Brain washing and neural health: role of age, sleep, and the cerebrospinal fluid melatonin rhythm

The brain lacks a classic lymphatic drainage system. How it is cleansed of damaged proteins, cellular debris, and molecular by-products has remained a mystery for decades. Recent discoveries have identified a hybrid system that includes cerebrospinal fluid (CSF)-filled perivascular spaces and classic lymph vessels in the dural covering of the brain and spinal cord that functionally cooperate to remove toxic and non-functional trash from the brain. These two components functioning together are referred to as the glymphatic system. We propose that the high levels of melatonin secreted by the pineal gland directly into the CSF play a role in flushing pathological molecules such as amyloid-β peptide (Aβ) from the brain via this network. Melatonin is a sleep-promoting agent, with waste clearance from the CNS being highest especially during slow wave sleep. Melatonin is also a potent and versatile antioxidant that prevents neural accumulation of oxidatively-damaged molecules which contribute to neurological decline. Due to its feedback actions on the suprachiasmatic nucleus, CSF melatonin rhythm functions to maintain optimal circadian rhythmicity, which is also critical for preserving neurocognitive health. Melatonin levels drop dramatically in the frail aged, potentially contributing to neurological failure and dementia. Melatonin supplementation in animal models of Alzheimer's disease (AD) defers Aβ accumulation, enhances its clearance from the CNS, and prolongs animal survival. In AD patients, preliminary data show that melatonin use reduces neurobehavioral signs such as sundowning. Finally, melatonin controls the mitotic activity of neural stem cells in the subventricular zone, suggesting its involvement in neuronal renewal.

Melatonin Use for SARS-CoV-2 Infection:Time to Diversify the Treatment Portfolio

We were pleased to read the publication by Lan and colleagues [1] which included a meta-analysis of the Randomized Controlled Trials (RTCs) in which melatonin was used as a treatment for COVID-19. This article is protected by copyright. All rights reserved.

Melatonin Mitigates Mitochondrial Meltdown: Interactions with SIRT3

Melatonin exhibits extraordinary diversity in terms of its functions and distribution. When discovered, it was thought to be uniquely of pineal gland origin. Subsequently, melatonin synthesis was identified in a variety of organs and recently it was shown to be produced in the mitochondria. Since mitochondria exist in every cell, with a few exceptions, it means that every vertebrate, invertebrate, and plant cell produces melatonin. The mitochondrial synthesis of melatonin is not photoperiod-dependent, but it may be inducible under conditions of stress. Mitochondria-produced melatonin is not released into the systemic circulation, but rather is used primarily in its cell of origin. Melatonin's functions in the mitochondria are highly diverse, not unlike those of sirtuin 3 (SIRT3). SIRT3 is an NAD+-dependent deacetylase which regulates, among many functions, the redox state of the mitochondria. Recent data proves that melatonin and SIRT3 post-translationally collaborate in regulating free radical generation and removal from mitochondria. Since melatonin and SIRT3 have cohabitated in the mitochondria for many eons, we predict that these molecules interact in many other ways to control mitochondrial physiology. It is predicted that these mutual functions will be intensely investigated in the next decade and importantly, we assume that the findings will have significant applications for preventing/delaying some age-related diseases and aging itself.

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.

Pineal Calcification, Melatonin Production, Aging, Associated Health Consequences and Rejuvenation of the Pineal Gland

The pineal gland is a unique organ that synthesizes melatonin as the signaling molecule of natural photoperiodic environment and as a potent neuronal protective antioxidant. An intact and functional pineal gland is necessary for preserving optimal human health. Unfortunately, this gland has the highest calcification rate among all organs and tissues of the human body. Pineal calcification jeopardizes melatonin's synthetic capacity and is associated with a variety of neuronal diseases. In the current review, we summarized the potential mechanisms of how this process may occur under pathological conditions or during aging. We hypothesized that pineal calcification is an active process and resembles in some respects of bone formation. The mesenchymal stem cells and melatonin participate in this process. Finally, we suggest that preservation of pineal health can be achieved by retarding its premature calcification or even rejuvenating the calcified gland.

Melatonin as a mitochondria-targeted antioxidant: one of evolution's best ideas

Melatonin is an ancient antioxidant. After its initial development in bacteria, it has been retained throughout evolution such that it may be or may have been present in every species that have existed. Even though it has been maintained throughout evolution during the diversification of species, melatonin's chemical structure has never changed; thus, the melatonin present in currently living humans is identical to that present in cyanobacteria that have existed on Earth for billions of years. Melatonin in the systemic circulation of mammals quickly disappears from the blood presumably due to its uptake by cells, particularly when they are under high oxidative stress conditions. The measurement of the subcellular distribution of melatonin has shown that the concentration of this indole in the mitochondria greatly exceeds that in the blood. Melatonin presumably enters mitochondria through oligopeptide transporters, PEPT1, and PEPT2. Thus, melatonin is specifically targeted to the mitochondria where it seems to function as an apex antioxidant. In addition to being taken up from the circulation, melatonin may be produced in the mitochondria as well. During evolution, mitochondria likely originated when melatonin-forming bacteria were engulfed as food by ancestral prokaryotes. Over time, engulfed bacteria evolved into mitochondria; this is known as the endosymbiotic theory of the origin of mitochondria. When they did so, the mitochondria retained the ability to synthesize melatonin. Thus, melatonin is not only taken up by mitochondria but these organelles, in addition to many other functions, also probably produce melatonin as well. Melatonin's high concentrations and multiple actions as an antioxidant provide potent antioxidant protection to these organelles which are exposed to abundant free radicals.

[Association between gestational weight gain and preterm birth: a retrospective epidemiological analysis in Wuhan]

OBJECTIVE

To understand the influence of gestational weight gain(GWG)on preterm birth in Wuhan.

METHODS

The retrospective epidemiological study was conducted in Wuhan Medical and Health Center for Women and Children between 2012 and 2014. Women who went to this hospital for antenatal care or giving birth were selected. Information was collected by using questionnaires, health care manual and clinical records. We used restricted cubic spline and multivariate logistic regression analysis to study the relationship between GWG and preterm birth.

RESULTS

A total of 11 323 pregnant women participated in the investigation with 11 020(97.32%)of them eligible for our study. The results from the restricted cubic spline indicated that after adjusting for confounding factors, a U-curve was observed for GWG and preterm births(non-linearity test P< 0.001). Multivariate logistic regression analysis also indicated that both inadequate GWG(weight gain<P10)and excessive GWG(weight gain>P90)were independent risk factors for preterm birth compared with normal GWG(weight gain P10-P90)with odds ratios of 1.59(1.25-2.01)and 1.46(1.13-1.88), respectively.

CONCLUSIONS

Inappropriate GWG was the risk factor for preterm birth. Weight monitoring should be strengthened for pregnant women to reduce risk of preterm birth.

Melatonin: exceeding expectations

Melatonin is a small, highly conserved indole with numerous receptor-mediated and receptor-independent actions. Receptor-dependent functions include circadian rhythm regulation, sleep, and cancer inhibition. The receptor-independent actions relate to melatonin's ability to function in the detoxification of free radicals, thereby protecting critical molecules from the destructive effects of oxidative stress under conditions of ischemia/reperfusion injury (stroke, heart attack), ionizing radiation, and drug toxicity, among others. Melatonin has numerous applications in physiology and medicine.

