Melatonin secretion occurs at a constant rate in both young and older men and women

Melatonin as a Therapy for Preterm Brain Injury: What Is the Evidence?

Despite significant improvements in survival following preterm birth in recent years, the neurodevelopmental burden of prematurity, with its long-term cognitive and behavioral consequences, remains a significant challenge in neonatology. Neuroprotective treatment options to improve neurodevelopmental outcomes in preterm infants are therefore urgently needed. Alleviating inflammatory and oxidative stress (OS), melatonin might modify important triggers of preterm brain injury, a complex combination of destructive and developmental abnormalities termed encephalopathy of prematurity (EoP). Preliminary data also suggests that melatonin has a direct neurotrophic impact, emphasizing its therapeutic potential with a favorable safety profile in the preterm setting. The current review outlines the most important pathomechanisms underlying preterm brain injury and correlates them with melatonin's neuroprotective potential, while underlining significant pharmacokinetic/pharmacodynamic uncertainties that need to be addressed in future studies.

A Randomized, Double-Blind, Crossover Study to Investigate the Pharmacokinetics of Extended-Release Melatonin Compared to Immediate-Release Melatonin in Healthy Adults

Exogenous melatonin can be helpful for treatment of some sleep disorders. However, immediate-release formulations are rapidly absorbed and cleared from the body making it difficult to provide coverage for an entire sleep period. Extended-release melatonin formulations can better mimic the naturally occurring melatonin profile and increase efficacy, but few studies have reported on their pharmacokinetics. To assess the pharmacokinetics of extended-release melatonin, we conducted a randomized, double-blind, crossover study of extended-release melatonin (4 mg) compared to immediate-release melatonin (4 mg) in 18 healthy adults, ages 18-65 years. Participants received immediate-release or extended-release melatonin in clinic after an 8 h fast, and blood samples were taken over a 10-h period. After a 7-day washout period, the same procedures were repeated with the melatonin form not previously received. Extended-release melatonin had a longer time to peak concentration (1.56 vs 0.6 h) and elimination half-life (1.63 vs 0.95 h) compared with immediate-release melatonin. Maximum concentration was lower for extended-release melatonin compared with immediate-release melatonin (7581 pg/mL vs 13120 pg/mL). Extended-release melatonin raised melatonin levels in as little as 15 min and sustained elevated melatonin levels (>300 pg/mL) for 6 h before falling below 50 pg/mL by 9 h. No clinically relevant adverse events were observed, and safety parameters remained within normal ranges for both formulations. The pharmacokinetic profile of this extended-release melatonin formulation suggests that it could be used for future efficacy studies of melatonin and sleep outcomes. This trial is registered at ClinicalTrials.gov, NCT04067791.

Melatonin and melatonergic drugs in sleep disorders

Melatonin is an endogenous chronobiological regulator secreted mainly from the pineal gland, which has been used as a dietary supplement in the treatment of sleep problems, including insomnia, parasomnia, and circadian rhythm sleep disorders. However, the short half-life and rapid metabolism of melatonin limit its suitability as a drug. There are many melatonergic drugs used in the treatment of sleep disorders and several drugs are under investigation for approval. Ramelteon was the first melatonergic agonist approved as hypnotic agent by U.S. Food and Drug Administration for the treatment of insomnia. It exhibits higher selective affinity for melatonin 1a (MT₁) receptor than melatonin 1b (MT₂) receptor. This selectivity suggests that it targets sleep onset with no significant adverse effect or dependency. Agomelatin, naphtahalenic compound, act as a potent MT₁/MT₂ melatonergic receptor agonist and serotonergic receptor antagonist was approved for treatment of depression in 2009. This dual action drug is the first melatonergic agent used in depression. Another melatonergic agonist, tasimelteon has high affinity for the MT₁/MT₂ receptors in humans. It was approved for the treatment of non-24 hours sleep-wake rhythm disorder. The newly developed melatonin and melatonergic drugs have the potential to be used extensively in various clinical situations and substitute the old benzodiazepine and its derivatives in the treatment of insomnia. However, the efficacy and safety of newly developed melatonergic drugs should be elucidated through long-term clinical trials.

Melatonin profile in healthy, elderly subjects - A systematic literature review

Melatonin plays an important role in regulation and maintaining of the circadian rhythm. In the elderly population, an array of disturbances of circadian rhythm and sleep can be observed; however the current knowledge within the group of healthy, elderly is scarce. This systematic literature review of studies on the melatonin profile measured in the blood of healthy, elderly individuals included 519 studies, found in the primary search on PubMed. After reviewing the title and abstract, 47 studies were found eligible for full text review. The inclusion criteria were defined as follows: healthy, elderly individuals, with a mean or average age over 65 years and analysis done in blood or plasma. In addition to the primary search, three studies were directly identified by the reference lists of already included studies. A final total of 23 studies were included in the systematic literature review. In reviewing the literature, a clear circadian melatonin profile with a nocturnal peak at 3 am and lower daytime levels was observed in the healthy, elderly population. In elderly over 75 years of age, the nocturnal level of melatonin may be lower; however, the circadian rhythmicity is maintained. In the comparison of elderly, independently living individuals and individuals living in care facilities, the latter group had lower levels of nocturnal melatonin peak as well as higher daytime levels; however one can wonder if elderly in care facilities are healthy. The 23 included studies in the systematic literature review had varying primary objectives and generally the term "healthy" within this population group proves difficult to clearly define. As a result of this, an obvious interstudy variability existed, which is a limitation of this systematic literature review. However, the graphs depicted represent the best possible estimation of the melatonin profile in a healthy, elderly population. Future research in the melatonin profile within this population should focus on clearly defined healthy elderly to ensure a valid normal material in this age group.

What do we really know about the safety and efficacy of melatonin for sleep disorders?

Melatonin is a hormonal product of the pineal gland, a fact that is often forgotten. Instead it is promoted as a dietary supplement that will overcome insomnia, as an antioxidant and as a prescription only drug in most countries outside the United States of America and Canada. The aim of this review is to step back and highlight what we know about melatonin following its discovery 60 years ago. What is the role of endogenous melatonin; what does melatonin do to sleep, body temperature, circadian rhythms, the cardiovascular system, reproductive system, endocrine system and metabolism when administered to healthy subjects? When used as a drug/dietary supplement, what safety studies have been conducted? Can we really say melatonin is safe when it has not been systematically studied and many studies show interactions with a wide range of physiological processes? Finally the results of studies investigating the efficacy of melatonin as a drug to alleviate insomnia are critically evaluated. In summary, melatonin is an endogenous pineal gland hormone with specific physiological functions in animals and humans, with its primary role in humans to maintain synchrony of sleep with the day/night cycle. When administered as a drug it affects a wide range of physiological systems and has clinically important drug interactions. With respect to efficacy for treating sleep disorders, melatonin can advance the time of sleep onset but the effect is modest and variable. In children with neurodevelopmental disabilities melatonin appears to have the greatest impact on sleep onset but little effect on sleep efficiency.

