Melatonin in relation to the "strong" and "weak" versions of the free radical theory of aging

Impact of endogenous melatonin on rhythmic behaviors, reproduction, and survival revealed in melatonin-proficient C57BL/6J congenic mice

The hormone melatonin is synthesized from serotonin by two enzymatic reactions (AANAT and ASMT/HIOMT) in the pineal gland following a circadian rhythm with low levels during the day and high levels at night. The robust nightly peak of melatonin secretion is an output signal of the circadian clock to the whole organism. However, so far the regulatory roles of endogenous melatonin in mammalian biological rhythms and physiology processes are poorly understood. Here, we establish congenic mouse lines (>N10 generations) that are proficient or deficient in melatonin synthesis (AH+/+ or AH-/- mice, respectively) on the C57BL/6J genetic background by crossing melatonin-proficient MSM/Ms with C57BL/6J. AH+/+ mice displayed robust nightly peak of melatonin secretion and had significantly higher levels of pineal and plasma melatonin vs AH-/- mice. Using this mice model, we investigated the role of endogenous melatonin in regulating multiple biological rhythms, physiological processes, and rhythmic behaviors. In the melatonin-proficient (AH+/+) mice, the rate of re-entrainment of wheel-running activity was accelerated following a 6-hour phase advance of dark onset when comparted with AH-/- mice, suggesting a role of endogenous melatonin in facilitating clock adjustment. Further in the AH+/+ mice, there was a significant decrease in body weight, gonadal weight and reproductive performance, and a significant increase in daily torpor (a hypothermic and hypometabolic state lasting only hours during adverse conditions). Endogenous melatonin, however, had no effect in the modulation of the diurnal rhythm of 2-[¹²⁵ I]-iodomelatonin receptor expression in the SCN, free-running wheel behavior in constant darkness, life span, spontaneous homecage behaviors, and various types of social-emotional behaviors. The findings also shed light on the role of endogenous melatonin in mice domestication and provide new insights into melatonin's action in reducing energy expenditure during a food shortage. In summary, the congenic mice model generated in this study offers a significant advantage toward understanding of the role of endogenous melatonin in regulating melatonin receptor-mediated rhythm behaviors and physiological functions.

Anthocyanidin Extract from Summer-black-grape Affects the Expression of Ki-67 in Testis, Ovary of D-Galactose-induced Aging Mice

The aim of this work was to analyze the expression of Ki-67 in ovary, testis of aging mice with anthocyanidin extract from Summer-black-grape. ICR mice (the aging group and the anthocyanidin-groups (50 mg/kg/D-group, 75 mg/kg/D-group and 100 mg/kg/D-group) were employed to evaluate the effect of grape anthocyanidin on reproductive system. The results showed that the anthocyanidin had strong scavenging ability for free radicals, the level of oxidation in serum of mice treated with anthocyanidin was low, and the pathological changes were not obvious. In the anthocyanidin group, the Ki-67 positive particles in the testis and ovary tissue were significantly decreased. The anthocyanidin of Summer-black-grape reduces the expression of Ki-67 protein in the testis or ovary of aging mice. In gonadal cells of aging mice, the anthocyanidin were shown protective effect in the proliferation.

Protective stabilization of mitochondrial permeability transition and mitochondrial oxidation during mitochondrial Ca2+ stress by melatonin's cascade metabolites C3-OHM and AFMK in RBA1 astrocytes

