Age-related changes in melatonin synthesis in rat extrapineal tissues

Mitochondria: Central Organelles for Melatonin's Antioxidant and Anti-Aging Actions

Melatonin, along with its metabolites, have long been known to significantly reduce the oxidative stress burden of aging cells or cells exposed to toxins. Oxidative damage is a result of free radicals produced in cells, especially in mitochondria. When measured, melatonin, a potent antioxidant, was found to be in higher concentrations in mitochondria than in other organelles or subcellular locations. Recent evidence indicates that mitochondrial membranes possess transporters that aid in the rapid uptake of melatonin by these organelles against a gradient. Moreover, we predicted several years ago that, because of their origin from melatonin-producing bacteria, mitochondria likely also synthesize melatonin. Data accumulated within the last year supports this prediction. A high content of melatonin in mitochondria would be fortuitous, since these organelles produce an abundance of free radicals. Thus, melatonin is optimally positioned to scavenge the radicals and reduce the degree of oxidative damage. In light of the "free radical theory of aging", including all of its iterations, high melatonin levels in mitochondria would be expected to protect against age-related organismal decline. Also, there are many age-associated diseases that have, as a contributing factor, free radical damage. These multiple diseases may likely be deferred in their onset or progression if mitochondrial levels of melatonin can be maintained into advanced age.

Pharmacological and physiological assessment of serotonin formation and degradation in isolated preparations from mouse and human hearts

Using transgenic (TG) mice that overexpress the human serotonin (5-HT)4a receptor specifically in cardiomyocytes, we wanted to know whether 5-HT can be formed and degraded in the mammalian heart and whether this can likewise lead to inotropic and chronotropic effects in this TG model. We noted that the 5-HT precursor 5-hydroxy-tryptophan (5-HTP) can exert inotropic and chronotropic effects in cardiac preparations from TG mice but not from wild-type (WT) mice; similar results were found in human atrial preparations as well as in intact TG animals using echocardiography. Moreover, by immunohistochemistry we could detect 5-HT metabolizing enzymes and 5-HT transporters in mouse hearts as well as in human atria. Hence, in the presence of an inhibitor of aromatic l-amino acid decarboxylase, the positive inotropic effects of 5-HTP were absent in TG and isolated human atrial preparations, and, moreover, inhibitors of enzymes involved in 5-HT degradation enhanced the efficacy of 5-HT in TG atria. A releaser of neurotransmitters increased inotropy in the isolated TG atrium, and this effect could be blocked by a 5-HT4a receptor antagonist. Fluoxetine, an inhibitor of 5-HT uptake, elevated the potency of 5-HT to increase contractility in the TG atrium. In addition, inhibitors of organic cation and monoamine transporters apparently reduced the positive inotropic potency of 5-HT in the TG atrium. Hence, we tentatively conclude that a local production and degradation of 5-HT in the mammalian heart and more specifically in mammalian myocytes probably occurs. Conceivably, this formation of 5-HT and possibly impaired degradation may be clinically relevant in cases of unexplained tachycardia and other arrhythmias.

NEW & NOTEWORTHY The present work suggests that inotropically active serotonin (5-HT) can be formed in the mouse and human heart and probably by cardiomyocytes themselves. Moreover, active degradation of 5-HT seems to occur in the mammalian heart. These findings may again increase the interest of researchers for cardiac effects of 5-HT.

NAMPT-Mediated NAD Biosynthesis as the Internal Timing Mechanism: In NAD+ World, Time Is Running in Its Own Way

The biological age of organisms differs from the chronological age and is determined by internal aging clock(s). How cells estimate time on a scale of 24 hours is relatively well studied; however, how biological time is measured by cells, tissues, organs, or organisms in longer time periods (years and decades) is largely unknown. What is clear and widely agreed upon is that the link to age and age-related diseases is not chronological, as it does not depend on a fixed passage of time. Rather, this link depends on the biological age of an individual cell, tissue, organ, or organism and not on time in a strictly chronological sense. Biological evolution does not invent new methods as often as improving upon already existing ones. It should be easier to evolve and remodel the existing (circadian) time clock mechanism to use it for measurement or regulation of longer time periods than to invent a new time mechanism/clock. Specifically, it will be demonstrated that the circadian clock can also be used to regulate circannual or even longer time periods. Nicotinamide phosphoribosyltransferase (NAMPT)-mediated nicotinamide adenine dinucleotide (NAD+) levels, being regulated by the circadian clock, might be the missing link between aging, cell cycle control, DNA damage repair, cellular metabolism and the aging clock, which is responsible for the biological age of an organism. The hypothesis that NAMPT/NAD+/SIRT1 might represent the time regulator that determines the organismal biological age will be presented. The biological age of tissues and organs might be regulated and synchronized through eNAMPT blood secretion. The "NAD World 2.0" concept will be upgraded with detailed insights into mechanisms that regulate NAD⁺-mediated aging clock ticking, the duration and amplitude of which are responsible for the aging rate of humans.

