Free-running activity rhythms in the rat: entrainment by melatonin

Receptor-Mediated and Receptor-Independent Actions of Melatonin in Vertebrates

Melatonin (N-acetyl-5-methoxytryptamine) is an indolamine that is synthesized from tryptophan in the pineal glands of vertebrates through four enzymatic reactions. Melatonin is a quite unique bioactive substance, characterized by a combination of both receptor-mediated and receptor-independent actions, which promote the diverse effects of melatonin. One of the main functions of melatonin, via its membrane receptors, is to regulate the circadian or seasonal rhythm. In mammals, light information, which controls melatonin synthesis, is received in the eye, and transmitted to the pineal gland, via the suprachiasmatic nucleus, where the central clock is located. Alternatively, in many vertebrates other than mammals, the pineal gland cells, which are involved in melatonin synthesis and secretion and in the circadian clock, directly receive light. Recently, it has been reported that melatonin possesses several metabolic functions, which involve bone and glucose, in addition to regulating the circadian rhythm. Melatonin improves bone strength by inhibiting osteoclast activity. It is also known to maintain brain activity during sleep by increasing glucose uptake at night, in an insulin-independent manner. Moreover, as a non-receptor-mediated action, melatonin has antioxidant properties. Melatonin has been proven to be a potent free radical scavenger and a broad-spectrum antioxidant, even protecting organisms against radiation from space. Melatonin is a ubiquitously distributed molecule and is found in bacteria, unicellular organisms, fungi, and plants. It is hypothesized that melatonin initially functioned as an antioxidant, then, in vertebrates, it combined this role with the ability to regulate rhythm and metabolism, via its receptors.

Melatonin protects against ketorolac induced gastric mucosal toxic injuries through molecular mechanism associated with the modulation of Arylakylamine N-Acetyltransferase (AANAT) activity

Ketorolac tromethamine (KT), is a widely used non-steroidal anti-inflammatory drug (NSAID) for treating moderate to severe pain. However, the use of KT has been restricted due to its highly toxic attributes that lead to severe gastric ulceration and bleeding. The protective effects of exogenous melatonin (MT) has been reported in conditions associated with gastro-intestinal disorders. This study aims at exploring the role of gastric endogenous MT level and it's metabolizing enzyme AANAT, at the onset of ketorolac mediated toxicities in the gastric mucosa. Gastric mucosal damage was induced in experimental rats by oral administration of graded doses of KT, where 50 mg/kg b.w. of KT was observed to incur maximum gastric lesions. However, gastric damages were found to be protected in rats, pre-treated with 60 mg/kg b.w. of MT. Post-sacrifice, mean ulcer index, oxidative status, total melatonin levels and enzyme activities associated with MT biosynthesis and catabolism were estimated. The results reveal that KT decreases AANAT activity with a concomitant decline in endogenous MT level which cumulatively aggravates gastric toxicity. Moreover, exogenous MT administration has been found to be protective in ameliorating this ulcerogenic process in rats, challenged with KT. Biochemical and histo-pathological observations revealed the reduction in oxidative stress level and replenishment of depleted gastric MT levels in MT pre-treated animals, which might be the causative factors in conferring protection to the gastric tissues and residing mitochondria. The results revealed a correlation between depleted gastric MT level and ulcer formation, which unveiled a novel ulcerogenic mechanism. This may bring forth future therapeutic relevance for treating patients suffering from KT mediated acute gastric toxicities.

Melatonin alleviates lung injury in H1N1-infected mice by mast cell inactivation and cytokine storm suppression

Influenza A virus (IAV) H1N1 infection is a constant threat to human health and it remains so due to the lack of an effective treatment. Since melatonin is a potent antioxidant and anti-inflammatory molecule with anti-viral action, in the present study we used melatonin to protect against H1N1 infection under in vitro and in vivo conditions. The death rate of the H1N1-infected mice was negatively associated with the nose and lung tissue local melatonin levels but not with serum melatonin concentrations. The H1N1-infected AANAT-/- melatonin-deficient mice had a significantly higher death rate than that of the WT mice and melatonin administration significantly reduced the death rate. All evidence confirmed the protective effects of melatonin against H1N1 infection. Further study identified that the mast cells were the primary targets of melatonin action, i.e., melatonin suppresses the mast cell activation caused by H1N1 infection. The molecular mechanisms involved melatonin down-regulation of gene expression for the HIF-1 pathway and inhibition of proinflammatory cytokine release from mast cells; this resulted in a reduction in the migration and activation of the macrophages and neutrophils in the lung tissue. This pathway was mediated by melatonin receptor 2 (MT2) since the MT2 specific antagonist 4P-PDOT significantly blocked the effects of melatonin on mast cell activation. Via targeting mast cells, melatonin suppressed apoptosis of alveolar epithelial cells and the lung injury caused by H1N1 infection. The findings provide a novel mechanism to protect against the H1N1-induced pulmonary injury, which may better facilitate the progress of new strategies to fight H1N1 infection or other IAV viral infections.

Different levels of circadian (de)synchrony -- where does it hurt?

A network of cellular timers ensures the maintenance of homeostasis by temporal modulation of physiological processes across the day. These so-called circadian clocks are synchronized to geophysical time by external time cues (or zeitgebers). In modern societies, natural environmental cycles are disrupted by artificial lighting, around-the-clock availability of food or shiftwork. Such contradictory zeitgeber input promotes chronodisruption, i.e., the perturbation of internal circadian rhythms, resulting in adverse health outcomes. While this phenomenon is well described, it is still poorly understood at which level of organization perturbed rhythms impact on health and wellbeing. In this review, we discuss different levels of chronodisruption and what is known about their health effects. We summarize the results of disrupted phase coherence between external and internal time vs. misalignment of tissue clocks amongst each other, i.e., internal desynchrony. Last, phase incoherence can also occur at the tissue level itself. Here, alterations in phase coordination can emerge between cellular clocks of the same tissue or between different clock genes within the single cell. A better understanding of the mechanisms of circadian misalignment and its effects on physiology will help to find effective tools to prevent or treat disorders arising from modern-day chronodisruptive environments.

Different levels of circadian (de)synchrony -- where does it hurt?

A network of cellular timers ensures the maintenance of homeostasis by temporal modulation of physiological processes across the day. These so-called circadian clocks are synchronized to geophysical time by external time cues (or zeitgebers). In modern societies, natural environmental cycles are disrupted by artificial lighting, around-the-clock availability of food or shift work. Such contradictory zeitgeber input promotes chronodisruption, i.e., the perturbation of internal circadian rhythms, resulting in adverse health outcomes. While this phenomenon is well described, it is still poorly understood at which level of organization perturbed rhythms impact on health and wellbeing. In this review, we discuss different levels of chronodisruption and what is known about their health effects. We summarize the results of disrupted phase coherence between external and internal time vs. misalignment of tissue clocks amongst each other, i.e., internal desynchrony. Last, phase incoherence can also occur at the tissue level itself. Here, alterations in phase coordination can emerge between cellular clocks of the same tissue or between different clock genes within the single cell. A better understanding of the mechanisms of circadian misalignment and its effects on physiology will help to find effective tools to prevent or treat disorders arising from modern-day chronodisruptive environments.

