scavenger and human hormone, to protect D<em>N</em>A in solution and in human cells against induction of complex D<em>N</em>A clusters and biological damage induced by low or high linear energy transfer radiation (100 kVp X-rays, 970 MeV/nucleon Fe ions).

METHODS

Plasmid D<em>N</em>A in solution was treated with increasing concentrations of melatonin (0.0-3.<em>5</em> mM) and were irradiated with X-rays. Human cells (28SC monocytes) were also irradiated with X-rays and Fe ions with and without 2 mM melatonin. Agarose plugs containing genomic D<em>N</em>A were subjected to Contour Clamped Homogeneous Electrophoretic Field (CHEF) followed by imaging and clustered D<em>N</em>A damages were measured by using <em>N</em>umber Average length analysis. Transformation experiments on human primary fibroblast cells using soft agar colony assay were carried out which were irradiated with Fe ions with or without 2 mM melatonin.

RESULTS

In plasmid D<em>N</em>A in solution, melatonin reduced the induction of single- and double-strand breaks. Pretreatment of human 28SC cells for 24 h before irradiation with 2 mM melatonin reduced the level of X-ray induced double-strand breaks by ∼<em>5</em>0%, of abasic clustered damages about 40%, and of Fe ion-induced double-strand breaks (41% reduction) and abasic clusters (34% reduction). It decreased transformation to soft agar growth of human primary cells by a factor of 10, but reduced killing by Fe ions only by 20-40%.

CONCLUSIONS

Melatonin's effective reduction of radiation-induced critical DNA damages, cell killing, and striking decrease of transformation suggest that it is an excellent candidate as a countermeasure against radiation exposure, including radiation exposure to astronaut crews in space travel.

Mammalian oocytes remain arrested at the first prophase of meiosis in ovarian follicles for an extended period. During this protracted arrest, oocytes are remarkably susceptible to the accumulation of D<em>N</em>A damage. Melatonin (<em>N</em>-<em>acetyl</em>-<em>5</em>-<em>methoxytryptamine</em>), a hormone secreted by the pineal gland, has diverse effects on various physiological processes. However, the effect of melatonin on D<em>N</em>A damage response in mammalian oocytes has not been explored. Here, we showed that melatonin protected mouse oocytes from D<em>N</em>A damage induced by double-strand breaks (DSBs) during prophase arrest and subsequently improved oocyte quality. We found that D<em>N</em>A damage during prophase arrest impaired subsequent meiotic maturation and deteriorated oocyte quality, increasing chromosome fragmentation, spindle abnormality, mitochondrial aggregation, and oxidative stress. However, melatonin treatment during D<em>N</em>A damage accumulation at prophase improved meiotic maturation and relieved the quality decline of oocytes. In addition, melatonin inhibited the accumulation of D<em>N</em>A damage during prophase arrest by reducing the γ-H2AX levels. Although activated ATM levels were decreased by melatonin treatment, the effect of melatonin on D<em>N</em>A damage response was not a direct consequence of ATM inhibition. Instead, melatonin enhanced D<em>N</em>A repair via nonhomologous end-joining (<em>N</em>HEJ) pathway. Interestingly, these actions of melatonin on D<em>N</em>A damage response are receptor-independent in mouse oocytes. Therefore, our results demonstrated that melatonin protects oocytes from D<em>N</em>A damage during prophase arrest by enhancing D<em>N</em>A repair via <em>N</em>HEJ and subsequently prevents the deterioration of oocyte quality during meiotic maturation.

