Melatonin as a chronobiotic

Melatonin and its atheroprotective effects: a review

Atherosclerosis is a chronic vascular disease in which oxidative stress and inflammation are commonly implicated as major causative factors. Identification of novel strategies that contribute to plaque stabilization or inhibition represents a continuing challenge for the medical community. The evidence from the last decade highlights that melatonin influences the cardiovascular system, but its mechanisms of action have not been definitively clarified. Melatonin has atheroprotective effects by acting on different pathogenic signaling processes; these result from its direct free radical scavenger activity, its indirect antioxidant properties and its anti-inflammatory actions. In this review, we summarize the many pieces of the puzzle which identified molecular targets for prevention and therapy against the atherosclerotic pathogenic processes and we evaluate the data documenting that melatonin treatment has important actions that protect against atherosclerosis and atherosclerosis-related cardiovascular diseases.

Could agomelatine be the ideal antidepressant?

Depressive disorders are a common cause of chronic and recurrent psychiatric dysfunction, constituting the fourth leading cause of global diseases. Depression is associated with a high rate of morbidity and mortality, and is a leading cause of global disability. Despite the effectiveness of most currently available antidepressants, many of them have a number of undesirable side effects. Agomelatine is the first melatonin (MT)(1)/MT(2) agonist having 5-hydroxytryptamine (5-HT)(2C) and 5-HT(2B) antagonist properties and antidepressant activity. Agomelatine is effective in several animal models of depression and anxiety. In addition, three large, multicenter, multinational, placebo-controlled studies and several double-blind, placebo-controlled trials of agomelatine have demonstrated that it is a clinically effective and well-tolerated antidepressant in acute trials. Since currently available antidepressants are not always adequate to cause complete remission of symptoms in severely depressed patients, the superior rate of response achieved with agomelatine in this group of patients underlines its future for clinical use in depressive disorders. In summary, the clinical advantage of agomelatine is attributed to its novel mechanism of action, which helps not only to exert antidepressant action, but also to regulate the sleep-wake rhythm.

Individual variations in serum melatonin levels through time: implications for epidemiologic studies

Melatonin, a marker for the circadian rhythm with serum levels peaking between 2AM and 5AM, is hypothesized to possess anti-cancer properties, making it a mechanistic candidate for the probable carcinogenic effect of circadian rhythm disruption. In order to weigh epidemiologic evidence on the association of melatonin with cancer, we must first understand the laboratory and biological sources of variability in melatonin levels measured in samples. Participants for this methodological study were men enrolled in the Prostate Lung Colorectal and Ovarian Cancer Screening Trial (PLCO). We measured serum melatonin levels over a five year period in 97 individuals to test if melatonin levels are steady over time. The Pearson correlation coefficient between two measures separated by 1 year was 0.87, while the correlation between two measures separated by 5 years was to 0.70. In an additional cross-sectional study of 292 individuals, we used Analysis of Variance to identify differences in melatonin levels between different lifestyle and environmental characteristics. Serum melatonin levels were slightly higher in samples collected from 130 individuals during the winter, (6.36±0.59 pg/ml) than in samples collected from 119 individuals during the summer (4.83±0.62 pg/ml). Serum melatonin levels were lowest in current smokers (3.02±1.25 pg/ml, p = 0.007) compared to never (6.66±0.66 pg/ml) and former (5.59±0.50 pg/ml) smokers whereas BMI did not significantly affect serum melatonin levels in this study. In conclusion, the high 5 year correlation of melatonin levels implies that single measurements may be used to detect population level associations between melatonin and risk of cancer. Furthermore, our results reiterate the need to record season of sample collection, and individual characteristics in order to maximize study power and prevent confounding.

The rat oocyte synthesises melatonin

Melatonin (N-acetyl-5-methoxytryptamine) is an indoleamine originally identified in the pineal gland, where it is synthesised enzymatically from serotonin (5-hydroxytryptamine) by the sequential action of arylalkylamine N-acetyltransferase (AANAT) and acetylserotonin O-methyltransferase (ASMT; also known as hydroxyindole O-methyltransferase). Melatonin directly affects ovarian functions and previous studies have suggested that melatonin is synthesised in the ovary. In the present study, we examined whether AANAT and ASMT are expressed in the adult rat ovary. Reverse transcription-polymerase chain reaction analyses demonstrated that both AANAT and ASMT mRNAs are expressed in the ovary. Western blotting for AANAT protein showed that the ovary, like the pineal gland, contains this enzymatic protein with a molecular mass of 24kDa. Immunohistochemistry revealed that the AANAT protein is localised to the oocyte, corpus luteum and medulla, including mast cells. AANAT protein was found in oocytes at all stages of follicular development, and its levels in oocytes increased progressively throughout follicular development. Furthermore, isolated oocytes metabolised exogenous serotonin to melatonin. These findings demonstrate that melatonin is synthesised from serotonin in oocytes. Melatonin synthesised in the oocyte may be implicated in its own growth or maturation, for example, by acting as a calmodulin antagonist or an antioxidant.

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.

Urban-like night illumination reduces melatonin release in European blackbirds (Turdus merula): implications of city life for biological time-keeping of songbirds

INTRODUCTION

Artificial light-at-night is known to affect a broad array of behaviours and physiological processes. In urbanized bird species, light-at-night advances important biological rhythms such as daily cycles of activity/rest and timing of reproduction, but our knowledge of the underlying physiological mechanisms is limited. Given its role as chronobiological signal, melatonin is a strong candidate for mediating the effects of light-at-night.

RESULTS

We exposed urban and rural European blackbirds (Turdus merula) to two light treatments equal in photoperiod but with different light intensities at night. The control group was exposed to 0.0001 lux (almost darkness), while the experimental group was exposed to 0.3 lux at night, simulating conditions recorded previously on free-living urban blackbirds. We obtained diel profiles of plasma melatonin for all birds in summer (July) and winter (January), while simultaneously recording locomotor activity. Daily patterns of melatonin concentrations were clearly affected by light-at-night in both seasons. In winter, melatonin concentrations of light-at-night birds were lower in the early and late night than in those of birds kept in darkness. In summer, melatonin concentrations of the light-at-night birds were lower through all night compared to birds kept in darkness. Locomotor activity in light-at-night birds was overall higher than in control individuals, both during the day and at night, and it increased sharply before dawn. In winter, the amount of activity before dawn in the light-at-night group correlated with changes in melatonin from midnight to late night: the greater the decrease in melatonin, the greater the amount of pre-dawn activity. Urban and rural birds responded similarly to light-at-night with respect to melatonin, but differed in their behaviour, with rural birds showing more locomotor activity than urban counterparts.

CONCLUSIONS

This study points to reduced melatonin release at night as a potential physiological mechanism underlying the advanced onset of morning activity of urbanized birds. Based on the pattern of melatonin secretion, we suggest that birds responded to light-at-night as if they were exposed to a longer day than birds kept under dark nights.