Cyclic 3-hydroxymelatonin (C3-OHM) and N1-acetyl-N2-formyl-5-methoxykynuramine (AFMK) are two major cascade metabolites of melatonin. We previously showed melatonin provides multiple levels of mitochondria-targeted protection beyond as a mitochondrial antioxidant during ionomycin-induced mitochondrial Ca²⁺ (mCa²⁺ ) stress in RBA1 astrocytes. Using noninvasive laser scanning fluorescence coupled time-lapse digital imaging microscopy, this study investigated whether C3-OHM and AFMK also provide mitochondrial levels of protection during ionomycin-induced mCa²⁺ stress in RBA1 astrocytes. Interestingly, precise temporal and spatial dynamic live mitochondrial images revealed that C3-OHM and AFMK prevented specifically mCa²⁺ -mediated mitochondrial reactive oxygen species (mROS) formation and hence mROS-mediated depolarization of mitochondrial membrane potential (△Ψ_m ) and permanent lethal opening of the MPT (p-MPT). The antioxidative effects of AFMK, however, were less potent than that of C3-OHM. Whether C3-OHM and AFMK targeted directly the MPT was investigated under a condition of "oxidation free-Ca²⁺ stress" using a classic antioxidant vitamin E to remove mCa²⁺ -mediated mROS stress and the potential antioxidative effects of C3-OHM and AFMK. Intriguingly, two compounds still effectively postponed "oxidation free-Ca²⁺ stress"-mediated depolarization of △Ψ_m and p-MPT. Measurements using a MPT pore-specific indicator Calcein further identified that C3-OHM and AFMK, rather than inhibiting, stabilized the MPT in its transient protective opening mode (t-MPT), a critical mechanism to reduce overloaded mROS and mCa²⁺ . These multiple layers of mitochondrial protection provided by C3-OHM and AFMK thus crucially allow melatonin to extend its metabolic cascades of mitochondrial protection during mROS- and mCa²⁺ -mediated MPT-associated apoptotic stresses and may provide therapeutic benefits against astrocyte-mediated neurodegeneration in the CNS.

Melatonin modifies basal and stimulated insulin secretion via NADPH oxidase

Melatonin is a hormone synthesized in the pineal gland, which modulates several functions within the organism, including the synchronization of glucose metabolism and glucose-stimulated insulin secretion (GSIS). Melatonin can mediate different signaling pathways in pancreatic islets through two membrane receptors and via antioxidant or pro-oxidant enzymes modulation. NADPH oxidase (NOX) is a pro-oxidant enzyme responsible for the production of the reactive oxygen specie (ROS) superoxide, generated from molecular oxygen. In pancreatic islets, NOX-derived ROS can modulate glucose metabolism and regulate insulin secretion. Considering the roles of both melatonin and NOX in islets, the aim of this study was to evaluate the association of NOX and ROS production on glucose metabolism, basal and GSIS in pinealectomized rats (PINX) and in melatonin-treated isolated pancreatic islets. Our results showed that ROS content derived from NOX activity was increased in PINX at baseline (2.8 mM glucose), which was followed by a reduction in glucose metabolism and basal insulin secretion in this group. Under 16.7 mM glucose, an increase in both glucose metabolism and GSIS was observed in PINX islets, without changes in ROS content. In isolated pancreatic islets from control animals incubated with 2.8 mM glucose, melatonin treatment reduced ROS content, whereas in 16.7 mM glucose, melatonin reduced ROS and GSIS. In conclusion, our results demonstrate that both basal and stimulated insulin secretion can be regulated by melatonin through the maintenance of ROS homeostasis in pancreatic islets.

Effects of Diet on Sleep Quality

There is much emerging information surrounding the impact of sleep duration and quality on food choice and consumption in both children and adults. However, less attention has been paid to the effects of dietary patterns and specific foods on nighttime sleep. Early studies have shown that certain dietary patterns may affect not only daytime alertness but also nighttime sleep. In this review, we surveyed the literature to describe the role of food consumption on sleep. Research has focused on the effects of mixed meal patterns, such as high-carbohydrate plus low-fat or low-carbohydrate diets, over the short term on sleep. Such studies highlight a potential effect of macronutrient intakes on sleep variables, particularly alterations in slow wave sleep and rapid eye movement sleep with changes in carbohydrate and fat intakes. Other studies instead examined the intake of specific foods, consumed at a fixed time relative to sleep, on sleep architecture and quality. Those foods, specifically milk, fatty fish, tart cherry juice, and kiwifruit, are reviewed here. Studies provide some evidence for a role of certain dietary patterns and foods in the promotion of high-quality sleep, but more studies are necessary to confirm those preliminary findings.

Melatonin: a potential intervention for hepatic steatosis

Melatonin (N-acetyl-5-methoxytryptamine, MLT) is a neuroendocrine hormone, which is primarily synthesized by the pineal gland in vertebrates. Melatonin is a remarkable molecule with diverse biological and physiological actions and is involved in the regulation of various important functions such as circadian rhythm, energy metabolism, the reproductive system, the cardiovascular system, and the neuropsychiatric system. It also plays a role in disease by having anti-neoplastic and anti-osteoarthritic effects among others. Recently, research has focused on the roles of melatonin in oxidative stress, lipid metabolism, and hepatic steatosis and its potential therapeutic roles.

