The influence of melatonin on the heart rhythm - An in vitro simulation with murine embryonic stem cell derived cardiomyocytes.

BACKGROUND: In healthy individuals, a major factor influencing the heart rate variability (HRV) is the circadian rhythm. The role of melatonin as an essential component of the circadian rhythm in the adult human organism and the beneficial effects of a treatment with melatonin during the fetal period is well described. Toxic effects of melatonin are discussed less frequently. Since pharmacological studies cannot be carried out on pregnant women, the establishment of an equivalent in vitro model is important. We therefore tested whether melatonin can influence the beat rate variability (BRV) of spontaneously beating cardiomyocytes derived from murine embryonic stem cells (mESCs) and whether melatonin exhibits toxic effects in this in vitro model. METHODS: Microelectrode Arrays recorded extracellular field potentials of spontaneously beating cardiomyocytes. Melatonin was applied in a concentration range from 10-11 M to 10-5 M. The analysis of the BRV focused on time domain methods. RESULTS: In line with clinical observations, melatonin decreased the beating frequency and increased the BRV. The effect of melatonin up to a concentration of 10-6 M was reversible, whereas the application of higher concentrations induced an irreversible effect. CONCLUSION: The study underlines the potential of this in vitro model to help explore the development of circadian rhythms and their modulation by melatonin in the embryonic phase. The results imply that melatonin influences the heart rhythm as early as during the embryonic heart development. Furthermore, the results indicate a potentially toxic effect of melatonin that has not been described in detail before.

The Effect of Orally Supplemented Melatonin on Larval Performance and Skeletal Deformities in Farmed Gilthead Seabream (Sparus aurata).

The gilthead seabream larval rearing in continuous light is common in most Mediterranean hatcheries to stimulate larval length growth and increase food consumption. Several studies have shown that continuous light affects larval development and increases the prevalence of skeletal deformities. Melatonin is a crucial pineal neurohormone that displays daily secretion patterns, stimulates cell proliferation and embryonic development in Atlantic salmon and zebrafish, and improves osseointegration in mice and humans. However, no studies have examined the effects of orally supplemented melatonin on skeletal deformities in Sparus aurata larvae. We administered exogenous melatonin to gilthead seabream larvae via enriched rotifers and nauplii of Artemia. Exogenous melatonin induced bone deformities and stimulated parathyroid hormone-related protein-coding gene (PTHrP) mRNA expression. In addition to the melatonin-induced PTHrP high expression level, the recorded non coordinated function of skeletal muscle and bone during growth can be the fountainhead of bone deformities. Both myosin light chain 2 (mlc2) and bone gamma-carboxyglutamate protein-coding gene (bglap) expression levels were significantly affected by melatonin administration in an inverse dose-response manner during the exogenous melatonin administration. This is the first study to report the effect of inducing melatonin bone deformities on Sparus aurata larvae reared under ordinary hatchery conditions.

Intravitreous delivery of melatonin affects the retinal neuron survival and visual signal transmission: in vivo and ex vivo study.

Intravitreal delivery can maximize the intensity of therapeutic agents and extend their residence time within ocular tissue. Melatonin is a lipophilic molecule that crosses freely biological barriers and cell membranes. This study intends to investigate the effects of intravitreally delivered melatonin on mouse retina. The visual function of administered mice is assessed by electrophysiological and behavior examinations three weeks after intravitreal delivery. Moreover, multi-electrode array (MEA) was used to assess the electrical activities of retinal ganglion cells (RGCs). We found that intravitreal delivery of high dosage melatonin (400-500 µg/kg) destroyed the retinal architecture and impaired the visual function of mice. Conversely, the melatonin administration at low dose (100-300 µg/kg) did not have any significant effects on the photoreceptor survival or visual function. As shown in the MEA recording, the photoreceptors activity of the central region was more severely disturbed by the high dose melatonin. A pronounced augment of the spontaneous firing frequency was recorded in these mice received high dosage melatonin, indicating that intravitreal delivery of high dosage melatonin would affect the electrical activity of RGCs. Immunostaining assay showed that the vitality of cone photoreceptor was impaired by high dose melatonin. These findings suggest that intravitreal melatonin is not always beneficial for ocular tissues, especially when it is administered at high dosage. These data add new perspectives to current knowledge about melatonin delivery at the ocular level. Further therapeutic strategies should take into consideration of these risks that caused by delivery approach.