A molecular and chemical perspective in defining melatonin receptor subtype selectivity

Melatonin is primarily synthesized and secreted by the pineal gland during darkness in a normal diurnal cycle. In addition to its intrinsic antioxidant property, the neurohormone has renowned regulatory roles in the control of circadian rhythm and exerts its physiological actions primarily by interacting with the G protein-coupled MT₁ and MT₂ transmembrane receptors. The two melatonin receptor subtypes display identical ligand binding characteristics and mediate a myriad of signaling pathways, including adenylyl cyclase inhibition, phospholipase C stimulation and the regulation of other effector molecules. Both MT₁ and MT₂ receptors are widely expressed in the central nervous system as well as many peripheral tissues, but each receptor subtype can be linked to specific functional responses at the target tissue. Given the broad therapeutic implications of melatonin receptors in chronobiology, immunomodulation, endocrine regulation, reproductive functions and cancer development, drug discovery and development programs have been directed at identifying chemical molecules that bind to the two melatonin receptor subtypes. However, all of the melatoninergics in the market act on both subtypes of melatonin receptors without significant selectivity. To facilitate the design and development of novel therapeutic agents, it is necessary to understand the intrinsic differences between MT₁ and MT₂ that determine ligand binding, functional efficacy, and signaling specificity. This review summarizes our current knowledge in differentiating MT₁ and MT₂ receptors and their signaling capacities. The use of homology modeling in the mapping of the ligand-binding pocket will be described. Identification of conserved and distinct residues will be tremendously useful in the design of highly selective ligands.

Sleep, its regulation and possible mechanisms of sleep disturbances

The state of sleep consists of different phases that proceed in successive, tightly regulated order through the night forming a physiological program, which for each individual is different but stabile from one night to another. Failure to accomplish this program results in feeling of unrefreshing sleep and tiredness in the morning. The program core is constructed by genetic factors but regulated by circadian rhythm and duration and intensity of day time brain activity. Many environmental factors modulate sleep, including stress, health status and ingestion of vigilance-affecting nutrients or medicines (e.g. caffeine). Acute sleep loss results in compromised cognitive performance, memory deficits, depressive mood and involuntary sleep episodes during the day. Moreover, prolonged sleep curtailment has many adverse health effects, as evidenced by both epidemiological and experimental studies. These effects include increased risk for depression, type II diabetes, obesity and cardiovascular diseases. In addition to voluntary restriction of sleep, shift work, irregular working hours, jet lag and stress are important factors that induce curtailed or bad quality sleep and/or insomnia. This review covers the current theories on the function of normal sleep and describes current knowledge on the physiologic effects of sleep loss. It provides insights into the basic mechanisms of the regulation of wakefulness and sleep creating a theoretical background for understanding different disturbances of sleep.

A meta-analytic approach to quantify the dose-response relationship between melatonin and core temperature

A melatonin-mediated reduction in body temperature could be useful as a "pre-cooling" intervention for athletes, as long as the melatonin dose is optimised so that substantial soporific effects are not induced. However, the melatonin-temperature dose-response relationship is unclear in humans. Individual studies have involved small samples of different sexes and temperature measurement sites. Therefore, we meta-analysed the effects of exogenous melatonin on body core temperature to quantify the dose-response relationship and to explore the influence of moderating variables such as sex and measurement site. Following a literature search, we meta-analysed 30 data-sets involving 193 participants and 405 ingestions of melatonin. The outcome was the mean difference (95 % confidence limits) in core temperature between the melatonin and placebo-controlled conditions in each study, weighted by the reciprocal of each standard error of the difference. The mean (95 % confidence interval) pooled reduction in core temperature was found to be 0.21 °C (0.18-0.24 °C). The dose-response relationship was found to be logarithmic (P < 0.0001). Doses of 0-5 mg reduced temperature by ~0.00-0.22 °C. Any further reductions in temperature were negligible with doses >5 mg. The pooled mean reduction was 0.13 °C (0.05-0.20 °C) for oral temperature vs 0.26 °C (0.20-0.32 °C) for tympanic and 0.22 °C (0.19-0.25 °C) for rectal temperature. In conclusion, our meta-regression revealed a logarithmic dose-response relationship between melatonin and its temperature lowering effects. A 5-mg dose of melatonin lowered core temperature by ~0.2 °C. Higher doses do not substantially increase this hypothermic effect and may induce greater soporific effects.

A meta-analytic approach to quantify the dose-response relationship between melatonin and core temperature

A melatonin-mediated reduction in body temperature could be useful as a "pre-cooling" intervention for athletes, as long as the melatonin dose is optimised so that substantial soporific effects are not induced. However, the melatonin-temperature dose-response relationship is unclear in humans. Individual studies have involved small samples of different sexes and temperature measurement sites. Therefore, we meta-analysed the effects of exogenous melatonin on body core temperature to quantify the dose-response relationship and to explore the influence of moderating variables such as sex and measurement site. Following a literature search, we meta-analysed 30 data-sets involving 193 participants and 405 ingestions of melatonin. The outcome was the mean difference (95 % confidence limits) in core temperature between the melatonin and placebo-controlled conditions in each study, weighted by the reciprocal of each standard error of the difference. The mean (95 % confidence interval) pooled reduction in core temperature was found to be 0.21 °C (0.18-0.24 °C). The dose-response relationship was found to be logarithmic (P < 0.0001). Doses of 0-5 mg reduced temperature by ~0.00-0.22 °C. Any further reductions in temperature were negligible with doses >5 mg. The pooled mean reduction was 0.13 °C (0.05-0.20 °C) for oral temperature vs 0.26 °C (0.20-0.32 °C) for tympanic and 0.22 °C (0.19-0.25 °C) for rectal temperature. In conclusion, our meta-regression revealed a logarithmic dose-response relationship between melatonin and its temperature lowering effects. A 5-mg dose of melatonin lowered core temperature by ~0.2 °C. Higher doses do not substantially increase this hypothermic effect and may induce greater soporific effects.

Effect of Light at Night on oxidative stress markers in Golden spiny mice (Acomys russatus) liver

Light at Night (LAN) suppresses melatonin (MLT) production, and effects metabolism, hormone secretion, gene expression and enzyme activity. Changes in antioxidant enzymes glutathione peroxidase (GPx) and superoxide dismutase (SOD), can be used as an indication for oxidative stress level. We assayed activity and expression of these enzymes in the liver of Acomys russatus exposed to LAN and treated with MLT. Short day (SD)-acclimated A. russatus, was exposed to 30min of LAN for two, seven or 21 nights. MLT impact was assessed simultaneously with two and seven nights of LAN exposure. GPx and SOD activities were measured. Gpx1 expression was evaluated by RT-PCR. There was a significant increase in GPx activity following LAN exposure for all acclimation durations, GPx activity was elevated after two nights of LAN and MLT treatment, Gpx1 expression was elevated by MLT after seven nights of LAN. SOD activity increased after two nights of LAN in MLT-treated A. russatus, GPx activity increased with the duration of LAN acclimation, indicating changes in liver redox status. Our results suggest that LAN is a stressor that influences oxidative stress. As in the other studies, MLT increases antioxidant activities, presumably attenuating stress response, in order to restore homeostasis.