Impact of Melatonin on RAW264.7 Macrophages during Mechanical Strain

The concentration of melatonin is elevated during the night when patients mainly wear removable orthodontic appliances. Next to periodontal ligament fibroblasts and osteoblasts, macrophages react to mechanical strain with an increased expression of inflammatory mediators. Here, we investigated the impact of melatonin on RAW264.7 macrophages exposed to tensile or compressive strain occurring during orthodontic tooth movement in the periodontal ligament. Before exposure to mechanical strain for 4 h, macrophages were pre-incubated with different melatonin concentrations for 24 h, to determine the dependence of melatonin concentration. Afterwards, we performed experiments with and without mechanical strain, the most effective melatonin concentration (25 µM), and the melatonin receptor 2 (MT2) specific antagonist 4P-PDOT. The expression of inflammatory genes and proteins was investigated by RT-qPCR, ELISAs, and immunoblot. Both tensile and compressive strain increased the expression of the investigated inflammatory factors interleukin-1-beta, interleukin-6, tumor necrosis factor alpha, and prostaglandin endoperoxide synthase-2. This effect was inhibited by the addition of melatonin. Incubation with 4P-PDOT blocked this anti-inflammatory effect of melatonin. Melatonin had an anti-inflammatory effect on macrophages exposed to mechanical strain, independent of the type of mechanical strain. As inhibition was possible with 4P-PDOT, the MT2 receptor might be involved in the regulation of the observed effects.

Circadian Regulation of Hormonal Timing and the Pathophysiology of Circadian Dysregulation

Circadian rhythms are endogenously generated, daily patterns of behavior and physiology that are essential for optimal health and disease prevention. Disruptions to circadian timing are associated with a host of maladies, including metabolic disease and obesity, diabetes, heart disease, cancer, and mental health disturbances. The circadian timing system is hierarchically organized, with a master circadian clock located in the suprachiasmatic nucleus (SCN) of the anterior hypothalamus and subordinate clocks throughout the CNS and periphery. The SCN receives light information via a direct retinal pathway, synchronizing the master clock to environmental time. At the cellular level, circadian rhythms are ubiquitous, with rhythms generated by interlocking, autoregulatory transcription-translation feedback loops. At the level of the SCN, tight cellular coupling maintains rhythms even in the absence of environmental input. The SCN, in turn, communicates timing information via the autonomic nervous system and hormonal signaling. This signaling couples individual cellular oscillators at the tissue level in extra-SCN brain loci and the periphery and synchronizes subordinate clocks to external time. In the modern world, circadian disruption is widespread due to limited exposure to sunlight during the day, exposure to artificial light at night, and widespread use of light-emitting electronic devices, likely contributing to an increase in the prevalence, and the progression, of a host of disease states. The present overview focuses on the circadian control of endocrine secretions, the significance of rhythms within key endocrine axes for typical, homeostatic functioning, and implications for health and disease when dysregulated. © 2022 American Physiological Society. Compr Physiol 12: 1-30, 2022.

Drugs Used in Circadian Sleep-Wake Rhythm Disturbances

This article focuses on melatonin and other melatonin receptor agonists and summarizes their circadian phase shifting and sleep-enhancing properties, along with their associated possible safety concerns. The circadian system and circadian rhythm sleep-wake disorders are described, along with the latest American Academy of Sleep Medicine recommendations for the use of exogenous melatonin in treating them. In addition, the practical aspects of using exogenous melatonin obtainable over the counter in the United States, consideration of the effects of concomitant light exposure, and assessing treatment response are discussed.

Environmental disruption of reproductive rhythms

Reproduction is a key biological function requiring a precise synchronization with annual and daily cues to cope with environmental fluctuations. Therefore, humans and animals have developed well-conserved photoneuroendocrine pathways to integrate and process daily and seasonal light signals within the hypothalamic-pituitary-gonadal axis. However, in the past century, industrialization and the modern 24/7 human lifestyle have imposed detrimental changes in natural habitats and rhythms of life. Indeed, exposure to an excessive amount of artificial light at inappropriate timing because of shift work and nocturnal urban lighting, as well as the ubiquitous environmental contamination by endocrine-disrupting chemicals, threaten the integrity of the daily and seasonal timing of biological functions. Here, we review recent epidemiological, field and experimental studies to discuss how light and chemical pollution of the environment can disrupt reproductive rhythms by interfering with the photoneuroendocrine timing system.

Circadian Rhythms and Melatonin Metabolism in Patients With Disorders of Gut-Brain Interactions

Circadian rhythms are cyclic patterns of physiological, behavioural and molecular events that occur over a 24-h period. They are controlled by the suprachiasmatic nucleus (SCN), the brain’s master pacemaker which governs peripheral clocks and melatonin release. While circadian systems are endogenous, there are external factors that synchronise the SCN to the ambient environment including light/dark cycles, fasting/fed state, temperature and physical activity. Circadian rhythms also provide internal temporal organisation which ensures that any internal changes that take place are centrally coordinated. Melatonin synchronises peripheral clocks to the external time and circadian rhythms are regulated by gene expression to control physiological function. Synchronisation of the circadian system with the external environment is vital for the health and survival of an organism and as circadian rhythms play a pivotal role in regulating GI physiology, disruption may lead to gastrointestinal (GI) dysfunction. Disorders of gut-brain interactions (DGBIs), also known as functional gastrointestinal disorders (FGIDs), are a group of diseases where patients experience reoccurring gastrointestinal symptoms which cannot be explained by obvious structural abnormalities and include functional dyspepsia (FD) and irritable bowel syndrome (IBS). Food timing impacts on the production of melatonin and given the correlation between food intake and symptom onset reported by patients with DGBIs, chronodisruption may be a feature of these conditions. Recent advances in immunology implicate circadian rhythms in the regulation of immune responses, and DGBI patients report fatigue and disordered sleep, suggesting circadian disruption. Further, melatonin treatment has been demonstrated to improve symptom burden in IBS patients, however, the mechanisms underlying this efficacy are unclear. Given the influence of circadian rhythms on gastrointestinal physiology and the immune system, modulation of these rhythms may be a potential therapeutic option for reducing symptom burden in these patients.

The Bidirectional Link Between Sleep Disturbances and Traumatic Brain Injury Symptoms: A Role for Glymphatic Dysfunction?