Discovery of novel indole-based aroylhydrazones as anticonvulsants: Pharmacophore-based design.

A number of novel melatonin derivatives, containing aroylhydrazone moieties, were synthesized and explored in vivo for anticonvulsant activity, neurotoxicity in ICR mice as well as in-vitro for cytoxicity and oxidative stress in rats. The structures and configurations were confirmed by NMR, FTIR, HRMS and crystal X-ray diffraction method. For selection of potent structures for synthesis a pharmacophore model was used. Two compounds 3e, with a 2-furyl moiety fragment and 3f with 2-thienyl fragment, showed a potency in maximal electroshock (MES) test (ED50 = 50.98 mg kg-1, PI > 5.88 and ED50 = 108.7 mg kg-1; PI > 2.76), respectively, higher than melatonin (ED50 = 160.3 mg kg-1, PI > 1.87). The compounds 3c, 3e, 3f and 3i suppressed psychomotor seizures in the 6 Hz test and 3c was the most potent with higher ED50 = 13.98 mg kg-1 and PI of > 21.46 compared to that of melatonin (ED50 = 49.76 mg kg-1 and PI of > 6.03) in mice. None of the compounds displayed neurotoxicity in the rota-rod test. The novel melatonin derivatives exerted weak cytotoxic effects while 3f showed the lowest hepatoxic effects comparable to that of the positive control melatonin in rats. The high affinities to the elucidated pharmacophore model of the novel melatonin compounds derived from the inclusion of aroylhydrazone moiety in the indole scaffold yielded suitable candidates with anticonvulsant activity in the MES and 6 Hz test of psychomotor seizures.

Melatonin-Induced Changes in Cytosolic Calcium Might be Responsible for Apoptosis Induction in Tumour Cells.

BACKGROUND/AIMS: Melatonin is a hormone transferring information about duration of darkness to the organism and is known to modulate several signaling pathways in the cells, e.g. generation of endoplasmic reticulum stress, oxidative status of the cells, etc. Melatonin has been shown to exert antiproliferative and cytotoxic effects on various human cancers. We proposed that this hormone can differently affect tumour cells and healthy cells. METHODS: We compared the effect of 24 h melatonin treatment on calcium transport (by fluorescent probes FLUO-3AM and Rhod-5N), ER stress (determined as changes in the expression of CHOP, XBP1 and fluorescently, using Thioflavin T), ROS formation (by CellROX® Green/Orange Reagent) and apoptosis induction (by Annexin-V-FLUOS/propidiumiodide) in two tumour cell lines - ovarian cancer cell line A2780 and stable cell line DLD1 derived from colorectal carcinoma, with non-tumour endothelial cell line EA.hy926. RESULTS: Melatonin increased apoptosis in both tumour cell lines more than twice, while in EA.hy926 cells the apoptosis was increased only by 30%. As determined by silencing with appropriate siRNAs, both, type 1 sodium/calcium exchanger and type 1 IP3 receptor are involved in the apoptosis induction. Antioxidant properties of melatonin were significantly increased in EA.hy926 cells, while in tumour cell lines this effect was much weaker. CONCLUSION: Taken together, melatonin has different antioxidative effects on tumour cells compared to non-tumour ones; it also differs in the ability to induce apoptosis through the type 1 sodium/calcium exchanger, and type 1 IP3 receptor. Different targeting of calcium transport systems in tumour and normal, non-tumour cells is suggested as a key mechanism how melatonin can exert its anticancer effects. Therefore, it might have a potential as a novel therapeutic implication in cancer treatment.

Safety assessment and toxicological profiling of a novel combinational sunprotective dermal formulation containing melatonin and pumpkin seed oil.