Melatonin and its metabolites as copper chelating agents and their role in inhibiting oxidative stress: a physicochemical analysis

The copper sequestering ability of melatonin and its metabolites cyclic 3-hydroxymelatonin (3OHM), N(1) -acetyl-N(2) -formyl-5-methoxykynuramine (AFMK), and N(1) -acetyl-5-methoxykynuramine (AMK) was investigated within the frame of the Density Functional Theory. It was demonstrated that these compounds are capable of chelating copper ions, yielding stable complexes. The most likely chelation sites were identified. Two different mechanisms were modeled, the direct-chelation mechanism (DCM) and the coupled-deprotonation-chelation mechanism (CDCM). It is proposed that, under physiological conditions, CDCM would be the main chelation route for Cu(II). It was found that melatonin and its metabolites fully inhibited the oxidative stress induced by Cu(II)-ascorbate mixtures, via Cu(II) chelation. In the same way, melatonin, AFMK, and 3OHM also prevented the first step of the Haber-Weiss reaction, consequently turning off the ˙OH production via the Fenton reaction. Therefore, it is proposed that, in addition to the previously reported free radical scavenging cascade, melatonin is also involved in a concurrent 'chelating cascade', thereby contributing to a reduction in oxidative stress. 3OHM was identified as the most efficient of the studied compounds for that purpose, supporting the important role of this metabolite in the beneficial effects of melatonin against oxidative stress.

Essential actions of melatonin in protecting the ovary from oxidative damage

Free radicals and other reactive species are involved in normal ovarian physiology. However, they are also highly reactive with complex cellular molecules (proteins, lipids, and DNA) and alter their functions leading to oxidative stress. Oxidative damage may play a prominent role in the development of disorders that considerably influence female fertility. Melatonin, because of its amphiphilic nature that allows for crossing morphophysiological barriers, is an effective antioxidant for protecting macromolecules against oxidative stress caused by reactive species. The balance between reactive oxygen species and antioxidants within the follicle seems to be critical to the function of the oocyte and granulosa cells and evidence has accumulated showing that melatonin is involved in the protection of these cells. Melatonin appears to have varied functions at different stages of follicle development, oocyte maturation, and luteal stage. Melatonin concentration in the growing follicle may be an important factor in avoiding atresia, because melatonin in the follicular fluid reduces apoptosis of critical cells. Melatonin also has protective actions during oocyte maturation reducing intrafollicular oxidative damage. An association between melatonin concentrations in follicular fluid and oocyte quality has been reported; this would allow a preovulatory follicle to fully develop and provide a competent oocyte for fertilization. The functional role of reactive species and the cytoprotective properties of melatonin on the ovary from oxidative damage are summarized in this brief review.

Melatonin and the circadian system: contributions to successful female reproduction

OBJECTIVE

To summarize the role of melatonin and circadian rhythms in determining optimal female reproductive physiology, especially at the peripheral level.

DESIGN

Databases were searched for the related English-language literature published up to March 1, 2014. Only papers in peer-reviewed journals are cited.

SETTING

Not applicable.

PATIENT(S)

Not applicable.

INTERVENTION(S)

Melatonin treatment, alterations of the normal light:dark cycle and light exposure at night.

MAIN OUTCOME MEASURE(S)

Melatonin levels in the blood and in the ovarian follicular fluid and melatonin synthesis, oxidative damage and circadian rhythm disturbances in peripheral reproductive organs.

RESULT(S)

The central circadian regulatory system is located in the suprachiasmatic nucleus (SCN). The output of this master clock is synchronized to 24 hours by the prevailing light-dark cycle. The SCN regulates rhythms in peripheral cells via the autonomic nervous system and it sends a neural message to the pineal gland where it controls the cyclic production of melatonin; after its release, the melatonin rhythm strengthens peripheral oscillators. Melatonin is also produced in the peripheral reproductive organs, including granulosa cells, the cumulus oophorus, and the oocyte. These cells, along with the blood, may contribute melatonin to the follicular fluid, which has melatonin levels higher than those in the blood. Melatonin is a powerful free radical scavenger and protects the oocyte from oxidative stress, especially at the time of ovulation. The cyclic levels of melatonin in the blood pass through the placenta and aid in the organization of the fetal SCN. In the absence of this synchronizing effect, the offspring may exhibit neurobehavioral deficits. Also, melatonin protects the developing fetus from oxidative stress. Melatonin produced in the placenta likewise may preserve the optimal function of this organ.

CONCLUSION(S)

Both stable circadian rhythms and cyclic melatonin availability are critical for optimal ovarian physiology and placental function. Because light exposure after darkness onset at night disrupts the master circadian clock and suppresses elevated nocturnal melatonin levels, light at night should be avoided.

Melatonin, energy metabolism, and obesity: a review

Melatonin is an old and ubiquitous molecule in nature showing multiple mechanisms of action and functions in practically every living organism. In mammals, pineal melatonin functions as a hormone and a chronobiotic, playing a major role in the regulation of the circadian temporal internal order. The anti-obesogen and the weight-reducing effects of melatonin depend on several mechanisms and actions. Experimental evidence demonstrates that melatonin is necessary for the proper synthesis, secretion, and action of insulin. Melatonin acts by regulating GLUT4 expression and/or triggering, via its G-protein-coupled membrane receptors, the phosphorylation of the insulin receptor and its intracellular substrates mobilizing the insulin-signaling pathway. Melatonin is a powerful chronobiotic being responsible, in part, by the daily distribution of metabolic processes so that the activity/feeding phase of the day is associated with high insulin sensitivity, and the rest/fasting is synchronized to the insulin-resistant metabolic phase of the day. Furthermore, melatonin is responsible for the establishment of an adequate energy balance mainly by regulating energy flow to and from the stores and directly regulating the energy expenditure through the activation of brown adipose tissue and participating in the browning process of white adipose tissue. The reduction in melatonin production, as during aging, shift-work or illuminated environments during the night, induces insulin resistance, glucose intolerance, sleep disturbance, and metabolic circadian disorganization characterizing a state of chronodisruption leading to obesity. The available evidence supports the suggestion that melatonin replacement therapy might contribute to restore a more healthy state of the organism.

On the free radical scavenging activities of melatonin's metabolites, AFMK and AMK

The reactions of N(1) -acetyl-N(2) -formyl-5-methoxykynuramine (AFMK) and N(1) -acetyl-5-methoxykynuramine (AMK) with (•) OH, (•) OOH, and •OOCCl3 radicals have been studied using the density functional theory. Three mechanisms of reaction have been considered: radical adduct formation (RAF), hydrogen transfer (HT), and single electron transfer (SET). Their relative importance for the free radical scavenging activity of AFMK and AMK has been assessed. It was found that AFMK and AMK react with •OH at diffusion-limited rates, regardless of the polarity of the environment, which supports their excellent •OH radical scavenging activity. Both compounds were found to be also very efficient for scavenging •OOCCl3 , but rather ineffective for scavenging •OOH. Regarding their relative activity, it was found that AFMK systematically is a poorer scavenger than AMK and melatonin. In aqueous solution, AMK was found to react faster than melatonin with all the studied free radicals, while in nonpolar environments, the relative efficiency of AMK and melatonin as free radical scavengers depends on the radical with which they are reacting. Under such conditions, melatonin is predicted to be a better •OOH and •OOCCl3 scavenger than AMK, while AMK is predicted to be slightly better than melatonin for scavenging •OH. Accordingly it seems that melatonin and its metabolite AMK constitute an efficient team of scavengers able of deactivating a wide variety of reactive oxygen species, under different conditions. Thus, the presented results support the continuous protection exerted by melatonin, through the free radical scavenging cascade.

Melatonin as a natural ally against oxidative stress: a physicochemical examination

Oxidative stress has been proven to be related to the onset of a large number of health disorders. This chemical stress is triggered by an excess of free radicals, which are generated in cells because of a wide variety of exogenous and endogenous processes. Therefore, finding strategies for efficiently detoxifying free radicals has become a subject of a great interest, from both an academic and practical points of view. Melatonin is a ubiquitous and versatile molecule that exhibits most of the desirable characteristics of a good antioxidant. The amount of data gathered so far regarding the protective action of melatonin against oxidative stress is overwhelming. However, rather little is known concerning the chemical mechanisms involved in this activity. This review summarizes the current progress in understanding the physicochemical insights related to the free radical-scavenging activity of melatonin. Thus far, there is a general agreement that electron transfer and hydrogen transfer are the main mechanisms involved in the reactions of melatonin with free radicals. However, the relative importance of other mechanisms is also analyzed. The chemical nature of the reacting free radical also has an influence on the relative importance of the different mechanisms of these reactions. Therefore, this point has also been discussed in detail in the current review. Based on the available data, it is concluded that melatonin efficiently protects against oxidative stress by a variety of mechanisms. Moreover, it is proposed that even though it has been referred to as the chemical expression of darkness, perhaps it could also be referred to as the chemical light of health.