Mild traumatic brain injury (mTBI), often referred to as concussion, is a major cause of morbidity and mortality worldwide. Sleep disturbances are common after mTBI. Moreover, subjects who develop subjective sleep complaints after mTBI also report more severe somatic, mental health, and cognitive impairment and take longer to recover from mTBI sequelae. Despite many previous studies addressing the role of sleep in post-mTBI morbidity, the mechanisms linking sleep to recovery after mTBI remain poorly understood. The glymphatic system is a brainwide network that supports fluid movement through the cerebral parenchyma and the clearance of interstitial solutes and wastes from the brain. Notably, the glymphatic system is active primarily during sleep. Clearance of cellular byproducts related to somatic, mental health, and neurodegenerative processes (e.g., amyloid-β and tau, among others) depends in part on intact glymphatic function, which becomes impaired after mTBI. In this viewpoint, we review the current knowledge regarding the association between sleep disturbances and post-mTBI symptoms. We also discuss the role of glymphatic dysfunction as a potential link between mTBI, sleep disruption, and posttraumatic morbidity. We outline a model where glymphatic dysfunction and sleep disruption caused by mTBI may have an additive effect on waste clearance, leading to cerebral dysfunction and impaired recovery. Finally, we review the novel techniques being developed to examine glymphatic function in humans and explore potential interventions to alter glymphatic exchange that may offer a novel therapeutic approach to those experiencing poor sleep and prolonged symptoms after mTBI.

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.

Methods to Assess Melatonin Receptor-Mediated Phase-Shift and Re-entrainment of Rhythmic Behaviors in Mouse Models

The neurohormone melatonin facilitates entrainment of biological rhythms to environmental light-dark conditions as well as phase-shifts of circadian rhythms in constant conditions via activation of the MT₁ and/or MT₂ receptors expressed within the suprachiasmatic nucleus of the hypothalamus. The efficacy of melatonin and related agonists to modulate biological rhythms can be assessed using two well-validated mouse models of rhythmic behaviors. These models serve as predictive measures of therapeutic efficacy for treatment of circadian phase disorders caused by internal (e.g., clock gene mutations, blindness, depression, seasonal affective disorder) or external (e.g., shift work, travel across time zones) causes in humans. Here we provide background and detailed protocols for quantitative assessment of the magnitude and efficacy of melatonin receptor ligands in mouse circadian phase-shift and re-entrainment paradigms. The utility of these models in the discovery of novel therapeutics acting on melatonin receptors will also be discussed.

Melatonin Promotes the Therapeutic Effect of Mesenchymal Stem Cells on Type 2 Diabetes Mellitus by Regulating TGF-β Pathway

Abundant evidence proves the therapeutic effect of adipose-derived mesenchymal stem cells (ADMSCs) in the treatment of diabetes mellitus. However, the problems have not been solved that viability of ADMSCs were inconsistent and the cells quickly undergo senescence after in vitro cell culture. In addition, the therapeutic effect of ADMSCs is still not satisfactory. In this study, melatonin (MLT) was added to canine ADMSC culture medium, and the treated cells were used to treat type 2 diabetes mellitus (T2DM). Our research reveals that adding MLT to ADMSC culture medium can promote the viability of ADMSCs. This effect depends on the binding of MLT and MLT receptors, which activates the transforming growth factor β (TGF-β) pathway and then changes the cell cycle of ADMSCs and improves the viability of ADMSCs. Since ADMSCs were found to be used to treat T2DM by anti-inflammatory and anti-endoplasmic reticulum (ER) stress capabilities, our data demonstrate that MLT augment several effects of ADMSCs in remission hyperglycemia, insulin resistance, and liver glycogen metabolism in T2DM patients. This suggest that ADMSCs and MLT-ADMSCs is safe and vabulable for pet clinic.

Mammalian circadian networks mediated by the suprachiasmatic nucleus

The brain has a complex structure composed of hundreds of regions, forming networks to cooperate body functions. Therefore, understanding how various brain regions communicate with each other and with peripheral organs is important to understand human physiology. The suprachiasmatic nucleus (SCN) in the brain is the circadian pacemaker. The SCN receives photic information from the environment and conveys this to other parts of the brain and body to synchronize all circadian clocks. The circadian clock is an endogenous oscillator that generates daily rhythms in metabolism and physiology in almost all cells via a conserved transcriptional-translational negative feedback loop. So, the information flow from the environment to the SCN to other tissues synchronizes locally distributed circadian clocks to maintain homeostasis. Thus, understanding the circadian networks and how they adjust to environmental changes will better understand human physiology. This review will focus on circadian networks mediated by the SCN to understand how the environment, brain, and peripheral tissues form networks for cooperation.

Sleep timing and the circadian clock in mammals: Past, present and the road ahead

Nearly all mammals display robust daily rhythms of physiology and behavior. These approximately 24-h cycles, known as circadian rhythms, are driven by a master clock in the suprachiasmatic nucleus (SCN) of the hypothalamus and affect biological processes ranging from metabolism to immune function. Perhaps the most overt output of the circadian clock is the sleep-wake cycle, the integrity of which is critical for health and homeostasis of the organism. In this review, we summarize our current understanding of the circadian regulation of sleep. We discuss the neural circuitry and molecular mechanisms underlying daily sleep timing, and the trajectory of circadian regulation of sleep across development. We conclude by proposing future research priorities for the field that will significantly advance our mechanistic understanding of the circadian regulation of sleep.

Melatonin and the circadian system: Keys for health with a focus on sleep

Melatonin (MLT), secreted during the night by the pineal gland, is an efferent hormonal signal of the master circadian clock located in the suprachiasmatic nucleus (SCN). Consequently, it is a reliable phase marker of the SCN clock. If one defines as "chronobiotic," a drug able to influence the phase and/or the period of the circadian clock, MLT is a very potent one. The most convincing data obtained so far come from studies on totally blind individuals. Exogenous MLT administered daily entrains the sleep-wake cycle of these individuals to a 24-h cycle. MLT, however, is not essential to sleep. In nocturnally, active mammals, MLT is released during the night concomitantly with the daily period of wakefulness. Therefore, MLT cannot be simply considered as a sleep hormone, but rather as a signal of darkness. Its role in the circadian system is to reinforce nighttime physiology, including timing of the sleep-wake cycle and other circadian rhythms. MLT exerts its effects on the sleep cycle especially by a direct action on the master circadian clock. The sleep-wake cycle is depending not only on the circadian clock but also on an orchestrated network of different centers in the brain. Thus, the control of sleep-wake rhythm might be explained by a parallel and concomitant action of MLT on the master clock (chronobiotic effect) and on sleep-related structures within the brain. MLT acts through two high-affinity membrane receptors (MT1 and MT2) with striking differences in their distribution pattern. MLT is a powerful synchronizer of human circadian rhythms, thus justifying the use of MLT and MLT agonists in clinical medicine as pharmacological tools to manipulate the sleep-wake cycle, and to treat sleep disorders and other circadian disorders. Available MLT analogs/drugs are all nonspecific MT1/MT2 agonists. The development of new ligands which are highly selectivity for each subtype is clearly a new challenge for the field and will be at the root of new therapeutic agents for curing specific pathologies, including sleep disorders.