Melatonin: Protection against age-related cardiac pathology

Aging is a complex and progressive process that involves physiological and metabolic deterioration in every organ and system. Cardiovascular diseases are one of the most common causes of mortality and morbidity among elderly subjects worldwide. Most age-related cardiovascular disorders can be influenced by modifiable behaviours such as a healthy diet rich in fruit and vegetables, avoidance of smoking, increased physical activity and reduced stress. The role of diet in prevention of various disorders is a well-established factor, which has an even more important role in the geriatric population. Melatonin, an indoleamine with multiple actions including antioxidant properties, has been identified in a very large number of plant species, including edible plant products and medical herbs. Among products where melatonin has been identified include wine, olive oil, tomato, beer, and others. Interestingly, consumed melatonin in plant foods or melatonin supplementation may promote health benefits by virtue of its multiple properties and it may counteract pathological conditions also related to cardiovascular disorders, carcinogenesis, neurological diseases and aging. In the present review, we summarized melatonin effects against age-related cardiac alterations and abnormalities with a special focus on heart ischemia/reperfusion (IR) injury and myocardial infarction.

Melatonin signaling in T cells: Functions and applications

Melatonin affects a variety of physiological processes including circadian rhythms, cellular redox status, and immune function. Importantly, melatonin significantly influences T-cell-mediated immune responses, which are crucial to protect mammals against cancers and infections, but are associated with pathogenesis of many autoimmune diseases. This review focuses on our current understanding of the significance of melatonin in T-cell biology and the beneficial effects of melatonin in T-cell response-based diseases. In addition to expressing both membrane and nuclear receptors for melatonin, T cells have the four enzymes required for the synthesis of melatonin and produce high levels of melatonin. Meanwhile, melatonin is highly effective in modulating T-cell activation and differentiation, especially for Th17 and Treg cells, and also memory T cells. Mechanistically, the influence of melatonin in T-cell biology is associated with membrane and nuclear receptors as well as receptor-independent pathways, for example, via calcineurin. Several cell signaling pathways, including ERK1/2-C/EBPα, are involved in the regulatory roles of melatonin in T-cell biology. Through modulation in T-cell responses, melatonin exerts beneficial effects in various inflammatory diseases, such as type 1 diabetes, systemic lupus erythematosus, and multiple sclerosis. These findings highlight the importance of melatonin signaling in T-cell fate determination, and T cell-based immune pathologies.

Daily NO rhythms in peripheral clocks in aging male Wistar rats: protective effects of exogenous melatonin

In mammals suprachiasmatic nucleus (SCN), acts as a light entrainable master clock and by generation of temporal oscillations regulates the peripheral organs acting as autonomous clocks resulting in overt behavioral and physiological rhythms. SCN also controls synthesis and release of melatonin (hormonal message for darkness) from pineal. Nitric Oxide (NO) acts as an important neurotransmitter in generating the phase shifts of circadian rhythms and participates in sleep-wake processes, maintenance of vascular tone as well as signalling and regulating inflammatory processes. Aging is associated with disruption of circadian timing system and decline in endogenous melatonin leading to several physiological disorders. Here we report the effect of aging on NO daily rhythms in various peripheral clocks such as kidney, intestine, liver, heart, lungs and testis. NO levels were measured at zeitgeber time (ZT) 0, 6, 12 and 18 in these tissues using Griess assay in male Wistar rats. Aging resulted in alteration of NO levels as well as phase of NO in both 12 and 24 months groups. Correlation analysis demonstrated loss of stoichiometric interaction between the various peripheral clocks with aging. Age induced alterations in NO daily rhythms were found to be most significant in liver and, interestingly least in lungs. Neurohormone melatonin, an endogenous synchroniser and an antiaging agent decreases with aging. We report further differential restoration with exogenous melatonin administration of age induced alterations in NO daily rhythms and mean levels in kidney, intestine and liver and the stoichiometric interactions between the various peripheral clocks.

