Matrix metalloproteinases (MMPs) are a family of zinc-dependent enzymes capable of degradation of extracellular matrix (ECM) and key player in various inflammatory diseases. We investigated the regulation of MMPs in chronic gastric ulceration in mice. We generated chronic gastric ulcers in mice by indomethacin and examined the activity and expression of MMP-9 and -3 in stomach. Melatonin (<em>N</em>-<em>acetyl</em>-<em>5</em>-<em>methoxytryptamine</em>) treatment has also been applied to mice to characterize the changes in expression and activities of MMPs in gastric tissues. We observed significant upregulation of MMP-9 and -3 expressions and activities in stomach with increasing doses and duration of indomethacin that corroborated with increased activity of activator protein (AP)-1. Substantial damage in gastric epithelial layer was found during chronic ulceration. Melatonin suppressed MMP-9 and -3 expressions and activities during prevention and healing of chronic gastric ulcers. It also suppressed protein oxidation, lipid peroxidation and antioxidant enzymes. Additionally, expression of tumor necrosis factor (T<em>N</em>F)-α, interleukin (IL)-1β and IL-8 was significantly high in ulcerated stomachs while melatonin treatment blocked them to control level. We found elevated phosphorylation of extracellular-regulated kinase (ERK)1/2 and c-Jun <em>N</em>-terminal kinase (J<em>N</em>K) during chronic gastric ulceration, which were significantly reversed by melatonin. Moreover, expression of <em>N</em>F-κB, c-fos and c-jun were inhibited by melatonin resulting down regulation of MMP-9 and -3 expressions. In summary, oxidative stress is preceded by chronic inflammation that enhances the expression of MMP-9 and -3, while melatonin arrests both of them via reduction of AP-1 activity during protection of ulcer.

Precise floral transition from vegetative growth phase to reproductive growth phase is very important in plant life cycle. In flowering genetic pathways, DELLA proteins are master transcriptional regulators of gibberelic acid (GA) pathway, and FLOWERI<em>N</em>G LOCUS C (FLC) is a core repressor of vernalization pathway as well as downstream of DELLAs. As a crucial messenger in plants, the possible involvement of melatonin (<em>N</em>-<em>acetyl</em>-<em>5</em>-<em>methoxytryptamine</em>) in flowering and underlying molecular mechanism are unknown in Arabidopsis. In this study, we found that exogenous melatonin treatment delayed floral transition in Arabidopsis. Exogenous melatonin treatment conferred protein stabilizations of DELLAs [REPRESSOR of ga1-3 (RGA) and RGA-LIKE3 (RGL3)], without regulating the transcripts of DELLAs and endogenous GA level. <em>N</em>otably, exogenous melatonin delayed plant flowering and DELLA-activated transcripts of FLC were alleviated in della mutants, and those were exacerbated in DELLA overexpressing plants. Taken together, this study provides direct link between melatonin and floral transition, and indicates the novel involvement of DELLAs-activated FLC in melatonin-mediated flowering in Arabidopsis.

OBJECTIVE

Melatonin (<em>N</em>-<em>acetyl</em>-<em>5</em>-<em>methoxytryptamine</em>) has been reported to suppress epithelial-mesenchymal transition and cancer stem cells in some types of cancer. However, the effects of melatonin on the osteosarcoma stem cells, epithelial-mesenchymal transition and metastasis of osteosarcoma are still not clear. The present study was conducted to dissect the activity of melatonin on the osteosarcoma stem cells and the underlying mechanisms.

METHODS

MTT, wound healing, transwell assay and western blotting were conducted to determine the effect of melatonin on osteosarcoma cell invasion and migration and downregulation of SOX9-mediated signaling. Tumor spheroid assay and FACS analysis were performed to analyze the inhibition of the osteosarcoma stem cells. In vivo model for tumor formation and metastasis from single cell clone was used to evaluate the suppression of osteosarcoma stem cells by melatonin.

RESULTS

We demonstrated that melatonin potently suppresses the migration and invasion of osteosarcoma cells. Furthermore, melatonin significantly inhibits the sarcosphere formation of osteosarcoma stem cells and regulates EMT markers of osteosarcoma cells. In vivo mice model showed that melatonin significantly inhibits the initiation and metastasis of osteosarcoma. SOX9 is the key transcription factor mediating the effect of melatonin. Melatonin inhibited of cancer stem cell by down-regulation of SOX9-mediated signaling pathway in osteosarcoma.

CONCLUSIONS

Collectively, these results deepen the understanding of the biological functions of melatonin and provide new insights for the intervention of osteosarcoma stem cells.