Drugs Used in Circadian Sleep-Wake Rhythm Disturbances

This article focuses on melatonin and other melatonin receptor agonists, and specifically their circadian phase shifting and sleep-enhancing properties. The circadian system and circadian rhythm sleep-wake disorders are briefly reviewed, followed by a summary of the circadian phase shifting, sleep-enhancing properties, and possible safety concerns associated with melatonin and other melatonin receptor agonists. The recommended use of melatonin, including dose and timing, in the latest American Academy of Sleep Medicine Clinical Practice Guidelines for the treatment of intrinsic circadian rhythm disorders is also reviewed. Lastly, the practical aspects of treatment and consideration of clinical treatment outcomes are discussed.

Temporal organization of pineal melatonin signaling in mammals

In mammals, the pineal gland is the sole endocrine source of melatonin, which is secreted according to daily and seasonal patterns. This mini-review synthesizes the established endocrine actions of melatonin in the following temporal contexts. Melatonin is a strictly regulated output of the circadian timing system, but under certain conditions, may also entrain the circadian pacemaker and clocks in peripheral tissues. As the waveform of nightly melatonin secretion varies seasonally, melatonin provides a hormonal representation of the time of year. The duration of elevated melatonin secretion regulates reproductive physiology and other seasonal adaptations either by entraining a circannual rhythm or by inducing seasonal responses directly. An entrainment action of nightly melatonin on clock gene expression in the pars tuberalis of the anterior pituitary may partly underly its mechanistic role as a photoperiodic switch. Melatonin has important functions developmentally to regulate multiple physiological systems and program timing of puberty. Endogenous melatonergic systems are disrupted by modern lifestyles of humans through altered circadian entrainment, acute suppression by light and self-administration of pharmacological melatonin. Non-endocrine actions of locally synthesized melatonin fall outside of the scope of this mini-review.

Melatonin alleviates circadian system disruption induced by chronic shifts of the light-dark cycle in Octodon degus

Modern 24-h society lifestyle is associated with experiencing frequent shifts in the lighting conditions which can negatively impact human health. Here, we use the degus, a species exhibiting diurnal and nocturnal chronotypes, to: (a) assess the impact of chronic shifts of the light:dark (LD) cycle in the animal's physiology and behaviour and (b) test the therapeutic potential of melatonin in enhancing rhythmicity under these conditions. Degus were subjected to a "5d + 2d" LD-shifting schedule for 19 weeks. This protocol aims to mimic lighting conditions experienced by humans during shift work: LD cycle was weekly delayed by 8h during 5 "working" days (Morning, Afternoon and Night schedule); during weekends (2 days), animals were kept under Morning schedule. After 9 weeks, melatonin was provided daily for 6h in the drinking water. The "5d + 2d" shifting LD schedule led to a disruption in wheel-running activity (WRA) and body temperature (Tb) rhythms which manifested up to three separate periods in the circadian range. This chronodisruption was more evident in nocturnal than in diurnal degus, particularly during the Afternoon schedule when a phase misalignment between WRA and Tb rhythms appeared. Melatonin treatment and, to a lesser extent, water restriction enhanced the 24-h component, suggesting a potential role in ameliorating the disruptive effects of shift work.

Approaches to the Pharmacological Management of Jet Lag

For many years now a treatment mitigating the debilitating effects of jet lag has been sought. Rapid travel across time zones leads, in most people, to temporary symptoms, in particular poor sleep, daytime alertness and poor performance. Mis-timed circadian rhythms are considered to be the main factor underlying jet-lag symptoms, together with the sleep deprivation from long haul flights. Virtually all aspects of physiology are rhythmic, from cells to systems, and circadian rhythms are coordinated by a central pacemaker or clock in the suprachiasmatic nucleus (SCN) of the hypothalamus. The SCN adapts slowly to changes in time zone, and peripheral clocks or oscillators adapt at different rates, such that the organism is in a state of desynchrony from the external environment and internally. Light exposure is the main factor controlling the circadian system and needs to be considered together with any pharmacological interventions. This review covers the relatively new chronobiotic drugs, which can hasten adaptation of the circadian system, together with drugs directly affecting alertness and sleep propensity. No current treatment can instantly shift circadian phase to a new time zone; however, adaptation can be hastened. The melatoninergic drugs are promising but larger trials in real-life situations are needed. For short stopovers it is recommended to preserve sleep and alertness without necessarily modifying the circadian system. New research suggests that modification of clock function via genetic manipulation may one day have clinical applications.

Wnt4 signaling mediates protective effects of melatonin on new bone formation in an inflammatory environment

Growing evidence shows that the inhibitory effect of inflammatory cytokines on new bone formation by osteogenic precursor cells is a critical cause of net bone-density reduction. Melatonin has been proven to be a potential therapeutic candidate for osteoporosis. However, whether it is capable of antagonizing the suppressing effect of inflammatory cytokines on osteogenic precursor cells is so far elusive. In this study, using the cell culture system of human bone marrow stromal cells and MC3T3-E1 preosteoblasts, we recorded the following vital observations that provided insights of melatonin-induced bone formation: 1) melatonin induced bone formation in both normal and inflammatory conditions; 2) Wnt4 was essential for melatonin-induced bone formation in inflammatory stimulation; 3) melatonin- and Wnt4-induced bone formation occurred via activation of β-catenin and p38-JNK MAPK pathways by interaction with a distinct frizzled LDL receptor-related protein complex; 4) melatonin suppressed the inhibitory effect of NF-κB on osteogenesis in a Wnt4-dependent manner; and 5) melatonin induced Wnt4 expression through the ERK1/2-Pax2-Egr1 pathway. In summary, we showed a novel mechanism of melatonin-induced bone formation in an inflammatory environment. Melatonin-induced Wnt4 expression is essential for its osteoinductive effect and the inhibitory effect of NF-κB on bone formation. Our novel findings may provide useful information for its potential translational application.-Li, X., Li, Z., Wang, J., Li, Z., Cui, H., Dai, G., Chen, S., Zhang, M., Zheng, Z., Zhan, Z., Liu, H. Wnt4 signaling mediates protective effects of melatonin on new bone formation in an inflammatory environment.

Circadian-Rhythm Sleep Disorders in Persons who are Totally Blind

People who are totally blind are prone to a cyclic form of insomnia, designated in medical terminology as non-24-hour sleep-wake syndrome. It is caused by a lack of synchrony between the internal body clock and the daily sleep-wake schedule. This article describes the clinical features and biological basis of the disorder and discusses the implications for its management and treatment.