Ultraviolet (UV) radiation exposure has been known to cause irreparable damages to human skin. The daunting risk of UV radiation exposure faced by military personnel led to the development of a sunscreen formulation which has superior sun protection factor combined with the ability to counteract reactive oxygen species. The present work deals with the preclinical safety evaluation of the sunscreen formulation comprising of four US FDA approved UV filters; namely avobenzone, octinoxate, oxybenzone, titanium dioxide along with melatonin and pumpkin seed oil, via OECD protocols of assessing acute oral and dermal toxicity; skin sensitizing; skin irritating; ocular irritating and genotoxic potential. Both oral and dermal LD50 values were found to be ˃2000 mg/kg body weight in adult Wistar albino rats using acute dermal and oral toxicity tests. The sunscreen formulation was found to be non-sensitizing to the skin of guinea pigs and non-irritating to both skin and eyes of rabbits. The sunscreen formulation was also found to be non-mutagenic which was affirmed by a battery of genotoxicity and muagenicity assays. The results obtained from this preclinical study indicated that the sunscreen formulation is non toxic and safe in animal models. This study along with additional preclinical evaluations may serve as a basis for considering the formulation as a potential candidate for further trials to establish its efficacy, tolerability and applicability.

Intranasal melatonin nanoniosomes: pharmacokinetic, pharmacodynamics and toxicity studies.

AIM: Intranasal melatonin encapsulated in nanosized niosomes was preclinically evaluated. METHODOLOGY: A formula of melatonin niosomes (MN) was selected through physicochemical and cytotoxic data for pharmacokinetic, pharmacodynamics and toxicity studies in male Wistar rats. RESULTS: Intranasal MN was bioequivalent to intravenous injection of melatonin, providing therapeutic level doses. Acute and subchronic toxicity screening showed no abnormal signs, symptoms or hematological effects in any animals. Transient nasal irritations with no inflammation were observed with intranasal MN, leading it to be categorized as relatively harmless. CONCLUSION: The intranasal MN could deliver melatonin to the brain to induce sleep and provide delayed systemic circulation, relative to intravenous injection and also distribute to peripheral tissue.

Synergistic Cytotoxicity of Melatonin and New-generation Anticancer Drugs Against Leukemia Lymphocytes But Not Normal Lymphocytes.

The present study demonstrates specific sensitization of leukemia lymphocytes towards anticancer drugs using melatonin and clarifies the role of reactive oxygen species (ROS) for induction of apoptosis. The study covers four conventional and 11 new-generation anticancer drugs. Four parameters were analyzed simultaneously in leukemia and normal lymphocytes treated with drug, melatonin, or their combination: cell viability, induction of apoptosis, level of reactive oxygen species (ROS), and level of protein-carbonyl products. Almost all investigated combinations of melatonin with new-generation anticancer drugs were characterized by synergistic cytotoxicity towards leukemia lymphocytes, while the combinations with conventional drugs exhibited additive or antagonistic effects on cell viability. In leukemia lymphocytes, the additive cytotoxicity of doxorubicin plus melatonin was accompanied by low levels of ROS and protein-carbonyl products, as well as by suppression of apoptosis. In normal lymphocytes, none of the studied parameters changed significantly compared to cells treated with doxorubicin only. The combinations of everolimus plus melatonin and barasertib plus melatonin exhibited impressive synergistic cytotoxic effects on leukemia lymphocytes but did not affect the viability of normal lymphocytes. In leukemia cells, the synergistic cytotoxicity was accompanied by strong induction of apoptosis but a decrease of ROS to a level below that of the control. In normal lymphocytes, these combinations did not affect the level of ROS nor of protein-carbonyl products, and did not induce apoptosis. The data suggest that melatonin is a promising supplementary component in chemotherapy which allows the therapeutic doses of anticancer drugs to be reduced, minimizing their side-effects.

Melatonin exacerbates acute experimental autoimmune encephalomyelitis by enhancing the serum levels of lactate: A potential biomarker of multiple sclerosis progression.