Melatonin (<em>N</em>-<em>acetyl</em>-<em>5</em>-<em>methoxytryptamine</em>) has recently gained attention as an anticancer agent and for combined cancer therapy. In this study, we investigated the underlying molecular mechanisms of the effects of melatonin on cancer cell death. Treatment with melatonin induced apoptosis and upregulated the expression of the pro-apoptotic protein Bcl-2-interacting mediator of cell death (Bim) in renal cancer Caki cells. Furthermore, downregulation of Bim expression by siR<em>N</em>A markedly reduced melatonin-mediated apoptosis. Melatonin increased Bim mR<em>N</em>A expression through the induction of Sp1 and E2F1 expression and transcriptional activity. We found that melatonin also modulated Bim protein stability through the inhibition of proteasome activity. However, melatonin-induced Bim upregulation was independent of melatonin's antioxidant properties and the melatonin receptor. Taken together, our results suggest that melatonin induces apoptosis through the upregulation of Bim expression at the transcriptional level and at the post-translational level.

Melatonin (<em>N</em>-<em>acetyl</em>-<em>5</em>-<em>methoxytryptamine</em>) prevents oxidative stress-induced cataract development, and previous studies have suggested that the ocular lens synthesizes melatonin. In the present study, we examined whether two key enzymes in melatonin biosynthesis, arylalkylamine <em>N</em>-<em>acetyl</em>transferase (AA<em>N</em>AT) and hydroxyindole-O-methyltransferase (HIOMT), are expressed in the lens of adult male rats. Reverse transcriptase-polymerase chain reaction analyses demonstrated that both AA<em>N</em>AT and HIOMT mR<em>N</em>As are expressed in the lens. Western blotting for AA<em>N</em>AT protein showed that the lens, like the pineal gland, contains this enzyme protein with a molecular mass of 24 kDa. Immunohistochemistry revealed that AA<em>N</em>AT protein is localized to the lens cortical fiber cells. Serotonin, which is a substrate for AA<em>N</em>AT and a melatonin precursor, was also found in this region. These findings demonstrate that the lens expresses AA<em>N</em>AT and HIOMT, and suggest that the cortical fiber cells are the main melatonin-synthesizing sites in the lens. Locally synthesized melatonin in the lens cortical fiber cells may protect the lens itself from cataract development.

BACKGROUND

Gastric cancer accounts 8% of the total cancer cases and 10% of total cancer deaths worldwide. The indoleamine <em>N</em>-<em>acetyl</em>-<em>5</em>-<em>methoxytryptamine</em>, better known as melatonin, is the principal hormone produced by the pineal gland. Recently, it has shown some anticancer role in some malignancies such as breast and colon cancer; also, some of its protective roles in the GI tract are as free radical scavenger and as antimitogenic and apoptotic agents. Based on the anticancer effects of melatonin and wide distribution of this neurohormone in the GI tract and some proposed physiologic and pharmacologic roles for this neurohormone, this study is initially scheduled to determine the expression of melatonin receptor MT2 in tissue samples of adenocarcinoma cancer patients.

METHODS

For this aim, a total of 30 gastric adenocarcinoma patients and 30 normal individuals were selected and examined for MT2 gene expression by real-time PCR.

RESULTS

Our results have shown interestingly high expression for MT2 receptor in cancer and marginal cancer tissues compared with normal people.

CONCLUSIONS

According to our results, it is concluded that for the first time, the expression of MT2 receptor in gastric adenocarcinoma tissues which was in parallel with breast and colon cancer studies and high expression of this receptor in the marginal tissues indicate refractory mechanism which shows the defending role of melatonin in the GI system. Our experiments has not shown any relationship between MT2 receptor expression and grade and clinicopathological features of gastric tumor, so we cannot conclude any relationship between this receptor expression and progression of the tumor, although this expression can be considered as an etiology.

Increasing male infertility of unknown aetiology can be associated with environmental factors. Extensive use of mobile phones has exposed the general population to unprecedented levels of radiofrequency radiations (RFRs) that may adversely affect male reproductive health. Therefore, the present study investigated the effect of RFR Global System for Mobile communication (GSM) type, 900 MHz and melatonin supplementation on germ cell development during spermatogenesis. Swiss albino mice were divided into four groups. One group received RFR exposure for 3 h twice/day for 3<em>5</em> days and the other group received the same exposure but with melatonin ( <em>N</em>-<em>acetyl</em>-<em>5</em>-<em>methoxytryptamine</em>) (MEL; <em>5</em> mg/kg bw/day). Two other groups received only MEL or remain unexposed. Sperm head abnormality, total sperm count, biochemical assay for lipid peroxides, reduced glutathione, superoxide dismutase activity and testis histology were evaluated. Additionally, flow cytometric evaluation of germ cell subtypes and comet assay were performed in testis. Extensive D<em>N</em>A damage in germ cells of RFR-exposed animals along with arrest in pre-meiotic stages of spermatogenesis eventually leading to low sperm count and sperm head abnormalities were observed. Furthermore, biochemical assays revealed excess free radical generation resulting in histological and morphological changes in testis and germ cells morphology, respectively. However, these effects were either diminished or absent in RFR-exposed animals supplemented with melatonin. Hence, it can be concluded that melatonin inhibits pre-meiotic spermatogenesis arrest in male germ cells through its anti-oxidative potential and ability to improve D<em>N</em>A reparative pathways, leading to normal sperm count and sperm morphology in RFR-exposed animals.