Trough Melatonin Levels Differ between Early and Late Phases of Alzheimer Disease

Objective

Melatonin has been considered to have an essential role in the pathophysiology of Alzheimer’s disease (AD) for its regulatory function on circadian rhythm and interaction with glutamate for the modulation of learning and memory. Previous studies revealed that melatonin levels decreased in patients with AD. However, melatonin supplement didn’t show promising efficacy for AD. This study compared trough melatonin levels among elderly people with different severities of cognitive deficits.

Methods

We enrolled 270 elder individuals (consisting four groups healthy elderly, amnestic mild cognitive impairment [MCI], mild AD, and moderate-severe AD) in the learning cohort. Trough melatonin levels in plasma were measured using ELISA. Cognitive function was evaluated by Clinical Dementia Rating Scale (CDR) and Mini-Mental State Examination (MMSE). An independent testing cohort, also consisting of four groups, was enrolled for ascertainment.

Results

In the learning cohort, trough melatonin levels decreased in the MCI group but elevated in the mild and moderate to severe AD groups. Trough melatonin levels were associated with CDR and MMSE in MCI or AD patients significantly. In the testing cohort, the results were similar to those in the learning cohort.

Conclusion

This study demonstrated that trough melatonin levels in the peripheral blood were decreased in MCI but increased with the severity of AD. The finding supports the trials indicating that melatonin showed efficacy only in MCI but not in AD. Whether trough melatonin level has potential to be a treatment response biomarker for AD, especially its early phase needs further studies.

Pharmacokinetics of exogenous melatonin in relation to formulation, and effects on sleep: A systematic review

There is conflicting evidence on the clinical efficacy of exogenous melatonin for the treatment of sleep disorders. This may be due to differences in the pharmacokinetic (PK) properties of melatonin formulations used in clinical trials. The aim of this systematic review was to understand the relationship between melatonin formulations and PK parameters and, where possible, the effects on sleep outcomes. To this purpose, we conducted a systematic review and nineteen papers were included. The studies included three melatonin transdermal formulation, thirteen oral formulations, one topical, two buccal, two intravenous and two nasogastric formulations. Seven studies investigated the effect of the melatonin formulation on sleep and six of them found a significant improvement in one or more sleep parameters. The potential for an improved controlled release formulation that delays maximum concentration (C_max) was identified. The different formulations and doses affect melatonin PK, suggesting that treatment efficacy maybe affected. Based on the current evidence, we are unable to provide recommendations of specific melatonin formulations and PK parameters for specific sleep disorders. Future studies should systematically investigate how different PK parameters of melatonin formulations affect efficacy treatment of sleep as well as circadian disorders.

Efficacy and safety of supplemental melatonin for delayed sleep-wake phase disorder in children: an overview

Delayed sleep–wake phase disorder (DSPD) is the most frequently occurring intrinsic circadian rhythm sleep–wake disorder, with the highest prevalence in adolescence. Melatonin is the first-choice drug treatment. However, to date melatonin (in a controlled-release formulation) is only authorised for the treatment of insomnia in children with autism or Smiths-Magenis syndrome. Concerns have been raised with respect to the safety and efficacy of melatonin for more general use in children, as melatonin has not undergone the formal safety testing required for a new drug, especially long-term safety in children. Melatonin is known to have profound effects on the reproductive systems of rodents, sheep and primates, as well as effects on the cardiovascular, immune and metabolic systems.

The objective of the present article was therefore to establish the efficacy and safety of exogenous melatonin for use in children with DSPD, based on in vitro, animal model and clinical studies by reviewing the relevant literature in the Medline database using PubMed.

Acute toxicity studies in rats and mice showed toxic effects only at extremely high melatonin doses (>400 mg/kg), some tens of thousands of times more than the recommended dose of 3–6 mg in a person weighing 70 kg. Longer-term administration of melatonin improved the general health and survival of ageing rats or mice. A full range of in vitro/in vivo genotoxicity tests consistently found no evidence that melatonin is genotoxic. Similarly long term administration of melatonin in rats or mice did not have carcinogenic effects, or negative effects on cardiovascular, endocrine and reproductive systems.

With regard to clinical studies, in 19 randomised controlled trials comprising 841 children and adolescents with DSPD, melatonin treatment (usually of 4 weeks duration) consistently improved sleep latency by 22–60 min, without any serious adverse effects. Similarly, 17 randomised controlled trials, comprising 1374 children and adolescents, supplementing melatonin for indications other than DSPD, reported no relevant adverse effects. In addition, 4 long-term safety studies (1.0–10.8 yr) supplementing exogenous melatonin found no substantial deviation of the development of children with respect to sleep quality, puberty development and mental health scores. Finally, post-marketing data for an immediate-release melatonin formulation (Bio-melatonin), used in the UK since 2008 as an unlicensed medicine for sleep disturbance in children, recorded no adverse events to date on sales of approximately 600,000 packs, equivalent to some 35 million individual 3 mg tablet doses (MHRA yellow card adverse event recording scheme).

In conclusion, evidence has been provided that melatonin is an efficacious and safe chronobiotic drug for the treatment of DSPD in children, provided that it is administered at the correct time (3–5 h before endogenous melatonin starts to rise in dim light (DLMO)), and in the correct (minimal effective) dose. As the status of circadian rhythmicity may change during long-time treatment, it is recommended to stop melatonin treatment at least once a year (preferably during the summer holidays).

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Melatonin improves sleep onset without serious adverse effects in youths with DSPD. Change th text after the fourth bullet into: Melatonin is an efficacious and safe chronobiotic drug for the treatment of DSPD in youths.

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Melatonin for indications other than DSPD, dose not cause relevant adverse effects.

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Long term melatonin treatment does not impair sleep, puberty, and mental health.

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Melatonin is an efficacious and safe chronobiotic drug for the treatment of DSPD in youths.

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Melatonin should be administered at the correct time and in the minimal effective dose.

Measuring melatonin by immunoassay

The pineal gland hormone melatonin continues to be of considerable interest to biomedical researchers. Of particular interest is the pattern of secretion of melatonin in relation to sleep timing as well as its potential role in certain diseases. Measuring melatonin in biological fluids such as blood and saliva presents particular methodological challenges since the production and secretion of the hormone are known to be extremely low during the light phase in almost all situations. Active secretion only occurs around the time of lights out in a wide range of species. The challenge then is to develop practical high-throughput assays that are sufficiently sensitive and accurate enough to detect levels of melatonin less than 1 pg/mL in biological fluids. Mass spectrometry assays have been developed that achieve the required sensitivity, but are really not practical or even widely available to most researchers. Melatonin radioimmunoassays and ELISA have been developed and are commercially available. But the quality of the results that are being published is very variable, partly not only because of poor experimental designs, but also because of poor assays. In this review, I discuss issues around the design of studies involving melatonin measurement. I then provide a critical assessment of 21 immunoassay kits marketed by 11 different companies with respect to validation, specificity and sensitivity. Technical managers of the companies were contacted in an attempt to obtain information not available online or in kit inserts. A search of the literature was also conducted to uncover papers that have reported the use of these assays, and where possible, both daytime and night-time plasma or saliva melatonin concentrations were extracted and tabulated. The results of the evaluations are disturbing, with many kits lacking any validation studies or using inadequate validation methods. Few assays have been properly assessed for specificity, while others report cross-reaction profiles that can be expected to result in over estimation of the melatonin levels. Some assays are not fit for purpose because they are not sensitive enough to determine plasma or saliva DLMO of 10 and 3 pg/mL, respectively. Finally, some assays produce unrealistically high daytime melatonin levels in humans and laboratory animals in the order of hundreds of pg/mL. In summary, this review provides a comprehensive and unique assessment of the current commercial melatonin immunoassays and their use in publications. It provides researchers new to the field with the information they need to design valid melatonin studies from both the perspective of experimental/clinical trial design and the best assay methodologies. It will also hopefully help journal editors and reviewers who may not be fully aware of the pitfalls of melatonin measurement make better informed decisions on publication acceptability.