Dim light at night: physiological effects and ecological consequences for infectious disease

Light pollution has emerged as a pervasive component of land development over the past century. Several detrimental impacts of this anthropogenic influence have been identified in night shift workers, laboratory rodents, and a plethora of wildlife species. Circadian, or daily, patterns are interrupted by the presence of light at night and have the capacity to alter rhythmic physiological or behavioral characteristics. Indeed, biorhythm disruption can lead to metabolic, reproductive, and immunological dysfunction depending on the intensity, timing, duration, and wavelength of light exposure. Light pollution, in many forms and by many pathways, is thus apt to affect the nature of host-pathogen interactions. However, no research has yet investigated this possibility. The goal of this manuscript is to outline how dim light at night, a relevant and common form of light pollution, may affect disease dynamics by interrupting circadian rhythms and regulation of immune responses as well as opportunities for host-parasite interactions and subsequent transmission risk including spillover into humans. We close by proposing some promising interventions including alternative lighting methods or vector control efforts.

Effects of melatonin on the synthesis of estradiol and gene expression in pig granulosa cells

The interaction of granulosa cells (GCs) with oocytes is important to regulate follicle development. The exogenous melatonin promoting the maturation of oocytes by GCs has been approved in pig, however, the transcriptome profile and the functions of the genes regulated by melatonin in GCs have not yet to be fully characterized. In this study, we found melatonin could stimulate the synthesis of estradiol in pig GCs. The RNA-seq was used to explore the effects of melatonin on gene expression, a total of 89 differentially expressed genes (DEGs) were identified. Gene ontology analysis showed DEGs which associated with regulation of cell proliferation, cell cycle, and anti-apoptosis were significantly enriched. The functions of two DEGs, NOTCH2 and FILIP1L, were studied in pig GCs. The results showed that NOTCH2 inhibited the synthesis of estradiol, but FILIP1L promoted the synthesis of estradiol. Furthermore, inhibiting NOTCH2 in granulosa cells cocultured with cumulus-oocyte-complexes had no obvious effect on the maturation of pig oocyte, but could upregulate the cleavage rate of oocyte. We proved that FILIP1L had no effect on the maturation and cleavage of pig oocytes. Our work deepens the understanding of melatonin's effects on GCs and oocyte. The DEGs we found will be beneficial to reveal mechanisms of melatonin acting on GCs and oocytes and design the pharmacological interventions.

Melatonin as a Hormone: New Physiological and Clinical Insights

Melatonin is a ubiquitous molecule present in almost every live being from bacteria to humans. In vertebrates, besides being produced in peripheral tissues and acting as an autocrine and paracrine signal, melatonin is centrally synthetized by a neuroendocrine organ, the pineal gland. Independently of the considered species, pineal hormone melatonin is always produced during the night and its production and secretory episode duration are directly dependent on the length of the night. As its production is tightly linked to the light/dark cycle, melatonin main hormonal systemic integrative action is to coordinate behavioral and physiological adaptations to the environmental geophysical day and season. The circadian signal is dependent on its daily production regularity, on the contrast between day and night concentrations, and on specially developed ways of action. During its daily secretory episode, melatonin coordinates the night adaptive physiology through immediate effects and primes the day adaptive responses through prospective effects that will only appear at daytime, when melatonin is absent. Similarly, the annual history of the daily melatonin secretory episode duration primes the central nervous/endocrine system to the seasons to come. Remarkably, maternal melatonin programs the fetuses' behavior and physiology to cope with the environmental light/dark cycle and season after birth. These unique ways of action turn melatonin into a biological time-domain-acting molecule. The present review focuses on the above considerations, proposes a putative classification of clinical melatonin dysfunctions, and discusses general guidelines to the therapeutic use of melatonin.

Drugs Used in Circadian Sleep-Wake Rhythm Disturbances

This article focuses on melatonin and other melatonin receptor agonists, and specifically their circadian phase shifting and sleep-enhancing properties. The circadian system and circadian rhythm sleep-wake disorders are briefly reviewed, followed by a summary of the circadian phase shifting, sleep-enhancing properties, and possible safety concerns associated with melatonin and other melatonin receptor agonists. The recommended use of melatonin, including dose and timing, in the latest American Academy of Sleep Medicine Clinical Practice Guidelines for the treatment of intrinsic circadian rhythm disorders is also reviewed. Lastly, the practical aspects of treatment and consideration of clinical treatment outcomes are discussed.

Melatonin as a Treatment after Traumatic Brain Injury: A Systematic Review and Meta-Analysis of the Pre-Clinical and Clinical Literature

Traumatic brain injury (TBI) is common; however, effective treatments of the secondary brain injury are scarce. Melatonin is a potent, nonselective neuroprotective and anti-inflammatory agent that is showing promising results in neonatal brain injury. The aim of this study was to systematically evaluate the pre-clinical and clinical literature on the effectiveness of melatonin in improving outcome after TBI. Using the systematic review protocol for animal intervention studies (SYRCLE) and Cochrane methodology for clinical studies, a search of English-language articles was performed. Eligible studies were identified and data were extracted. Quality assessment was performed using the SYRCLE risk of bias tool. Meta-analyses were performed using standardized mean differences (SMD). Seventeen studies (15 pre-clinical, 2 clinical) met inclusion criteria. There was heterogeneity in the studies, and all had moderate-to-low risk of bias. Meta-analysis of pre-clinical data revealed an overall positive effect on neurobehavioural outcome with SMD of 1.51 (95% CI: 1.06-1.96). Melatonin treatment had a favorable effect on neurological status, by an SMD of 1.35 (95% CI: 0.83-1.88), and on cognition by an SMD of 1.16 (95% CI: 0.4-1.92). Melatonin decreased the size of the contusion by an SMD of 2.22 (95% CI: 0.8--3.59) and of cerebral edema by an SMD of 1.91 (95% CI: 1.08-2.74). Only two clinical studies were identified. They were of low quality, were used for symptom management, and were of uncertain significance. In conclusion, there is evidence that melatonin treatment after TBI significantly improves both behavioral outcomes and pathological outcomes; however, significant research gaps exist, especially in clinical populations.

Bright light at night alters the perception of daylength in Indian weaver bird (Ploceus philippinus)

The brighter nights have posed new challenges to the wild species by affecting their temporal physiology. The present study on Indian weaver bird (Ploceus philippinus) investigated if exposure to bright light at different phases of night affects their clock-mediated daily functions. Birds were placed individually in specially designed activity cages under short days and long nights (8L:16D; L = 100 lux, D < 0.1 lux) for ∼3 weeks (19 days). Thereafter, they were divided into four groups (n = 6-9), and given ∼2 lux light either for the entire night (ZT 08-24; zeitgeber time 0 = time of light on; pattern A) or for 4 hr (pattern B), placed in 16 hr night such that its onset coincides with the onset of night (early night group, ZT 08-12), its end with the end of night (late night group, ZT 20-24), or the night was interrupted in the middle (midnight group, ZT 14-18). The results showed that bright light in entire night induced early onset of day activity and fragmented rest at night, however, if given at different phases of night, it made the days longer by delaying end (early night group) or advancing onset of daily activity (late night group). It also suppressed the melatonin levels and increased body temperature. These results suggest that bright light at night alters the perception of daylength and affects the underlying physiology. The findings may be useful in adopting a strategy for use of night light without disturbing species fitness in their environment.