The times they're a-changing: effects of circadian desynchronization on physiology and disease

Circadian rhythms are endogenous and need to be continuously entrained (synchronized) with the environment. Entrainment includes both coupling internal oscillators to external periodic changes as well as synchrony between the central clock and peripheral oscillators, which have been shown to exhibit different phases and resynchronization speed. Temporal desynchronization induces diverse physiological alterations that ultimately decrease quality of life and induces pathological situations. Indeed, there is a considerable amount of evidence regarding the deleterious effect of circadian dysfunction on overall health or on disease onset and progression, both in human studies and in animal models. In this review we discuss the general features of circadian entrainment and introduce diverse experimental models of desynchronization. In addition, we focus on metabolic, immune and cognitive alterations under situations of acute or chronic circadian desynchronization, as exemplified by jet-lag and shiftwork schedules. Moreover, such situations might lead to an enhanced susceptibility to diverse cancer types. Possible interventions (including light exposure, scheduled timing for meals and use of chronobiotics) are also discussed.

Bright light therapy in Parkinson's disease: an overview of the background and evidence

Sleep disorders are common in Parkinson's disease (PD) and seem to be strongly associated with depression. It has been suggested that sleep disorders as well as depression are caused by a disturbed circadian rhythm. Indeed, PD patients are prone to misalignment of their circadian rhythm due to various factors, and many patients with PD display a phase advance of their circadian rhythm. Current treatment options for sleep disorders and depression in patients with PD are limited and can have serious side effects; alternative treatments are therefore badly needed. Bright light therapy (BLT) restores circadian rhythmicity effectively in mood- and sleep-disturbed patients without PD. The few studies that focused on the efficacy of BLT in patients with PD demonstrated a positive effect of BLT not only on sleep and mood but also on motor function. More research on the neurobiology and efficacy of BLT in PD is warranted.

Cadmium as an endocrine disruptor: correlation with anterior pituitary redox and circadian clock mechanisms and prevention by melatonin

To examine the effect of a low dose of cadmium (Cd) as an endocrine disruptor, male Wistar rats received CdCl2 (5ppm Cd) in drinking water or drinking water alone. After 1 month, the rats were euthanized at one of six time intervals around the clock and the 24-h pattern of adenohypophysial prolactin (PRL) synthesis and release, lipid peroxidation, and redox enzyme and metallothionein (MT) gene expression was examined. Cd suppressed 24-h rhythmicity in expression of the PRL gene and in circulating PRL by increasing them at early photophase only, in correlation with an augmented pituitary lipid peroxidation and redox enzyme expression. CdCl2 treatment effectively disrupted the 24-h variation in expression of every pituitary parameter tested except for MT-3. In a second experiment the effect of melatonin (3μg/ml in drinking water) was assessed at early photophase, the time of maximal endocrine-disrupting effect of Cd. Melatonin treatment blunted the effect of Cd on PRL synthesis and release, decreased Cd-induced lipid peroxidation, and counteracted the effect of Cd on expression of most redox enzymes. A third experiment was performed to examine whether melatonin could counteract Cd-induced changes in the 24-h pattern of pituitary circadian clock gene expression and plasma PRL, luteinizing hormone (LH), thyrotropin (TSH), and corticosterone levels. Rats receiving CdCl2 exhibited a suppressed daily rhythm of Clock expression and a significant disruption in daily rhythms of pituitary Bmal1, Per1, Per2, Cry1, and Cry2. The coadministration of melatonin restored rhythmicity in Clock and Bmal1 expression but shifted the maxima in pituitary Per1, Cry1, and Cry2 expression to the scotophase. Melatonin also counteracted the effect of Cd on 24-h rhythmicity of circulating PRL, LH, TSH, and corticosterone. The results highlight the occurrence of a significant endocrine disruptor effect of a low dose of Cd. Generally melatonin counteracted the effects of Cd and ameliorated partially the circadian disruption caused by the pollutant.

Geographical distribution of adolescent body height with respect to effective day length in Japan: an ecological analysis

The height of Japanese youth raised in the northern region tends to be greater than that of youth raised in the southern region; therefore, a geographical gradient in youth body height exists. Although this gradient has existed for about 100 years, the reasons for it remain unclear. Consideration of the nutritional improvement, economic growth, and intense migration that has occurred in this period indicates that it is probably the result of environmental rather than nutritional or genetic factors. To identify possible environmental factors, ecological analysis of prefecture-level data on the body size of 8- to 17-year-old youth averaged over a 13-year period (1996 to 2008) and Japanese mesh climatic data on the climatic variables of temperature, solar radiation, and effective day length (duration of photoperiod exceeding the threshold of light intensity) was performed. The geographical distribution of the standardized height of Japanese adolescents was found to be inversely correlated to a great extent with the distribution of effective day length at a light intensity greater than 4000 lx. The results of multiple regression analysis of effective day length, temperature, and weight (as an index of food intake) indicated that a combination of effective day length and weight was statistically significant as predictors of height in early adolescence; however, only effective day length was statistically significant as a predictor of height in late adolescence. Day length may affect height by affecting the secretion of melatonin, a hormone that inhibits sexual and skeletal maturation, which in turn induces increases in height. By affecting melatonin production, regional differences in the duration of the photoperiod may lead to regional differences in height. Exposure to light intensity greater than 4000 lx appears to be the threshold at which light intensity begins to affect the melatonin secretion of humans who spend much of their time indoors.

DSM-IV psychiatric comorbidity according to symptoms of insomnia: a nationwide sample of Korean adults

PURPOSE

The diagnosis of insomnia is based on the presence of four different symptoms: difficulty in initiating sleep (DIS), difficulty in maintaining sleep (DMS), early morning awakening (EMA), and non-restorative sleep (NRS). This study investigated the differences in sociodemographic correlates and psychiatric comorbidity between the four symptoms of insomnia in the general population of South Korea.

METHODS

A sample of the population aged 18-64 (N = 6,510) was questioned using a face-to-face interview. Insomnia was defined as having at least one of the four following symptoms three or more times per week: DIS, DMS, EMA, and NRS. Psychiatric disorders were evaluated using the Korean version of Composite International Diagnostic Interview. Logistic regression analysis was used to test each of the sleep outcomes (DIS, DMS, EMA, or NRS) for an association with sociodemographic and clinical variables.

RESULTS

The prevalence of DIS, DMS, EMA, and NRS were 7.9 % (95 % CI 6.6-9.5 %), 7.9 % (95 % CI 6.5-9.6 %), 4.9 % (95 % CI 3.9-6.0 %), and 14.8 % (95 % CI 12.6-17.4 %), respectively. The overall prevalence of insomnia was 19.0 % (95 % CI 16.1-22.2 %). Being separated, divorced, or widowed, being single, having a part-time job, having a psychiatric illness, and having a physical illness were all significantly related to insomnia. Older age also increased the risk of DMS and EMA, and younger age was a risk factor for NRS. The presence of most psychiatric disorders was significantly related to insomnia. However, the relationship between the psychiatric illness and each insomnia symptom varied and was dependent on the insomnia symptom.