Melatonin and Mesenchymal Stem Cells as a Key for Functional Integrity for Liver Cancer Treatment

Hepatocellular carcinoma (HCC) is the most common hepatobiliary malignancy with limited therapeutic options. On the other hand, melatonin is an indoleamine that modulates a variety of potential therapeutic effects. In addition to its important role in the regulation of sleep–wake rhythms, several previous studies linked the biologic effects of melatonin to various substantial endocrine, neural, immune and antioxidant functions, among others. Furthermore, the effects of melatonin could be influenced through receptor dependent and receptor independent manner. Among the other numerous physiological and therapeutic effects of melatonin, controlling the survival and differentiation of mesenchymal stem cells (MSCs) has been recently discussed. Given its controversial interaction, several previous reports revealed the therapeutic potential of MSCs in controlling the hepatocellular carcinoma (HCC). Taken together, the intention of the present review is to highlight the effects of melatonin and mesenchymal stem cells as a key for functional integrity for liver cancer treatment. We hope to provide solid piece of information that may be helpful in designing novel drug targets to control HCC.

Serum melatonin in dogs with congenital portosystemic shunting, with and without hepatic encephalopathy

BACKGROUND

Melatonin is a hormone produced and secreted primarily by the pineal gland and mainly metabolised in the liver. Increased melatonin concentrations have been reported in human cirrhosis and hepatic encephalopathy (HE), a syndrome of neurological dysfunction. The pathogenesis of canine HE is incompletely understood. Melatonin has been hypothesised as a contributor to the development of HE. The aim of this study was to investigate whether serum melatonin concentrations are increased in canine congenital portosystemic shunting (cPSS), with and without HE.

METHODS

Medical records were retrospectively reviewed, for which archived (-80°C) serum samples were available. A canine competitive ELISA was used to measure melatonin in two cohorts: dogs with a final diagnosis of cPSS (n=23) with and without clinical signs of HE, and healthy dogs (n=15).

RESULTS

Melatonin concentrations were not significantly different (P=0.81) between healthy controls (median 27.2 pg/mL, range 19.8-161.5 pg/mL) and dogs with cPSS (median 25.7 pg/mL, range 18.5-244.9 pg/mL). Serum melatonin did not differ between cPSS patients with and without clinical signs of HE (P>0.99). No correlation was found between serum melatonin and blood ammonia (Spearman rank correlation coefficient, r_s =-0.41, P=0.08).

CONCLUSION

Serum melatonin is not increased in canine cPSS with and without HE. We found no evidence that altered melatonin metabolism plays a role in the pathogenesis of cPSS-associated HE.

A critical review of melatonin assays: Past and present

There has been increased interest in the measurement of melatonin in plasma and saliva recently either as a marker of circadian phase or to understand the physiological role of melatonin. For both situations, there is a need for a specific assay for melatonin that is sensitive enough to detect low concentrations (<2 pg/mL). Since the mid-1970s, there have been many assays developed to measure melatonin in blood and saliva. Radioimmunoassays and ELISA have predominated because of their relative simplicity and high throughput. In this review, I show that the early radioimmunoassays while providing valuable information about nocturnal melatonin levels in humans, generally produced inaccurate basal (daytime) levels. Mass spectrometry assays, however, have provided us with the target values that immunoassays need to achieve, that is, daytime plasma melatonin levels <1 pg/mL. There are now many contemporary commercial assays available utilising both RIA and ELISA technologies, but not all achieve the standards set by the mass spectrometry assays. The performance of these assays is reviewed. I conclude with recommendations on issues researchers need to consider when conducting melatonin studies, including the importance of time of day of collection, validation of assays, the potential causes of poor assay specificity at low levels, the advantages/disadvantages of using saliva vs plasma and extraction assays vs direct assays, kit manufacturers responsibilities and the reporting requirements when publishing melatonin studies.

A unified model of melatonin, 6-sulfatoxymelatonin, and sleep dynamics

A biophysical model of the key aspects of melatonin synthesis and excretion has been developed, which is able to predict experimental dynamics of melatonin in plasma and saliva, and of its urinary metabolite 6-sulfatoxymelatonin (aMT6s). This new model is coupled to an established model of arousal dynamics, which predicts sleep and circadian dynamics based on light exposure and times of wakefulness. The combined model thus predicts melatonin levels over the sleep-wake/dark-light cycle and enables prediction of melatonin-based circadian phase markers, such as dim light melatonin onset (DLMO) and aMT6s acrophase under conditions of normal sleep and circadian misalignment. The model is calibrated and tested against group average data from 10 published experimental studies and is found to reproduce quantitatively the key dynamics of melatonin and aMT6s, including the timing of release and amplitude, as well as response to controlled lighting and shift work.

N,N-dimethyltryptamine and the pineal gland: Separating fact from myth

The pineal gland has a romantic history, from pharaonic Egypt, where it was equated with the eye of Horus, through various religious traditions, where it was considered the seat of the soul, the third eye, etc. Recent incarnations of these notions have suggested that N,N-dimethyltryptamine is secreted by the pineal gland at birth, during dreaming, and at near death to produce out of body experiences. Scientific evidence, however, is not consistent with these ideas. The adult pineal gland weighs less than 0.2 g, and its principal function is to produce about 30 µg per day of melatonin, a hormone that regulates circadian rhythm through very high affinity interactions with melatonin receptors. It is clear that very minute concentrations of N,N-dimethyltryptamine have been detected in the brain, but they are not sufficient to produce psychoactive effects. Alternative explanations are presented to explain how stress and near death can produce altered states of consciousness without invoking the intermediacy of N,N-dimethyltryptamine.

Premedication with melatonin vs midazolam: efficacy on anxiety and compliance in paediatric surgical patients

Preoperative anxiety is a major problem in paediatric surgical patients. Melatonin has been used as a premedicant agent and data regarding effectiveness are controversial. The primary outcome of this randomized clinical trial was to evaluate the effectiveness of oral melatonin premedication, in comparison to midazolam, in reducing preoperative anxiety in children undergoing elective surgery. As secondary outcome, compliance to intravenous induction anaesthesia was assessed. There were 80 children undergoing surgery randomly assigned, 40 per group, to receive oral midazolam (0.5 mg/kg, max 20 mg) or oral melatonin (0.5 mg/kg, max 20 mg). Trait anxiety of children and their mothers (State-Trait Anxiety Inventory) at admission, preoperative anxiety and during anaesthesia induction (Modified Yale Pre-operative Anxiety Scale), and children's compliance with anaesthesia induction (Induction Compliance Checklist) were all assessed. Children premedicated with melatonin and midazolam did not show significant differences in preoperative anxiety levels, either in the preoperative room or during anaesthesia induction. Moreover, compliance during anaesthesia induction was similar in both groups.