Development and validation of new methods for the determination of melatonin and its oxidative metabolites by high performance liquid chromatography and capillary electrophoresis, using multivariate optimization

Melatonin (N-acetyl-5-metoxytriptamine, MEL) has focused a lot of attention as consequence of its multiple functions. MEL is a potent endogenous antioxidant and a free radical scavenger that reacts with several sort of radicals generating various metabolites. Two of them are N1-acetyl-N2-formyl-5-methoxykynurenine (AFMK) and N1-acetyl-5-methoxykynurenine (AMK). These compounds are important because they have also antioxidant actions as well as other important biological properties. In the present work, we develop two methods to detect and quantify these compounds (MEL, AFMK and AMK) in the same sample. For this purpose we used an experimental design, and utilized high performance liquid chromatography (HPLC-DAD) and micellar electrokinetic chromatography (MEKC) techniques with diode array detector in both of them. The limit of detection/quantification for MEL, AFMK and AMK were respectively 44/94, 18/38 and 23/51 ng mL(-1) by using HPLC and 13/44, 37/124 and 47/156 ng mL(-1) by using MEKC. This is the first time that these compounds have been separated in the same chromatogram or electroferogram. The time of analysis was faster using MEKC. Furthermore, this technique showed better resolution but HPLC offered better limit of detection and quantification for metabolites. Both methods were validated and correlation coefficients were higher than 0.999 and the range of recovery of those methods were 99.6-103.7%. Precision was evaluated as repeatability and intermediate precision with relative standard derivation <5%. When a 5 microg mL(-1) solution of these compounds were analyzed with both methods we do not observed any statistically significance differences. Moreover, we analyzed 3COHM (cyclic-3-hydroximelatonin), another known metabolite of melatonin, by using the same methods. The employment of these methods will offer a useful tool to contribute to answer the role of MEL, AFMK and AMK in biological system and both methods can be used in routine analysis for these compounds.

The potential of melatonin in reducing morbidity-mortality after craniocerebral trauma

Craniocerebral trauma (CCT) is the most frequent cause of morbidity-mortality as a result of an accident. The probable origins and etiologies are multifactorial and include free radical formation and oxidative stress, the suppression of nonspecific resistance, lymphocytopenia (disorder in the adhesion and activation of cells), opportunistic infections, regional macro and microcirculatory alterations, disruptive sleep-wake cycles and toxicity caused by therapeutic agents. These pathogenic factors contribute to the unfavorable development of clinical symptoms as the disease progresses. Melatonin (N-acetyl-5-methoxytryptamine) is an indoleamine endogenously produced in the pineal gland and in other organs and it is protective agent against damage following CCT. Some of the actions of melatonin that support its pharmacological use after CCT include its role as a scavenger of both oxygen and nitrogen-based reactants, stimulation of the activities of a variety of antioxidative enzymes (e.g. superoxide dismutase, glutathione peroxidase, glutathione reductase and catalase), inhibition of pro-inflammatory cytokines and activation-adhesion molecules which consequently reduces lymphocytopenia and infections by opportunistic organisms. The chronobiotic capacity of melatonin may also reset the natural circadian rhythm of sleep and wakefulness. Melatonin reduces the toxicity of the drugs used in the treatment of CCT and increases their efficacy. Finally, melatonin crosses the blood-brain barrier and reduces contusion volume and stabilizes cellular membranes preventing vasospasm and apoptosis of endothelial cells that occurs as a result of CCT.

Medical implications of melatonin: receptor-mediated and receptor-independent actions

The functional versatility and diversity of melatonin has exceeded everyone's expectations. The evidence is substantial that melatonin has multiple receptor-mediated and receptor-independent actions. Considering the unexpectedly widespread distribution of cellular membrane receptors as well as the existence of nuclear binding sites/receptors and the fact that some of melatonin's actions are receptor-independent means that melatonin likely functions in every cell with which it comes in contact. This is highlighted by the fact that there are no morpho-physiological barriers to melatonin, e.g., the blood-brain barrier. In addition to its widespread actions, melatonin synthesis occurs in widely diverse tissues with its production not being relegated to the pineal gland. This should not be unexpected given that it is present throughout the animal kingdom including species that lack a pineal gland, e.g., insects, and in single cell organisms. In this review, only a few of melatonin's effects that involve the interaction of the indoleamine with receptors are described. These functions include the control of seasonal reproduction, modulation of sleep processes and influences on bone growth and osteoporosis. Among the actions of melatonin that are likely receptor independent and that are reviewed herein include its ability to neutralize free radicals which leads to a reduction in cataract formation, reducing oxidative stress due to exposure to hyperbaric hyperoxia, ameliorating hyperthyroidism and abating the toxicity of sepsis and septic shock. These actions alone speak to the diversity of beneficial effects of melatonin; however, the review is no way near exhaustive in terms of what melatonin is capable of doing. Because of its ubiquitous benefits, the pharmaceutical industry is developing melatonin analogues which interact with melatonin receptors. Clearly, the intent of the drugs is to take advantage of some of melatonin's numerous beneficial effects.

Apoptosis in primary lymphoid organs with aging

Age-associated changes in the immune system are responsible for an increased likelihood of infection, autoimmune diseases, and cancer in the elderly. Immunosenescence is characterized by reduced levels of the peripheral naive T cell pool derived from thymus and the loss of immature B lineage cells in the bone marrow. Primary lymphoid organs, i.e., bone marrow and thymus, exhibit a loss of cellularity with age, which is especially dramatic in the thymus. A summary of major changes associated with aging in primary lymphoid organs is described in this article. The participation of apoptosis in cell loss in the immune system, a change associated with age, as well as a description of molecular machinery involved, is presented. Finally, the involvement of different hormonal and non-hormonal agents in counteracting apoptosis in thymus and bone marrow during aging is explained. Here, we underlie the important role of glucocorticoids as immunodepressors and melatonin as an immunostimulatory agent.

Melatonin and cell death: differential actions on apoptosis in normal and cancer cells

Melatonin is a natural compound synthesized by a variety of organs. It has been shown to function as a cell-protective agent. Since 1994, when the first paper was published documenting the role of melatonin in apoptosis, the number of reports in this area has increased rapidly. Much of the research conducted falls into three major categories: first, the role of melatonin in inhibiting apoptosis in immune cells; second, the role of melatonin in preventing neuronal apoptosis and finally, the role of melatonin in increasing apoptotic cell death in cancer cells. The mechanisms whereby melatonin influences apoptosis have not clarified, although a number of mechanistic options have been suggested. Apoptotic cell death is a physiological phenomenon related to homeostasis and proper functioning of tissues and organs; however, a failure in the apoptotic program is related to a number of diseases. The participation of melatonin in apoptosis in numerous cell types and its potential importance in a variety of diseases such as immunodeficiency, neurodegeneration and cancer is summarized in this review.

Melatonin in Chinese medicinal herbs

Melatonin is a highly conserved molecule that not only exists in animals, but also is present in bacteria, unicellular organisms and in plants. Since melatonin is an antioxidant, in plants melatonin was speculated to protect them from intrinsic and environmental oxidative stress. More importantly, melatonin in edible plants inevitably enters animals and human through feed and food. In this study, more than 100 Chinese medicinal herbs were analyzed using the methods of solid phase extraction and HPLC-FD on-line with MS to determine whether melatonin is present in these commonly used herbs. Melatonin was detected in majority of these plants. Sixty-four of them contain melatonin in excess of 10 ng per gram dry mass. Melatonin levels in several herbs are in excess of 1000 ng/g. It is well known that normal average physiological plasma levels of melatonin are only 10-60 pg/mL. These high level-melatonin containing plants are traditionally used to treat diseases which presumably involve free radical damage. The current study provides new information concerning one potentially effective constituent present in a large number of medicinal herbs. The results suggest that these herbs should be reevaluated in reference to their nutritional and medicinal value.