CONCLUSIONS

Most psychiatric disorders were significantly associated with each insomnia symptom in different ways. Differences in sociodemographic and clinical correlates between the four insomnia symptoms implied the heterogeneous characteristics of insomnia as defined by the current diagnostic criteria.

Nightshift work job exposure matrices and urinary 6-sulfatoxymelatonin levels among healthy Chinese women

OBJECTIVE

Six-sulfatoxymelatonin (aMT6s) is a primary urinary metabolite of melatonin. We examined the association between aMT6s levels and shift work estimated by a job exposure matrix (JEM) among healthy participants of the Shanghai Women's Health Study.

METHODS

Creatinine-adjusted aMT6s levels were measured in the urine samples of 300 women and related to JEM shift work categories.

RESULTS

Adjusted geometric means of aMT6s levels from urine samples collected before 08:00 hours were lower among persons holding nighttime shift work jobs. The adjusted aMT6s levels (ng/mg creatinine) were 8.36 [95% confidence intervals (95% CI) 4.47-15.6], 6.37 (95% CI 3.53-11.5), 6.20 (95% CI 3.33-11.5), 3.81 (95% CI 2.02-7.19), and 3.70 (95% CI 1.92-7.11) from the lowest (never held a shift work job) to the highest (current job likely involved all-night shift work) shift work JEM scores (P=0.05).

CONCLUSION

Our results indicate that nightshift work JEM scores were significantly and inversely associated with aMT6s levels in early morning spot urine samples collected between 07:00-08:00 hours.

Repeated melatonin supplementation improves sleep in hypertensive patients treated with beta-blockers: a randomized controlled trial

STUDY OBJECTIVES

In the United States alone, approximately 22 million people take beta-blockers chronically. These medications suppress endogenous nighttime melatonin secretion, which may explain a reported side effect of insomnia. Therefore, we tested whether nightly melatonin supplementation improves sleep in hypertensive patients treated with beta-blockers.

DESIGN

Randomized, double-blind, placebo-controlled, parallel-group design.

SETTING

Clinical and Translational Research Center at Brigham and Women's Hospital, Boston.

PATIENTS

Sixteen hypertensive patients (age 45-64 yr; 9 women) treated with the beta-blockers atenolol or metoprolol.

INTERVENTIONS

Two 4-day in-laboratory admissions including polysomnographically recorded sleep. After the baseline assessment during the first admission, patients were randomized to 2.5 mg melatonin or placebo (nightly for 3 weeks), after which sleep was assessed again during the second 4-day admission. Baseline-adjusted values are reported. One patient was removed from analysis because of an unstable dose of prescription medication.

MEASUREMENTS AND RESULTS

In comparison with placebo, 3 weeks of melatonin supplementation significantly increased total sleep time (+36 min; P = 0.046), increased sleep efficiency (+7.6%; P = 0.046), and decreased sleep onset latency to Stage 2 (-14 min; P = 0.001) as assessed by polysomnography. Compared with placebo, melatonin significantly increased Stage 2 sleep (+41 min; P = 0.037) but did not significantly change the durations of other sleep stages. The sleep onset latency remained significantly shortened on the night after discontinuation of melatonin administration (-25 min; P = 0.001), suggesting a carryover effect.

CONCLUSION

n hypertensive patients treated with beta-blockers, 3 weeks of nightly melatonin supplementation significantly improved sleep quality, without apparent tolerance and without rebound sleep disturbance during withdrawal of melatonin supplementation (in fact, a positive carryover effect was demonstrated). These findings may assist in developing countermeasures against sleep disturbances associated with beta-blocker therapy.

CLINICAL TRIAL INFORMATION

his study is registered with ClinicalTrials.gov, identifier: NCT00238108; trial name: Melatonin Supplements for Improving Sleep in Individuals with Hypertension; URL: http://www.clinicaltrials.gov/ct2/show/NCT00238108.

[Chronodisruption and ageing]

Modern life leads to a more active nocturnal lifestyle, reduced sleep hours and sometimes abrupt shifts across time zones (such as jet lag and shift work) that generate chronodisruption (CD) which can result in premature ageing. CD is defined as a significant disturbance of the internal temporal order of biochemical, physiological and behavioural circadian rhythms. Epidemiological studies show that CD induced by shift work, chronic jet lag, social jet lag and excessive exposure of bright light at night is associated with an increased incidence of metabolic syndrome, cardiovascular disease, cognitive and affective impairment, sleep disorders, some cancers and premature ageing. CD may be the result of disturbances in different components of the circadian system (central pacemaker and peripheral oscillators, inputs to central clock, mainly due to visual deficiencies, and output signals from the pacemaker and oscillators). Exposure to different synchronizers (light, meal times, physical and social activities) with a regular pattern results in a chronoenhacement that can prevent age-related CD.

Circadian disruption and remedial interventions: effects and interventions for jet lag for athletic peak performance

Jet lag has potentially serious deleterious effects on performance in athletes following transmeridian travel, where time zones are crossed eastwards or westwards; as such, travel causes specific effects related to desynchronization of the athlete's internal body clock or circadian clock. Athletes are particularly sensitive to the effects of jet lag, as many intrinsic aspects of sporting performance show a circadian rhythm, and optimum competitive results require all aspects of the athlete's mind and body to be working in tandem at their peak efficiency. International competition often requires transmeridian travel, and competition timings cannot be adjusted to suit individual athletes. It is therefore in the interest of the individual athlete and team to understand the effects of jet lag and the potential adaptation strategies that can be adopted. In this review, we describe the underlying genetic and physiological mechanisms controlling the circadian clock and its inherent ability to adapt to external conditions on a daily basis. We then examine the fundamentals of the various adaptation stimuli, such as light, chronobiotics (e.g. melatonin), exercise, and diet and meal timing, with particular emphasis on their suitability as strategies for competing athletes on the international circuit. These stimuli can be artificially manipulated to produce phase shifts in the circadian rhythm to promote adaptation in the optimum direction, but care must be taken to apply them at the correct time and dose, as the effects produced on the circadian rhythm follow a phase-response curve, with pronounced shifts in direction at different times. Light is the strongest realigning stimulus and careful timing of light exposure and avoidance can promote adjustment. Chronobiotics such as melatonin can also be used to realign the circadian clock but, as well as timing and dosage issues, there are also concerns as to its legal status in different countries and with the World Anti-Doping Agency. Experimental data concerning the effects of food intake and exercise timing on jet lag is limited to date in humans, and more research is required before firm guidelines can be stated. All these stimuli can also be used in pre-flight adaptation strategies to promote adjustment in the required direction, and implementation of these is described. In addition, the effects of individual variability at the behavioural and genetic levels are also discussed, along with the current limitations in assessment of these factors, and we then put forward three case studies, as examples of practical applications of these strategies, focusing on adaptations to travel involving competition in the Rugby Sevens World Cup and the 2016 Summer Olympics in Rio de Janeiro, Brazil. Finally, we provide a list of practice points for optimal adaptation of athletes to jet lag.