CONCLUSIONS

This study adds new encouraging data, further supporting the potential use of melatonin premedication in reducing anxiety and improving compliance to induction of anaesthesia in children undergoing surgery. Nevertheless, further larger controlled clinical trials are needed to confirm the real effectiveness of melatonin as a premedicant agent in paediatric population. What is Known: • Although midazolam represents the preferred treatment as a premedication for children before induction of anaesthesia, it has several side effects. • Melatonin has been successfully used as a premedicant agent in adults, while data regarding effectiveness in children are controversial. What is New: • In this study, melatonin was as effective as midazolam in reducing children's anxiety in both preoperative room and at induction of anaesthesia.

Physiological melatonin levels in healthy older people: A systematic review

OBJECTIVE

Melatonin plays a major role in maintaining circadian rhythm. Previous studies showed that its secretion pattern and levels could be disturbed in persons with dementia, psychiatric disorders, sleep disorders or with cancer. Also ageing is a factor that could alter melatonin levels, although previous research provides contradicting results. As melatonin supplementation is increasingly applied in older persons as sleep medication, it is important to know if melatonin levels decrease in healthy ageing and/or secretion patterns change. The objective of this study is to determine physiological levels and secretion patterns of melatonin in healthy older people.

METHODS

We performed a systematic review and searched PubMed and Embase for studies published between January 1st 1980 and October 5th 2015 that measured melatonin in healthy persons aged ≥65years.

RESULTS

Nineteen studies were retrieved. The number of participants ranged from 5 to 60 per study. Melatonin was mostly measured by radioimmunoassay (RIA) and the number of measurements per 24hours varied from 1 to 96. Sixteen studies showed a secretion pattern with a clear peak concentration, mostly at 0200h or 0300h. Maximum concentrations varied greatly from 11.2 to 91.3pgml(-1). Maximum melatonin level in studies with participants mean aged 65-70years was 49.3pgml(-1) and in studies with participants mean aged ≥75years 27.8pgml(-1), p-value <0.001.

CONCLUSION

Total melatonin production in 24hours seems not to change in healthy ageing, but the maximal nocturnal peak concentration of melatonin might decline. It is important to take this into account when prescribing melatonin supplementation to older people.

Melatonin and cortisol profiles in late midlife and their association with age-related changes in cognition

Previous studies have reported an association between circadian disturbances and age-related cognitive impairment. The aim was to study the 24-hour profiles of melatonin and cortisol in relation to cognitive function in middle-aged male subjects. Fifty healthy middle-aged males born in 1953 were recruited from a population-based cohort based on previous cognitive assessments in young adulthood and late midlife. The sample included 24 cognitively high-functioning and 26 cognitively impaired participants. Saliva samples were collected every 4 hours over a 24-hour period and analyzed for cortisol and melatonin levels by immunoassay. All participants exhibited clear circadian rhythms of salivary melatonin and cortisol. Salivary melatonin concentrations had a nocturnal peak at approximately 4 am. The median nocturnal melatonin response at 4 am was significantly lower in the cognitively impaired group than in the high-functioning group (-4.6 pg/mL, 95% CI: -7.84, -1.36, P=0.006). The 24-hour mean melatonin concentration (high-functioning group: 4.80±0.70 pg/mL, vs cognitively impaired group: 4.81±0.76 pg/mL; P>0.05) (or the area under the curve, AUC) was not significantly different between the two groups. Cortisol levels were low during the night, and peaked at approximately 8 am. Median cortisol concentrations were similar at all times, as were the 24-hour mean cortisol concentrations and AUC. To the best of our knowledge, ours is the first study to assess circadian measures (ie, melatonin and cortisol) in healthy middle-aged men with different cognitive trajectories in midlife. We found evidence of altered circadian rhythms with a reduced nocturnal melatonin response at 4 am in men with cognitive impairment. The 24-hour concentration and AUC of melatonin and cortisol were similar in the cognitively high-functioning group and in the cognitively impaired.

The effect of melatonin treatment on postural stability, muscle strength, and quality of life and sleep in postmenopausal women: a randomized controlled trial

BACKGROUND

Melatonin is often used as a sleeping aid in elderly adults. As previous studies suggest a protective role of melatonin against osteoporosis, it is important to document its safety. Treatment should not cause any hangover effect that could potentially lead to falls and fractures. We therefore aimed to evaluate the effect of melatonin on balance- and muscle function.

METHODS AND PATIENTS

In a double-blind placebo-controlled study, we randomized 81 postmenopausal women with osteopenia to receive 1 or 3 mg melatonin, or placebo nightly for 12 months. Postural balance as well as muscle function was measured. In addition, we assessed quality of life and sleep at baseline and after 12 months treatment.

RESULTS

Compared to placebo, one-year treatment with melatonin did not affect postural balance or risk of falls. Furthermore, no significant changes between groups were observed in muscle strength in neither upper- nor lower extremities. Treatment did not affect quality of life or sleep. However, in the subgroup of women with sleep disturbances at baseline, a trend towards an improved sleep quality was seen (p = 0.08).

CONCLUSION

Treatment with melatonin is safe in postmenopausal women with osteopenia. There is no hangover effect affecting balance- and muscle function following the intake of melatonin. In women with a good quality of sleep, melatonin has no effect, however in poor quality of sleep, small doses of melatonin trended towards improving the quality.

TRIAL REGISTRATION

(# NCT01690000).

Association of Urinary 6-Sulfatoxymelatonin (aMT6s) Levels and Objective and Subjective Sleep Measures in Older Men: The MrOS Sleep Study

BACKGROUND

Sleep and melatonin have been associated with healthy aging. In this study, we examine the association between melatonin levels and sleep among older men.

METHODS

Cross-sectional study of a community-dwelling cohort of 2,821 men aged 65 years or older recruited from six U.S. centers. First morning void urine samples were collected to measure melatonin's major urinary metabolite, 6-sulfatoxymelatonin (aMT6s). We also assessed objective and subjective sleep parameters. We used logistic regression models to calculate multivariate (MV) odds ratios (ORs), and 95% confidence intervals (CIs) adjusted for important demographic variables and comorbidities.

RESULTS

In the overall sample, the only significant finding in fully adjusted models was that aMT6s levels were inversely associated with subjectively measured daytime sleepiness (sleepiness mean score of 5.79 in the top aMT6s quartile, and 6.26 in the bottom aMT6s quartile, MV OR, 1.32; 95% CI, 0.95-1.84; p trend ≤ .02). When restricting to men without β-blocker use (a known melatonin suppressant), aMT6s levels were significantly associated with shorter sleep time, that is, less than 5 hours (MV OR, = 1.90; 95% CI, 1.21-2.99; p trend = .01), and worse sleep efficiency, that is, less than 70% (MV OR, 1.58; 95% CI, 1.28-2.65; p trend < .001). aMT6s were not associated with subjective sleep quality or respiratory disturbance in any of our analyses.