Melatonin ameliorates neurologic damage and neurophysiologic deficits in experimental models of stroke

This review summarizes the numerous reports that have documented the neuroprotective actions of melatonin in experimental models of ischemia/reperfusion injury (stroke). In these investigations, which have used three species (rat, gerbil, and cat), melatonin was universally found to reduce brain damage that normally occurs as a consequence of the temporary interruption of blood flow followed by the reflow of oxygenated blood to the brain. The exogenous administration of melatonin in these experimental stroke models reduced infarct volume, lowered the frequency of apoptosis, increased the number of surviving neurons, reduced reactive gliosis, lowered the oxidation of neural lipids and oxidatively damaged DNA, induced bcl-2 gene expression (the activity of which improves cell survival), upregulated excision repair cross-complementing factor 6 (an essential gene for preferential DNA excision repair), restrained poly(ADP ribose) synthetase (which depletes cellular NAD resulting in the loss of ATP) activity, and improved neurophysiologic outcomes. Under no circumstances did melatonin exacerbate the damage associated with ischemia/reperfusion injury. As well as the beneficial pharmacologic actions of melatonin, several studies show that a relative deficiency of endogenous melatonin exaggerates neural damage due to stroke; this suggests that even physiologic concentrations of melatonin normally serve to protect the brain against damage. The primary action to explain melatonin's protective effects may relate to its ubiquitous direct and indirect antioxidative actions, although other beneficial functions of melatonin are not precluded.

Protection against oxidative protein damage induced by metal-catalyzed reaction or alkylperoxyl radicals: comparative effects of melatonin and other antioxidants

Melatonin is a well-known hydroxyl radical (*OH) scavenger that protects DNA and lipids from free radical attack. In this paper, we studied the ability of melatonin to prevent oxidative damage to bovine serum albumin (BSA) induced by two different paradigms: the metal-catalyzed oxidation (MCO) induced by Cu(2+)/H(2)O(2) and the alkoxyl and alkylperoxyl radicals formed by the azo initiator 2,2'-azobis(2-amidinopropane) hydrochloride (AAPH, 40 mM). The protective effects of melatonin were compared with 6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid (trolox), glutathione (GSH), ascorbate, 3,4',5-trihydroxy-trans-stilbene (resveratrol, 0.1 microM-4 mM) and mannitol (50 microM-100 mM). Melatonin efficiently prevented protein modification induced by both models, as assayed by polyacrylamide gel electrophoresis and carbonyl content. Both trolox and ascorbate had an obvious pro-oxidant effect in the Cu(2+)/H(2)O(2) model, whereas both prevented BSA damage induced by AAPH. In the MCO model, the efficacy of GSH in terms of protein protection was higher than melatonin at relatively high concentrations (250 microM-4 mM); however, at lower concentrations (50-250 microM), the efficacy of melatonin was superior to GSH. D-Mannitol (50 microM-100 mM) and resveratrol did not protect BSA from the site-specific damage induced by Cu(2+)/H(2)O(2). On the other hand, the relative protective efficiency in the AAPH model was melatonin approximately trolox>GSH>ascorbate.

Biochemical reactivity of melatonin with reactive oxygen and nitrogen species: a review of the evidence

Melatonin (N-acetyl-5-methoxytryptamine), an endogenously produced indole found throughout the animal kingdom, was recently reported, using a variety of techniques, to be a scavenger of a number of reactive oxygen and reactive nitrogen species both in vitro and in vivo. Initially, melatonin was discovered to directly scavenge the high toxic hydroxyl radical (*OH). The methods used to prove the interaction of melatonin with the *OH included the generation of the radical using Fenton reagents or the ultraviolet photolysis of hydrogen peroxide (H202) with the use of spin-trapping agents, followed by electron spin resonance (ESR) spectroscopy, pulse radiolysis followed by ESR, and several spectrofluorometric and chemical (salicylate trapping in vivo) methodologies. One product of the reaction of melatonin with the *OH was identified as cyclic 3-hydroxymelatonin (3-OHM) using high-performance liquid chromatography with electrochemical (HPLC-EC) detection, electron ionization mass spectrometry (EIMS), proton nuclear magnetic resonance (1H NMR) and COSY 1H NMR. Cyclic 3-OHM appears in the urine of humans and other mammals and in rat urine its concentration increases when melatonin is given exogenously or after an imposed oxidative stress (exposure to ionizing radiation). Urinary cyclic 3-OHM levels are believed to be a biomarker (footprint molecule) of in vivo *OH production and its scavenging by melatonin. Although the data are less complete, besides the *OH, melatonin in cell-free systems has been shown to directly scavenge H2O2, singlet oxygen (1O2) and nitric oxide (NO*), with little or no ability to scavenge the superoxide anion radical (O2*-) In vitro, melatonin also directly detoxifies the peroxynitrite anion (ONOO-) and/or peroxynitrous acid (ONOOH), or the activated form of this molecule, ONOOH*; the product of the latter interaction is proposed to be 6-OHM. How these in vitro findings relate to the in vivo antioxidant actions of melatonin remains to be established. The ability of melatonin to scavenge the lipid peroxyl radical (LOO*) is debated. The weight of the evidence is that melatonin is probably not a classic chain-breaking antioxidant, since its ability to scavenge the LOO* seems weak. Its ability to reduce lipid peroxidation may stem from its function as a preventive antioxidant (scavenging initiating radicals), or yet unidentified actions. In sum, in vitro melatonin acts as a direct free radical scavenger with the ability to detoxify both reactive oxygen and reactive nitrogen species; in vivo, it is an effective pharmacological agent in reducing oxidative damage under conditions in which excessive free radical generation is believed to be involved.

Biochemical reactivity of melatonin with reactive oxygen and nitrogen species: a review of the evidence

Melatonin (N-acetyl-5-methoxytryptamine), an endogenously produced indole found throughout the animal kingdom, was recently reported, using a variety of techniques, to be a scavenger of a number of reactive oxygen and reactive nitrogen species both in vitro and in vivo. Initially, melatonin was discovered to directly scavenge the high toxic hydroxyl radical (*OH). The methods used to prove the interaction of melatonin with the *OH included the generation of the radical using Fenton reagents or the ultraviolet photolysis of hydrogen peroxide (H202) with the use of spin-trapping agents, followed by electron spin resonance (ESR) spectroscopy, pulse radiolysis followed by ESR, and several spectrofluorometric and chemical (salicylate trapping in vivo) methodologies. One product of the reaction of melatonin with the *OH was identified as cyclic 3-hydroxymelatonin (3-OHM) using high-performance liquid chromatography with electrochemical (HPLC-EC) detection, electron ionization mass spectrometry (EIMS), proton nuclear magnetic resonance (1H NMR) and COSY 1H NMR. Cyclic 3-OHM appears in the urine of humans and other mammals and in rat urine its concentration increases when melatonin is given exogenously or after an imposed oxidative stress (exposure to ionizing radiation). Urinary cyclic 3-OHM levels are believed to be a biomarker (footprint molecule) of in vivo *OH production and its scavenging by melatonin. Although the data are less complete, besides the *OH, melatonin in cell-free systems has been shown to directly scavenge H2O2, singlet oxygen (1O2) and nitric oxide (NO*), with little or no ability to scavenge the superoxide anion radical (O2*-) In vitro, melatonin also directly detoxifies the peroxynitrite anion (ONOO-) and/or peroxynitrous acid (ONOOH), or the activated form of this molecule, ONOOH*; the product of the latter interaction is proposed to be 6-OHM. How these in vitro findings relate to the in vivo antioxidant actions of melatonin remains to be established. The ability of melatonin to scavenge the lipid peroxyl radical (LOO*) is debated. The weight of the evidence is that melatonin is probably not a classic chain-breaking antioxidant, since its ability to scavenge the LOO* seems weak. Its ability to reduce lipid peroxidation may stem from its function as a preventive antioxidant (scavenging initiating radicals), or yet unidentified actions. In sum, in vitro melatonin acts as a direct free radical scavenger with the ability to detoxify both reactive oxygen and reactive nitrogen species; in vivo, it is an effective pharmacological agent in reducing oxidative damage under conditions in which excessive free radical generation is believed to be involved.