Effect of melatonin on motor performance and brain cortex mitochondrial function during ethanol hangover

Increased reactive oxygen species generation and mitochondrial dysfunction occur during ethanol hangover. The aim of this work was to study the effect of melatonin pretreatment on motor performance and mitochondrial function during ethanol hangover. Male mice received melatonin solution or its vehicle in drinking water during 7 days and i.p. injection with EtOH (3.8 g/kg BW) or saline at the eighth day. Motor performance and mitochondrial function were evaluated at the onset of hangover (6h after injection). Melatonin improved motor coordination in ethanol hangover mice. Malate-glutamate-dependent oxygen uptake was decreased by ethanol hangover treatment and partially prevented by melatonin pretreatment. Melatonin alone induced a decrease of 30% in state 4 succinate-dependent respiratory rate. Also, the activity of the respiratory complexes was decreased in melatonin-pretreated ethanol hangover group. Melatonin pretreatment before the hangover prevented mitochondrial membrane potential collapse and induced a 79% decrement of hydrogen peroxide production as compared with ethanol hangover group. Ethanol hangover induced a 25% decrease in NO production. Melatonin alone and as a pretreatment before ethanol hangover significantly increased NO production by nNOS and iNOS as compared with control groups. No differences were observed in nNOS protein expression, while iNOS expression was increased in the melatonin group. Increased NO production by melatonin could be involved in the decrease of succinate-dependent oxygen consumption and the inhibition of complex IV observed in our study. Melatonin seems to act as an antioxidant agent in the ethanol hangover condition but also exhibited some dual effects related to NO metabolism.

Melatonin and female reproduction

Melatonin (N-acetyl-5-methoxytryptamine) is secreted during the dark hours at night by the pineal gland. After entering the circulation, melatonin acts as an endocrine factor and a chemical messenger of light and darkness. It regulates a variety of important central and peripheral actions related to circadian rhythms and reproduction. It also affects the brain, immune, gastrointestinal, cardiovascular, renal, bone and endocrine functions and acts as an oncostatic and anti-aging molecule. Many of melatonin's actions are mediated through interactions with specific membrane-bound receptors expressed not only in the central nervous system, but also in peripheral tissues. Melatonin also acts through non-receptor-mediated mechanisms, for example serving as a scavenger for reactive oxygen species and reactive nitrogen species. At both physiological and pharmacological concentrations, melatonin attenuates and counteracts oxidative stress and regulates cellular metabolism. Growing scientific evidence of reproductive physiology supports the role of melatonin in human reproduction. This review was conducted to investigate the effects of melatonin on female reproduction and to summarize our findings in this field.

Chrononutrition against oxidative stress in aging

Free radicals and oxidative stress have been recognized as important factors in the biology of aging and in many age-associated degenerative diseases. Antioxidant systems deteriorate during aging. It is, thus, considered that one way to reduce the rate of aging and the risk of chronic disease is to avoid the formation of free radicals and reduce oxidative stress by strengthening antioxidant defences. Phytochemicals present in fruits, vegetables, grains, and other foodstuffs have been linked to reducing the risk of major oxidative stress-induced diseases. Some dietary components of foods possess biological activities which influence circadian rhythms in humans. Chrononutrition studies have shown that not only the content of food, but also the time of ingestion contributes to the natural functioning of the circadian system. Dietary interventions with antioxidant-enriched foods taking into account the principles of chrononutrition are of particular interest for the elderly since they may help amplify the already powerful benefits of phytochemicals as natural instruments with which to prevent or delay the onset of common age-related diseases.

Can melatonin delay oxidative damage of human erythrocytes during prolonged incubation?

PURPOSE

Melatonin (MEL) is an effective antioxidant in numerous experimental models, both in vitro and in vivo. However, it should be stressed that there are also papers reporting limited antioxidative activity of MEL or even giving evidence for its pro-oxidative properties. In the present paper we investigated the influence of MEL on the oxidative damage of human erythrocytes during prolonged incubation.