CONCLUSION

Lower nocturnal melatonin levels were associated with worsened daytime sleepiness, sleep efficiency, and shorter sleep time in older men. The role of circadian interventions, and whether melatonin levels are a modifiable risk factor for poor sleep in older men, warrants further study.

Melatonin use for neuroprotection in perinatal asphyxia: a randomized controlled pilot study

OBJECTIVE

Melatonin has been shown to be neuroprotective in animal models. The objective of this study is to examine the effect of melatonin on clinical, biochemical, neurophysiological and radiological outcomes of neonates with hypoxic-ischemic encephalopathy (HIE).

STUDY DESIGN

We conducted a prospective trial on 45 newborns, 30 with HIE and 15 healthy controls. HIE infants were randomized into: hypothermia group (N=15; received 72-h whole-body cooling) and melatonin/hypothermia group (N=15; received hypothermia and five daily enteral doses of melatonin 10 mg kg(-1)). Serum melatonin, plasma superoxide dismutase (SOD) and serum nitric oxide (NO) were measured at enrollment for all infants (N=45) and at 5 days for the HIE groups (N=30). In addition to electroencephalography (EEG) at enrollment, all surviving HIE infants were studied with brain magnetic resonance imaging (MRI) and repeated EEG at 2 weeks of life. Neurologic evaluations and Denver Developmental Screening Test II were performed at 6 months.

RESULT

Compared with healthy neonates, the two HIE groups had increased melatonin, SOD and NO. At enrollment, the two HIE groups did not differ in clinical, laboratory or EEG findings. At 5 days, the melatonin/hypothermia group had greater increase in melatonin (P<0.001) and decline in NO (P<0.001), but less decline in SOD (P=0.004). The melatonin/hypothermia group had fewer seizures on follow-up EEG and less white matter abnormalities on MRI. At 6 months, the melatonin/hypothermia group had improved survival without neurological or developmental abnormalities (P<0.001).

CONCLUSION

Early administration of melatonin to asphyxiated term neonates is feasible and may ameliorate brain injury.

Lower melatonin secretion in older females: gender differences independent of light exposure profiles

Background

Melatonin is associated with a variety of diseases in advanced age, including insomnia, depression, and dementia, and its secretion is influenced by light exposure. Although studies in young and middle-aged subjects have shown that females tend to have higher melatonin levels than males, gender differences in melatonin levels among older people remain unclear.

Methods

To determine the gender differences in melatonin levels among older people in home settings, we conducted a cross-sectional study in 528 older people. We measured overnight urinary 6-sulfatoxymelatonin excretion (UME; an index of melatonin secretion), and ambulatory light intensity.

Results

The mean age of females was 1.8 years younger, and average intensity of daytime light exposure was half that in males (P < 0.01). In a univariate comparison, UME was significantly lower in females than in males (P < 0.01). A multivariate model using analysis of covariance showed that log-transformed UME remained significantly lower in females after adjustment for potential confounding factors, including age and daytime and nighttime light exposure profiles (males vs. females: 1.90 vs. 1.73 log µg; adjusted mean difference 0.17 log µg [95% confidence interval [CI] 0.02–0.32]; P = 0.02). This result indicates that older females have 18.4% (95% CI, 2.2–37.4%) lower UME than older males.

Conclusions

Older females have significantly lower UME than older males, an association which is independent of light exposure profiles in home settings. Our findings may be useful as basic data for further research to investigate gender differences in several diseases associated with melatonin in the elderly.

Pharmacokinetics of melatonin in preterm infants

AIMS

Preterm infants are deprived of the normal intra-uterine exposure to maternal melatonin and may benefit from replacement therapy. We conducted a pharmacokinetic study to guide potential therapeutic trials.

METHODS

Melatonin was administered to 18 preterm infants in doses ranging from 0.04-0.6 μg kg(-1) over 0.5-6 h. Pharmacokinetic profiles were analyzed individually and by population methods.

RESULTS

Baseline melatonin was largely undetectable. Infants receiving melatonin at 0.1 μg kg(-1)  h(-1) for 2 h showed a median half-life of 15.82 h and median maximum plasma concentration of 203.3 pg ml(-1) . On population pharmacokinetics, clearance was 0.045 l h(-1) , volume of distribution 1.098 l and elimination half-life 16.91 h with gender (P = 0.047) and race (P < 0.0001) as significant covariates.

CONCLUSIONS

A 2 h infusion of 0.1 μg kg(-1)  h(-1) increased blood melatonin from undetectable to approximately peak adult concentrations. Slow clearance makes replacement of a typical maternal circadian rhythm problematic. The pharmacokinetic profile of melatonin in preterm infants differs from that of adults so dosage of melatonin for preterm infants cannot be extrapolated from adult studies. Data from this study can be used to guide therapeutic clinical trials of melatonin in preterm infants.

Is melatonin ready to be used in preterm infants as a neuroprotectant?

The prevention of neurological disabilities following preterm birth remains a major public health challenge and efforts are still needed to test the neuroprotective properties of candidate molecules. Melatonin serves as a neuroprotectant in adult models of cerebral ischemia through its potent antioxidant and anti-inflammatory effects. An increasing number of preclinical studies have consistently demonstrated that melatonin protects the damaged developing brain by preventing abnormal myelination and an inflammatory glial reaction, a major cause of white matter injury. The main questions asked in this review are whether preclinical data on the neuroprotective properties of melatonin are sufficient to translate this concept into the clinical setting, and whether melatonin can reduce white matter damage in preterm infants. This review provides support for our view that melatonin is now ready to be tested in human preterm neonates, and discusses ongoing and planned clinical trials.

A physiologically based pharmacokinetics model for melatonin--effects of light and routes of administration

Physiologically based pharmacokinetic (PBPK) models were developed using MATLAB Simulink(®) to predict diurnal variations of endogenous melatonin with light as well as pharmacokinetics of exogenous melatonin via different routes of administration. The model was structured using whole body, including pineal and saliva compartments, and parameterized based on the literature values for endogenous melatonin. It was then optimized by including various intensities of light and various dosage and formulation of melatonin. The model predictions generally have a good fit with available experimental data as evaluated by mean squared errors and ratios between model-predicted and observed values considering large variations in melatonin secretion and pharmacokinetics as reported in the literature. It also demonstrates the capability and usefulness in simulating plasma and salivary concentrations of melatonin under different light conditions and the interaction of endogenous melatonin with the pharmacokinetics of exogenous melatonin. Given the mechanistic approach and programming flexibility of MATLAB Simulink(®), the PBPK model could provide predictions of endogenous melatonin rhythms and pharmacokinetic changes in response to environmental (light) and experimental (dosage and route of administration) conditions. Furthermore, the model may be used to optimize the combined treatment using light exposure and exogenous melatonin for maximal phase advances or delays.