Biochemical reactivity of melatonin with reactive oxygen and nitrogen species: a review of the evidence

Melatonin (N-acetyl-5-methoxytryptamine), an endogenously produced indole found throughout the animal kingdom, was recently reported, using a variety of techniques, to be a scavenger of a number of reactive oxygen and reactive nitrogen species both in vitro and in vivo. Initially, melatonin was discovered to directly scavenge the high toxic hydroxyl radical (*OH). The methods used to prove the interaction of melatonin with the *OH included the generation of the radical using Fenton reagents or the ultraviolet photolysis of hydrogen peroxide (H202) with the use of spin-trapping agents, followed by electron spin resonance (ESR) spectroscopy, pulse radiolysis followed by ESR, and several spectrofluorometric and chemical (salicylate trapping in vivo) methodologies. One product of the reaction of melatonin with the *OH was identified as cyclic 3-hydroxymelatonin (3-OHM) using high-performance liquid chromatography with electrochemical (HPLC-EC) detection, electron ionization mass spectrometry (EIMS), proton nuclear magnetic resonance (1H NMR) and COSY 1H NMR. Cyclic 3-OHM appears in the urine of humans and other mammals and in rat urine its concentration increases when melatonin is given exogenously or after an imposed oxidative stress (exposure to ionizing radiation). Urinary cyclic 3-OHM levels are believed to be a biomarker (footprint molecule) of in vivo *OH production and its scavenging by melatonin. Although the data are less complete, besides the *OH, melatonin in cell-free systems has been shown to directly scavenge H2O2, singlet oxygen (1O2) and nitric oxide (NO*), with little or no ability to scavenge the superoxide anion radical (O2*-) In vitro, melatonin also directly detoxifies the peroxynitrite anion (ONOO-) and/or peroxynitrous acid (ONOOH), or the activated form of this molecule, ONOOH*; the product of the latter interaction is proposed to be 6-OHM. How these in vitro findings relate to the in vivo antioxidant actions of melatonin remains to be established. The ability of melatonin to scavenge the lipid peroxyl radical (LOO*) is debated. The weight of the evidence is that melatonin is probably not a classic chain-breaking antioxidant, since its ability to scavenge the LOO* seems weak. Its ability to reduce lipid peroxidation may stem from its function as a preventive antioxidant (scavenging initiating radicals), or yet unidentified actions. In sum, in vitro melatonin acts as a direct free radical scavenger with the ability to detoxify both reactive oxygen and reactive nitrogen species; in vivo, it is an effective pharmacological agent in reducing oxidative damage under conditions in which excessive free radical generation is believed to be involved.

Melatonin reduces oxidant damage and promotes mitochondrial respiration: implications for aging

Melatonin has a number of properties as a consequence of which it could be beneficial to animals as they age. Of particular interest are its ubiquitous actions as a direct and indirect antioxidant and free radical scavenger. Besides directly detoxifying a variety of reactive oxygen and reactive nitrogen species, at least one product that is formed as a result of these interactions is also a potent free radical scavenger. Thus, the product that is formed when melatonin detoxifies hydrogen peroxide, that is, N1-acetyl-N2-formyl-5-methoxykynuramine is an efficient scavenger, at least equivalent to melatonin itself. This antioxidant cascade increases the ability of melatonin to resist oxidative damage. Other actions of melatonin, such as stimulation of antioxidative enzymes also improves its status as an antioxidant. Finally, recent observations documenting melatonin's ability to stimulate electron transport and ATP production in the inner-mitochondrial membrane also has relevance for melatonin as an agent that could alter processes of aging. These findings, coupled with diminished melatonin production in advanced age, has prompted scientists to consider melatonin in the context of aging. As of this writing there is no definitive evidence to prove that melatonin alters the rate of aging, although data relating to melatonin deferring some age-related degenerative conditions is accumulating rapidly.

Inhibitory effect of melatonin on homocysteine-induced lipid peroxidation in rat brain homogenates

Oxidative damage is implicated in several pathologies including cardiovascular disease. As a model system to study the response of cells to oxidative insults, homocysteine toxicity was examined since it is an independent risk factor for atherosclerotic disease. The levels of malondialdehyde and 4-hydroxyalkenals were assayed as an index of oxidatively damaged lipid. In in vitro experiments, the increase of lipid peroxidation products induced by homocysteine were concentration- and time-dependent. To study the protective effect of melatonin on homocystine induced lipid peroxidation, brain homogenates were treated with different concentrations of melatonin. The accumulation of malondialdehyde and 4-hydroxyalkenals induced by homocysteine was significantly reduced by melatonin in a concentration-dependent manner. Additionally, a melatonin concentration of 1.5 mM reduced the levels of oxidatively damaged lipid products below those measured in control homogenates (no homocysteine, no melatonin). These data suggest that melatonin, an endogenous antioxidant may have a role in protecting cells from oxidative damage due to homocysteine and they support the idea that pharmacological concentrations could be used as a therapeutic agent in reducing cardiovascular disease where homocysteine may be a causative or contributing agent.

Effects of melatonin treatment in septic newborns

Free radicals have been implicated in the pathogenesis of neonatal sepsis and its complications. This study was conducted to determine the changes in the clinical status and the serum levels of lipid peroxidation products [malondialdehyde (MDA) and 4-hydroxylalkenals (4-HDA)] in 10 septic newborns treated with the antioxidant melatonin given within the first 12 h after diagnosis. Ten other septic newborns in a comparable state were used as "septic" controls, while 10 healthy newborns served as normal controls. A total of 20 mg melatonin was administered orally in two doses of 10 mg each, with a 1-h interval. One blood sample was collected before melatonin administration and two additional blood samples (at 1 and 4 h) were collected after melatonin administration to assess serum levels of lipid peroxidation products. Serum MDA + 4-HDA concentrations in newborns with sepsis were significantly higher than those in healthy infants without sepsis; in contrast, in septic newborns treated with melatonin there was a significant reduction (p < 0.05) of MDA + 4-HDA to the levels in the normal controls at both 1 and 4 h (p < 0.05). Melatonin also improved the clinical outcome of the septic newborns as judged by measurement of sepsis-related serum parameters after 24 and 48 h. Three of 10 septic children who were not treated with melatonin died within 72 h after diagnosis of sepsis; none of the 10 septic newborns treated with melatonin died. To our knowledge, this is the first study where melatonin was given to human newborns.

Autoxidation and toxicant-induced oxidation of lipid and DNA in monkey liver: reduction of molecular damage by melatonin

Melatonin, the main secretory product of the pineal gland, is a free radical scavenger and antioxidant which protects against oxidative damage due to a variety of toxicants. However, there is little information regarding melatonin's antioxidative capacity in tissues of primates. In this study we examined the protective effects of melatonin in monkey liver homogenates against lipid damage that occurred as a result of autoxidation or that induced by exogenous addition of H202 and ferrous iron (Fe2+). Additionally, we tested melatonin's protective effect against oxidative damage to DNA induced by chromium(III) (CrIII) plus H202. The levels of malondialdehyde and 4-hydroxyalkenals were assayed as an index of lipid peroxidation, and the concentrations of 8-hydroxydeoxyguanosine (8-OHdG) as an endpoint of oxidative DNA damage. The increases in malondialdehyde+4-hydroxyalkenals concentrations as a consequence of autoxidation or after the addition of H202 plus Fe2+ to the homogenates were time-dependent. The accumulation of these damaged products due to either auto-oxidative processes or induced by H202 and Fe2+ were significantly reduced by melatonin in a concentration-dependent-manner. The levels of 8-OHdG were elevated in purified monkey liver DNA incubated with a combination of CrCl3 plus H2O2. This rise in oxidatively damaged DNA was prevented by 10 microM concentration of melatonin. Also, melatonin reduced the damage to DNA that was caused by auto-oxidative processes. These findings in monkey liver tissue document the ability of melatonin to protect against oxidative damage to both lipid and DNA in primate tissue, as observed previously in rodent tissue. The findings provide support for the use of melatonin as suitable agent to reduce damage inflicted by free radical species in primates.