Melatonin is an antioxidant. Since other antioxidants inhibit the production of tumor necrosis factor (T<em>N</em>F) induced by lipopolysaccharide, we investigated its effect on T<em>N</em>F production in vivo and in vitro and on lethality associated with endotoxic shock. Administration of melatonin to mice (<em>5</em> mg/kg, s.c., 30 min before or simultaneously with lipopolysaccharide) inhibited serum T<em>N</em>F levels by <em>5</em>0-80% and improved survival of mice treated with a lethal dose of lipopolysaccharide. By studying other, structurally related, indolamines (<em>N</em>-<em>acetyl</em>-<em>5</em>-hydroxytryptamine, <em>5</em>-<em>methoxytryptamine</em> and <em>5</em>-hydroxytryptamine) we found a good correlation between antioxidant activity (for which the <em>5</em>-methoxy group is essential) and the inhibition of T<em>N</em>F production in vivo and in vitro in mononuclear cells. Melatonin did not increase serum corticosterone and did not modify the elevation of serum corticosterone levels by lipopolysaccharide or by interleukin-1. Furthermore, it exerted its inhibitory effect in adrenalectomized or hypophysectomized mice also, indicating that its effect is independent of the hypothalamus-pituitary-adrenal axis.

Recent studies on several fish species, especially carp, implicated pineal hormone melatonin (<em>N</em>-<em>acetyl</em>-<em>5</em>-<em>methoxytryptamine</em>) as a potent candidate in the regulatory mechanism of seasonal reproduction. Under natural conditions, the temporal pattern of serum melatonin varied with daily light-dark cycle and the reproductive status of the fish as well. Carefully controlled study revealed that exogenous administration of melatonin may result in stimulation or inhibition or no influences at all on the gonadal functions depending on the reproductive status of fish. Cross-talk between the melatonin and ovarian steroid has been evident from in vitro study, in which melatonin accelerated the action of 17α,20β-dihydroxy-4-pregnen-3-one or maturation inducing hormone (MIH) on meiotic cell cycle resumption in carp oocytes by formation of maturation promoting factor (MPF) - a complex of two proteins, cyclin B and cyclin dependant kinase Cdk1. While several lines of evidence suggest melatonin effects on hypothalamo-hypophyseal-gonadal axis, localization and dynamics of a 37-kDa melatonin receptor protein in carp oocytes argued in favor of extra-hypothalamic direct action of melatonin on fish reproduction. A recent study in carp indicated that influences of an identical regimen of photoperiods in different parts of annual cycle on ovarian functions vary in relation to the profiles of serum melatonin, but not to any rhythm parameters of MT1 or MT2 receptors on the gonad or brain. The purpose of this short review is to bring together the current knowledge on the biological effects of melatonin on fish reproduction mainly focusing the recent findings on carp.

Previous work has shown that daily injections of the pineal hormone melatonin (<em>N</em>-<em>acetyl</em>, <em>5</em>-<em>methoxytryptamine</em>) entrain the free-running locomotor rhythms of rats held in constant darkness (with a median effective dose [ED<em>5</em>0] of <em>5</em>.4<em>5</em> +/- 1.33 micrograms/kg) and in constant bright light. The present experiments determined the dose-response characteristics of entrainment and phase shifting to daily and single melatonin injections in both sham-operated (SHAM) and pinealectomized (PI<em>N</em>X) rats. The data indicated an ED<em>5</em>0 of 332 +/- <em>5</em>3 ng/kg and 121 +/- 22 ng/kg for SHAM and PI<em>N</em>X rats, respectively, during the entrainment experiment. The ED<em>5</em>0's for the entrainment experiment were considerably lower than doses previously employed, and much lower than doses employed in reproductive and metabolic studies in rats and hamsters. The data indicated that no partial entrainment occurred; nor were there differences in phase angle, length of activity, or period among all effective doses. <em>N</em>ext, a single injection of 1 mg/kg melatonin has previously been shown to cause a phase advance of approximately 4<em>5</em> min when administered at about circadian time (CT) 10. We found that both SHAM and PI<em>N</em>X animals phase-advanced, in a dose-dependent manner to a single melatonin injection given at CT 10. The data for the phase-shifting experiment indicated an ED<em>5</em>0 of 8.19 +/- 0.<em>5</em>72 micrograms/kg and 2.16 +/- 0.326 micrograms/kg for SHAM and PI<em>N</em>X animals, respectively, with an average phase advance of 40 min for both groups. Together, the data suggest that the presence of the pineal gland is not necessary for the effects of melatonin on the rat circadian system, and that PI<em>N</em>X animals are marginally more sensitive to melatonin than their SHAM controls.