Neurobiology, pathophysiology, and treatment of melatonin deficiency and dysfunction

Melatonin is a highly pleiotropic signaling molecule, which is released as a hormone of the pineal gland predominantly during night. Melatonin secretion decreases during aging. Reduced melatonin levels are also observed in various diseases, such as types of dementia, some mood disorders, severe pain, cancer, and diabetes type 2. Melatonin dysfunction is frequently related to deviations in amplitudes, phasing, and coupling of circadian rhythms. Gene polymorphisms of melatonin receptors and circadian oscillator proteins bear risks for several of the diseases mentioned. A common symptom of insufficient melatonin signaling is sleep disturbances. It is necessary to distinguish between symptoms that are curable by short melatonergic actions and others that require extended actions during night. Melatonin immediate release is already effective, at moderate doses, for reducing difficulties of falling asleep or improving symptoms associated with poorly coupled circadian rhythms, including seasonal affective and bipolar disorders. For purposes of a replacement therapy based on longer-lasting melatonergic actions, melatonin prolonged release and synthetic agonists have been developed. Therapies with melatonin or synthetic melatonergic drugs have to consider that these agents do not only act on the SCN, but also on numerous organs and cells in which melatonin receptors are also expressed.

Complete absence of evening melatonin increase in tetraplegics

Individuals with a spinal cord injury (SCI), especially with tetraplegia, experience poor sleep quality, and this may be related to impaired control of circadian rhythmicity. Here, we examined the evening onset of melatonin secretion, an important hormone for the initiation of sleep, in people with a complete cervical (tetraplegia) and thoracic (paraplegia) SCI, and age- and sex-matched able-bodied control participants. Multiple samples of salivary melatonin were obtained during the evening hours and analyzed by ELISA methods in 10 control partcipants, 9 individuals with paraplegia, and 6 individuals with tetraplegia. Sleep quality was assessed using questionnaires. Interactive effects of group and time were found for melatonin levels (P=0.022). In the control and paraplegia groups, the mean melatonin level increased significantly from 2.59 ± 1.04 and 4.28 ± 3.28 pg/ml at 7 PM to 10.62 ± 4.59 and 13.10 ± 7.39 pg/ml at 11 PM, respectively (P<0.001). In the tetraplegia group, melatonin level was 5.25 ± 3.72 at 7 PM but only 2.41 ± 1.25 pg/ml at 11 PM (P>0.05). Decreased sleep quality was more prevalent in individuals with tetraplegia (83%) and paraplegia (75%) compared with controls (20%; P=0.02). Unlike in the control and paraplegia groups, the evening increase in melatonin concentration was completely absent in the tetraplegia group. This provides biological insight into sleep regulation in humans and provides better understanding of the poor sleep quality in people with tetraplegia.

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.

Effects of morning melatonin administration on electroencephalographic theta to alpha power ratio in reproductive versus postmenopausal healthy female volunteers

OBJECTIVE

The aim of the present study was to investigate the effect of exogenous morning melatonin administration on the electroencephalogram of reproductive versus postmenopausal women.

METHODS

Twenty-six female, reproductive and postmenopausal healthy volunteers were randomly assigned to receive melatonin or placebo at 9:00 in the morning. Twelve electroencephalographic recording sessions were performed before the intake of melatonin or placebo and at 15, 30, 45, 60, 75, 90, 120, 150, 180, 240, and 300 min. Theta to alpha ratios for every subject, channel and session were mathematically processed to yield the logarithm (base 10) of the spectral (theta power)/(alpha power) ratio for the 12 electroencephalographic sessions, weighted to the baseline ratio (LwRs). The LwRs were compared between melatonin groups (reproductive versus postmenopausal women) and also between melatonin and control groups.

RESULTS

Data from 24 women were analyzed. The LwRs in the reproductive women were significantly lower than the LwRs in postmenopausal women at 60, 180, 240 and 300 min after melatonin consumption (p=0.007, 0.041, 0.008 and 0.040 respectively). In reproductive women, the LwRs of subjects who received melatonin were significantly lower compared to their controls at 60, 240 and 300 min after melatonin or placebo intake (p=0.005, 0.006 and 0.019 respectively). In postmenopausal women, no significant differences in the LwRs were calculated for any time point between melatonin and control groups.

CONCLUSIONS

Our results show that morning melatonin administration produces no electroencephalographic changes in postmenopausal women. In contrast, electroencephalographic changes suggesting a possible awaking effect were observed in reproductive women.

Relaxation drinks and their use in adolescents

OBJECTIVES

A new class of beverages called relaxation drinks advertises calming effects and an easy way to wind down when life gets stressful. This article examines these drinks in the context of their use in adolescents.

METHODS

A review of the literature relevant to relaxation drinks and their functional ingredients was conducted.

RESULTS

The beverages contain ingredients such as melatonin, valerian, kava, tryptophan, and other products traditionally thought to play a role in sleep, sedation, or neurocognitive function. Studies of the efficacy and safety of these supplements are limited and many have significant methodological limitations. Despite appropriate warnings placed on the labels of relaxation drinks, marketing is cleverly designed to appeal to young consumers and often evokes the experiences produced by alcohol and drug use.

CONCLUSION

Although moderate consumption of these beverages by healthy individuals is likely safe, an objective reduction in stress is improbable and associated adverse effects are possible.

Therapeutic potential of melatonin and its analogs in Parkinson's disease: focus on sleep and neuroprotection

Sleep disorders constitute major nonmotor features of Parkinson's disease (PD) that have a substantial effect on patients' quality of life and can be related to the progression of the neurodegenerative disease. They can also serve as preclinical markers for PD, as it is the case for rapid eye movement (REM)-associated sleep behavior disorder (RBD). Although the etiology of sleep disorders in PD remains undefined, the assessment of the components of the circadian system, including melatonin secretion, could give therapeutically valuable insight on their pathophysiopathology. Melatonin is a regulator of the sleep/wake cycle and also acts as an effective antioxidant and mitochondrial function protector. A reduction in the expression of melatonin MT(1) and MT(2) receptors has been documented in the substantia nigra of PD patients. The efficacy of melatonin for preventing neuronal cell death and for ameliorating PD symptoms has been demonstrated in animal models of PD employing neurotoxins. A small number of controlled trials indicate that melatonin is useful in treating disturbed sleep in PD, in particular RBD. Whether melatonin and the recently developed melatonergic agents (ramelteon, tasimelteon, agomelatine) have therapeutic potential in PD is also discussed.

Melatonin for non-respiratory sleep disorders in visually impaired children

BACKGROUND

Exogenous melatonin helps in regulating the circadian rhythm and is widely used for the management of sleep disorders in visually impaired children.

OBJECTIVES

The aim of the review was to assess melatonin therapy for treatment of non-respiratory sleep disorders in visually impaired children, with regard to improvement in sleep habit, sleep scheduling and sleep maintenance, when compared with placebo or no treatment.