MATERIAL/METHODS

Human erythrocytes suspended in phosphate-buffered saline (PBS), pH 7.4 were incubated at 37ºC either in absence or presence of melatonin at concentration range 0.02 mM-3 mM for up to 96 hrs. The influence of MEL on erythrocyte damage was assessed on the basis of the intensity of intracellular oxidation processes (the oxidation of HbO₂, GSH, fluorescent label DCFH₂) as well as damage to the plasma membrane (lipid peroxidation, the potassium leakage) and the kinetics of hemolysis.

RESULTS

The prolonged incubation of erythrocytes induced a progressive destruction of erythrocytes. Melatonin prevented lipid peroxidation and hemolysis whereas the oxidation of HbO₂ and DCFH₂ was enhanced by melatonin at concentrations higher than 0.6 mM. In the case of erythrocytes incubated with 3 mM of MEL, the hemolysis rate constant (0.0498±0.0039 H%•h⁻¹) was 50% lower than that of the control while the HbO₂ oxidation rate constants were about 1.4 and 1.5 times higher for 1.5 and 3 mM of MEL, respectively. Melatonin had no influence on the oxidation of GSH and the potassium leakage.

CONCLUSIONS

Probably, MEL can stabilize the erythrocyte membrane due to interaction with lipids, thus prolonging the existence of cells. On the contrary, in the presence of MEL the accelerated oxidation of HbO₂ and generally, increased oxidative stress was observed in erythrocytes. Pro- and antioxidative properties of melatonin depend on the type of cells, redox state, as well as experimental conditions.

Plasma melatonin and urinary 6-hydroxymelatonin levels in patients with pulmonary tuberculosis

Tuberculosis (TB) is the second most frequent cause of death in the world, after AIDS. Delay in diagnosing TB is an important worldwide problem. It seriously threatens public health. Cell-mediated immune responses play an important role in the pathogenesis of TB infection. The course of Mycobacterium tuberculosis (MTb) infection is regulated by two distinct T cell cytokine patterns. Melatonin is a biomolecule (mainly secreted by the pineal gland) with free radical scavenging, antioxidant and immunoregulatory properties. Melatonin has both its direct and indirect immunomodulatory effects on the immune system. In this study, we measured plasma melatonin and urine 6-hydroxy melatonin sulphate (6-HMS) concentrations in patients with newly diagnosed TB for the purpose of investigating whether there was a relationship between their levels and MTb infection. Thirty-one newly diagnosed patients presenting with active TB and 31 healthy subjects as the control group were included in this study. Blood and 24-h urine samples were collected from all individuals. Plasma melatonin levels and urine 6-HMS were measured. Our results show that in patients with TB, mean melatonin and 6-HMS concentrations were significantly lower than in the control subjects (p = 0.037, p < 0.001, respectively). We believe that the treatment of TB patients with melatonin might result in a wide range of health benefits including improved quality of life and reduced severity of infection in these patients. Supplementation with melatonin may be considered as an adjunctive therapy to classic treatment of pulmonary TB, especially during the acute phase of infection.

Oxidative stress and immunosenescence: therapeutic effects of melatonin

Age-associated deterioration in the immune system, which is referred to as immunosenescence, contributes to an increased susceptibility to infectious diseases, autoimmunity, and cancer in the elderly. A summary of major changes associated with aging in immune system is described in this paper. In general, immunosenescence is characterized by reduced levels of peripheral naïve T cells derived from thymus and the loss of immature B lineage cells in the bone marrow. As for macrophages and granulocytes, they show functional decline with advancing age as evidenced by their diminished phagocytic activity and impairment of superoxide generation. The indole melatonin is mainly secreted in the pineal gland although it has been also detected in many other tissues. As circulating melatonin decreases with age coinciding with the age-related decline of the immune system, much interest has been focused on melatonin's immunomodulatory effect in recent years. Here, we underlie the antioxidant and immunoenhancing actions displayed by melatonin, thereby providing evidence for the potential application of this indoleamine as a “replacement therapy” to limit or reverse some of the effects of the changes that occur during immunosenescence.