N-acetylserotonin suppresses hepatic microsomal membrane rigidity associated with lipid peroxidation

N-acetylserotonin, the immediate precursor of melatonin in the tryptophan metabolic pathway in the pineal gland, has been reported to be an antioxidant. The aim of this work was to test the effect of N-acetylserotonin in stabilizing biological membranes against oxidative stress. Hepatic microsomal membranes from male adult rats were incubated with N-acetylserotonin (0.001-3 mM) before inducing lipid peroxidation using FeCl(3), ADP and NADPH. Control experiments were done by incubating microsomal membranes with N-acetylserotonin in the absence of lipid peroxidation-inducing drugs. Membrane fluidity was assessed by fluorescence spectroscopy and malonaldehyde plus 4-hydroxyalkenals concentrations were measured to estimate the degree of lipid peroxidation. Free radicals induced by the combination of FeCl(3)+ADP+NADPH produced a significant decrease in the microsomal membrane fluidity, which was associated with an increase in the malonaldehyde plus 4-hydroxyalkenals levels. These changes were suppressed in a concentration-dependent manner when N-acetylserotonin was added in the incubation buffer. In the absence of lipid peroxidation, N-acetylserotonin (0.001-3 mM) did not change membrane fluidity nor malonaldehyde plus 4-hydroxyalkenals levels. These results suggest that the protective role of N-acetylserotonin in preserving optimal levels of fluidity of the biological membranes may be related to its ability to reduce lipid peroxidation.

Detection and quantification of the antioxidant melatonin in Montmorency and Balaton tart cherries (Prunus cerasus)

The antioxidant melatonin was recently identified in a variety of edible plants and seeds in high concentrations. In plants, as in animals, melatonin is believed to function as a free radical scavenger and possibly in photoperiodism. In this study, melatonin was detected and quantified in fresh-frozen Balaton and Montmorency tart cherries (Prunus cerasus) using high-performance liquid chromatography. Both cherry species contain high levels of melatonin compared to the melatonin concentrations in the blood of mammals. Montmorency cherries (13.46 +/- 1.10 ng/g) contain approximately 6 times more melatonin than do Balaton cherries (2.06 +/- 0.17 ng/g). Neither the orchard of origin nor the time of harvest influenced the amount of melatonin in fresh cherries. The implication of the current findings is that consuming cherries could be an important source of dietary melatonin inasmuch as melatonin is readily absorbed when taken orally. Also, previously published data and the results presented here show that melatonin is not only endogenously produced but also present in the diet.

N1-acetyl-N2-formyl-5-methoxykynuramine, a biogenic amine and melatonin metabolite, functions as a potent antioxidant

The biogenic amine The biogenic amine N1-acetyl-N2-formyl-5-methoxykynuramine (AFMK) was investigated for its potential antioxidative capacity. AFMK is a metabolite generated through either an enzymatic or a chemical reaction pathway from melatonin. The physiological function of AFMK remains unknown. To our knowledge, this report is the first to document the potent antioxidant action of this biogenic amine. Cyclic voltammetry (CV) shows that AFMK donates two electrons at potentials of 456 mV and 668 mV, and therefore it functions as a reductive force. This function contrasts with all other physiological antioxidants that donate a single electron only when they neutralize free radicals. AFMK reduced 8-hydroxydeoxyguanosine formation induced by the incubation of DNA with oxidants significantly. Lipid peroxidation resulting from free radical damage to rat liver homogenates was also prevented by the addition of AFMK. The inhibitory effects of AFMK on both DNA and lipid damage appear to be dose-response related. In cell culture, AFMK efficiently reduced hippocampal neuronal death induced by either hydrogen peroxide, glutamate, or amyloid b25-35 peptide. AFMK is a naturally occurring molecule with potent free radical scavenging capacity (donating two electrons/molecule) and thus may be a valuable new antioxidant for preventing and treating free radical-related disorders.

Individual and synergistic antioxidative actions of melatonin: studies with vitamin E, vitamin C, glutathione and desferrioxamine (desferoxamine) in rat liver homogenates

The pharmacological effects of melatonin, vitamin E, vitamin C, glutathione and desferrioxamine (desferoxamine) alone and in combination on iron-induced membrane lipid damage in rat liver homogenates were examined by estimating levels of malondialdehyde and 4-hydroxyalkenals (MDA+4-HDA). Individually, melatonin (2.5-1600 microM), vitamin E (0.5-50 microM), glutathione (100-7000 microM) and desferrioxamine (1-8 microM) inhibited lipid peroxidation in a concentration-dependent manner. Vitamin C had both a pro-oxidative (25-2000 microM) and an antioxidative (2600-5000 microM) effect. The IC50 (concentration that reduces damage by 50%) values were 4, 10, 426, 2290 and 4325 microM for vitamin E, desferrioxamine, melatonin, glutathione and vitamin C, respectively. The synergistic actions of melatonin with vitamin C, vitamin E, and glutathione were systematically investigated. When melatonin was combined with vitamin E, glutathione, or vitamin C, the protective effects against iron-induced lipid peroxidation were dramatically enhanced. Even though melatonin was added at very low concentrations, it still showed synergistic effects with other antioxidants at certain concentrations. Furthermore, melatonin not only reversed the pro-oxidative effects of vitamin C, but its efficacy in reducing lipid peroxidation was improved when it was combined with pro-oxidative concentrations of vitamin C. The results provide new information in terms of the possible pharmacological use of the combination of melatonin and classical antioxidants to treat free radical-related conditions.

Melatonin in plants

Once thought to be exclusively a molecule of the animal kingdom, melatonin has now been found to exist in plants as well. Among a number of actions, melatonin is a direct free radical scavenger and an indirect antioxidant. Melatonin directly detoxifies the hydroxyl radical (OH), hydrogen peroxide, nitric oxide, peroxynitrite anion, peroxynitrous acid, and hypochlorous acid. The products from each of these reactions have been identified in pure chemical systems and in at least one case in vivo; the interaction product of melatonin with the OH, ie., cyclic 3-hydroxymelatonin, is found in the urine of humans and rats. Some of the products that are produced when melatonin detoxifies reactive species are also highly efficient scavengers. As a result, a cascade of scavenging reactions may enhance the antioxidant capacity of melatonin. Additionally, melatonin increases the activity of several antioxidative enzymes, thereby improving its ability to protect macromolecules from oxidative stress. Melatonin is endogenously produced and is also consumed in edible plants. In animal experiments, feeding melatonin-containing foods raised blood levels of the indole. Because physiologic concentrations of melatonin in the blood are known to correlate with the total antioxidant capacity of the serum, consuming food-stuffs containing melatonin may be helpful in lowering oxidative stress.