SEARCH METHODS

We searched the following databases between February 2011 and July 2011: the Cochrane Central Register of Controlled Trials (CENTRAL) 2011(1) searched on 4th February 2011; MEDLINE (1950 to June Week 3, 2011) searched on 20th June 2011; EMBASE (1980 to June Week 4, 2011) searched on 7th July 2011; CINAHL (1937 to 21 September 2011); the metaRegister of Controlled Trials (this includes ClinicalTrial.gov) searched 20 July 2011, and reference lists of papers identified after initial screening.

SELECTION CRITERIA

We planned to include randomized controlled trials (RCTs) and quasi-RCTs, including cross-over studies. Treatment would be exogenous melatonin. Control groups could be placebo, other medication for sleep disorders or no treatment. Outcomes sought were improved sleep with regard to timing and duration, quality of life and adverse events.

DATA COLLECTION AND ANALYSIS

Three review authors independently assessed trials for inclusion in the review.

MAIN RESULTS

We did not find any studies fulfilling the inclusion criteria, therefore no outcome data are reported.We identified nine studies after initial screening and, after further evaluation, we excluded these. The excluded studies involved a total of 163 individuals aged two years to 18 years. We excluded studies for three main reasons: they were non-randomized or case series studies, they were studies of people over 18 years of age or even where the study was randomised, the study population was mixed and results pertaining to the visually impaired cohort could not be independently evaluated. No significant adverse effects of melatonin were reported in these excluded studies.

AUTHORS' CONCLUSIONS

There is currently no high quality data to support or refute the use of melatonin for sleep disorders in visually impaired children. Placebo-controlled trials examining important clinical outcomes such as sleep quality, sleep latency, duration of sleep and night-time awakenings are needed. As the numbers of children meeting study inclusion criteria are likely to be low at individual sites, multicentre collaboration between developmental paediatricians, sleep physicians and other health care professionals is essential to achieve sufficient sample size for controlled studies. Such collaboration would help facilitate local recruitment at multiple sites, with study oversight being provided by paediatricians with expertise in sleep disorders. Participation of collaborators with experience in evidence-based practice research is also desirable due to the lack of protocols on melatonin therapy in the target population.

A survey of molecular details in the human pineal gland in the light of phylogeny, structure, function and chronobiological diseases

The human pineal gland is a neuroendocrine transducer that forms an integral part of the brain. Through the nocturnally elevated synthesis and release of the neurohormone melatonin, the pineal gland encodes and disseminates information on circadian time, thus coupling the outside world to the biochemical and physiological internal demands of the body. Approaches to better understand molecular details behind the rhythmic signalling in the human pineal gland are limited but implicitly warranted, as human chronobiological dysfunctions are often associated with alterations in melatonin synthesis. Current knowledge on melatonin synthesis in the human pineal gland is based on minimally invasive analyses, and by the comparison of signalling events between different vertebrate species, with emphasis put on data acquired in sheep and other primates. Together with investigations using autoptic pineal tissue, a remnant silhouette of premortem dynamics within the hormone's biosynthesis pathway can be constructed. The detected biochemical scenario behind the generation of dynamics in melatonin synthesis positions the human pineal gland surprisingly isolated. In this neuroendocrine brain structure, protein-protein interactions and nucleo-cytoplasmic protein shuttling indicate furthermore a novel twist in the molecular dynamics in the cells of this neuroendocrine brain structure. These findings have to be seen in the light that an impaired melatonin synthesis is observed in elderly and/or demented patients, in individuals affected by Alzheimer's disease, Smith-Magenis syndrome, autism spectrum disorder and sleep phase disorders. Already, recent advances in understanding signalling dynamics in the human pineal gland have significantly helped to counteract chronobiological dysfunctions through a proper restoration of the nocturnal melatonin surge.

Shift work: coping with the biological clock

The internal circadian clock adapts slowly, if at all, to rapid transitions between different shift schedules. This leads to misalignment (desynchrony) of rhythmic physiological systems, such as sleep, alertness, performance, metabolism and the hormones melatonin and cortisol, with the imposed work-rest schedule. Consequences include sleep deprivation and poor performance. Clock gene variants may influence tolerance of sleep deprivation. Shift work is associated with an increased risk of major disease (heart disease and cancer) and this may also, at least in part, be attributed to frequent circadian desynchrony. Abnormal metabolism has been invoked as a contributory factor to the increased risk of heart disease. There is recent evidence for an increased risk of certain cancers, with hypothesized causal roles of light at night, melatonin suppression and circadian desynchrony. Various strategies exist for coping with circadian desynchrony and for hastening circadian realignment (if desired). The most important factor in manipulating the circadian system is exposure to and/or avoidance of bright light at specific times of the 'biological night'.

Melatonin: both master clock output and internal time-giver in the circadian clocks network

Daily rhythms in physiological and behavioral processes are controlled by a network of circadian clocks, reset by inputs and delivering circadian signals to the brain and peripheral organs. In mammals, at the top of the network is a master clock located in the suprachiasmatic nuclei (SCN) of the hypothalamus, mainly reset by ambient light. The nocturnal synthesis and release of melatonin by the pineal gland are tightly controlled by the SCN clock and inhibited by light exposure. Several roles of melatonin in the circadian system have been identified. As a major hormonal output, melatonin distributes temporal cues generated by the SCN to the multitude of tissue targets expressing melatonin receptors. In some target structures, like the Pars tuberalis of the adenohypophysis, these melatonin signals can drive daily rhythmicity that would otherwise be lacking. In other target structures, melatonin signals are used for the synchronization (i.e., adjustment of the timing of existing oscillations) of peripheral oscillators, such as the fetal adrenal gland. Due to the expression of melatonin receptors in the SCN, endogenous melatonin is also able to feedback onto the master clock, although its physiological significance needs further characterization. Of note, pharmacological treatment with exogenous melatonin can synchronize the SCN clock. From a clinical point of view, provided that the subject is not exposed to light at night, the daily profile of circulating melatonin provides a reliable estimate of the timing of the human SCN. During the past decade, a number of melatonin agonists have been developed for treating circadian, psychiatric and sleep disorders. These drugs may target the SCN for improving circadian timing or act indirectly at some downstream level of the circadian network to restore proper internal synchronization.

Scheduled Food Hastens Re-Entrainment More Than Melatonin Does after a 6-h Phase Advance of the Light-Dark Cycle in Rats

Circadian desynchrony occurs when individuals are exposed to abrupt phase shifts of the light-dark cycle, as in jet lag. For reducing symptoms and for speeding up resynchronization, several strategies have been suggested, including scheduled exercise, exposure to bright light, drugs, and especially exogenous melatonin administration. Restricted feeding schedules have shown to be powerful entraining signals for metabolic and hormonal daily cycles, as well as for clock genes in tissues and organs of the periphery. This study explored in a rat model of jet lag the contribution of exogenous melatonin or scheduled feeding on the re-entrainment speed of spontaneous general activity and core temperature after a 6-h phase advance of the light-dark cycle. In a first phase, the treatment was scheduled for 5 days prior to the phase shift, while in a second stage, the treatment was simultaneous with the phase advance of the light-dark cycle. Melatonin administration and especially scheduled feeding simultaneous with the phase shift improved significantly the re-entrainment speed. The evaluation of the free-running activity and temperature following the 5-day treatment proved that both exogenous melatonin and specially scheduled feeding accelerated re-entrainment of the SCN-driven general activity and core temperature, respectively, with 7, 5 days ( p < 0.01) and 3, 3 days ( p < 0.001). The present results show the relevance of feeding schedules as entraining signals for the circadian system and highlight the importance of using them as a strategy for preventing internal desynchrony.