Melatonin has a beneficial role in adult rat models of multiple sclerosis (MS). In this study, melatonin treatment (10 mg/kg/d) was investigated in young age (5-6 weeks old) Lewis rat model of acute experimental autoimmune encephalomyelitis (EAE) followed by assessing serum levels of lactate and melatonin. Results showed that clinical outcomes were exacerbated in melatonin- (neurological score = 6) vs PBS-treated EAE rats (score = 5). Melatonin caused a significant increase in serum IFN-γ, in comparison to PBS-treated EAE rats whereas no considerable change in IL-4 levels were found, although they were significantly lower than those of controls. The ratio of IFN-γ/IL-4, an indicator of Th-1/Th-2, was significantly higher in PBS- and melatonin- treated EAE rats, in comparison to controls. Moreover, results showed increased lymphocyte infiltration, activated astrocytes (GFAP+ cells) but also higher demyelinated plaques (MBP-deficient areas) in the lumbar spinal cord of melatonin-treated EAE rats. Finally, serum levels of lactate, but not melatonin, significantly increased in the melatonin group, compared to untreated EAE and normal rats. In conclusion, our results indicated a relationship between age and the development of EAE since a negative impact was found for melatonin on EAE recovery of young rats by enhancing IFN-γ, the ratio of Th1/Th2 cells, and astrocyte activation, which seems to delay the remyelination process. While melatonin levels decline in MS patients, lactate might be a potential diagnostic biomarker for prediction of disease progression. Early administration of melatonin in the acute phase of MS might be harmful and needs further investigations.

Synthesis and evaluation of multi-target-directed ligands for the treatment of Alzheimer's disease based on the fusion of donepezil and melatonin.

A novel series of compounds obtained by fusing the acetylcholinesterase (AChE) inhibitor donepezil and the antioxidant melatonin were designed as multi-target-directed ligands for the treatment of Alzheimer's disease (AD). In vitro assay indicated that most of the target compounds exhibited a significant ability to inhibit acetylcholinesterase (eeAChE and hAChE), butyrylcholinesterase (eqBuChE and hBuChE), and ß-amyloid (Aß) aggregation, and to act as potential antioxidants and biometal chelators. Especially, 4u displayed a good inhibition of AChE (IC50 value of 193nM for eeAChE and 273nM for hAChE), strong inhibition of BuChE (IC50 value of 73nM for eqBuChE and 56nM for hBuChE), moderate inhibition of Aß aggregation (56.3% at 20µM) and good antioxidant activity (3.28trolox equivalent by ORAC assay). Molecular modeling studies in combination with kinetic analysis revealed that 4u was a mixed-type inhibitor, binding simultaneously to catalytic anionic site (CAS) and the peripheral anionic site (PAS) of AChE. In addition, 4u could chelate metal ions, reduce PC12 cells death induced by oxidative stress and penetrate the blood-brain barrier (BBB). Taken together, these results strongly indicated the hybridization approach is an efficient strategy to identify novel scaffolds with desired bioactivities, and further optimization of 4u may be helpful to develop more potent lead compound for AD treatment.

Effects of acute administration of melatonin on attentional, executive, and working memory processes in rats.

Melatonin is a potential candidate for additive therapy in cancer, neurodegenerative, and mental disorders requiring administration during the activity phase. Nevertheless, because melatonin has mostly been used as a hypnotic, less is known about its cognitive effects. In this study, we investigated the effects of acute administration of melatonin on executive, attentional, and working memory processes in rats during the activity phase. Three doses of melatonin (6, 18, or 36 mg/kg) were tested and compared to a saline control group in two behavioral tests: the Attentional Set Shifting task (for attentional and executive processes assessment) and the Spontaneous Alternation test in a Y-maze (for working memory assessment). Our results revealed that, up to 36 mg/kg, the acute administration dose of melatonin did not alter the attentional or executive processes, nor the working memory in rats. Consequently, this result may be encouraging for the use of melatonin in additive therapy during the activity phase.

Xanthohumol impairs glucose uptake by a human first-trimester extravillous trophoblast cell line (HTR-8/SVneo cells) and impacts the process of placentation.