Melatonin is able to delay endoplasmic reticulum stress-induced apoptosis in leukocytes from elderly humans

The mechanisms regulating neutrophil apoptosis are basically unaffected by the aging process. However, a significant impairment of cell survival occurs in elderly individuals following neutrophil challenge with pro-inflammatory stimuli, such as granulocyte-macrophage colony-stimulating factor (GM-CSF). The goal of the present study was to prove the effects of melatonin supplementation on apoptosis induced by calcium signaling in human leukocytes from elderly volunteers. Treatments with the specific inhibitor of cytosolic calcium re-uptake, thapsigargin, and/or the calcium mobilizing agonist, N-formyl-methionyl-leucyl-phenylalanine (fMLP), induced mitochondrial membrane depolarization, caspase activation, phosphatidylserine (PS) externalization, and DNA fragmentation in leukocytes from both young and elderly volunteers, although such effects were much more evident in aged leukocytes. Importantly, melatonin treatment substantially preserved mitochondrial membrane potential, reversed caspase activation, reduced PS exposure and forestalled DNA fragmentation in leukocytes from both age groups. In conclusion, melatonin is able to delay endoplasmic reticulum stress-induced apoptosis in aged leukocytes and may counteract, at the cellular level, age-related degenerative phenomena linked to oxidative stress.

Diets enriched with a Jerte Valley cherry-based nutraceutical product reinforce nocturnal behaviour in young and old animals of nocturnal (Rattus norvegicus) and diurnal (Streptopelia risoria) chronotypes

The decline in melatonin secretion with age seems to be one of the major reasons for increased sleep disruption in older animals. Previously, we showed that the administration with melatonin or its precursor, tryptophan, improved activity/rest rhythms in aged individuals. Here, it was evaluated the effect of a 10-day consumption of a Jerte Valley cherry-based nutraceutical product (patent no. ES2342141B1), which contains high levels of tryptophan, serotonin and melatonin, on the activity/rest rhythms of young and old rats (Rattus norvegicus) and ringdoves (Streptopelia risoria) as representatives of animals with nocturnal and diurnal habits, respectively, and its possible relationship with the serum levels of melatonin and glucose. Total diurnal and nocturnal activity pulses were logged at control, during, and up to 3 days after the treatment. Melatonin and glucose were measured with ELISA and testing kits respectively. In both young and old rats, the intake of the cherry nutraceutical decreased diurnal activity, whereas nocturnal activity increased. The opposite effect was observed for ringdoves. The treatment increased the circulating levels of melatonin in both species and restored the amplitude of the activity rhythm in the old animals to that of the non-treated young groups. The consumption of a Jerte Valley cherry-based nutraceutical product may help to counteract the impaired activity/rest rhythm found in aged animals.

Disrupting the circadian clock: gene-specific effects on aging, cancer, and other phenotypes

The circadian clock imparts 24-hour rhythmicity on gene expression and cellular physiology in virtually all cells. Disruption of the genes necessary for the circadian clock to function has diverse effects, including aging-related phenotypes. Some circadian clock genes have been described as tumor suppressors, while other genes have less clear functions in aging and cancer. In this Review, we highlight a recent study [Dubrovsky et al., Aging 2: 936-944, 2010] and discuss the much larger field examining the relationship between circadian clock genes, circadian rhythmicity, aging-related phenotypes, and cancer.

Significance of high levels of endogenous melatonin in Mammalian cerebrospinal fluid and in the central nervous system

Levels of melatonin in mammalian circulation are well documented; however, its levels in tissues and other body fluids are yet only poorly established. It is obvious that melatonin concentrations in cerebrospinal fluid (CSF) of mammals including humans are substantially higher than those in the peripheral circulation. Evidence indicates that melatonin produced in pineal gland is directly released into third ventricle via the pineal recess. In addition, brain tissue is equipped with the synthetic machinery for melatonin production and the astrocytes and glial cells have been proven to produce melatonin. These two sources of melatonin may be responsible for its high levels in CNS. The physiological significance of the high levels of melatonin in CNS presumably is to protect neurons and glia from oxidative stress. Melatonin as a potent antioxidant has been reported to be a neuroprotector in animals and in clinical studies. It seems that long term melatonin administration which elevates CSF melatonin concentrations will retard the progression of neurodegenerative disorders, for example, Alzheimer disease.