Melatonin: buffering the immune system

Melatonin modulates a wide range of physiological functions with pleiotropic effects on the immune system. Despite the large number of reports implicating melatonin as an immunomodulatory compound, it still remains unclear how melatonin regulates immunity. While some authors argue that melatonin is an immunostimulant, many studies have also described anti-inflammatory properties. The data reviewed in this paper support the idea of melatonin as an immune buffer, acting as a stimulant under basal or immunosuppressive conditions or as an anti-inflammatory compound in the presence of exacerbated immune responses, such as acute inflammation. The clinical relevance of the multiple functions of melatonin under different immune conditions, such as infection, autoimmunity, vaccination and immunosenescence, is also reviewed.

Older poor-sleeping women display a smaller evening increase in melatonin secretion and lower values of melatonin and core body temperature than good sleepers

Melatonin concentration and core body temperature (CBT) follow endogenous circadian biological rhythms. In the evening, melatonin level increases and CBT decreases. These changes are involved in the regulation of the sleep-wake cycle. Therefore, the authors hypothesized that age-related changes in these rhythms affect sleep quality in older people. In a cross-sectional study design, 11 older poor-sleeping women (aged 62-72 yrs) and 9 older good-sleeping women (60-82 yrs) were compared with 10 younger good-sleeping women (23-28 yrs). The older groups were matched by age and body mass index. Sleep quality was assessed by the Pittsburgh Sleep Quality Index questionnaire. As an indicator of CBT, oral temperature was measured at 1-h intervals from 17:00 to 24:00 h. At the same time points, saliva samples were collected for determining melatonin levels by enzyme-linked immunosorbent assay (ELISA). The dim light melatonin onset (DLMO), characterizing the onset of melatonin production, was calculated. Evening changes in melatonin and CBT levels were tested by the Friedman test. Group comparisons were performed with independent samples tests. Predictors of sleep-onset latency (SOL) were assessed by regression analysis. Results show that the mean CBT decreased in the evening from 17:00 to 24:00 h in both young women (from 36.57°C to 36.25°C, p < .001) and older women (from 36.58°C to 35.88°C, p < .001), being lowest in the older poor sleepers (p < .05). During the same time period, mean melatonin levels increased in young women (from 16.2 to 54.1 pg/mL, p < .001) and older women (from 10.0 to 23.5 pg/mL, p < .001), being lowest among the older poor sleepers (from 20:00 to 24:00 h, p < .05 vs. young women). Older poor sleepers also showed a smaller increase in melatonin level from 17:00 to 24:00 h than older good sleepers (mean ± SD: 7.0 ± 9.63 pg/mL vs. 15.6 ± 24.1 pg/mL, p = .013). Accordingly, the DLMO occurred at similar times in young (20:10 h) and older (19:57 h) good-sleeping women, but was delayed ∼50 min in older poor-sleeping women (20:47 h). Older poor sleepers showed a shorter phase angle between DLMO and sleep onset, but a longer phase angle between CBT peak and sleep onset than young good sleepers, whereas older good sleepers had intermediate phase angles (insignificant). Regression analysis showed that the DLMO was a significant predictor of SOL in the older women (R(2) = 0.64, p < .001), but not in the younger women. This indicates that melatonin production started later in those older women who needed more time to fall asleep. In conclusion, changes in melatonin level and CBT were intact in older poor sleepers in that evening melatonin increased and CBT decreased. However, poor sleepers showed a weaker evening increase in melatonin level, and their DLMO was delayed compared with good sleepers, suggesting that it is not primarily the absolute level of endogenous melatonin, but rather the timing of the circadian rhythm in evening melatonin secretion that might be related to disturbances in the sleep-wake cycle in older people.

Melatonin agonists in primary insomnia and depression-associated insomnia: are they superior to sedative-hypnotics?

Current pharmacological treatment of insomnia involves the use of sedative-hypnotic benzodiazepine and non-benzodiazepine drugs. Although benzodiazepines improve sleep, their multiple adverse effects hamper their application. Adverse effects include impairment of memory and cognitive functions, next-day hangover and dependence. Non-benzodiazepines are effective for initiating sleep but are not as effective as benzodiazepines for improving sleep quality or efficiency. Furthermore, their prolonged use produces adverse effects similar to those observed with benzodiazepines. Inasmuch as insomnia may be associated with decreased nocturnal melatonin, administration of melatonin is a strategy that has been increasingly used for treating insomnia. Melatonin can be effective for improving sleep quality without the adverse effects associated with hypnotic-sedatives. Ramelteon, a synthetic analog of melatonin which has a longer half life and a stronger affinity for MT1 and MT2 melatonergic receptors, has been reportedly effective for initiating and improving sleep in both adult and elderly insomniacs without showing hangover, dependence, or cognitive impairment. Insomnia is also a major complaint among patients suffering from depressive disorders and is often aggravated by conventional antidepressants especially the specific serotonin reuptake inhibitors. The novel antidepressant agomelatine, a dual action agent with affinity for melatonin MT1 and MT2 receptors and 5-HT2c antagonistic properties, constitutes a new approach to the treatment of major depressive disorders. Agomelatine ameliorates the symptoms of depression and improves the quality and efficiency of sleep. Taken together, the evidence indicates that MT1/MT2 receptor agonists like ramelteon or agomelatine may be valuable pharmacological tools for insomnia and for depression-associated insomnia.

Endogenous antioxidants and radical scavengers

All living organisms are constantly exposed to oxidant agents deriving from both endogenous and exogenous sources capable to modify biomolecules and induce damages. Free radicals generated by oxidative stress exert an important role in the development of tissue damage and aging. Reactive species (RS) derived from oxygen (ROS) and nitrogen (RNS) pertain to free radicals family and are constituted by various forms of activated oxygen or nitrogen. RS are continuosly produced during normal physiological events but can be removed by antioxidant defence mechanism: the imbalance between RS and antioxidant defence mechanism leads to modifications in cellular membrane or intracellular molecules. In this chapter only endogenous antioxidant molecules will be critically discussed, such as Glutathione, Alpha-lipoic acid, Coenzyme Q, Ferritin, Uric acid, Bilirubin, Metallothioneine, L-carnitine and Melatonin.

Use of transdermal melatonin delivery to improve sleep maintenance during daytime

Oral melatonin (MEL) can improve daytime sleep, but the hormone's short elimination half-life limits its use as a hypnotic in shift workers and individuals with jet lag or other sleep problems. Here we show, in healthy subjects, that transdermal delivery of MEL during the daytime can elevate plasma MEL and reduce waking after sleep onset, by promoting sleep in the latter part of an 8-h sleep opportunity. Transdermal MEL may have advantages over fast-release oral MEL in improving sleep maintenance during adverse circadian phases.

Assessment of the effects of physiological release of melatonin on arterial distensibility and blood pressure

AIM

The aim of our study was to investigate the effects of endogenous melatonin on arterial distensibility using measurements of the velocity of the aortic pulse wave between the carotid and femoral arteries in healthy young students assessed in the supine position.