Evidence of melatonin synthesis in the ram reproductive tract

Melatonin is a ubiquitous molecule found in a wide range of fluids, one of them being ram seminal plasma, in which it can reach higher concentrations than those found in blood, suggesting an extrapineal secretion by the reproductive tract. In order to identify the source of the melatonin found in ram seminal plasma, we first tried to determine whether the melatonin levels were maintained during the day. For this purpose, melatonin concentrations were measured in seminal plasma obtained from first ejaculates of six rams at 6:00 a.m. in total darkness, at 10:00 a.m. and at 14:00 p.m. The melatonin concentration was higher (p < 0.05) in ejaculates collected at 6:00 a.m. than at 10:00 and 14:00. There was no statistical difference between the latter. To further corroborate an extrapineal secretion of melatonin, the presence of the two key enzymes involved in melatonin synthesis, arylalkylamine-N-acetyltransferase (AANAT) and N-acetylserotonin-O-methyltransferase (ASMT) was analyzed by RT-PCR, q-PCR and Western-blot in ram testes, epididymis, and accessory glands. The RT-PCR showed the presence of the m-RNA codifying both AANAT and ASTM in all the tissues under study, but the q-PCR and Western-blot revealed that gene expression of these enzymes was significantly higher in the testis (p < 0.05). Immunohistochemistry confirmed the presence of AANAT and ASMT in the testis and revealed that they were found in the Leydig cells, spermatocytes, and spermatids. Also, measurable levels of melatonin were found in testicular tissue and the tail of the epididymis. In conclusion, our study indicates that the testes are one of the likely sources of the high levels of melatonin found in ram seminal plasma, at least during the day.

Effect of daytime-restricted feeding in the daily variations of liver metabolism and blood transport of serotonin in rat

The biogenic amine serotonin is a signaling molecule in the gastrointestinal tract, platelets, and nervous tissue. In nervous system, serotonin and its metabolites are under the control of the circadian timing system, but it is not known if daily variations of serotonin exist in the liver. To explore this possibility, we tested if the rhythmic pattern of serotonin metabolism was regulated by daytime restricted feeding (DRF) which is a protocol associated to the expression of the food entrained oscillator (FEO). The DRF involved food access for 2 h each day for 3 weeks. Control groups included food ad libitum (AL) as well as acute fasting and refeeding. Serotonin-related metabolites were measured by high pressure liquid chromatography, the anabolic and catabolic enzymes were evaluated by western blot, qPCR, and immunohistochemistry to generate 24-h profiles. The results showed in the AL group, liver serotonin, tryptophan hydroxylase-1 activity, and protein abundance as well as serotonin in plasma and serum were rhythmic and coordinated. The DRF protocol disrupted this coordinated response and damped the rhythmic profile of these parameters. We demonstrated the daily synthesis and the degradation of serotonin as well as its transport in blood. This rhythm could influence the physiological role played by serotonin in peripheral organs. DRF caused an uncoordinated response in the liver and blood serotonin rhythm. This modification could be a part of the physiology of the FEO.

Expression of the MT1 melatonin receptor in ovarian cancer cells

Ovarian cancer (OC) is the leading cause of death among women with genital tract disorders. Melatonin exhibits oncostatic properties which it may effect through binding to its membrane receptor, MT1. The aim of this study was to determine the expression of MT1 in OC cells and to correlate this with clinical and pathological data. Immunohistochemistry was performed on 84 cases of OC. Normal ovarian epithelial (IOSE 364) and OC (SK-OV-3, OVCAR-3) cell lines were used to examine the MT1 expression at protein level using the western blot and immunofluorescence technique. The expression of MT1 was observed as cytoplasmic-membrane (MT1_CM) and membrane (MT1_M) reactions. A positive correlation between MT1_CM and MT1_M was found in all the studied cases. There were no significant differences between the expression of MT1_CM, MT1_M, and histological type, staging, grading, presence of residual disease, or overall survival time. Immunofluorescence showed both MT1_M and MT1_CM expression in all the tested cell lines. Western blot illustrated the highest protein level of MT1 in IOSE 364 and the lowest in the OVCAR-3. The results indicate the limited prognostic significance of MT1 in OC cells.