Jerte Valley cherry-enriched diets improve nocturnal rest and increase 6-sulfatoxymelatonin and total antioxidant capacity in the urine of middle-aged and elderly humans

Tryptophan, serotonin, and melatonin, present in Jerte Valley cherries, participate in sleep regulation and exhibit antioxidant properties. The effect of the intake of seven different Jerte Valley cherry cultivars on the sleep-wake cycle, 6-sulfatoxymelatonin levels, and urinary total antioxidant capacity in middle-aged and elderly participants was evaluated. Volunteers were subjected to actigraphic monitoring to record and display the temporal patterns of their nocturnal activity and rest. 6-sulfatoxymelatonin and total antioxidant capacity were quantified by enzyme-linked immunosorbent assay and colorimetric assay kits, respectively. The intake of each of the cherry cultivars produced beneficial effects on actual sleep time, total nocturnal activity, assumed sleep, and immobility. Also, there were significant increases in 6-sulfatoxymelatonin levels and total antioxidant capacity in urine after the intake of each cultivar. These findings suggested that the intake of Jerte Valley cherries exerted positive effect on sleep and may be seen as a potential nutraceutical tool to counteract oxidation.

Melatonin counteracts alterations in oxidative metabolism and cell viability induced by intracellular calcium overload in human leucocytes: changes with age

Ageing is associated with an increased production of free radicals and alterations in the mechanisms of adaptation to oxidative stress. In fact, the free radical theory of ageing proposes that deleterious actions of free radicals are responsible for the functional deterioration associated with ageing. Moreover, a close relationship exists between calcium homeostasis and oxidative stress. The current work was aimed at proving that intracellular calcium overload induced by N-formyl-methionyl-leucyl-phenylalanine (FMLP) and/or thapsigargin leads to oxidative stress. We additionally examined the effect of melatonin on the levels of reactive oxygen species (ROS) and cell viability in human leucocytes collected from young (20-30-year-old) and elderly (65-75-year-old) individuals under both basal and oxidative stress-induced conditions. Treatments with 10 nM FMLP and/or 1 microM thapsigargin induced a transient increase in cytosolic free-calcium concentration ([Ca(2 + )](c)) in human leucocytes due to calcium release from internal stores, and led in turn to oxidative stress, as assessed by intracellular ROS measurement. Non-treated leucocytes from aged individuals exhibited higher ROS levels and lower rates of cell survival when compared to leucocytes from young individuals. Similar results were obtained in FMLP and/or thapsigargin-treated leucocytes from elderly individuals when compared to those from the young individuals. Melatonin treatment significantly reduced both hydrogen peroxide (H(2)O(2)) and superoxide anion levels, likely due to its free-radical scavenging properties, and enhanced leucocyte viability in both age groups. Therefore, melatonin may be a useful tool for the treatment of disease states and processes where an excessive production of oxidative damage occurs.

Visualization of melatonin's multiple mitochondrial levels of protection against mitochondrial Ca(2+)-mediated permeability transition and beyond in rat brain astrocytes

Melatonin protects cells against various types of oxidative stress-induced apoptosis due primarily to its ability to effectively scavenge pathological and disease condition-augmented generation of mitochondrial reactive oxygen species (mROS). Once produced, mROS indiscriminately damage mitochondrial components and more importantly they crucially activate directly the mitochondrial permeability transition (MPT), one of the critical mechanisms for initiating post mitochondrial apoptotic signaling. Whether or not melatonin targets directly the MPT, however, remains inconclusive, particularly during oxidative stress. This study, thus, investigated this possibility of an 'oxidation free Ca(2+) stress' in the presence of vitamin E after ionomycin exposure as a sole Ca(2+)-mediated MPT in order to exclude melatonin's primary antioxidative effects as well as Ca(2+)-mediated oxidative stress. The studies were carried out using cultured rat brain astrocytes RBA-1. With the application of laser scanning multiple fluorescence imaging microscopy, we visualized for the first time multiple mitochondrial protective effects provided by melatonin during Ca(2+) stress. First, melatonin, due to its primary antioxidative actions, completely prevented mCa(2+)-induced mROS formation during ionomycin exposure. Secondly, when melatonin(')s antioxidative effects were prevented due to the addition of vitamin E, melatonin significantly prevented mCa(2+)-mediated MPT and apoptosis suggesting its direct targeting of the MPT. Surprisingly, in the presence of cyclosporin A, a MPT inhibitor, melatonin reduced further mCa(2+)-mediated apoptosis during ionomycin exposure also suggesting its targeting beyond the MPT. As astrocytes are actively involve in regulating synaptic transmission and neurovascular coupling in the CNS, these multiple mitochondrial layers of protection provided by melatonin against mCa(2+)-and/or mROS-mediated apoptosis in astrocytes may be crucial for future therapeutic prevention and treatment of astrocyte-mediated neurodegenerative diseases in the CNS.