In this study, we aimed to investigate modulation of glucose uptake by the HTR-8/SVneo human first-trimester extravillous trophoblast cell line by a series of compounds and to study its consequences upon cell proliferation, viability and migration. We observed that uptake of (3)H-deoxy-d-glucose ((3)H-DG; 10 nM) was time-dependent, saturable, inhibited by cytochalasin B (50 and 100 µM), phloretin (0.5 mM) and phloridzin (1 mM), insulin-insensitive and sodium-independent. In the short term (30 min), neither 5-HT (100-1000 µM), melatonin (10 nM) nor the drugs of abuse ethanol (100 mM), nicotine (100 µM), cocaine (25 µM), amphetamine (10-25 µM) and 3,4-methylenedioxy-N-methamphetamine (10 µM) affected (3)H-DG uptake, while dexamethasone (100-1000 µM), fluoxetine (100-300 µM), quercetin, epigallocatechin-3-gallate (30-1000 µM), xanthohumol (XH) and resveratrol (1-500 µM) decreased it. XH was the most potent inhibitor [IC50 = 3.55 (1.37-9.20) µM] of (3)H-DG uptake, behaving as a non-competitive inhibitor of (3)H-DG uptake, both after short- and long-term (24 h) treatment. The effect of XH (5 µM; 24 h) upon (3)H-DG uptake involved mammalian target of rapamycin, tyrosine kinases and c-Jun N-terminal kinases intracellular pathways. Moreover, XH appeared to decrease cellular uptake of lactate due to inhibition of the monocarboxylate transporter 1. Additionally, XH (24 h; 5 µM) decreased cell viability, proliferation, culture growth and migration. The effects of XH upon cell viability and culture growth, but not the antimigratory effect, were mimicked by low extracellular glucose conditions and reversed by high extracellular glucose conditions. We thus suggest that XH, by inhibiting glucose cellular uptake and impairing HTR-8/SVneo cell viability and proliferation, may have a deleterious impact in the process of placentation.

Melatonin induces apoptosis through biomolecular changes, in SK-LU-1 human lung adenocarcinoma cells.

OBJECTIVES: Anti-cancer effects of melatonin (N-acetyl-5-methoxytryptamine, an indole-amine), have been widely reported, however, little has been known, regarding its mechanism(s) of action in lung cancer. Thus, we investigated its induction of apoptosis through biomolecular changes (lipid, protein and nucleic acid/DNA) in the SK-LU-1 human lung cancer cell line. MATERIALS AND METHODS: We used Fourier transform infrared (FTIR) microspectroscopy, and conventional methods, to confirm changes in lipid (annexin V/PI staining for membrane alteration), protein (caspase-3/7 protein activity) and DNA (DAPI staining for DNA fragmentation). RESULTS: We observed from FTIR data that melatonin increased lipid content and reduced intensity of nucleic acid/DNA, confirmed by annexin V/PI and DAPI respectively. Secondary protein structure at 1656 cm(-1) (α-helix) was reduced and peak position of ß-sheet structure (1637 cm(-1) ) was shifted to lower frequency. Alteration in apoptotic proteins was demonstrated via caspase-3/7 activity induction. CONCLUSIONS: High melatonin concentration exerted anti-cancer effects by changing biomolecular structure of lipids, nucleic acids and proteins, supporting its enhancement of apoptotic induction.

Effects of melatonin on aluminium-induced neurobehavioral and neurochemical changes in aging rats.

This study aimed to investigate the potential protective effects of melatonin (Mel) against aluminium-induced neurodegenerative changes in aging Wistar rats (24-28months old). Herein, aluminium chloride (AlCl3) (50mg/kg BW/day) was administered by gavage, and melatonin (Mel) was co-administered to a group of Al-treated rats by an intra-peritoneal injection at a daily dose of 10mg/kg BW for four months. The findings revealed that aluminium administration induced a significant decrease in body weight associated with marked mortality for the old group of rats, which was more pronounced in old Al-treated rats. Behavioural alterations were assessed by 'open fields', 'elevated plus maze' and 'Radial 8-arms maze' tests. The results demonstrated that Mel co-administration alleviated neurobehavioral changes in both old and old Al-treated rats. Melatonin was noted to play a good neuroprotective role, reducing lipid peroxidation (TBARs), and enhancing enzymatic (SOD, CAT and GPx) activities in the brain organs of old control and old Al-treated rats. Mel treatment also reversed the decrease of AChE activity in the brain tissues, which was confirmed by histological sections. Overall, the results showed that Mel administration can induce beneficial effects for the treatment of Al-induced neurobehavioral and neurochemical changes in the central nervous system (CNS).