Pineal hormone melatonin (<em>N</em>-<em>acetyl</em>-<em>5</em>-<em>methoxytryptamine</em>) is thought to modulate the calcium/calmodulin signaling pathway either by changing intracellular Ca(2+) concentration via activation of its G-protein-coupled membrane receptors, or through a direct interaction with calmodulin (CaM). The present work studies the direct interaction of melatonin with intact calcium-saturated CaM both experimentally, by fluorescence and nuclear magnetic resonance spectroscopies, and theoretically, by molecular dynamics simulations. The analysis of the experimental data shows that the interaction is calcium-dependent. The affinity, as obtained from monitoring (1<em>5</em>)<em>N</em> and (1)H chemical shift changes for a melatonin titration, is weak (in the millimolar range) and comparable for the <em>N</em>- and C-terminal domains. Partial replacement of diamagnetic Ca(2+) by paramagnetic Tb(3+) allowed the measurement of interdomain <em>N</em>MR pseudocontact shifts and residual dipolar couplings, indicating that each domain movement in the complex is not correlated with the other one. Molecular dynamics simulations allow us to follow the dynamics of melatonin in the binding pocket of CaM. Overall, this study provides an example of how a combination of experimental and theoretical approaches can shed light on a weakly interacting system of biological and pharmacological significance.

We examined the effect of <em>5</em>-hydroxytryptamine (<em>5</em>-HT) on <em>N</em>a+ and Cl- flux (J) and short-circuit current (Isc) in human jejunal mucosa. Segments of jejunum, taken at the time of gastric bypass surgery, were stripped of the seromuscular layers (and attached neural ganglia) and mounted as flat mucosal sheets in Ussing chambers under short-circuit conditions. <em>5</em>-HT (0.1-100 microM) produced a concentration-dependent rise in Isc (mean effective concn = 2.<em>5</em> microM). Using 22<em>N</em>a and 36Cl, we measured flux across control tissues and in those exposed to <em>5</em>-HT. <em>5</em>-HT decreased both net J<em>N</em>a and JCl and increased Isc (-1.1 +/- 0.6, -1.7 +/- 0.6, and 0.6 +/- 0.1 mueq.cm-2.h-1, respectively). Thus the <em>5</em>-HT-induced rise in Isc could be accounted for by reduced net J<em>N</em>a and JCl. <em>5</em>-HT induced a significant (P < 0.0<em>5</em>) Cl- secretion (serosal-to-mucosal flux) when glucose was included in the buffer bathing the mucosal surface. <em>N</em>either tetrodotoxin, the adrenergic receptor antagonists prazosin and propranolol, nor the cholinergic receptor antagonists atropine and hexamethonium inhibited the change (delta) in Isc induced by <em>5</em>-HT. <em>5</em>-<em>Methoxytryptamine</em> (<em>5</em>-MeOT) and zacopride, known <em>5</em>-HT4 receptor agonists, induced significant delta Isc. The <em>5</em>-HT receptor antagonists <em>N</em>-<em>acetyl</em>-<em>5</em>-hydroxytryptophyl-<em>5</em>-hydroxytryptamine (<em>5</em>-HT1P), ketanserin (<em>5</em>-HT2), and ICS-20<em>5</em>-930 (preferential for <em>5</em>-HT3 at 0.1 microM had no effect on delta Isc.(ABSTRACT TRU<em>N</em>CATED AT 2<em>5</em>0 WORDS)

Melatonin (<em>N</em>-<em>acetyl</em>-<em>5</em>-<em>methoxytryptamine</em>), the principal hormone of the vertebral pineal gland, elicits several neurobiological effects. However, the effects of melatonin on cardiac muscle are still unknown. The first goal of the study was to investigate the role of melatonin on myocardial contractility in isolated rat papillary muscle using dose-response curves to melatonin, to isoproterenol and calcium either in the presence or in the absence of melatonin (0.3 nM). Response curves to isoproterenol were additionally performed in the presence of melatonin plus the specific receptor antagonist <em>N</em>-<em>acetyl</em>tryptamine (10 microM); the adenylate-cyclase stimulator forskolin (10 microM) was also used. Melatonin has no direct inotropic effect in isolated rat papillary muscle but counteracts isoproterenol but not [Ca2+] effects. In fact, the EC<em>5</em>0 for isoproterenol was significantly higher in the presence than in the absence of melatonin (p < 0.001). This anti-adrenergic action occurs through an interaction to a specific cardiac receptor. Forskolin-stimulated adenylate cyclase induced an increase of contractile force (+118 +/- 2<em>5</em>%) which was reduced in the presence of melatonin (+26 +/- 10%; p < 0.01). In conclusion, we found that melatonin possess anti-adrenergic effect in isolated rat papillary muscle. This phenomenon was abolished in the presence of its receptor antagonist <em>N</em>-<em>acetyl</em>-tryptamine demonstrating that melatonin operates through a specific cardiac receptor. The reduction of contractility increase, induced by forskolin-stimulated adenylate cyclase, shows that melatonin may act through a reduction of cyclic AMP accumulation.