Non-24-Hour Sleep-Wake Rhythm Disorder in the Totally Blind: Diagnosis and Management

Several aspects of human physiology and behavior are dominated by 24-h circadian rhythms with key impacts on health and well-being. These include mainly the sleep–wake cycle, vigilance and performance patterns, and some hormone secretions. The rhythms are generated spontaneously by an internal “pacemaker,” the suprachiasmatic nuclei within the anterior hypothalamus. This master clock has, for most humans, an intrinsic rhythm slightly longer than 24 h. Daily retinal light exposure is necessary for the synchronization of the circadian rhythms with the external 24-h solar environment. This daily synchronization process generally poses no problems for sighted individuals except in the context of jetlag or working night shifts being conditions of circadian desynchrony. However, many blind subjects with no light perception had periodical circadian desynchrony, in the absence of light information to the master clock leading to poor circadian rhythm synchronization. Affected patients experience cyclical or periodic episodes of poor sleep and daytime dysfunction, severely interfering with social, academic, and professional life. The diagnosis of Non-24 Sleep–Wake Rhythm Disorder, also named free-running disorder, non-entrained disorder, or hypernycthemeral syndrome, remains challenging from a clinical point of view due to the cyclical symptoms and should be confirmed by measurements of circadian biomarkers such as urinary melatonin to demonstrate a circadian period outside the normal range. Management includes behavioral modification and melatonin. Tasimelteon, a novel melatonin receptor 1 and 2 agonist, has demonstrated its effectiveness and safety with an evening dose of 20 mg and is currently the only treatment approved by the FDA and the European Medicines Agency.

Diurnal pattern in skin Na+ and water content is associated with salt-sensitive hypertension in ETB receptor-deficient rats

Impairment in the ability of the skin to properly store Na⁺ nonosmotically (without water) has recently been hypothesized as contributing to salt-sensitive hypertension. Our laboratory has shown that endothelial production of endothelin-1 (ET-1) is crucial to skin Na⁺ handling. Furthermore, it is well established that loss of endothelin type B receptor (ET_B) receptor function impairs Na⁺ excretion by the kidney. Thus we hypothesized that rats lacking functional ET_B receptors (ET_B-def) will have a reduced capacity of the skin to store Na⁺ during chronic high-salt (HS) intake. We observed that ET_B-def rats exhibited salt-sensitive hypertension with an approximate doubling in the diurnal amplitude of mean arterial pressure compared with genetic control rats on a HS diet. Two weeks of HS diet significantly increased skin Na⁺ content relative to water; however, there was no significant difference between control and ET_B-def rats. Interestingly, HS intake led to a 19% increase in skin Na⁺ and 16% increase in water content (relative to dry wt.) during the active phase (zeitgeber time 16) versus inactive phase (zeitgeber time 4, P < 0.05) in ET_B-def rats. There was no significant circadian variation in total skin Na⁺ or water content of control rats fed normal or HS. These data indicate that ET_B receptors have little influence on the ability to store Na⁺ nonosmotically in the skin during long-term HS intake but, rather, appear to regulate diurnal rhythms in skin Na⁺ content and circadian blood pressure rhythms associated with a HS diet.

The hormone melatonin: Animal studies

The Melatonin (MLT), secreted rhythmically by the pineal, is an efferent hormonal signal of the circadian clock. MLT presents overall pleitropic effects but it is the role of MLT as a hormonal circadian signal which is the best documented. MLT-receptors are present in numerous structures/organs and the MLT is now considered as an endogenous synchronizer within the circadian system. The presence of MLT-receptors within the circadian clock, explains that exogenous MLT is a chronobiotic drug. Trials in humans, have confirmed the efficacy of MLT in circadian rhythm disorders. Subtypes of MLT-receptors have been characterized (MT1 and MT2). Striking differences are observed in the distribution pattern of these 2 subtypes. Up to now, MTL-analogues commercialized as drugs, are all non-specific MT₁/MT₂ agonists acting on the SCN. The development of new specific agonists/antagonists for both subtypes, the identification of the link between MLT target sites within different parts of the brain or the body and the association of specific MLT receptor subtypes and particular physiological effects open great therapeutic potential.

Circadian rhythm in melatonin release as a mechanism to reinforce the temporal organization of the circadian system in crayfish

Melatonin (MEL) is a conserved molecule with respect to its synthesis pathway and functions. In crayfish, MEL content in eyestalks (Ey) increases at night under the photoperiod, and this indoleamine synchronizes the circadian rhythm of electroretinogram amplitude, which is expressed by retinas and controlled by the cerebroid ganglion (CG). The aim of this study was to determine whether MEL content in eyestalks and CG or circulating MEL in hemolymph (He) follows a circadian rhythm under a free-running condition; in addition, it was tested whether MEL might directly influence the spontaneous electrical activity of the CG. Crayfish were maintained under constant darkness and temperature, a condition suitable for studying the intrinsic properties of circadian systems. MEL was quantified in samples obtained from He, Ey, and CG by means of an enzyme-linked immunosorbent assay, and the effect of exogenous MEL on CG spontaneous activity was evaluated by electrophysiological recording. Variation of MEL content in He, Ey, and CG followed a circadian rhythm that peaked at the same circadian time (CT). In addition, a single dose of MEL injected into the crayfish at different CTs reduced the level of spontaneous electrical activity in the CG. Results suggest that the circadian increase in MEL content directly affects the CG, reducing its spontaneous electrical activity, and that MEL might act as a periodical signal to reinforce the organization of the circadian system in crayfish.

The Central Nervous System and Bone Metabolism: An Evolving Story

Our understanding of the control of skeletal metabolism has undergone a dynamic shift in the last two decades, primarily driven by our understanding of energy metabolism. Evidence demonstrating that leptin not only influences bone cells directly, but that it also plays a pivotal role in controlling bone mass centrally, opened up an investigative process that has changed the way in which skeletal metabolism is now perceived. Other central regulators of bone metabolism have since been identified including neuropeptide Y (NPY), serotonin, endocannabinoids, cocaine- and amphetamine-regulated transcript (CART), adiponectin, melatonin and neuromedin U, controlling osteoblast and osteoclast differentiation, proliferation and function. The sympathetic nervous system was originally identified as the predominant efferent pathway mediating central signalling to control skeleton metabolism, in part regulated through circadian genes. More recent evidence points to a role of the parasympathetic nervous system in the control of skeletal metabolism either through muscarinic influence of sympathetic nerves in the brain or directly via nicotinic receptors on osteoclasts, thus providing evidence for broader autonomic skeletal regulation. Sensory innervation of bone has also received focus again widening our understanding of the complex neuronal regulation of bone mass. Whilst scientific advance in this field of bone metabolism has been rapid, progress is still required to understand how these model systems work in relation to the multiple confounders influencing skeletal metabolism, and the relative balance in these neuronal systems required for skeletal growth and development in childhood and maintaining skeletal integrity in adulthood.