Melatonin is catabolized both enzymatically and nonenzymatically. <em>N</em>onenzymatic processes mediated by free radicals, singlet oxygen, other reactive intermediates such as HOCl and peroxynitrite, or pseudoenzymatic mechanisms are not species- or tissue-specific, but vary considerably in their extent. Higher rates of nonenzymatic melatonin metabolism can be expected upon UV exposure, e.g., in plants and in the human skin. Additionally, melatonin is more strongly nonenzymatically degraded at sites of inflammation. Typical products are several hydroxylated derivatives of melatonin and <em>N</em>¹-<em>acetyl</em>-<em>N</em>²-formyl-<em>5</em>-methoxykynuramine (AFMK). Most of these products are also formed by enzymatic catalysis. Considerable taxon- and site-specific differences are observed in the main enzymatic routes of catabolism. Formation of 6-hydroxymelatonin by cytochrome P4<em>5</em>0 subforms are prevailing in vertebrates, predominantly in the liver, but also in the brain. In pineal gland and non-mammalian retina, de<em>acetyl</em>ation to <em>5</em>-<em>methoxytryptamine</em> (<em>5</em>-MT) plays a certain role. This pathway is quantitatively prevalent in dinoflagellates, in which <em>5</em>-MT induces cyst formation and is further converted to <em>5</em>-methoxyindole-3-acetic acid, an end product released to the water. In plants, the major route is catalyzed by melatonin 2-hydroxylase, whose product is tautomerized to 3-acetamidoethyl-3-hydroxy-<em>5</em>-methoxyindolin-2-one (AMIO), which exceeds the levels of melatonin. Formation and properties of various secondary products are discussed.

L-<em>5</em>-hydroxytryptophan (<em>5</em>-HTP) is both a drug and a natural component of some dietary supplements. <em>5</em>-HTP is produced from tryptophan by tryptophan hydroxylase (TPH), which is present in two isoforms (TPH1 and TPH2). Decarboxylation of <em>5</em>-HTP yields serotonin (<em>5</em>-hydroxytryptamine, <em>5</em>-HT) that is further transformed to melatonin (<i><em>N</em></i>-<em>acetyl</em>-<em>5</em>-<em>methoxytryptamine</em>). <em>5</em>-HTP plays a major role both in neurologic and metabolic diseases and its synthesis from tryptophan represents the limiting step in serotonin and melatonin biosynthesis. In this review, after an look at the main natural sources of <em>5</em>-HTP, the chemical analysis and synthesis, biosynthesis and microbial production of <em>5</em>-HTP by molecular engineering will be described. The physiological effects of <em>5</em>-HTP are discussed in both animal studies and human clinical trials. The physiological role of <em>5</em>-HTP in the treatment of depression, anxiety, panic, sleep disorders, obesity, myoclonus and serotonin syndrome are also discussed. <em>5</em>-HTP toxicity and the occurrence of toxic impurities present in tryptophan and <em>5</em>-HTP preparations are also discussed.

<strong class="sub-title"> Keywords: </strong> <em>5</em>-hydroxytryptophan; animal; biosynthetic pathways; human; microbial production; natural sources; physiological effects.

Melatonin (<em>N</em>-<em>acetyl</em>-<em>5</em>-<em>methoxytryptamine</em>) is a derivative of tryptophan which is produced and secreted mainly by the pineal gland and regulates a variety of important central and peripheral actions. To examine the potential effects of melatonin on the proliferation and differentiation of bovine intramuscular preadipocytes (BIPs), BIPs were incubated with different concentrations of melatonin. Melatonin supplementation at 1 mM significantly increased peroxisome proliferator-activated receptor γ (PPARγ), CCAAT/enhancer-binding protein (C/EBP) β, and C/EBPα expression and promoted the differentiation of BIPs into adipocytes with large lipid droplets and high cellular triacylglycerol (TAG) levels. Melatonin also significantly enhanced lipolysis and up-regulated the expression of lipolytic genes and proteins, including hormone sensitive lipase (HSL), adipocyte triglyceride lipase (ATGL), and perilipin 1 (PLI<em>N</em>1). Moreover, melatonin reduced intracellular reactive oxygen species (ROS) levels by increasing the expression levels and activities of superoxide dismutase 1 (SOD1) and glutathione peroxidase 4 (GPX4). Finally, the positive effects of melatonin on adipogenesis, lipolysis, and redox status were reversed by treatment with luzindole, anantagonist of nonspecific melatonin receptors 1 (MT1) and 2 (MT2), and 4-phenyl-2-propionamidotetraline (4P-PDOT), a selective MT2 antagonist. These results reveal that melatonin promotes TAG accumulation via MT2 receptor during differentiation in BIPs.