The aim of this work is to i<em>n</em>vestigate the a<em>n</em>tioxidative effect of melato<em>n</em>i<em>n</em> (<em>N</em>-<em>acetyl</em>-<em>5</em>-<em>methoxytryptamine</em>) o<em>n</em> the oxidatio<em>n</em> of D<em>N</em>A a<em>n</em>d huma<em>n</em> erythrocytes i<em>n</em>duced by 2,2'-azobis(2-amidi<em>n</em>opropa<em>n</em>e hydrochloride) (AAPH). First, the <em>5</em>0% i<em>n</em>hibitio<em>n</em> co<em>n</em>ce<em>n</em>tratio<em>n</em> (IC<em>5</em>0) of melato<em>n</em>i<em>n</em> is measured by reacti<em>n</em>g with two radical species, i.e., 2,2'-azi<em>n</em>obis(3-ethylbe<em>n</em>zothiazoli<em>n</em>e-6-sulfo<em>n</em>ate) radical catio<em>n</em> (ABTS*+) a<em>n</em>d 2,2'-diphe<em>n</em>yl-1-picrylhydrazyl (DPPH). The IC<em>5</em>0 of melato<em>n</em>i<em>n</em> are 7<em>5</em>microM a<em>n</em>d 300microM whe<em>n</em> melato<em>n</em>i<em>n</em> reacts with ABTS*+ a<em>n</em>d DPPH, respectively. Especially, the reactio<em>n</em>s of melato<em>n</em>i<em>n</em> with ABTS*+ a<em>n</em>d DPPH are the direct evide<em>n</em>ce for melato<em>n</em>i<em>n</em> to trap radicals. The<em>n</em>, melato<em>n</em>i<em>n</em> is applied to protect D<em>N</em>A a<em>n</em>d huma<em>n</em> erythrocytes agai<em>n</em>st oxidative damage a<em>n</em>d hemolysis i<em>n</em>duced by 2,2'-azobis(2-amidi<em>n</em>opropa<em>n</em>e hydrochloride) (AAPH). The prese<em>n</em>ce of melato<em>n</em>i<em>n</em> prolo<em>n</em>gs the occurre<em>n</em>ce of the oxidative damage of D<em>N</em>A a<em>n</em>d hemolysis of erythrocytes, ge<em>n</em>erati<em>n</em>g a<em>n</em> i<em>n</em>hibitio<em>n</em> period (t(i<em>n</em>h)). The proportio<em>n</em>al relatio<em>n</em>ship betwee<em>n</em> t(i<em>n</em>h) a<em>n</em>d the co<em>n</em>ce<em>n</em>tratio<em>n</em> of melato<em>n</em>i<em>n</em> ([MLT]) is treated by the chemical ki<em>n</em>etic equatio<em>n</em>, t(i<em>n</em>h)=(<em>n</em>/R(i))[MLT], i<em>n</em> which <em>n</em> mea<em>n</em>s the <em>n</em>umber of peroxyl radical trapped by a<em>n</em> a<em>n</em>tioxida<em>n</em>t, a<em>n</em>d R(i) sta<em>n</em>ds for the i<em>n</em>itiatio<em>n</em> rate of the radical reactio<em>n</em>. It is fou<em>n</em>d that every molecule of melato<em>n</em>i<em>n</em> ca<em>n</em> trap almost two radicals i<em>n</em> protecti<em>n</em>g D<em>N</em>A a<em>n</em>d erythrocytes. Furthermore, qua<em>n</em>tum calculatio<em>n</em> proves that the i<em>n</em>dole-type radical derived from melato<em>n</em>i<em>n</em> is much stable tha<em>n</em> amide-type radical. Fi<em>n</em>ally, melato<em>n</em>i<em>n</em> is able to accelerate hemolysis of erythrocytes i<em>n</em>duced by hemi<em>n</em>, i<em>n</em>dicati<em>n</em>g that melato<em>n</em>i<em>n</em> leads to the collapse of the erythrocyte membra<em>n</em>e i<em>n</em> the prese<em>n</em>ce of hemi<em>n</em>. This may provide detailed i<em>n</em>formatio<em>n</em> for the usage of melato<em>n</em>i<em>n</em> a<em>n</em>d helpful refere<em>n</em>ce for the desig<em>n</em> of i<em>n</em>dole-related drugs.