Melatonin: A Review of Its Potential Functions and Effects on Dental Diseases

Melatonin is a hormone synthesised and secreted by the pineal gland and other organs. Its secretion, controlled by an endogenous circadian cycle, has been proven to exert immunological, anti-oxidant, and anti-inflammatory effects that can be beneficial in the treatment of certain dental diseases. This article is aimed at carrying out a review of the literature published about the use of melatonin in the dental field and summarising its potential effects. In this review article, an extensive search in different databases of scientific journals was performed with the objective of summarising all of the information published on melatonin use in dental diseases, focussing on periodontal diseases and dental implantology. Melatonin released in a natural way into the saliva, or added as an external treatment, may have important implications for dental disorders, such as periodontal disease, as well as in the osseointegration of dental implants, due to its anti-inflammatory and osseoconductive effects. Melatonin has demonstrated to have beneficial effects on dental pathologies, although further research is needed to understand the exact mechanisms of this molecule.

Comparing the Behavioural Effects of Exogenous Growth Hormone and Melatonin in Young and Old Wistar Rats

Growth hormone (GH) and melatonin are two hormones with quite different physiological effects. Curiously, their secretion shows parallel and severe age-related reductions. This has promoted many reports for studying the therapeutic supplementation of both hormones in an attempt to avoid or delay the physical, physiological, and psychological decay observed in aged humans and in experimental animals. Interestingly, the effects of the external administration of low doses of GH and of melatonin were surprisingly similar, as both hormones caused significant improvements in the functional capabilities of aged subjects. The present report aims at discerning the eventual difference between cognitive and motor effects of the two hormones when administered to young and aged Wistar rats. The effects were tested in the radial maze, a test highly sensitive to the age-related impairments in working memory and also in the rotarod test, for evaluating the motor coordination. The results showed that both hormones caused clear improvements in both tasks. However, while GH improved the cognitive capacity and, most importantly, the physical stamina, the effects of melatonin should be attributed to its antioxidant, anxiolytic, and neuroprotective properties.

Alterations of the circadian system in Parkinson's disease patients

Alterations of circadian rhythms are among the most debilitating non-motor symptoms in Parkinson's Disease (PD). Although a growing awareness towards these symptoms has occurred during the last decade, their underlying neuropathophysiology remains poorly understood and consequently no effective therapeutic strategies are available to alleviate these problems. Recent studies have investigated multiple circadian rhythms at different stages of PD. The advances made have allowed an accurate evaluation of the affected underlying pathways and mechanisms. Here I dissect, over disease progression, the relative causal contribution to health impairments in PD patients of dysfunctions in the different components of the neural network governing circadian rhythms. A deeper understanding of these mechanisms will provide not only a greater understanding of disease neuropathology, but also hold the promise for effective therapies. © 2016 International Parkinson and Movement Disorder Society.

Melatonin Signal Transduction Pathways Require E-Box-Mediated Transcription of Per1 and Per2 to Reset the SCN Clock at Dusk

Melatonin is released from the pineal gland into the circulatory system at night in the absence of light, acting as “hormone of darkness” to the brain and body. Melatonin also can regulate circadian phasing of the suprachiasmatic nucleus (SCN). During the day-to-night transition, melatonin exposure advances intrinsic SCN neural activity rhythms via the melatonin type-2 (MT₂) receptor and downstream activation of protein kinase C (PKC). The effects of melatonin on SCN phasing have not been linked to daily changes in the expression of core genes that constitute the molecular framework of the circadian clock. Using real-time RT-PCR, we found that melatonin induces an increase in the expression of two clock genes, Period 1 (Per1) and Period 2 (Per2). This effect occurs at CT 10, when melatonin advances SCN phase, but not at CT 6, when it does not. Using anti-sense oligodeoxynucleotides (α ODNs) to Per 1 and Per 2, as well as to E-box enhancer sequences in the promoters of these genes, we show that their specific induction is necessary for the phase-altering effects of melatonin on SCN neural activity rhythms in the rat. These effects of melatonin on Per1 and Per2 were mediated by PKC. This is unlike day-active non-photic signals that reset the SCN clock by non-PCK signal transduction mechanisms and by decreasing Per1 expression. Rather, this finding extends roles for Per1 and Per2, which are critical to photic phase-resetting, to a nonphotic zeitgeber, melatonin, and suggest that the regulation of these clock gene transcripts is required for clock resetting by diverse regulatory cues.

Decreased 6-Sulfatoxymelatonin Excretion in Male GH-Deficient Children and Adolescents

AIM

To evaluate melatonin secretion in a group of untreated and treated male growth hormone (GH)-deficient children and adolescents.

METHODS

We studied 44 male subjects: 8 untreated GH-deficient patients (GHDnt), 16 treated GH-deficient patients (GHDt) and 20 healthy children and adolescents as control group (CG). We measured urinary 6-sulfatoxymelatonin (6-SM) in total (24-hour samples), nocturnal (18.00-8.00 h) and diurnal samples (8.00-18.00 h). Levels of 6-SM were expressed as micrograms excreted per time interval and x0394; values (difference between nighttime and daytime values).

RESULTS

Significant differences were observed among the 3 groups of pediatric subjects studied for total 6-SM (p < 0.0001), nocturnal 6-SM (p < 0.0001) and x0394; values (p < 0.0001). Subsequent analysis showed significantly higher levels for total 6-SM, nocturnal 6-SM and nighttime-daytime x0394; in the CG versus the GHDnt (p < 0.01) and in the CG versus the GHDt group (p < 0.01). No significant correlations were found between 6-SM excretion and insulin-like growth factor-1 values in the children and adolescents studied.

CONCLUSIONS

GH-deficient patients showed lower levels of 6-SM. Our findings provide a different insight to a further understanding of some chronobiological disorders involved in GH deficiency in children.

A new role for 5-methoxytryptophol on bone cells function in vitro

The present study investigates the direct action of 5-methoxytryptophol (5-MTX) in both MC3T3-E1 and RAW264.7 cells and compares it with melatonin (MEL), another 5-methoxyindol known to play a significant role on bone metabolism. We first screened increasing doses of both 5-MTX and MEL to determine their effect on metabolic activity and viability of preosteoblastic MC3T3-E1 cells. The optimal dose was used to determine its effect on differentiation of MC3T3-E1 cells and preosteoclastic RAW264.7 cells. Finally, we investigated the mechanism of action by adding the melatonin receptor antagonist luzindole (LUZ) and detecting the immunostaining of phospho-ERK. In MC3T3-E1 cells, most of the 5-MTX doses reduced slightly the metabolic activity of osteoblasts compared with the control, while MEL only decreased it for the highest dose (2.5 mM). As regards to cytotoxicity, low doses (0.001-0.1 mM) of both indoles showed a protective effect on osteoblasts, while the highest dose of MEL showed a higher cytotoxicity than the 5-MTX one. After 14 days of cell culture, Rankl mRNA levels were decreased, especially for 5-MTX. 5-MTX also induced a higher osteocalcin secretion and mineralization capacity than MEL. In RAW264.7 cells, 5-MTX decreased the number of osteoclast formed and its activity whereas MEL did not affect significantly the number of multinucleated TRAP-positive cells formed and showed a lower activity. Finally, MEL and 5-MTX promoted activation of the ERK1/2 pathway through the phosphorylation of ERK, while LUZ addition suppressed this effect. In conclusion, the present study demonstrates a new role of 5-MTX inhibiting osteoclastogenesis and promoting osteoblast differentiation.