Melatonin elevates apoptosis in human platelets via ROS mediated mitochondrial damage.

Melatonin is a pineal hormone that regulates circadian and seasonal rhythms. The chronobiotic role of melatonin corresponds with a repertoire of pharmacological properties. Besides, it has a wide range of therapeutic applications. However, recent studies have demonstrated its direct interaction with platelets: at physiological concentration it promotes platelet aggregation; on the other hand, at pharmacological doses it raises intracellular Ca(2+) leading to platelet activation, thrombus formation and cardiovascular disorders. In order to further probe its effects on platelets, the current study targeted platelet apoptosis and melatonin was found to stimulate apoptosis. The mitochondrial pathway of apoptosis was mainly investigated because of its susceptibility to oxidative stress-inducing factors including therapeutic and dietary elements. Melatonin significantly increased the generation of intracellular ROS and Ca(2+), facilitating mitochondrial membrane depolarization, cytochrome c release, caspase activation, protein phosphorylation and phosphatidylserine externalization. Further, the overall toxicity of melatonin on platelets was confirmed by MTT and lactate dehydrogenase assays. The elevated rate of platelet apoptosis has far reaching consequences including thrombocytopenia. Besides, platelets undergoing apoptosis release microparticles, which fuel thrombus formation and play a significant role in the pathophysiology of a number of diseases. In many parts of the world melatonin is an over-the-counter dietary supplement and alternative medicine. Since, melatonin displays platelet proapoptotic effect at a concentration attainable through therapeutic dosage, the present study sends a warning signal to the chronic use of melatonin as a therapeutic drug and questions its availability without a medical prescription.

Neuroprotective effect of melatonin against hypoxia-induced retinal ganglion cell death in neonatal rats.

The purpose of this study was to determine whether melatonin treatment would mitigate retinal ganglion cell (RGC) death in the developing retina following a hypoxic insult. Lipid peroxidation (LPO), glutathione (GSH), tumor necrosis factor-α (TNF-α) and interleukin-1ß (IL-1ß) concentrations, expression of vascular endothelial growth factor receptors, Flt-1 and Flk-1, release of cytochrome c from mitochondria, and caspase-3 expression were examined in the retinas of 1-day-old rats at 3 hr to 14 days after a hypoxic exposure. The mRNA and protein expression of Flt-1 and Flk-1 and the tissue concentration of LPO, TNF-α, and IL-1ß were upregulated significantly after the hypoxic exposure, whereas the content of GSH was decreased significantly. RGC cultures also showed increased LPO and decreased GSH levels after hypoxic exposure but these effects were reversed in cells treated with melatonin. TNF-α and IL-1ß expression was specifically located on microglial cells, whereas Flt-1 and Flk-1 was limited to RGCs as confirmed by double immunofluorescence labeling. Cultures of hypoxic microglial cells treated with melatonin showed a significant reduction in the release of these cytokines as compared to untreated hypoxic cells. Hypoxia induced increase in the cytosolic cytochrome c and caspase-3 in RGCs was attenuated with melatonin treatment. The results suggest that, in hypoxic injuries, melatonin is neuroprotective to RGCs in the developing retina through its antioxidative, anti-inflammatory, and anti-apoptotic effects. Melatonin suppressed Flt-1 and Flk-1 expression in retinal blood vessels, which may result in reduced retinal vascular permeability and it also preserved mitochondrial function as shown by a reduction in cytochrome c leakage into the cytosol. The results may have therapeutic implications for the management of retinopathy of prematurity.