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.

Perioperative melatonin use

Melatonin is a substance chiefly produced by the pineal gland and has a key role in the sleep-wake cycle. It also has an important antioxidant role. Exogenous melatonin has a short half-life and is available in a range of preparations. Newer analogues targeted for the recently discovered melatonin MT1 and MT2 receptors have also been developed. Exogenous melatonin is used as a resynchronisation agent in jet lag and for other sleep disturbances. Perioperatively, melatonin has been used as a premedicant, sedative and analgesic. It decreases paediatric emergence delirium. The antioxidant properties of melatonin are being investigated for use in sepsis and reperfusion injuries. It would appear that patients on melatonin supplements should continue taking them perioperatively because there may be benefits. Melatonin and its analogues will be increasingly encountered in the perioperative setting.

Melatonin in mitochondrial dysfunction and related disorders

Mitochondrial dysfunction is considered one of the major causative factors in the aging process, ischemia/reperfusion (I/R), septic shock, and neurodegenerative disorders like Parkinson's disease (PD), Alzheimer's disease (AD), and Huntington's disease (HD). Increased free radical generation, enhanced mitochondrial inducible nitric oxide (NO) synthase activity, enhanced NO production, decreased respiratory complex activity, impaired electron transport system, and opening of mitochondrial permeability transition pore all have been suggested as factors responsible for impaired mitochondrial function. Melatonin, the major hormone of the pineal gland, also acts as an antioxidant and as a regulator of mitochondrial bioenergetic function. Both in vitro and in vivo, melatonin was effective for preventing oxidative stress/nitrosative stress-induced mitochondrial dysfunction seen in experimental models of PD, AD, and HD. In addition, melatonin is known to retard aging and to inhibit the lethal effects of septic shock or I/R lesions by maintaining respiratory complex activities, electron transport chain, and ATP production in mitochondria. Melatonin is selectively taken up by mitochondrial membranes, a function not shared by other antioxidants. Melatonin has thus emerged as a major potential therapeutic tool for treating neurodegenerative disorders such as PD or AD, and for preventing the lethal effects of septic shock or I/R.

Cadmium-Induced Disruption in 24-h Expression of Clock and Redox Enzyme Genes in Rat Medial Basal Hypothalamus: Prevention by Melatonin

In a previous study we reported that a low daily p.o. dose of cadmium (Cd) disrupted the circadian expression of clock and redox enzyme genes in rat medial basal hypothalamus (MBH). To assess whether melatonin could counteract Cd activity, male Wistar rats (45 days of age) received CdCl₂ (5 ppm) and melatonin (3 μg/mL) or vehicle (0.015% ethanol) in drinking water. Groups of animals receiving melatonin or vehicle alone were also included. After 1 month, MBH mRNA levels were measured by real-time PCR analysis at six time intervals in a 24-h cycle. In control MBH Bmal1 expression peaked at early scotophase, Per1 expression at late afternoon, and Per2 and Cry2 expression at mid-scotophase, whereas neither Clock nor Cry1 expression showed significant 24-h variations. This pattern was significantly disrupted (Clock, Bmal1) or changed in phase (Per1, Per2, Cry2) by CdCl₂ while melatonin counteracted the changes brought about by Cd on Per1 expression only. In animals receiving melatonin alone the 24-h pattern of MBH Per2 and Cry2 expression was disrupted. CdCl₂ disrupted the 24-h rhythmicity of Cu/Zn- and Mn-superoxide dismutase (SOD), nitric oxide synthase (NOS)-1, NOS-2, heme oxygenase (HO)-1, and HO-2 gene expression, most of the effects being counteracted by melatonin. In particular, the co-administration of melatonin and CdCl₂ increased Cu/Zn-SOD gene expression and decreased that of glutathione peroxidase (GPx), glutathione reductase (GSR), and HO-2. In animals receiving melatonin alone, significant increases in mean Cu/Zn and Mn-SOD gene expression, and decreases in that of GPx, GSR, NOS-1, NOS-2, HO-1, and HO-2, were found. The results indicate that the interfering effect of melatonin on the activity of a low dose of CdCl₂ on MBH clock and redox enzyme genes is mainly exerted at the level of redox enzyme gene expression.

Melatonin for disordered sleep in individuals with autism spectrum disorders: systematic review and discussion

Sleep disturbance is common in autism spectrum disorders (ASD) and melatonin is widely prescribed in such cases despite a lack of guidelines. The aim of this paper is to provide a systematic review of efficacy and safety of exogenous melatonin for treating disordered sleep in individuals with ASD. We performed a Pubmed(®) documentary search enlarged by a manual review of references, which finally supplied 12 citations (4 case reports, 3 retrospective studies, 2 open-label clinical trials, and 3 placebo-controlled trials). As a whole, we found that the literature supports the existence of a beneficial effect of melatonin on sleep in individuals with ASD, with only few and minor side effects. However, considering the small number of studies and their methodological limits, these conclusions cannot yet be regarded as evidence-based. Randomized controlled trials and long-term follow-up data are still lacking to better assess efficacy and safety of exogenous melatonin for disordered sleep in individuals with ASD.

Light-dependent and circadian clock-regulated activation of sterol regulatory element-binding protein, X-box-binding protein 1, and heat shock factor pathways

The circadian clock is phase-delayed or -advanced by light when given at early or late subjective night, respectively. Despite the importance of the time-of-day-dependent phase responses to light, the underlying molecular mechanism is poorly understood. Here, we performed a comprehensive analysis of light-inducible genes in the chicken pineal gland, which consists of light-sensitive clock cells representing a prototype of the clock system. Light stimulated expression of 62 genes and 40 ESTs by >2.5-fold, among which genes responsive to the heat shock and endoplasmic reticulum stress as well as their regulatory transcription factors heat shock factor (HSF)1, HSF2, and X-box-binding protein 1 (XBP1) were strongly activated when a light pulse was given at late subjective night. In contrast, the light pulse at early subjective night caused prominent induction of E4bp4, a key regulator in the phase-delaying mechanism of the pineal clock, along with activation of a large group of cholesterol biosynthetic genes that are targets of sterol regulatory element-binding protein (SREBP) transcription factor. We found that the light pulse stimulated proteolytic formation of active SREBP-1 that, in turn, transactivated E4bp4 expression, linking SREBP with the light-input pathway of the pineal clock. As an output of light activation of cholesterol biosynthetic genes, we found light-stimulated pineal production of a neurosteroid, 7α-hydroxypregnenolone, demonstrating a unique endocrine function of the pineal gland. Intracerebroventricular injection of 7α-hydroxypregnenolone activated locomotor activities of chicks. Our study on the genome-wide gene expression analysis revealed time-of-day-dependent light activation of signaling pathways and provided molecular connection between gene expression and behavior through neurosteroid release from the pineal gland.