Melatonin (<em>N</em>-<em>acetyl</em>-<em>5</em>-<em>methoxytryptamine</em>), a pineal neurohormone, is a hydroxyl radical scavenger and antioxidant, and plays an important role in the immune system. We studied the effect of exogenous melatonin on the pathogenesis of experimental autoimmune encephalomyelitis (EAE). EAE was induced in Lewis rats by immunization with rat spinal cord homogenates. Subsequent oral administration of melatonin at <em>5</em> mg/kg significantly reduced the clinical severity of EAE paralysis compared with administration of the vehicle alone (p<0.01). Infiltration of ED1+ macrophages and CD4+ T cells into spinal cords occurred both in the absence and presence of melatonin treatment, but melatonin-treated rats had less spinal cord infiltration of inflammatory cells than did the control group. ICAM-1 immunoreactivity in the blood vessels of EAE lesions was decreased in melatonin-treated rats compared to vehicle-treated rats. These findings suggest that exogenous melatonin ameliorates EAE via a mechanism involving reduced expression of ICAM-1 and lymphocyte function associated antigen-1a in autoimmune target organs.

OBJECTIVE

Melatonin (<em>N</em>-<em>acetyl</em>-<em>5</em>-<em>methoxytryptamine</em>) is the main indolamine secreted by the pineal gland. Many studies showed that premedication with melatonin is associated with preoperative anxiolysis and sedation without impairment of cognitive and psychomotor skills and without prolonging recovery. We hypothesized that melatonin decreases the amount of propofol required to produce an adequate depth of hypnosis at induction time.

METHODS

After approval from the research committee of the anaesthesia department, informed written consent was taken from 4<em>5</em> adult patients undergoing different surgical procedures. They were allocated randomly into three groups according to the premedication. At 100 min preoperatively, premedication was given in the form of oral melatonin 3 mg (M3 group), oral melatonin <em>5</em> mg (M<em>5</em> group) or no premedication (P group). After preoxygenation an anaesthesiologist who was blinded to the premedication injected propofol 10 mg over <em>5</em> s every 1<em>5</em> s until the bispectral index (BIS) score fell to 4<em>5</em>. The total dose of propofol required to achieve a BIS score of 4<em>5</em> was recorded. Response to verbal commands and eyelash reflex was evaluated and correlated to the BIS score and propofol dosage. When a BIS score of 4<em>5</em> was reached, tracheal intubation was accomplished after administration of a narcotic and muscle relaxant.

RESULTS

The mean (standard devitation (SD)) induction dose of propofol producing a BIS score of 4<em>5</em> was 134 (2<em>5</em>) mg in the placebo group vs. 11<em>5</em> (19.<em>5</em>) and 114 (20.9) mg in the M3 and M<em>5</em> groups, respectively (P < 0.0<em>5</em>). The propofol dose required to achieve loss of eyelash reflex and loss of response to verbal commands was more in the placebo group. Anxiety score as assessed by visual analogue scale (VAS) scored more in the placebo group than both melatonin groups. Time spent in the recovery room did not differ between the three groups.

CONCLUSIONS

Melatonin premedication, in an oral dose of either 3 or <em>5</em> mg, reduced the required dose of propofol to achieve a BIS score of 4<em>5</em>, reflecting a sufficient level of hypnosis for tracheal intubation without prolongation of postoperative recovery room stay.

Melatonin (<em>N</em> -<em>acetyl</em>-<em>5</em>-<em>methoxytryptamine</em>) was detected in extracts of albino rabbit lens using radioimmunoassay. Furthermore, melatonin precursors, tryptophan and serotonin (<em>5</em>-hydroxytryptamine), were found in the lens extracts by high-performance liquid chromatography coupled with fluorometric detection. Also, activities of two melatonin-synthesizing enzymes, serotonin <em>N</em> -<em>acetyl</em>transferase (<em>N</em>AT) and hydroxyindole- O -methyltransferase (HIOMT), were found in the lens. The apparent Michaelis constants (K m) for substrates of <em>N</em>AT in the lens were similar to those reported for the pineal gland, although the apparent K m values for substrates of HIOMT in the lens were 10-fold higher than those in the pineal gland. When the rabbits were entrained to a 14-hr light: 10-hr dark cycle, melatonin levels and <em>N</em>AT activity in the lens showed significant day/night changes with high levels during the dark period, but HIOMT activity did not show these changes. These findings strongly suggest that the rabbit lens may synthesize melatonin from serotonin by the sequential action of <em>N</em>AT and HIOMT, and that the melatonin synthesis may fluctuate in a diurnal and/or circadian manner.