Melatonin (<em>N</em>-<em>acetyl</em>-<em>5</em>-<em>methoxytryptamine</em>), secreted by the pineal gland is known to perform multiple functions including, antioxidant, anti-hypertensive, anti-cancerous, immunomodulatory, sedative and tranquilizing functions. Melatonin is also known to be involved in the regulation of body mass index, control the gastrointestinal system and play an important role in cardioprotection, thermoregulation, and reproduction. Recently, several studies have reported the efficacy of Melatonin in treating various pain syndromes. The current paper reviews the studies on Melatonin and its analogs, particularly in <em>N</em>europathic pain. Here, we first briefly summarized research in preclinical studies showing the possible mechanisms through which Melatonin and its analogs induce analgesia in <em>N</em>europathic pain. Second, we reviewed research indicating the role of Melatonin in attenuating analgesic tolerance. Finally, we discussed the recent studies that reported novel Melatonin agonists, which were proven to be effective in treating <em>N</em>europathic pain.

<AbstractText>The ubiquitous sig<em>n</em>ali<em>n</em>g molecule melato<em>n</em>i<em>n</em> (<em>N</em>-<em>acetyl</em>-<em>5</em>-<em>methoxytryptamine</em>) (MT) plays vital roles i<em>n</em> pla<em>n</em>t developme<em>n</em>t a<em>n</em>d stress tolera<em>n</em>ce. Sele<em>n</em>ium (Se) may be phytotoxic at high co<em>n</em>ce<em>n</em>tratio<em>n</em>s. I<em>n</em>teractio<em>n</em>s betwee<em>n</em> MT a<em>n</em>d Se (IV) stress i<em>n</em> higher pla<em>n</em>ts are poorly u<em>n</em>derstood. The aim of this study was to evaluate the defe<em>n</em>sive roles of exoge<em>n</em>ous MT (0 μM, <em>5</em>0 μM, a<em>n</em>d 100 μM) agai<em>n</em>st Se (IV) (0 μM, <em>5</em>0 μM, 100 μM, a<em>n</em>d 200 μM) stress based o<em>n</em> the physiological a<em>n</em>d biochemical properties, thiol biosy<em>n</em>thesis, a<em>n</em>d a<em>n</em>tioxida<em>n</em>t system of Brassica <em>n</em>apus pla<em>n</em>ts subjected to these treatme<em>n</em>ts.</AbstractText><p><div><b>RESULTS</b></div>Se (IV) stress i<em>n</em>hibited B. <em>n</em>apus growth a<em>n</em>d biomass accumulatio<em>n</em>, reduced pigme<em>n</em>t co<em>n</em>te<em>n</em>t, a<em>n</em>d lowered <em>n</em>et photosy<em>n</em>thetic rate (P_<em>n</em>) a<em>n</em>d PSII photochemical efficie<em>n</em>cy (Fv/Fm) i<em>n</em> a dose-depe<em>n</em>de<em>n</em>t ma<em>n</em><em>n</em>er. All of the aforeme<em>n</em>tio<em>n</em>ed respo<em>n</em>ses were effectively alleviated by exoge<em>n</em>ous MT treatme<em>n</em>t. Exoge<em>n</em>ous MT mitigated oxidative damage a<em>n</em>d lipid peroxidatio<em>n</em> a<em>n</em>d protected the plasma membra<em>n</em>es from Se toxicity by reduci<em>n</em>g Se-i<em>n</em>duced reactive oxyge<em>n</em> species (ROS) accumulatio<em>n</em>. MT also alleviated osmotic stress by restori<em>n</em>g foliar water a<em>n</em>d sugar levels. Relative to sta<em>n</em>dalo<em>n</em>e Se treatme<em>n</em>t, the combi<em>n</em>atio<em>n</em> of MT a<em>n</em>d Se upregulated the ROS-detoxifyi<em>n</em>g e<em>n</em>zymes SOD, APX, GR, a<em>n</em>d CAT, i<em>n</em>creased proli<em>n</em>e, free ami<em>n</em>o acids, a<em>n</em>d the thiol compo<em>n</em>e<em>n</em>ts GSH, GSSG, GSH/GSSG, <em>N</em>PTs, PCs, a<em>n</em>d cys a<em>n</em>d upregulated the metabolic e<em>n</em>zymes γ-ECS, GST, a<em>n</em>d PCS. Therefore, MT applicatio<em>n</em> atte<em>n</em>uates Se-i<em>n</em>duce oxidative damage i<em>n</em> pla<em>n</em>ts. MT promotes the accumulatio<em>n</em> of chelati<em>n</em>g age<em>n</em>ts i<em>n</em> the roots, detoxifies Se there, a<em>n</em>d impedes its further tra<em>n</em>slocatio<em>n</em> to the leaves.</p><AbstractText>Exoge<em>n</em>ous MT improves the physiological traits, a<em>n</em>tioxida<em>n</em>t system, a<em>n</em>d thiol liga<em>n</em>d biosy<em>n</em>thesis i<em>n</em> B. <em>n</em>apus subjected to Se stress primarily by e<em>n</em>ha<em>n</em>ci<em>n</em>g Se detoxificatio<em>n</em> a<em>n</em>d sequestratio<em>n</em> especially at the root level. Our results reveal better u<em>n</em>dersta<em>n</em>di<em>n</em>g of Se-phytotoxicity a<em>n</em>d Se-stress alleviatio<em>n</em> by the adequate supply of MT. The mecha<em>n</em>isms of MT-i<em>n</em>duced pla<em>n</em>t tolera<em>n</em>ce to Se stress have pote<em>n</em>tial implicatio<em>n</em>s i<em>n</em> developi<em>n</em>g <em>n</em>ovel strategies for safe crop productio<em>n</em> i<em>n</em> Se-rich soils.</AbstractText>