Antitumour activity of melatonin in a mouse model of human prostate cancer: relationship with hypoxia signalling

Melatonin is known to exert antitumour activity in several types of human cancers, but the underlying mechanisms as well as the efficacy of different doses of melatonin are not well defined. Here, we test the hypothesis whether melatonin in the nanomolar range is effective in exerting antitumour activity in vivo and examine the correlation with the hypoxia signalling mechanism, which may be a major molecular mechanism by which melatonin antagonizes cancer. To test this hypothesis, LNCaP human prostate cancer cells were xenografted into seven-wk-old Foxn1nu/nu male mice that were treated with melatonin (18 i.p. injections of 1 mg/kg in 41 days). Saline-treated mice served as control. We found that the melatonin levels in plasma and xenografted tissue were 4× and 60× higher, respectively, than in control samples. Melatonin tended to restore the redox imbalance by increasing expression of Nrf2. As part of the phenotypic response to these perturbations, xenograft microvessel density was less in melatonin-treated animals, indicative of lower angiogenesis, and the xenograft growth rate was slower (P < 0.0001). These changes were accompanied by a reduced expression of Ki67, elevated expression of HIF-1α and increased phosphorylation of Akt in melatonin than saline-treated mice. We conclude that the beneficial effect of melatonin in reducing cancer growth in vivo was evident at melatonin plasma levels as low as 4 nm and was associated with decreased angiogenesis. Higher HIF-1α expression in xenograft tissue indicates that the antitumour effect cannot be due to a postulated antihypoxic effect, but may stem from lower angiogenesis potential.

Extrapineal melatonin: sources, regulation, and potential functions

Endogenous melatonin is synthesized from tryptophan via 5-hydroxytryptamine. It is considered an indoleamine from a biochemical point of view because the melatonin molecule contains a substituted indolic ring with an amino group. The circadian production of melatonin by the pineal gland explains its chronobiotic influence on organismal activity, including the endocrine and non-endocrine rhythms. Other functions of melatonin, including its antioxidant and anti-inflammatory properties, its genomic effects, and its capacity to modulate mitochondrial homeostasis, are linked to the redox status of cells and tissues. With the aid of specific melatonin antibodies, the presence of melatonin has been detected in multiple extrapineal tissues including the brain, retina, lens, cochlea, Harderian gland, airway epithelium, skin, gastrointestinal tract, liver, kidney, thyroid, pancreas, thymus, spleen, immune system cells, carotid body, reproductive tract, and endothelial cells. In most of these tissues, the melatonin-synthesizing enzymes have been identified. Melatonin is present in essentially all biological fluids including cerebrospinal fluid, saliva, bile, synovial fluid, amniotic fluid, and breast milk. In several of these fluids, melatonin concentrations exceed those in the blood. The importance of the continual availability of melatonin at the cellular level is important for its physiological regulation of cell homeostasis, and may be relevant to its therapeutic applications. Because of this, it is essential to compile information related to its peripheral production and regulation of this ubiquitously acting indoleamine. Thus, this review emphasizes the presence of melatonin in extrapineal organs, tissues, and fluids of mammals including humans.

Protective effects of melatonin in reducing oxidative stress and in preserving the fluidity of biological membranes: a review

Free radicals generated within subcellular compartments damage macromolecules which lead to severe structural changes and functional alterations of cellular organelles. A manifestation of free radical injury to biological membranes is the process of lipid peroxidation, an autooxidative chain reaction in which polyunsaturated fatty acids in the membrane are the substrate. There is considerable evidence that damage to polyunsaturated fatty acids tends to reduce membrane fluidity. However, adequate levels of fluidity are essential for the proper functioning of biological membranes. Thus, there is considerable interest in antioxidant molecules which are able to stabilize membranes because of their protective effects against lipid peroxidation. Melatonin is an indoleamine that modulates a wide variety of endocrine, neural and immune functions. Over the last two decades, intensive research has proven this molecule, as well as its metabolites, to possess substantial antioxidant activity. In addition to their ability to scavenge several reactive oxygen and nitrogen species, melatonin increases the activity of the glutathione redox enzymes, that is, glutathione peroxidase and reductase, as well as other antioxidant enzymes. These beneficial effects of melatonin are more significant because of its small molecular size and its amphipathic behaviour, which facilitates ease of melatonin penetration into every subcellular compartment. In the present work, we review the current information related to the beneficial effects of melatonin in maintaining the fluidity of biological membranes against free radical attack, and further, we discuss its implications for ageing and disease.