Phase advance with separate and combined melatonin and light treatment

INTRODUCTION

Melatonin and light treatment are recommended for hastening adaptation to time zone change. We evaluated an afternoon regimen of 3 mg sustained release (SR) melatonin with and without next morning green light treatment for circadian phase advance. Effects of melatonin and light were tested separately and then combined to determine if the total phase change is additive or synergistic.

MATERIAL AND METHODS

For each condition (melatonin, placebo, light, melatonin plus light), 11 subjects spent from Tuesday evening until Friday afternoon in the laboratory. For all four conditions, the following sleep schedule was maintained: night 1, 2345 to 0630 hours, night 2, 1600 to 0530 hours, and night 3, 2345 to 0700 hours. For the light-only condition, light treatment was administered between 0700 and 0800 hours on Thursday. For melatonin-only or placebo conditions, capsules were administered at 1600 hours on Wednesday. For the combined condition, melatonin was administered at 1600 hours on Wednesday with light treatment between 0600 and 0700 hours on Thursday. Circadian phase was assessed by calculating dim light melatonin onset (DLMO) from salivary melatonin, using a mean baseline +2 standard deviations (BL+2 SD) threshold. For all four conditions, pre-treatment and post-treatment DLMO assessments were on Tuesday and Thursday evenings, respectively.

RESULTS

Phase advances were: melatonin at 1600 hours, 0.72 h p<0.005, light treatment from 0700 to 0800 hours, 0.31 h, non-significant, and the combined treatment, 1.04 h p<0.0002.

CONCLUSION

The phase advance from the combination of afternoon melatonin with next morning light is additive.

Genetics of Type 2 Diabetes

BACKGROUND

Type 2 diabetes (T2D) is a complex disorder that is affected by multiple genetic and environmental factors. Extensive efforts have been made to identify the disease-affecting genes to better understand the disease pathogenesis, find new targets for clinical therapy, and allow prediction of disease.

CONTENT

Our knowledge about the genes involved in disease pathogenesis has increased substantially in recent years, thanks to genomewide association studies and international collaborations joining efforts to collect the huge numbers of individuals needed to study complex diseases on a population level. We have summarized what we have learned so far about the genes that affect T2D risk and their functions. Although more than 40 loci associated with T2D or glycemic traits have been reported and reproduced, only a minor part of the genetic component of the disease has been explained, and the causative variants and affected genes are unknown for many of the loci.

SUMMARY

Great advances have recently occurred in our understanding of the genetics of T2D, but much remains to be learned about the disease etiology. The genetics of T2D has so far been driven by technology, and we now hope that next-generation sequencing will provide important information on rare variants with stronger effects. Even when variants are known, however, great effort will be required to discover how they affect disease risk.

Effects of light and melatonin treatment on body temperature and melatonin secretion daily rhythms in a diurnal rodent, the fat sand rat

Many mammals display predictable daily rhythmicity in both neuroendocrine function and behavior. The basic rest-activity cycles are usually consistent for a given species and vary from night-active (nocturnal), those mostly active at dawn and dusk (i.e., crepuscular), and to day-active (diurnal) species. A number of daily rhythms are oppositely phased with respect to the light/dark (LD) cycle in diurnal compared with nocturnal mammals, whereas others are equally phased with respect to the LD cycle, regardless of diurnality/nocturnality. Pineal produced melatonin (MLT) perfectly matches this phase-locked feature in that its production and secretion always occurs during the night in both diurnal and nocturnal mammals. As most rodents studied to date in the field of chronobiology are nocturnal, the aim in this study was to evaluate the effect of light manipulations and different photoperiods on a diurnal rodent, the fat sand rat, Psammomys obesus. The authors studied its daily rhythms of body temperature (T(b)) and 6-sulphatoxymelatonin (6-SMT) under various photoperiodic regimes and light manipulations (acute and chronic exposures) while maintaining a constant ambient temperature of 30 degrees C +/- 1 degrees C. The following protocols were used: (A) Control (CON) conditions 12L:12D; (A1) exposure to one light interference (LI) of CON-acclimated individuals for 30 min, 5 h after lights-off; (A2) short photoperiod (SP) acclimation (8L:16D) for 3 wks; (A3) 3 wks of SP acclimation with chronic LI of 15 min, three times a night at 4-h intervals; (A4) chronic exposure to constant dim blue light (470 nm, 30 lux) for 24 h for 3 wks (LL). (B) The response to exogenous MLT administration, provided in drinking water, was measured under the following protocols: (B1) After chronic exposure to SP with LI, MLT was provided once, starting 1 h before the end of photophase; (B2) after a continuous exposure to dim blue light, MLT was provided at 15:00 h for 2 h for 2 wks; (B3) to CON animals, MLT was given intraperitoneally (i.p.) at 14:00 h. The results demonstrate that under CON acclimation, Psammomys obesus has robust T(b) and 6-SMT daily rhythms in which the acrophase (peak time) of T(b) is during the photophase, whereas that of 6-SMT is during scotophase. LI resulted in an elevation of T(b) and a reduction of 6-SMT levels. A significant difference in the response was noted between acute and chronic exposure to LI, particularly in 6-SMT levels, which were lower than CON after LI and higher after chronic LI, implying an acclimation process. Constant exposure to blue light abolished T(b) and 6-SMT rhythms in all the animals. MLT administration resumed the T(b) daily rhythm in these animals, and had a recovery effect on the chronic LI-exposed animals, resulting in a T(b) decrease. Altogether, the authors show in this study the different modifications of T(b) rhythms and MLT levels in response to environmental light manipulations. These series of experiments may serve as a basis for establishing P. obesus as an animal model for further studies in chronobiology.

Jet lag, circadian rhythm sleep disturbances, and depression: the role of melatonin and its analogs

Traveling through several time zones results in a constellation of symptoms known as jet lag. These include reduced alertness, daytime fatigue, loss of appetite, reduced cognitive skills, and disruption of the sleep/wake cycle. In susceptible air travel passengers, jet lag may exacerbate affective illness and result in psychiatric morbidity. Dysregulation of circadian rhythms and melatonin secretion represent the common underlying factor in jet lag and other circadian disorders. Recent studies have established the effectiveness of strategically timed administration of melatonin and appropriate timed exposure to environmental schedules including light in counteracting the dysregulation (chronobiologic actions). With the introduction of melatonergic agonists such as ramelteon and tasimelteon, which have both a stronger affinity for MT₁ and MT₂ melatonin receptors and a longer half-life, new therapeutic options now exist for treating the sleep disturbances associated with jet lag. The melatonin analogs are unique inasmuch as they can also enhance daytime alertness. The recently introduced melatonergic antidepressant agomelatine, which has established its supremacy over other antidepressants in having a significant chronobiologic activity, represents a good choice for treating depressive symptoms that are associated with jet lag.