Melatonin influences antioxidant homeostasis and basal metabolism in the BALB/c mouse model.

OBJECTIVES: Melatonin is a hormone with strong antioxidant activity. It is biosynthesized in the pineal gland and serves in the biological signaling and control of the circadian rhythm. Though there is evidence of beneficial effects of melatonin, the substance was not investigated in greater details associated with specific regulation of oxidative stress in organs and tissues. DESIGN: The experiment is based on exposure of BALB/c mice to doses from 10 µg to 1mg of melatonin. Mice were euthanized after one and 24 hours, respectively. Biochemical markers in plasma, ferric reducing antioxidant power (FRAP), thiobarbituric acid reactive substances (TBARS) and activity of caspase-3 were examined in selected organs. RESULTS: We confirmed significant alteration in high-density lipoprotein and total cholesterols and glucose. After one day, levels of glucose and high-density lipoprotein cholesterol were decreased, while total cholesterol increased in a dose dependent manner. FRAP values increased in spleen, liver, kidney, heart, and brain indicating a growing potential of low molecular weight antioxidants 24 hours after exposure. However, TBARS values indicating oxidative stress were elevated in heart, kidney, and liver. CONCLUSIONS: Despite the antioxidant properties of melatonin, its effect on the organism is more complicated. It influences not only the oxidative homeostasis but also the basal metabolism, as represented by, e.g., cholesterol and glucose. This substance could thus be used for therapeutical purposes such as amelioration of pathologies associated with generation of reactive species or some metabolic dysfunctions.

Effect of melatonin on cyclooxygenase-2 expression and nuclear factor-kappa B activation in RAW264.7 macrophage-like cells stimulated with fimbriae of Porphyromonas gingivalis.

BACKGROUND: The possible link between melatonin and anti-inflammatory activity is currently a focus of interest. In the present study, COX-2 expression and NF-κB activation in RAW264.7 macrophage-like cells stimulated with the fimbriae of Porphyromonas gingivalis, an oral anaerobe, in the absence and presence of melatonin were investigated. MATERIALS AND METHODS: The cytotoxicity of melatonin and indole against RAW264.7 cells was determined using a cell counting kit. The regulatory effect of melatonin, and of indole on the expression of COX-2 mRNA stimulated by exposure to the fimbriae was investigated by Northern blot analysis. NF-κB activation was evaluated by both electrophoretic mobility-shift assay and Western blot analysis. RESULTS: The half maximal (50%) effective concentration (EC(50)) values for melatonin and indole were 3300 µM and 130 µM, respectively. Melatonin at non-cytotoxic concentrations significantly inhibited the fimbria-induced expression of COX-2. The fimbria-stimulated binding of NF-κB to its consensus sequence and phosphorylation-dependent proteolysis of inhibitor κB-α were markedly inhibited by melatonin. However, indole did not inhibit COX-2 expression and NF-κB activation. CONCLUSION: Melatonin may be able to prevent diseases induced by oral bacteria.

Pro-oxidant effect of melatonin in tumour leucocytes: relation with its cytotoxic and pro-apoptotic effects.

Melatonin has many effects on a wide range of physiological functions and is involved in a number of pathological events including oncostatic and neoplastic processes. The tissue protective actions of melatonin are attributed to its well-known antioxidant activity though melatonin might also exert pro-oxidant effects, particularly in tumour cells. This study evaluated the pro-oxidant effects of melatonin in tumour cell lines of human haematopoietic origin. Melatonin treatment is able to stimulate production of intracellular reactive oxygen species (ROS), as revealed by the increase in rhodamine-123 fluorescence, which was associated with significant cytotoxicity and activation of caspase activities. Furthermore, pre-treatment of cells with well-known antioxidants, such as N-acetyl-L-cysteine (NAC), trolox, PEG-catalase and reduced glutathione (GSH), reversed the effects of melatonin on both intracellular ROS production, as on the cytotoxicity and caspase activation. This pro-oxidant action of melatonin may assist in limiting tumour cell growth.