Antioxidants are often added to culture media as cytoprotective agents. We examined the effects of antioxidants on the results and interpretation of the 3-[4,<em>5</em>-dimethylthiazol-2-yl]-2,<em>5</em>-diphenyltetrazolium bromide (MTT) assay for cell viability. Without cells, the thiol-containing antioxidant compounds beta-mercaptoethanol, dithiothreitol, pyrrolidine-dithiocarbamate, and <em>N</em>-<em>acetyl</em>-L-cysteine (<em>acetyl</em>cysteine) reduced MTT tetrazolium salts to a blue formazan product in a dose-dependent manner. Addition of the compounds L-ascorbic acid and (+)-alpha-tocopherol acid succinate had different effects. In contrast, addition of the antioxidants <em>N</em>-<em>acetyl</em>-<em>5</em>-<em>methoxytryptamine</em> and (-)-2-oxo-4-thiazolidine carboxylic acid, which do not contain reactive thiol groups, did not result in the development of blue formazan product. These results showed that antioxidants, and potentially other chemotherapeutic compounds that contain free thiol groups or other reducing equivalents, readily reduce MTT to produce the blue formazan, irrespective of the viability of the cells present. This undescribed reaction can, therefore, significantly influence the results and interpretation of cell-viability experiments.

Melatonin (<em>N</em>-<em>acetyl</em>-<em>5</em>-<em>methoxytryptamine</em>), originally discovered in the pineal gland, is now known also to be present in the gastrointestinal tract from the stomach to the colon. It is localized and likely synthesized in the enterochromaffin cells of the mucosal lining. Its functions in the gut generally seem to be protective of the mucosa from erosion and ulcer formation and to possibly influence movement of the gastrointestinal contents through the digestive system. In this brief review, we summarize the work documenting the function of melatonin in influencing bicarbonate secretion in the stomach and its role in preventing and repairing ulcers in the stomach and duodenum. Melatonin's actions in the control of bicarbonate secretion involve the central and peripheral sympathetic nervous systems and the actions are receptor mediated. Conversely, melatonin's actions in reducing ulcer formation also seemingly involve the ability of the indole to directly scavenge toxic oxygen-based reactants, e.g., the hydroxyl radical, and possibly to promote antioxidative enzyme activities. These same processes may be involved in the mechanisms by which melatonin promotes ulcer healing. Additionally, however, melatonin's effects on the healing of ulcers includes actions of blood flow in the margins of the ulcer and also on the sensory nerves. All indications are that melatonin has a variety of beneficial effects in the gastrointestinal tract. It is likely, however, that additional actions of melatonin on the digestive system will be uncovered.

OBJECTIVE

Adriamycin is one of the most widely used anticancer drugs. The major limiting factor of using this drug is the development of cardiotoxicity. However, melatonin (<em>N</em>-<em>acetyl</em>-<em>5</em>-<em>methoxytryptamine</em>) is a ubiquitous molecule as a good antioxidant that may protect the heart. We investigated whether or not pretreatment with melatonin can attenuate adriamycin-induced cardiotoxicity.

METHODS

All procedures and experiments were approved by the Animal Ethics Committee of Gazi Osman Paşa University (2012-HADYEK-022). Adult male Wistar-Albino rats were randomly divided into four groups, namely control (CO<em>N</em>, n=7), melatonin (MEL, n=7), adriamycin (ADR, n=7), and adriamycin+melatonin (ADR+MEL, n=7) groups. Cardiotoxicity in rats was induced by adriamycin injection (cumulative dose: 18 mg/kg, intraperitoneal [i.p.]) at an interval of 24 hours (h) on the <em>5</em>th, 6th and 7th days. Rats receiving melatonin treatment in the adriamycin group received melatonin (10 mg/kg/day, i.p.) for 7 days and were injected with adriamycin (18 mg/kg, i.p.) on <em>5</em>th, 6th and 7th days. On the 8th day, gravimetric, electrocardiography (ECG) and biochemical parameters were assessed.

RESULTS

Adriamycin induction caused changes in the ECG pattern, including ST-segment elevation and decreased R-amplitude, increase in the serum levels of cardiac injury markers (creatine kinase [CK], CK-MB, aspartate transaminase, and lactate dehydrogenase), decrease in the antioxidant enzymes activity (superoxide dismutase, glutathione peroxidase), elevated lipid peroxidation (malondialdehyde), and altered lipid profile in the serum. Melatonin treatment prevented all the parameters of adriamycin-induced cardiotoxicity in rats.

CONCLUSIONS

Melatonin has a protective effect on the heart against adriamycin-induced cardiotoxicity in rats.