MATERIAL AND METHODS

We studied 29 healthy young students, aged between 18 and 27 years, with 19 being male. The measured the velocity of the aortic pulse wave between the carotid and femoral arteries, along the blood pressures and heart rate, while the subjects were in the supine position at two time points, namely from 01.30-02.30 and 13:30-14:30 hours, during a day, also taking plasma to measure the concentrations of melatonin. The velocity of the pulse waves was determined using an automatic device, the Complior Colson (France), which allowed on-line recording and automatic calculation of the velocity, the calculations being made by measuring the transit time of the pulse wave as it traversed the distance between two sites of recording according, the velocity of the pulse wave in meter per second being equal to the distance in meters divided by the time of transit in seconds.

RESULTS

Although the velocity of the pulse wave, systolic, diastolic, and mean blood pressures, and heart rate were all increased in the morning relative to measurement made later in the day, levels of melatonin in the plasma were increased in the night. There was negative correlation between diurnal levels of melatonin and the velocity of the pulse wave.

CONCLUSION

Our findings indicate that increased levels of melatonin during the night may cause a decreased velocity of the aortic pulse wave, along with blood pressures and heart rate.

Daytime levels of melatonin in patients with age-related macular degeneration

PURPOSE

Melatonin (N-acetyl-5-methoxytryptamine) (MT) is a hormone that acts as an antioxidant. It is produced by the pineal gland and within the retina; its release is blocked by light entering the eye. We examined whether MT daytime levels differ between pseudophakic patients with age-related macular degeneration (ARMD) and pseudophakic subjects without any ocular pathology of the same age.

METHODS

A prospective, cross-sectional, observational study was performed. Pseudophakic patients of the same age group were included. Patients underwent complete ophthalmic examinations and blood sampling between 08:00 and 10:00 hr. MT daytime value in the serum was the main outcome measure.

RESULTS

Sixty-nine pseudophakic patients were included. Fifty patients with exudative and non-exudative ARMD were in the study group while 19 patients were controls. Patients with ARMD had significantly higher daytime levels of MT (P = 0.003). There were significant differences in MT daytime levels between the exudative and non-exudative forms (P = 0.009). MT values also correlated with the best-corrected visual acuity (r = -0.285, P = 0.019).

CONCLUSION

These data indicate that pseudophakic patients with ARMD produce more MT during the day compared to pseudophakic subjects without ARMD. This may be caused by the reduced visual acuity in patients with ARMD, whereby less light reaches the photoreceptors, allowing MT secretion to continue during the day. Because MT also acts as an antioxidant and daytime levels are higher in patients with ARMD, these results might be interpreted as a rescue factor.

Melatonin in Alzheimer's disease and other neurodegenerative disorders

Increased oxidative stress and mitochondrial dysfunction have been identified as common pathophysiological phenomena associated with neurodegenerative disorders such as Alzheimer's disease (AD), Parkinson's disease (PD) and Huntington's disease (HD). As the age-related decline in the production of melatonin may contribute to increased levels of oxidative stress in the elderly, the role of this neuroprotective agent is attracting increasing attention. Melatonin has multiple actions as a regulator of antioxidant and prooxidant enzymes, radical scavenger and antagonist of mitochondrial radical formation. The ability of melatonin and its kynuramine metabolites to interact directly with the electron transport chain by increasing the electron flow and reducing electron leakage are unique features by which melatonin is able to increase the survival of neurons under enhanced oxidative stress. Moreover, antifibrillogenic actions have been demonstrated in vitro, also in the presence of profibrillogenic apoE4 or apoE3, and in vivo, in a transgenic mouse model. Amyloid-β toxicity is antagonized by melatonin and one of its kynuramine metabolites. Cytoskeletal disorganization and protein hyperphosphorylation, as induced in several cell-line models, have been attenuated by melatonin, effects comprising stress kinase downregulation and extending to neurotrophin expression. Various experimental models of AD, PD and HD indicate the usefulness of melatonin in antagonizing disease progression and/or mitigating some of the symptoms. Melatonin secretion has been found to be altered in AD and PD. Attempts to compensate for age- and disease-dependent melatonin deficiency have shown that administration of this compound can improve sleep efficiency in AD and PD and, to some extent, cognitive function in AD patients. Exogenous melatonin has also been reported to alleviate behavioral symptoms such as sundowning. Taken together, these findings suggest that melatonin, its analogues and kynuric metabolites may have potential value in prevention and treatment of AD and other neurodegenerative disorders.

Melatonin, immune function and aging

Aging is associated with a decline in immune function (immunosenescence), a situation known to correlate with increased incidence of cancer, infectious and degenerative diseases. Innate, cellular and humoral immunity all exhibit increased deterioration with age. A decrease in functional competence of individual natural killer (NK) cells is found with advancing age. Macrophages and granulocytes show functional decline in aging as evidenced by their diminished phagocytic activity and impairment of superoxide generation. There is also marked shift in cytokine profile as age advances, e.g., CD3+ and CD4+ cells decline in number whereas CD8+ cells increase in elderly individuals. A decline in organ specific antibodies occurs causing reduced humoral responsiveness. Circulating melatonin decreases with age and in recent years much interest has been focused on its immunomodulatory effect. Melatonin stimulates the production of progenitor cells for granulocytes-macrophages. It also stimulates the production of NK cells and CD4+ cells and inhibits CD8+ cells. The production and release of various cytokines from NK cells and T-helper lymphocytes also are enhanced by melatonin. Melatonin presumably regulates immune function by acting on the immune-opioid network, by affecting G protein-cAMP signal pathway and by regulating intracellular glutathione levels. Melatonin has the potential therapeutic value to enhance immune function in aged individuals and in patients in an immunocompromised state.

Melatonin and sleep in aging population

The neurohormone melatonin is released from the pineal gland in close association with the light-dark cycle. There is a temporal relationship between the nocturnal rise in melatonin secretion and the 'opening of the sleep gate' at night. This association, as well as the sleep promoting effect of exogenous melatonin, implicates the pineal product in the physiological regulation of sleep. Aging is associated with a significant reduction in sleep continuity and quality. A decreased production of melatonin with age is documented in a majority of studies. Diminished nocturnal melatonin secretion with severe disturbances in sleep/wake rhythm has been consistently reported in Alzheimer's disease (AD). A recent survey on the effects of melatonin in sleep disturbances, including all age groups, failed to document significant and clinically meaningful effects of exogenous melatonin on sleep quality, efficiency and latency. However, in clinical trials involving elderly insomniacs and AD patients suffering from sleep disturbances exogenous melatonin has repeatedly been found to be effective in improving sleep. The results indicate that exogenous melatonin is more effective to promote sleep in the presence of a diminished production of endogenous melatonin. A MT1/MT2 receptor analog of melatonin (ramelteon) has recently been introduced as a new type of hypnotics with no evidence of abuse or dependence.