The changing biological roles of melatonin during evolution: from an antioxidant to signals of darkness, sexual selection and fitness

Melatonin is a molecule present in a multitude of taxa and may be ubiquitous in organisms. It has been found in bacteria, unicellular eukaryotes, macroalgae, fungi, plants and animals. A primary biological function of melatonin in primitive unicellular organisms is in antioxidant defence to protect against toxic free radical damage. During evolution, melatonin has been adopted by multicellular organisms to perform many other biological functions. These functions likely include the chemical expression of darkness in vertebrates, environmental tolerance in fungi and plants, sexual signaling in birds and fish, seasonal reproductive regulation in photoperiodic mammals, and immunomodulation and anti-inflammatory activity in all vertebrates tested. Moreover, its waning production during aging may indicate senescence in terms of a bio-clock in many organisms. Conversely, high melatonin levels can serve as a signal of vitality and health. The multiple biological functions of melatonin can partially be attributed to its unconventional metabolism which is comprised of multi-enzymatic, pseudo-enzymatic and non-enzymatic pathways. As a result, several bioactive metabolites of melatonin are formed during its metabolism and some of the presumed biological functions of melatonin reported to date may, in fact, be mediated by these metabolites. The changing biological roles of melatonin seem to have evolved from its primary function as an antioxidant.

Melatonin promotes neurogenesis in dentate gyrus in the pinealectomized rat

It was previously shown that pinealectomy causes delayed loss of pyramidal neurons in rat hippocampal layers CA1/3 and that this is reversed by melatonin supplementation. Here, we used immunohistologic detection of doublecortin, a protein expressed in newborn neurons, to determine if melatonin supplementation promotes neurogenesis after pinealectomy. It was found that melatonin supplementation significantly increased the number of doublecortin immunoreactive neurons in the dentate gyrus over the postsurgical intervals of 2, 4, 6, 8, 10 and 17 months. The increase was most evident at 6 months postsurgery and thereafter, and was apparent despite a severe decline in doublecortin-labeled cells over the 17 month postsurgical interval in all groups of rats. Doublecortin immunoreactive cells were not observed in the pyramidal layer itself. These results indicate that melatonin promotes neurogenesis in the dentate gyrus of pinealectomized rats. However, it is equivocal that these newborn neurons migrate to the pyramidal layer and account for the reappearance of neurons at this location in these rats. This study provides further evidence for a role of melatonin in promoting neurogenesis, adding another role to its already remarkably pleiotropic profile. The scope and significance of this newly discovered role remains to be determined.

Reducing oxidative/nitrosative stress: a newly-discovered genre for melatonin

The discovery of melatonin and its derivatives as antioxidants has stimulated a very large number of studies which have, virtually uniformly, documented the ability of these molecules to detoxify harmful reactants and reduce molecular damage. These observations have clear clinical implications given that numerous age-related diseases in humans have an important free radical component. Moreover, a major theory to explain the processes of aging invokes radicals and their derivatives as causative agents. These conditions, coupled with the loss of melatonin as organisms age, suggest that some diseases and some aspects of aging may be aggravated by the diminished melatonin levels in advanced age. Another corollary of this is that the administration of melatonin, which has an uncommonly low toxicity profile, could theoretically defer the progression of some diseases and possibly forestall signs of aging. Certainly, research in the next decade will help to define the role of melatonin in age-related diseases and in determining successful aging. While increasing life span will not necessarily be a goal of these investigative efforts, improving health and the quality of life in the aged should be an aim of this research.