Melatonin in the oral cavity: physiological and pathological implications

BACKGROUND AND OBJECTIVES

The purpose of this article was to summarize what is known about the function of melatonin in the oral cavity.

MATERIAL AND METHODS

Databases were searched for the relevant published literature to 30 November, 2013. The following search items were used in various combinations: melatonin, gingiva, periodontium, inflammation, herpes, alveolar bone, periodontal ligament, dental implants, xerostomia, methacrylate, chlorhexidine, cancer. The literature uncovered is summarized herein.

RESULTS

Salivary melatonin levels exhibit a circadian rhythm with highest values at night. Melatonin has both receptor-mediated and receptor-independent actions in cells of the oral cavity. Melatonin is released into the saliva by the acinar cells of the major salivary glands and via the gingival fluid. Functions of melatonin in the oral cavity are likely to relate primarily to its anti-inflammatory and antioxidant activities. These actions may suppress inflammation of the gingiva and periodontium, reduce alveolar bone loss, abrogate herpes lesions, enhance osteointegration of dental implants, limit oral cancer, and suppress disorders that have a free radical component. Sublingual melatonin tablets or oral melatonin sprays and topical melatonin-containing gel, if used on a regular basis, may improve overall oral health and reduce mucosal lesions.

CONCLUSION

Collectively, the results indicate that endogenously-produced and exogenously-applied melatonin are beneficial to the oral cavity.

Differential role of melatonin in restoration of age-induced alterations in daily rhythms of expression of various clock genes in suprachiasmatic nucleus of male Wistar rats

Aging is associated with changes in several basic parameters of circadian rhythms in mammals leading to circadian dysfunction. The hypothalamic Suprachiasmatic nucleus (SCN) regulates neuronal, endocrine and behavioral rhythms through the expression of various clock genes and release of melatonin from pineal gland. In the present study, we investigated the effect of aging on daily rhythms of various clock genes such as rPer1, rPer2, rCry1, rCry2 and rBmal1 in the SCN of male Wistar rats. The m-RNA expression levels of these genes were studied by using quantitative Polymerase Chain Reaction (qPCR) in 3 age groups [3 (adult), 12 and 24 month (m)] at variable time points (Zeitgeber time (ZT)-0, 6, 12 and 18). The m-RNA expression for all genes studied was rhythmic in SCN of adult rats with maximum for rPer1 at ZT-6, rPer2, rCry1 and rCry2 at ZT-12 and rBmal1 at ZT-18. However in 12 and 24 m, the phases of expression of these genes were significantly altered with abolition of daily rhythms of rCry1, rCry2 and rBmal1 in 24 m. Melatonin, messenger of darkness, an endogenous synchronizer of rhythm, an antioxidant and an antiaging drug, declines with aging. We therefore studied the effects of melatonin administered subcutaneously at 1 h before the onset of darkness (ZT-11) for 11 days on age induced desynchronization in expression of these genes. We report here differential restoration of daily rhythm, phase, levels and stoichiometric interaction of m-RNA expression of these genes in various age groups in rat SCN with melatonin treatment.

Melatonin in the mammalian olfactory bulb

Melatonin is a neurohormone associated with circadian rhythms. A diurnal rhythm in olfactory sensitivity has been previously reported and melatonin receptor mRNAs have been observed in the olfactory bulb, but the effects of melatonin in the olfactory bulb have not been explored. First, we corroborated data from a previous study that identified melatonin receptor messenger RNAs in the olfactory bulb. We then investigated whether melatonin treatment would affect cells in the olfactory bulbs of rats. Using a combination of polymerase chain reaction (PCR), quantitative PCR (qPCR), cell culture, and electrophysiology, we discovered that melatonin receptors and melatonin synthesis enzymes were present in the olfactory bulb and we observed changes in connexin43 protein, GluR1 mRNA, GluR2 mRNA, Per1 mRNA, Cry2 mRNA, and K(+) currents in response to 2-iodomelatonin. Via qPCR, we observed that messenger RNAs encoding melatonin receptors and melatonin biosynthesis enzymes fluctuated in the olfactory bulb across 24h. Together, these data show that melatonin receptors are present in the olfactory bulb and likely affect olfactory function. Additionally, these data suggest that melatonin may be locally synthesized in the olfactory bulb.