The human pineal gland and melatonin in aging and Alzheimer's disease

The pineal gland is a central structure in the circadian system which produces melatonin under the control of the central clock, the suprachiasmatic nucleus (SCN). The SCN and the output of the pineal gland, i.e. melatonin, are synchronized to the 24-hr day by environmental light, received by the retina and transmitted to the SCN via the retinohypothalamic tract. Melatonin not only plays an important role in the regulation of circadian rhythms, but also acts as antioxidant and neuroprotector that may be of importance in aging and Alzheimer's disease (AD). Circadian disorders, such as sleep-wake cycle disturbances, are associated with aging, and even more pronounced in AD. Many studies have reported disrupted melatonin production and rhythms in aging and in AD that, as we showed, are taking place as early as in the very first preclinical AD stages (neuropathological Braak stage I-II). Degeneration of the retina-SCN-pineal axis may underlie these changes. Our recent studies indicate that a dysfunction of the sympathetic regulation of pineal melatonin synthesis by the SCN is responsible for melatonin changes during the early AD stages. Reactivation of the circadian system (retina-SCN-pineal pathway) by means of light therapy and melatonin supplementation, to restore the circadian rhythm and to relieve the clinical circadian disturbances, has shown promising positive results.

Role of melatonin in neurodegenerative diseases

The pineal product melatonin has remarkable antioxidant properties. It scavenges hydroxyl, carbonate and various organic radicals, peroxynitrite and other reactive nitrogen species. Melatonyl radicals formed by scavenging combine with and, thereby, detoxify superoxide anions in processes terminating the radical reaction chains. Melatonin also enhances the antioxidant potential of the cell by stimulating the synthesis of antioxidant enzymes like superoxide dismutase, glutathione peroxidase and glutathione reductase, and by augmenting glutathione levels. The decline in melatonin production in aged individuals has been suggested as one of the primary contributing factors for the development of age-associated neurodegenerative diseases, e.g., Alzheimer's disease. Melatonin has been shown to be effective in arresting neurodegenerative phenomena seen in experimental models of Alzheimer's disease, Parkinsonism and ischemic stroke. Melatonin preserves mitochondrial homeostasis, reduces free radical generation, e.g., by enhancing mitochondrial glutathione levels, and safeguards proton potential and ATP synthesis by stimulating complex I and IV activities. Therapeutic trials with melatonin have been effective in slowing the progression of Alzheimer's disease but not of Parkinson's disease. Melatonin's efficacy in combating free radical damage in the brain suggests that it may be a valuable therapeutic agent in the treatment of cerebral edema after traumatic brain injury.

Women's sleep in health and disease

A huge amount of knowledge about sleep has accumulated during the last 5 decades following the discovery of rapid eye movement (REM) sleep. Nevertheless, there are numerous areas of considerable ignorance. One of these concerns the particularities of sleep in women. Most basic and clinical studies have been performed in male subjects, and only very recently research groups around the world have addressed women's sleep in health and disease. In this review, we summarize the present knowledge on the influence of oestrogens on the brain and on the distinctive changes of sleep across the menstrual cycle, during pregnancy and menopause. In addition, studies in female rodents are reviewed as well as the knowledge on female peculiarities regarding the interactions between sleep regulation and age-related changes in circadian rhythms. We also address specific aspects of sleep loss and sleep disorders in women. Finally, very recent studies on the sociology of sleep are summarized and future directions in the field are discussed.

Decreased nocturnal synthesis of melatonin in patients with coronary artery disease

In human beings, cardiovascular activity has a distinct circadian variation: Heart rate, blood pressure, and vascular tone decrease at night. Nocturnal cardiovascular blunting is at least partially linked to the autonomic activity and increased risk of cardiac and cerebral events. To assess whether decreased nocturnal melatonin synthesis and secretion in coronary artery disease (CAD), we investigated nocturnal secretion pattern of melatonin in patients with CAD and healthy subjects. The present study performed in 16 patients with angiographically documented CAD (aged 46-71 years) and in nine healthy controls (aged 36-66 years). Blood samples were collected every 2 h between 22:00 and 08:00 h. Melatonin levels were measured with a commercially available radioimmunoassay kit. We found large interindividual variation in the pattern of melatonin secretion in both groups. Patients with CAD secreted less nocturnal melatonin at 02:00, 04:00 and 08:00 h than control subjects (P=0.014, P=0.04 and P=0.025, respectively). Peak and Delta melatonin (peak-lowest melatonin) were found lower in patients with CAD (48.6 [19.1-75.4] vs. 131.4 [67.8-137.2] pg/ml, P=0.006 and 43 [10.5-68.5] vs. 107.6 [55.7-113.1] pg/ml, P=0.002, respectively). Peak time of melatonin secretion was observed earlier in patients with CAD (02:00 h [23:00-02:00 h] vs. 03:45 h [02:00-05:00 h], P=0.04). Our study provides useful and preliminary information about decreased nocturnal melatonin synthesis and release in patients with CAD might help physicians in managing these patients.

Role of melatonin in the induction and maintenance of sleep

Pharmacokinetic studies of melatonin in young and elderly human volunteers, and the measurement of hypnotic effects in chicks under alternate light-dark or permanent light conditions, show that melatonin is a bioprecursor of hypnotic acetyl metabolites produced by the enzymatic acetylation of both melatonin and 2-oxomelatonin under the control of serotonin N-acetyltransferases (NATs), which are present in the pineal gland. The acetyl metabolite of melatonin, which we call carbo2, is an N-acetyl-β-carboline. The electroencephalographs (EEG) architecture of the sleep produced by this compound is similar to thai of physiological sleep, and is characterized by the significant proportion of slow-wave deep sleep and rapid eye movement sleep. This is in sharp contrast to the EEG sleep architecture observed with GABAergic (GABA, γ-aminobutyric acid) compounds. Since insomnia and sleep disorders are believed to be due to a lack of NAT enzymes in the pineal gland, a new therapeutic approach of sleep disorders by administration of such hypnotic acetyl metabolites of melatonin, or synthetic analogs thereof, can be en visaged.

Senescence, sleep, and circadian rhythms

The goal of this review article is to summarize our knowledge and understanding of the overlapping (interdisciplinary) areas of senescence, sleep, and circadian rhythms. Our overview comprehensively (and visually wherever possible), emphasizes the organizational, dynamic, and plastic nature of both sleep and circadian timing system (CTS) during senescent processes in animals and in humans. In this review, we focus on the studies that deal with sleep and circadian rhythms in aged animals and how these studies have closely correlated to and advanced our understanding of similar processes in ageing humans. Our comprehensive summary of various aspects of the existing research on animal and human ageing, both normal and pathological, presented in this review underscores the invaluable advantage of close collaboration between clinicians and basic research scientists and the future challenges inherent in this collaboration. First, our review addresses the common age-related changes that occur in sleep and temporal organization of both animals and humans. Second, we examine the specific modifications that often accompany sleep and CTS during aging. Third, we discuss the clinical epidemiology of sleep dysfunctions during ageing and their current clinical management, both pharmacological and non-pharmacological. Finally, we predict the possible future promises for complementary and alternative medicine (CAM) that pave the way to the emergence of a "Holistic Sleep Medicine" approach to the treatment of sleep disorders in the ageing population. Further studies will provide additional valuable insights into the understanding of both sleep and circadian rhythms during senescence.