Melatonin and tryptophan counteract lipid peroxidation and modulate superoxide dismutase activity in ringdove heterophils in vivo. Effect of antigen-induced activation and age

Aging is associated with an increased production of free radicals and alterations in the mechanisms of adaptation to stress. A number of studies have shown a causal connection between age-related oxidant/antioxidant imbalance and the diminution of an organism's melatonin levels in old age. Restoration of this rhythm may contribute to the re-stabilization of cellular homeostasis. The present work was aimed at examining the effect of the administration of melatonin or its precursor, the amino acid tryptophan, on heterophil lipid peroxidation (LPO) levels and superoxide dismutase (SOD) activity in heterophils from young (4-5 year) and old (12-14 year) ringdoves (Streptopelia risoria) under both basal and antigen-induced (stressful) conditions. Young animals were treated for 3 consecutive days with a single daily oral dose (0.25 mg) of melatonin at 1900 hours while old animals were treated for 3 consecutive days with either an oral dose (2.5 mg) of melatonin at 1900 hours or an oral capsule of 300 mg/kg body weight of L-tryptophan at 0900 hours. Non-treated old animals presented lower circulating levels of melatonin at night and higher levels of malonaldehyde (MDA) both day and night when compared to young birds. In both age groups, LPO levels were lower at night than during the day. Melatonin or tryptophan treatments significantly increased serum melatonin levels, reinforced SOD activity, and reduced MDA levels induced by the antigen. Melatonin and tryptophan may be useful agents for the treatment of disease states and processes in which an excessive production of oxidative damage occurs.

Effect of melatonin and tryptophan on humoral immunity in young and old ringdoves (Streptopelia risoria)

Melatonin is involved in the regulation of both cellular and humoral immunity. In the present study we have evaluated the effect of the oral administration of melatonin and its precursor, the amino acid tryptophan, on humoral immune response in ringdoves (Streptopelia risoria) from different age groups. Male and female ringdoves of 4-5years of age (young) and 12-14years of age (old) were used in this study. The animals received a single capsule of 300mg/kg b.w. of tryptophan (old animals) for 3 consecutive days 1h after lights on or a single oral dose (0.25 or 2.5mg/kg body weight/0.1ml per animal/day, young and old animals, respectively) of melatonin, for 3 consecutive days 1h before lights off. Blood samples were taken before beginning the treatment (basal values) and at the end of the treatment. Immunoglobulins, bactericidal and haemolytic activity were measured. Our results show that in old animals the humoral immune response was reduced with respect to the young. Both melatonin and tryptophan treatment increased the immunoglobulin concentration, with the nocturnal values being significantly higher than diurnal values and with a major effect in old animals. The bactericidal activity of the S. risoria serum against Staphylococcus aureus, after the treatment with melatonin or tryptophan, was increased at night with a greater effect in old animals. No significant differences were observed in the haemolytic activity of the serum in young animals, but there was an increase in old animals, with higher values at night after treatment with melatonin. In general, the oral administration of melatonin or tryptophan produced a stimulation of humoral immune response with greater effects in old ringdoves.

Nutrition through the life span. Part 3: adults aged 65 years and over

The UK has an ageing population, but this is not being matched by a similar increase in healthy life expectancy. The greatest challenge in the 21st century will be to improve the quality of life as ageing occurs. Health is the most important prerequisite for people to enjoy life in their older years (Brundtland, 1988). Diet is one factor that is believed to play a key role in the prevention and treatment of chronic diseases associated with ageing. The third and final part of this series addressing the concept of nutrition through the lifespan seeks to educate health-care professionals as to what constitutes a healthy diet for the elderly population, and gives practical guidance as to how to try and prevent the ever-growing problem of malnutrition within this age group. It is suggested that when the older adult is hospitalized their risk of malnutrition increases. Therefore, some guidance for the use of oral nutritional supplements in this population is given. Good nutrition and physical exercise are essential for healthy ageing from both a physical and psychological perspective (NICE, 2008). Therefore a multidisciplinary life course approach to ageing is vital to minimizing its complications for quality of life and subsequent public health (Denny, 2008).