Adaptations of the aging animal to exercise: role of daily supplementation with melatonin

The pineal gland, through melatonin, seems to be of fundamental importance in determining the metabolic adaptations of adipose and muscle tissues to physical training. Evidence shows that pinealectomized animals fail to develop adaptive metabolic changes in response to aerobic exercise and therefore do not exhibit the same performance as control-trained animals. The known prominent reduction in melatonin synthesis in aging animals led us to investigate the metabolic adaptations to physical training in aged animals with and without daily melatonin replacement. Male Wistar rats were assigned to four groups: sedentary control (SC), trained control (TC), sedentary treated with melatonin (SM), and trained treated with melatonin (TM). Melatonin supplementation lasted 16 wk, and the animals were subjected to exercise during the last 8 wk of the experiment. After euthanasia, samples of liver, muscle, and adipose tissues were collected for analysis. Trained animals treated with melatonin presented better results in the following parameters: glucose tolerance, physical capacity, citrate synthase activity, hepatic and muscular glycogen content, body weight, protein expression of phosphatidylinositol 3-kinase (PI3K), mitogen-activated protein kinase (MAPK), and protein kinase activated by adenosine monophosphate (AMPK) in the liver, as well as the protein expression of the glucose transporter type 4 (GLUT4) and AMPK in the muscle. In conclusion, these results demonstrate that melatonin supplementation in aging animals is of great importance for the required metabolic adaptations induced by aerobic exercise. Adequate levels of circulating melatonin are, therefore, necessary to improve energetic metabolism efficiency, reducing body weight and increasing insulin sensitivity.

Melatonin attenuates methamphetamine-induced disturbances in mitochondrial dynamics and degeneration in neuroblastoma SH-SY5Y cells

Methamphetamine (METH) is a psychostimulant drug that can cause toxicity and degeneration in the brain. The toxicity due to METH involves multiple pathways, including the mitochondrial-dependent death pathway. Several pieces of evidence have emphasized that the fragmentation of mitochondria into smaller structures plays some role in the cell-death process. In this study, we investigated the role of mitochondrial dynamics in METH-induced toxicity in human dopaminergic neuroblastoma SH-SY5Y cultured cell lines. In addition, the protective effect of melatonin against METH-induced toxicity was investigated. Our results show that METH significantly decreased cell viability and increased the levels of the mitochondrial fission protein, Fis1 and the Drp1 oligomer. However, the levels of the mitochondrial fusion proteins OPA1 and Mfn1 did not change in METH-treated cells. Melatonin can reverse the toxic effects of the METH-induced reduction in cell viability and the production of the Fis1 protein and the Drp1 oligomer. Moreover, the morphological alteration of mitochondria was investigated in METH-treated cells in the presence of melatonin using transmission electron microscopy (TEM). At 24 hr after METH exposure, typical cell shrinkage was observed in SH-SY5Y cells. Mitochondria were fragmented into small globular structures in a large proportion of METH-treated cells, but tubular networks of mitochondria were present in large proportions of control-untreated cells and METH-treated cells in the presence of melatonin. The results of the present study demonstrate the potential of melatonin to reduce cell death and restore mitochondrial function in neurons affected by METH-induced toxicity.

Melatonin improves insulin sensitivity independently of weight loss in old obese rats

In aged rats, insulin signaling pathway (ISP) is impaired in tissues that play a pivotal role in glucose homeostasis, such as liver, skeletal muscle, and adipose tissue. Moreover, the aging process is also associated with obesity and reduction in melatonin synthesis from the pineal gland and other organs. The aim of the present work was to evaluate, in male old obese Wistar rats, the effect of melatonin supplementation in the ISP, analyzing the total protein amount and the phosphorylated status (immunoprecipitation and immunoblotting) of the insulin cascade components in the rat hypothalamus, liver, skeletal muscle, and periepididymal adipose tissue. Melatonin was administered in the drinking water for 8- and 12 wk during the night period. Food and water intake and fasting blood glucose remained unchanged. The insulin sensitivity presented a 2.1-fold increase both after 8- and 12 wk of melatonin supplementation. Animals supplemented with melatonin for 12 wk also presented a reduction in body mass. The acute insulin-induced phosphorylation of the analyzed ISP proteins increased 1.3- and 2.3-fold after 8- and 12 wk of melatonin supplementation. The total protein content of the insulin receptor (IR) and the IR substrates (IRS-1, 2) remained unchanged in all investigated tissues, except for the 2-fold increase in the total amount of IRS-1 in the periepididymal adipose tissue. Therefore, the known age-related melatonin synthesis reduction may also be involved in the development of insulin resistance and the adequate supplementation could be an important alternative for the prevention of insulin signaling impairment in aged organisms.