Five indole compounds have been isolated from bovine pineal tissue and characterized as <em>5</em>-methoxytryptophol, <em>N</em>-<em>acetyl</em>-<em>5</em>-<em>methoxytryptamine</em> (melatonin), <em>5</em>-hydroxytryptophol, <em>5</em>-methoxyindole-3-acetic acid, and <em>5</em>-hydroxyindole-3-acetic acid. Pineal hydroxyindole-O-methyltransferase, with S-adenosylmethionine, converts <em>5</em>-hydroxytryptophol to <em>5</em>-methoxytryptophol.

The lipid peroxidation of triglycerides enriched in polyunsaturated fatty acids was investigated by photoemission techniques and the TBARS assay. Butylated hydroxytoluene, <em>5</em>-OH-tryptophan and <em>N</em>-<em>acetyl</em>serotonin inhibited light emission and TBARS formation in a concentration dependent manner. However, it was enhanced in the presence of melatonin and <em>5</em>-<em>methoxytryptamine</em> and was dependent on its concentration. The total relative luminic units were found to be lower in those systems incubated in the presence of butylated hydroxytoluene, <em>N</em>-<em>acetyl</em>serotonin or <em>5</em>-OH-tryptophan; this decreased proportionally to the concentration of the compound tested. The order of inhibition was <em>5</em>-OH-tryptophan><em>N</em>-<em>acetyl</em>serotonin>butylated hydroxytoluene with the following IC<em>5</em>0 values: 0.6<em>5</em>, 6.<em>5</em> and 9.0 mM respectively. The free-radical scavenging activity of the indole derivatives was also analyzed by the DPPH method, and the results indicate that <em>5</em>-OH-tryptophan, and <em>N</em>-<em>acetyl</em>serotonin exhibited a dose-dependent free-radical scavenging ability at all of the tested concentrations. Thus, at 10 microM concentration a decrease of 84.71% and 73.<em>5</em>0% of initial DPPH was observed, compared to <em>5</em>1.00% of BHT. Melatonin and <em>5</em>-methoxytriptamine decreased the initial concentration of DPPH only 1.8<em>5</em>% and <em>5</em>.0%, respectively. The possible formation of <em>N</em>(1)-<em>acetyl</em>-<em>N</em>(2) formyl-<em>5</em>-methoxykynuramine (AFMK) during lipid peroxidation of triglycerides enriched in PUFAs with cumene hydroperoxide in the presence of melatonin was also analyzed.

Melatonin (<em>N</em>-<em>acetyl</em>-<em>5</em>-<em>methoxytryptamine</em>) is a hormone derived from the pineal gland that has a wide range of clinical applications. While melatonin was originally assessed as a hormone specializing in regulation of the normal circadian rhythm in mammals, it now has been shown to be an effective free radical scavenger and antioxidant. Current research has focused on central nervous system (C<em>N</em>S) disorders, stroke in particular, for potential melatonin-based therapeutics. As of now, the realm of potential therapy regimens is focused on three main treatments: exogenously delivered melatonin, pineal gland grafting, and melatonin-mediated stem cell therapy. All therapies contain both costs and benefits, and current research is still focused on finding the best treatment plan. While comprehensive research has been conducted, more research regarding the safety of such therapies is needed in order to transition into the clinical level of testing. Antioxidants such as traditional Chinese medicine, (-)-epigallocatechin-3-gallate (EGCG), and lavender oil, which have been used for thousands of years as treatment, are now gaining recognition as effective melatonin treatment alternatives. This review will further discuss relevant studies assessing melatonin-based therapeutics and provide evidence of other natural melatonin treatment alternatives for the treatment of stroke.

Melatonin, <em>N</em>-<em>acetyl</em>-<em>5</em>-<em>methoxytryptamine</em>, the major hormone produced by the pineal gland under the influence of the dark/light cycle, has been shown to have a large number of therapeutic possibilities. It has been utilized in several countries for circadian rhythm disorders, sleep disturbances, jet lag, and sleep-wake cycle disturbances in blind people, and shift workers. In our mechanism of act, the G(i) protein-coupled metabotropic melatonin receptors MT1 and MT2 are the primary mediators of the physiological actions of melatonin. This hormone plays an important role in the regulation of physiological and neuroendocrine functions, such as synchronization of seasonal reproductive rhythms and entrainment of circadian cycles. In addition to its chronobiological role, several pharmacological effects of melatonin have been reported in mammals including sedative, antioxidant, anxiolytic, antidepressant, anticonvulsant, and analgesic activities. There is some evidence from clinical trials that melatonin can be helpful in that event. Current trends of pharmacological functions of melatonin pointed out its use in the treatment of neurodegenerative and neoplastic diseases. These effects and uses of melatonin are mentioned but further confirmatory studies are needed in most of them.