Free radical-mediated molecular damage. Mechanisms for the protective actions of melatonin in the central nervous system

This review briefly summarizes the multiple actions by which melatonin reduces the damaging effects of free radicals and reactive oxygen and nitrogen species. It is well documented that melatonin protects macromolecules from oxidative damage in all subcellular compartments. This is consistent with the protection by melatonin of lipids and proteins, as well as both nuclear and mitochondrial DNA. Melatonin achieves this widespread protection by means of its ubiquitous actions as a direct free radical scavenger and an indirect antioxidant. Thus, melatonin directly scavenges a variety of free radicals and reactive species including the hydroxyl radical, hydrogen peroxide, singlet oxygen, nitric oxide, peroxynitrite anion, and peroxynitrous acid. Furthermore, melatonin stimulates a number of antioxidative enzymes including superoxide dismutase, glutathione peroxidase, glutathione reductase, and catalase. Additionally, melatonin experimentally enhances intracellular glutathione (another important antioxidant) levels by stimulating the rate-limiting enzyme in its synthesis, gamma-glutamylcysteine synthase. Melatonin also inhibits the proxidative enzymes nitric oxide synthase and lipoxygenase. Finally, there is evidence that melatonin stabilizes cellular membranes, thereby probably helping them resist oxidative damage. Most recently, melatonin has been shown to increase the efficiency of the electron transport chain and, as a consequence, to reduce election leakage and the generation of free radicals. These multiple actions make melatonin a potentially useful agent in the treatment of neurological disorders that have oxidative damage as part of their etiological basis.

DNA oxidatively damaged by chromium(III) and H(2)O(2) is protected by the antioxidants melatonin, N(1)-acetyl-N(2)-formyl-5-methoxykynuramine, resveratrol and uric acid

Chromium (Cr) compounds are widely used industrial chemicals and well known carcinogens. Cr(III) was earlier found to induce oxidative damage as documented by examining the levels of 8-hydroxydeoxyguanosine (8-OH-dG), an index for DNA damage, in isolated calf thymus DNA incubated with CrCl(3) and H(2)O(2). In the present in vitro study, we compared the ability of the free radical scavengers melatonin, N(1)-acetyl-N(2)-formyl-5-methoxykynuramine (AFMK), resveratrol and uric acid to reduce DNA damage induced by Cr(III). Each of these scavengers markedly reduced the DNA damage in a concentration-dependent manner. The concentrations that reduced 8-OH-dG formation by 50% (IC(50)) were 0.10 microM for both resveratrol and melatonin, and 0.27 microM for AFMK. However, the efficacy of the fourth endogenous antioxidant, i.e. uric acid, in terms of its inhibition of DNA damage in the same in vitro system was about 60--150 times less effective than the other scavengers; the IC(50) for uric acid was 15.24 microM. These findings suggest that three of the four antioxidants tested in these studies may have utility in protecting against the environmental pollutant Cr and that the protective effects of these free radical scavengers against Cr(III)-induced carcinogenesis may relate to their direct hydroxyl radical scavenging ability. In the present study, the formation of 8-OH-dG was likely due to a Cr(III)-mediated Fenton-type reaction that generates hydroxyl radicals, which in turn damage DNA. Once formed, 8-OH-dG can mutate eventually leading to cancer; thus the implication is that these antioxidants may reduce the incidence of Cr-related cancers.

Melatonin, vitamin E, and estrogen reduce damage induced by kainic acid in the hippocampus: potassium-stimulated GABA release

Melatonin, vitamin E and estrogen have been shown to exert neuroprotective effects against kainic acid (KA)-induced damage in the hippocampus. The aim of the present study was to examine the changes in potassium-evoked gamma-aminobutyric acid (GABA) release in the hippocampus of KA-treated rats and to test the possible protective effects of melatonin, vitamin E or estrogen. Following the treatment of mice with KA, a marked reduction in potassium-evoked [3H]GABA release was observed. Melatonin or estrogen prevented the reduction in potassium-evoked GABA release due to kainate administration. Vitamin E also exhibited some protective effect, but it was less than that provided by melatonin or estrogen. Melatonin, estrogen and, to a lesser extent, vitamin E reduce the physiological toxicity of KA. Since KA is believed to cause neuronal alterations via oxidative processes, it is assumed that the free radical scavenging and oxidative properties of melatonin, estrogen and vitamin E account for the protective effects of these agents.

Resynchronization of hormonal rhythms after an eastbound flight in humans: effects of slow-release caffeine and melatonin

The aim of this work was to investigate the potential chronobiotic properties of slow-release caffeine, in comparison with melatonin, on resynchronization of endogenous melatonin and cortisol secretions after an eastbound flight by jet incurring a time loss of 7 h. A group of 27 reservists of the US Air Force received either slow-release caffeine (300 mg), melatonin (5 mg) or placebo before, during and/or after the transmeridian flight. Saliva and urine were sampled before the flight in the United States (from day -2 to day 0) and after the flight in France (from day 1 to day 10). Saliva was collected once a day on waking to determine saliva melatonin and cortisol concentrations. In addition, concentrations of caffeine in saliva were determined three times a day and of 6-sulphatoxymelatonin in urine collected overnight to check that the treatment regimes had been complied with. From day 3 to day 5, post-flight saliva melatonin concentrations were significantly different from control values in the placebo group only. During treatment with melatonin, the mean urinary 6-sulphatoxymelatonin concentration in the melatonin group was more than twice as high as in the two other groups. In the slow-release caffeine group and the melatonin group, mean saliva cortisol concentrations were significantly lower than control from day 2 to day 5, whereas the placebo group had a mean saliva cortisol concentration significantly lower than the control value from day 2 to day 9. In conclusion, these results indicate that administration of slow-release caffeine, as well as of melatonin, allows a faster resynchronization of hormone rhythms during the 4 days following an eastbound flight incurring the loss of 7 h.

Melatonin attenuates estradiol-induced oxidative damage to DNA: relevance for cancer prevention

Estrogens exert pro-oxidative effects and have been shown to damage DNA, potentially leading to cancer. Melatonin is a well-known antioxidant, free radical scavenger, and oncostatic agent. Changes in the levels of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodGuo), an index of DNA damage, and the levels of malondialdehyde + 4-hydroxyalkenals, an index of lipid peroxidation, were measured in kidneys, liver, and testes from hamsters treated with E2 (75 mg/kg body wt) and were collected 3 or 5 hr later. Other animals were treated with melatonin (15 mg/kg body wt, 30 min before and 120 min after E2 treatment) or were given both compounds. Additionally, lipid peroxidation was measured in liver homogenates exposed to ferrous sulfate (15 microM) in vitro. E2 treatment caused an increase in 8-oxodGuo levels in kidneys collected 5 hr after E2 administration, and in liver 3 hr after estrogen treatment. Melatonin completely prevented E2-induced DNA damage in both organs. Melatonin alone or when given with E2 and examined 3 hr later decreased the base level of 8-oxodGuo in testes. A tendency for a reduction in in vivo lipid peroxidation was observed after treatment of hamsters with either melatonin, E2, or both compounds, with a statistically significant decrease being measured in the liver following E2 administration. In vitro exposure to iron significantly enhanced lipid peroxidation in hepatic homogenates from untreated, melatonin-treated, or E2-injected hamsters; in the hepatic homogenates of hamsters given both E2 and melatonin, ferrous sulfate failed to augment lipid peroxidation. Our results confirm the dual actions of estrogens relative to oxidative damage, i.e., estrogen increases oxidative destruction of DNA while reducing lipid peroxidation. Melatonin had antioxidative actions in reducing oxidative damage to both DNA and to membrane lipids. Melatonin completely prevented the damaging action of E2 on DNA and synergized with the steroid to reduce lipid peroxidation.