High levels of melatonin generated during the brewing process

Beer is a beverage consumed worldwide. It is produced from cereals (barley or wheat) and contains a wide array of bioactive phytochemicals and nutraceutical compounds. Specifically, high melatonin concentrations have been found in beer. Beers with high alcohol content are those that present the greatest concentrations of melatonin and vice versa. In this study, gel filtration chromatography and ELISA were combined for melatonin determination. We brewed beer to determine, for the first time, the beer production steps in which melatonin appears. We conclude that the barley, which is malted and ground in the early process, and the yeast, during the second fermentation, are the largest contributors to the enrichment of the beer with melatonin.

Peripheral reproductive organ health and melatonin: ready for prime time

Melatonin has a wide variety of beneficial actions at the level of the gonads and their adnexa. Some actions are mediated via its classic membrane melatonin receptors while others seem to be receptor-independent. This review summarizes many of the published reports which confirm that melatonin, which is produced in the ovary, aids in advancing follicular maturation and preserving the integrity of the ovum prior to and at the time of ovulation. Likewise, when ova are collected for in vitro fertilization-embryo transfer, treating them with melatonin improves implantation and pregnancy rates. Melatonin synthesis as well as its receptors have also been identified in the placenta. In this organ, melatonin seems to be of particular importance for the maintenance of the optimal turnover of cells in the villous trophoblast via its ability to regulate apoptosis. For male gametes, melatonin has also proven useful in protecting them from oxidative damage and preserving their viability. Incubation of ejaculated animal sperm improves their motility and prolongs their viability. For human sperm as well, melatonin is also a valuable agent for protecting them from free radical damage. In general, the direct actions of melatonin on the gonads and adnexa of mammals indicate it is an important agent for maintaining optimal reproductive physiology.

A Comparison of B16 Melanoma Cells and 3T3 Fibroblasts Concerning Cell Viability and ROS Production in the Presence of Melatonin, Tested Over a Wide Range of Concentrations

Melatonin is a pleiotropic molecule with many cellular and systemic actions, including chronobiotic effects. Beneficial effects are widely documented concerning the treatment of neoplastic diseases in vivo as well as reductions in viability of cultured cells from melanoma, one of the most aggressive cancers in humans. However, studies of its effects on non-tumor cells in vitro have not focused on viability, except for experiments aiming to protect against oxidotoxicity or other toxicological insults. Furthermore, there is no agreement on the range of effective melatonin concentrations in vitro, and the mechanisms that reduce cell viability have remained unclear. Tumor cell-specific increases in the production of reactive oxygen and nitrogen species (ROS/RNS) may provide a possible explanation. Our aim was to analyze the potential inhibition of tumor (B16 melanoma 4A5) and non-tumor cell (3T3 Swiss albino) viability using a wide range of melatonin concentrations (10⁻¹¹–10⁻² M), and to determine whether intracellular ROS enhancement was involved in this process. In the absence of fetal bovine serum (FBS), low melatonin concentrations (10⁻⁹–10⁻⁵ M) reduced the proliferation of melanoma cells with no effect in fibroblasts, whereas, in the presence of FBS, they had no effect or even increased the proliferation of both fibroblast and melanoma cells. Melatonin concentrations in the upper millimolar range increased ROS levels and reduced the viability of both cell types, but more markedly so in non-tumor cells. Thus, low melatonin concentrations reduce proliferation in this specific melanoma cell line, whereas high concentrations affect the viability of both tumor (B16 4A5 melanoma) and non-tumor (3T3 fibroblasts) cells. Increased ROS levels in both lines indicate a role for ROS production in the reduction of cell viability at high—but not low—melatonin concentrations, although the mechanism of action still remains to be elucidated.