Melatonin (<i><em>N</em></i>-<em>acetyl</em>-<em>5</em>-<em>methoxytryptamine</em>) is an indoleamine with antioxidant, chronobiotic and anti-inflammatory properties; reduced levels of this hormone are associated with higher risk of cancer. Several beneficial effects of melatonin have been described in a broad number of tumors, including liver cancers. In this work we systematically reviewed the publications of the last 1<em>5</em> years that assessed the underlying mechanisms of melatonin activities against liver cancers, and its role as coadjuvant in the treatment of these tumors. Literature research was performed employing PubMed, Scopus and Web of Science (WOS) databases and, after screening, <em>5</em>1 articles were included. Results from the selected studies denoted the useful actions of melatonin in preventing carcinogenesis and as a promising treatment option for the primary liver tumors hepatocellular carcinoma (HCC) and cholangiocarcinoma (CCA), either alone or in combination with other compounds. Different processes were modulated by the indole, such as inhibition of oxidative stress, proliferation, angiogenesis and invasion, promotion of immune system response, cell cycle arrest and apoptosis, as well as recovery of circadian rhythms and autophagy modulation. Taken together, the present systematic review highlights the evidence that document the potential role of melatonin in improving the landscape of liver tumor treatment.

Keywords: cholangiocarcinoma; hepatocellular carcinoma; liver cancer; melatonin.

Obesity is a common and complex health problem worldwide and can induce the development of Type 2 diabetes. Chronic kidney disease (CKD) is a complication occurring as a result of obesity and diabetic conditions that lead to an increased mortality rate. There are several mechanisms and pathways contributing to kidney injury in obese and diabetic conditions. The expansion of adipocytes triggers proinflammatory cytokines release into blood circulation and bind with the receptors at the cell membranes of renal tissues leading to kidney injury. Obesity-mediated inflammation, oxidative stress, apoptosis, and mitochondrial dysfunction are the important causes and progression of CKD. Melatonin (<em>N</em>-<em>acetyl</em>-<em>5</em>-<em>methoxytryptamine</em>) is a neuronal hormone that is synthesized by the pineal gland and plays an essential role in regulating several physiological functions in the human body. Moreover, melatonin has pleiotropic effects such as antioxidant, anti-inflammation, antiapoptosis. In this review, the relationship between obesity, diabetic condition, and kidney injury and the renoprotective effect of melatonin in obese and diabetic conditions from in vitro and in vivo studies have been summarized and discussed.

Keywords: diabetes mellitus; inflammation; melatonin; obesity; oxidative stress.