The Impact of Melatonin in Research

Citation indexes represent helpful tools for evaluating the impact of articles on research. The aim of this study was to obtain the top-100 ranking of the most cited papers on melatonin, a relevant neurohormone mainly involved in phase-adjusting the biological clock and with certain sleep-promoting capability. An article search was carried out on the Institute for Scientific Information (ISI) Web of Science platform. Numbers of citations, names of authors, journals and their 2014-impact factor, year of publication, and experimental designs of studies were recorded. The ranking of the 100-most cited articles on melatonin research (up to February 2016) revealed a citation range from 1623 to 310. Narrative reviews/expert opinions were the most frequently cited articles, while the main research topics were oxidative stress, sleep physiology, reproduction, circadian rhythms and melatonin receptors. This study represents the first detailed analysis of the 100 top-cited articles published in the field of melatonin research, showing its impact and relevance in the biomedical field.

Melatonin: a possible link between the presence of artificial light at night and reductions in biological fitness

The mechanisms underpinning the ecological impacts of the presence of artificial night lighting remain elusive. One suspected underlying cause is that the presence of light at night (LAN) supresses nocturnal production of melatonin, a key driver of biological rhythm and a potent antioxidant with a proposed role in immune function. Here, we briefly review the evidence for melatonin as the link between LAN and changes in behaviour and physiology. We then present preliminary data supporting the potential for melatonin to act as a recovery agent mitigating the negative effects of LAN in an invertebrate. Adult crickets (Teleogryllus commodus), exposed to constant illumination, were provided with dietary melatonin (concentrations: 0, 10 or 100 µg ml(-1)) in their drinking water. We then compared survival, lifetime fecundity and, over a 4-week period, immune function (haemocyte concentration, lysozyme-like and phenoloxidase (PO) activity). Melatonin supplementation was able only partially to mitigate the detrimental effects of LAN: it did not improve survival or fecundity or PO activity, but it had a largely dose-dependent positive effect on haemocyte concentration and lysozyme-like activity. We discuss the implications of these relationships, as well as the usefulness of invertebrates as model species for future studies that explore the effects of LAN.

Tasimelteon for non-24-hour sleep-wake disorder in totally blind people (SET and RESET): two multicentre, randomised, double-masked, placebo-controlled phase 3 trials

BACKGROUND

Most totally blind people have non-24-hour sleep-wake disorder (non-24), a rare circadian rhythm disorder caused by an inability of light to reset their circadian pacemaker. In two consecutive placebo-controlled trials (SET and RESET), we assessed safety and efficacy (in terms of circadian entrainment and maintenance) of once-daily tasimelteon, a novel dual-melatonin receptor agonist.

METHODS

We undertook the placebo-controlled, randomised, double-masked trials in 27 US and six German clinical research centres and sleep centres. We screened totally blind adults (18-75 years of age), who were eligible for the randomisation phase of SET if they had a non-24-hour circadian period (τ) of 24·25 h or longer (95% CI greater than 24·0 and up to 24·9 h), as calculated from measurements of urinary 6-sulphatoxymelatonin rhythms. For SET, we used block randomisation to assign patients (1:1) to receive tasimelteon (20 mg) or placebo every 24 h at a fixed clock time 1 h before target bedtime for 26 weeks. Patients who entered the open-label group receiving tasimelteon in SET or who did not meet the SET inclusion criteria but did meet the RESET inclusion criteria were screened for RESET. A subset of the patients who entered the open-label group before the RESET study and who had eligible τ values were screened for RESET after completing the open-label treatment. In RESET, we withdrew tasimelteon in a randomised manner (1:1) in patients who responded (ie, entrained) after a tasimelteon run-in period. Entrainment was defined as having τ of 24·1 h or less and a 95% CI that included 24·0 h. In SET, the primary endpoint was the proportion of entrained patients, assessed in the intention-to-treat population. The planned step-down primary endpoint assessed the proportion of patients who had a clinical response (entrainment at month 1 or month 7 plus clinical improvement, measured by the Non-24 Clinical Response Scale). In RESET, the primary endpoint was the proportion of non-entrained patients, assessed in the intention-to-treat population. Safety assessments included adverse events and clinical laboratory measures, assessed in all treated patients. These trials are registered with ClinicalTrials.gov, numbers NCT01163032 and NCT01430754.

FINDINGS

Between Aug 25, 2010, and July 5, 2012, we screened 391 totally blind patients for SET, of whom 84 (22%) were assigned to receive tasimelteon (n=42) or placebo (n=42). Two patients in the tasimelteon group and four in the placebo group discontinued the study before τ was measured, due to adverse events, withdrawal of consent, and a protocol deviation. Circadian entrainment occurred in eight (20%) of 40 patients in the tasimelteon group compared with one (3%) of 38 patients in the placebo group at month 1 (difference 17%, 95% CI 3·2-31·6; p=0·0171). Nine (24%) of 38 patients showed a clinical response, compared with none of 34 in the placebo group (difference 24%, 95% CI 8·4-39·0; p=0·0028). Between Sept 15, 2011, and Oct 4, 2012, we screened 58 patients for eligibility in RESET, 48 (83%) of whom had τ assessed and entered the open-label tasimelteon run-in phase. 24 (50%) patients entrained, and 20 (34%) were enrolled in the randomisation phase. Two (20%) of ten patients who were withdrawn to placebo remained entrained compared with nine (90%) of ten who continued to receive tasimelteon (difference 70%, 95% CI 26·4-100·0; p=0·0026). No deaths were reported in either study, and discontinuation rates due to adverse events were comparable between the tasimelteon (3 [6%] of 52 patients) and placebo (2 [4%] of 52 patients) treatment courses. The most common side-effects associated with tasimelteon in SET were headache (7 [17%] of 42 patients given tasimelteon vs 3 [7%] of 42 patients given placebo), elevated liver enzymes (4 [10%] vs 2 [5%]), nightmares or abnormal dreams (4 [10%] vs none), upper respiratory tract infection (3 [7%] vs none], and urinary tract infections (3 [7%] vs 1 [2%]).

INTERPRETATION

Once-daily tasimelteon can entrain totally blind people with non-24; however, continued tasimelteon treatment is necessary to maintain these improvements.

FUNDING

Vanda Pharmaceuticals.