Melatonin administration differentially affects age-induced alterations in daily rhythms of lipid peroxidation and antioxidant enzymes in male rat liver

A central clock/pacemaker, suprachiasmatic nuclei of the hypothalamus coordinates and entrains circadian oscillations in the peripheral tissues such as the liver, kidney, heart, lungs etc. called peripheral clocks. These also have endogenous circadian oscillations. The circadian rhythms of antioxidants present in cytosol signify redox state of the cell during day/night cycle. The liver has a major impact on homeostasis through its control on serum protein composition and plays a pivotal role in the metabolism of nutrients, drugs, hormones, and metabolic waste products and undergoes substantial changes in structure and function upon aging. In present study, the temporal patterns of oxidative stress indicators in liver were studied. Daily rhythms of lipid peroxidation end products, reduced glutathione (GSH), oxidized glutathione (GSSG) and antioxidant enzymes such as glutathione peroxidase (GPx), superoxide dismutase (SOD) and catalase (CAT) were studied in liver at variable time points (Zeitgeber Time (ZT) 0, 6, 12 and 18) in three age groups: 3 (adult), 12 and 24 months old male Wistar rats. There was increase in oxidative stress in 12 and 24 months old rats indicated through a significant increase in lipid peroxidation, decrease in GSH/GSSG ratio and antioxidant enzyme activities. In 3 months old rats, lipid peroxidation was maximum at ZT-12 whereas GSH, SOD and CAT activities were minimum at ZT-12. The maximum level in 24 h i.e., acrophases of lipid peroxidation, GPx, SOD and CAT activities in liver cell free extracts altered upon aging. As melatonin, messenger of darkness, an endogenous synchronizer of rhythm, an antioxidant and an antiaging drug, declines with aging we studied the effects of melatonin on activities of these antioxidant enzymes in aging rats. Melatonin administration resulted in differential restoration of acrophases, amplitude, mean as well as daily rhythms of lipid peroxidation and antioxidants in liver of 12 and 24 months old rats.

Extrapineal melatonin: analysis of its subcellular distribution and daily fluctuations

We studied the subcellular levels of melatonin in cerebral cortex and liver of rats under several conditions. The results show that melatonin levels in the cell membrane, cytosol, nucleus, and mitochondrion vary over a 24-hr cycle, although these variations do not exhibit circadian rhythms. The cell membrane has the highest concentration of melatonin followed by mitochondria, nucleus, and cytosol. Pinealectomy significantly increased the content of melatonin in all subcellular compartments, whereas luzindole treatment had little effect on melatonin levels. Administration of 10 mg/kg bw melatonin to sham-pinealectomized, pinealectomized, or continuous light-exposed rats increased the content of melatonin in all subcellular compartments. Melatonin in doses ranging from 40 to 200 mg/kg bw increased in a dose-dependent manner the accumulation of melatonin on cell membrane and cytosol, although the accumulations were 10 times greater in the former than in the latter. Melatonin levels in the nucleus and mitochondria reached saturation with a dose of 40 mg/kg bw; higher doses of injected melatonin did not further cause additional accumulation of melatonin in these organelles. The results suggest some control of extrapineal accumulation or extrapineal production of melatonin and support the existence of regulatory mechanisms in cellular organelles, which prevent the intracellular equilibration of the indolamine. Seemingly, different concentrations of melatonin can be maintained in different subcellular compartments. The data also seem to support a requirement of high doses of melatonin to obtain therapeutic effects. Together, these results add information that assists in explaining the physiology and pharmacology of melatonin.

Blocking of melatonin synthesis and MT(1) receptor impairs the activation of Jurkat T cells

Melatonin has been proposed as regulating the immune system by affecting cytokine production in immunocompetent cells, enhancing the production of several T helper (Th)1 cytokines. To further investigate the melatonin's role in IL-2/IL-2R system, we established an inducible T-REx expression system in Jurkat cells in which the protein levels of HIOMT enzyme or MT(1) receptor were significantly down-regulated upon tetracycline incubation. We found that T-REx Jurkat cells with lower levels of HIOMT activity, and consequently lower content of endogenous melatonin, showed IL-2 production decrease after activation with lectin. Likewise, tetracycline-inducible stable cell line expressing MT(1) antisense produced decreased amounts of IL-2 (mRNA and protein levels) after stimulation. Moreover, in T-Rex-MT(1) cells incubated with tetracycline, a sub-optimal PHA dose failed to induce the early activation marker CD25 on the cell surface. The results shown here support the relevance of endogenous melatonin and its signaling in T cell activation.