Characterization of the protective effects of melatonin and related indoles against alpha-naphthylisothiocyanate-induced liver injury in rats

The protective effect of melatonin, 6-hydroxymelatonin and N-acetylserotonin against alpha-naphthylisothiocyanate (ANIT)-induced liver injury was investigated and compared in rats injected once with the hepatotoxicant (75 mg/kg body weight). In rats injected with ANIT alone, liver injury with cholestasis developed within 24 h, as indicated by both serum levels of alanine aminotransferase (SGPT) and aspartic acid aminotransferase (SGOT) activities and serum total bilirubin concentration. The administration of melatonin or 6-hydroxymelatonin (10 mg/kg body weight) to ANIT-injected rats reduced significantly the serum levels of both SGPT and SGOT and the serum total bilirubin concentration. For all hepatic biochemical markers, melatonin was more effective that 6-hydroxymelatonin. By comparison, the administration of N-acetylserotonin (10 mg/kg body weight) to ANIT-injected rats did not reduce the serum levels of either hepatic enzymes or the serum total bilirubin concentration. In ANIT-injected rats, hepatic lipid peroxidation (LPO) was significantly higher than in control animals and this increase was significantly reduced by either melatonin, 6-hydroxymelatonin or N-acetylserotonin. Furthermore, ANIT treatment caused a significant reduction in liver microsomal membrane fluidity and this reduction was completely reversed by the three indoles. The liver from ANIT-injected rats showed several histopathological alterations; above all there was an acute infiltration of polymorphonuclear neutrophils and an increase in the number of apparent apoptotic hepatocytes. The concurrent administration of melatonin reduced the severity of all morphological alterations, specially the neutrophil infiltration and the number of presumed apoptotic cells. On the contrary, the administration of 6-hydroxymelatonin or N-acetylserotonin did not provide any protective effect in terms of the histopathological alterations. These results indicate that melatonin protects against ANIT-induced liver injury with cholestasis in rats, and suggests that this protective effect is likely due to its antioxidant properties and above all to its capacity to inhibit liver neutrophil infiltration, a critical factor in the pathogenesis of ANIT-induced liver injury. 6-hydroxymelatonin, although able to provide partial protection against the ANIT-induced hepatic injury, probably through its antioxidant properties by mechanisms that are unclear, was unable to reduce neutrophil infiltration. Finally, N-acetylserotonin in the experimental conditions of this study, only exhibited some antioxidant protection but had no protective effect against ANIT-induced hepatic damage.

Characterization of the protective effects of melatonin and related indoles against alpha-naphthylisothiocyanate-induced liver injury in rats

The protective effect of melatonin, 6-hydroxymelatonin and N-acetylserotonin against alpha-naphthylisothiocyanate (ANIT)-induced liver injury was investigated and compared in rats injected once with the hepatotoxicant (75 mg/kg body weight). In rats injected with ANIT alone, liver injury with cholestasis developed within 24 h, as indicated by both serum levels of alanine aminotransferase (SGPT) and aspartic acid aminotransferase (SGOT) activities and serum total bilirubin concentration. The administration of melatonin or 6-hydroxymelatonin (10 mg/kg body weight) to ANIT-injected rats reduced significantly the serum levels of both SGPT and SGOT and the serum total bilirubin concentration. For all hepatic biochemical markers, melatonin was more effective that 6-hydroxymelatonin. By comparison, the administration of N-acetylserotonin (10 mg/kg body weight) to ANIT-injected rats did not reduce the serum levels of either hepatic enzymes or the serum total bilirubin concentration. In ANIT-injected rats, hepatic lipid peroxidation (LPO) was significantly higher than in control animals and this increase was significantly reduced by either melatonin, 6-hydroxymelatonin or N-acetylserotonin. Furthermore, ANIT treatment caused a significant reduction in liver microsomal membrane fluidity and this reduction was completely reversed by the three indoles. The liver from ANIT-injected rats showed several histopathological alterations; above all there was an acute infiltration of polymorphonuclear neutrophils and an increase in the number of apparent apoptotic hepatocytes. The concurrent administration of melatonin reduced the severity of all morphological alterations, specially the neutrophil infiltration and the number of presumed apoptotic cells. On the contrary, the administration of 6-hydroxymelatonin or N-acetylserotonin did not provide any protective effect in terms of the histopathological alterations. These results indicate that melatonin protects against ANIT-induced liver injury with cholestasis in rats, and suggests that this protective effect is likely due to its antioxidant properties and above all to its capacity to inhibit liver neutrophil infiltration, a critical factor in the pathogenesis of ANIT-induced liver injury. 6-hydroxymelatonin, although able to provide partial protection against the ANIT-induced hepatic injury, probably through its antioxidant properties by mechanisms that are unclear, was unable to reduce neutrophil infiltration. Finally, N-acetylserotonin in the experimental conditions of this study, only exhibited some antioxidant protection but had no protective effect against ANIT-induced hepatic damage.

Melatonin and its relation to the immune system and inflammation

Melatonin (N-acetyl-5-methoxytryptamine) was initially thought to be produced exclusively in the pineal gland. Subsequently its synthesis was demonstrated in other organs, for example, the retinas, and very high concentrations of melatonin are found at other sites, for example, bone marrow cells and bile. The origin of the high level of melatonin in these locations has not been definitively established, but it is likely not exclusively of pineal origin. Melatonin has been shown to possess anti-inflammatory effects, among a number of actions. Melatonin reduces tissue destruction during inflammatory reactions by a number of means. Thus melatonin, by virtue of its ability to directly scavenge toxic free radicals, reduces macromolecular damage in all organs. The free radicals and reactive oxygen and nitrogen species known to be scavenged by melatonin include the highly toxic hydroxyl radical (.OH), peroxynitrite anion (ONOO-), and hypochlorous acid (HOCl), among others. These agents all contribute to the inflammatory response and associated tissue destruction. Additionally, melatonin has other means to lower the damage resulting from inflammation. Thus, it prevents the translocation of nuclear factor-kappa B (NF-kappa B) to the nucleus and its binding to DNA, thereby reducing the upregulation of a variety of proinflammatory cytokines, for example, interleukins and tumor neurosis factor-alpha. Finally, there is indirect evidence that melatonin inhibits the production of adhesion molecules that promote the sticking of leukocytes to endothelial cells. By this means melatonin attenuates transendothelial cell migration and edema, which contribute to tissue damage.

Melatonin prevents delta-aminolevulinic acid-induced oxidative DNA damage in the presence of Fe2+

Delta-aminolevulinic acid (ALA), a heme precursor which accumulates during lead poisoning and acute intermittent porphyria, is reported to cause liver cancer. The carcinogenic mechanisms of ALA may relate to its ability to generate free radicals through metal-catalyzed oxidation which cause oxidative DNA damage. The aim of this study was to compare the efficacy of melatonin, trolox (vitamin E) and mannitol in altering DNA damage induced by ALA. Herein, we found, in the presence of Fe2+, that ALA-induced formation of 8-hydroxydeoxyguanosine in calf thymus DNA was dose and time-dependent. Melatonin, mannitol and trolox, all of which are free radical scavengers, inhibited the formation of 8-hydroxydeoxyguanosine in a concentration-dependent manner. The concentration of each (melatonin, mannitol and trolox) required to reduce DNA damage by 50%, i.e., the IC50, was 0.52, 0.84 and 0.90 mM, respectively.

Melatonin directly scavenges hydrogen peroxide: a potentially new metabolic pathway of melatonin biotransformation

A potential new metabolic pathway of melatonin biotransformation is described in this investigation. Melatonin was found to directly scavenge hydrogen peroxide (H(2)O(2)) to form N(1)-acetyl-N(2)-formyl-5-methoxykynuramine and, thereafter this compound could be enzymatically converted to N(1)-acetyl-5-methoxykynuramine by catalase. The structures of these kynuramines were identified using proton nuclear magnetic resonance, carbon nuclear magnetic resonance, and mass spectrometry. This is the first report to reveal a possible physiological association between melatonin, H(2)O(2), catalase, and kynuramines. Melatonin scavenges H(2)O(2) in a concentration-dependent manner. This reaction appears to exhibit two distinguishable phases. In the rapid reaction phase, the interaction between melatonin and H(2)O(2) reaches equilibrium rapidly (within 5 s). The rate constant for this phase was calculated to be 2.3 x 10(6) M(-1)s(-1). Thereafter, the relative equilibrium of melatonin and H(2)O(2) was sustained for roughly 1 h, at which time the content of H(2)O(2) decreased gradually over a several hour period, identified as the slow reaction phase. These observations suggest that melatonin, a ubiquitously distributed small nonenzymatic molecule, might serve to directly detoxify H(2)O(2) in living organisms. H(2)O(2) and melatonin are present in all subcellular compartments; thus, presumably, one important function of melatonin may be complementary in function to catalase and glutathione peroxidase in keeping intracellular H(2)O(2) concentrations at steady-state levels.