Measuring melatonin by immunoassay

Resetting of the Human Circadian Melatonin Rhythm by Ambient Hypoxia

Circadian clocks in the body drive daily cycles in physiology and behavior. A master clock in the brain maintains synchrony with the environmental day-night cycle and uses internal signals to keep clocks in other tissues aligned. Work in cell cultures uncovered cyclic changes in tissue oxygenation that may serve to reset and synchronize circadian clocks. Here we show in healthy humans, following a randomized controlled single-blind counterbalanced crossover study design, that one-time exposure to moderate ambient hypoxia (FiO2 ~15%, normobaric) for ~6.5 h during the early night advances the dim-light onset of melatonin secretion by 9 min (95% CI: 1-16 min). Exposure to moderate hypoxia may thus be strong enough to entrain circadian clocks to a 24-h cycle in the absence of other entraining cues. Together, the results provide direct evidence for an interaction between the body's hypoxia-sensing pathway and circadian clocks. The finding offers a mechanism through which behaviors that change tissue oxygenation (e.g., exercise and fasting/eating) can affect circadian timing and through which hypoxia-related diseases (e.g., obstructive sleep apnea and chronic obstructive pulmonary disease) can result in circadian misalignment and associated pathologies. Trial Registration: Registration number: DRKS00023387; German Clinical Trials Register: http://www.drks.de.

Evaluation of salivary melatonin and MMP-9 levels in periodontal diseases

OBJECTIVE

The aim of this study was to evaluate salivary matrix metalloproteinase-9 (MMP-9) and melatonin levels in individuals with periodontal health, gingivitis, and periodontitis.

DESIGN

A total of 170 participants were enrolled in this study. They included 57 periodontally healthy individuals, 58 gingivitis patients, and 55 periodontitis patients. Saliva samples were collected by passive drool technique. The levels of MMP-9 and melatonin in saliva were measured biochemically using the ELISA method.

RESULTS

Salivary MMP-9 levels in the periodontitis group were significantly higher than those in the gingivitis and periodontally healthy groups, while salivary melatonin levels were significantly lower (p<0.001). A positive correlation was observed between clinical periodontal parameters and salivary MMP-9 levels, while salivary melatonin levels were negatively correlated (p<0.001). A negative correlation was also observed between salivary MMP-9 levels and salivary melatonin levels (p<0.001).

CONCLUSION

This study shows that the level of melatonin in saliva is associated with periodontal disease and with the level of MMP-9 in saliva, which plays a role in this disease.

Antioxidant and Anti-Inflammatory Properties of Melatonin in Secondary Traumatic Brain Injury

Traumatic brain injury (TBI) is a disease resulting from external physical forces acting against the head, leading to transient or chronic damage to brain tissue. Primary brain injury is an immediate and, therefore, rather irreversible effect of trauma, while secondary brain injury results from a complex cascade of pathological processes, among which oxidative stress and neuroinflammation are the most prominent. As TBI is a significant cause of mortality and chronic disability, with high social costs all over the world, any form of therapy that may mitigate trauma-evoked brain damage is desirable. Melatonin, a sleep-wake-cycle-regulating neurohormone, exerts strong antioxidant and anti-inflammatory effects and is well tolerated when used as a drug. Due to these properties, it is very reasonable to consider melatonin as a potential therapeutic molecule for TBI treatment. This review summarizes data from in vitro studies, animal models, and clinical trials that focus on the usage of melatonin in TBI.

The appropriate and inappropriate uses of saliva melatonin measurements

Melatonin is produced in the pineal gland under very tight control through the influences of light and the suprachiasmatic nucleus. As such, melatonin circulates in the blood at levels <3 pg/ml during the day and is only actively secreted at night reaching levels of approximately 100 pg/ml. As a consequence of binding to plasma proteins, free melatonin appears in saliva at approximately one third the plasma concentration. Measurement of melatonin is technically challenging because of these very low concentrations and while a number of commercial immunoassay kits are available and mass spectrometry assay methods have been published, not all are fit for purpose and can lead to unreliable conclusions. In this review I discuss the aspects of pineal melatonin production that saliva melatonin reflects, the factors influencing melatonin production or metabolism, saliva collection and analysis methods. Examples are provided of the appropriate use of saliva melatonin measurements; Dim Light Melatonin Onset (DLMO) assessment, impact of light on melatonin and the monitoring of rhythms prior to specific treatments. Examples of inappropriate use of saliva melatonin measurements are also provided including the use of poorly validated assays, morning saliva collections, attempts to stimulate melatonin, and linking specific illnesses to saliva melatonin levels.

Melatonin reverses EGFR-TKI therapeutic resistance by modulating crosstalk between circadian-related gene signature and immune infiltration patterns in patients with COVID-19 and lung adenocarcinoma

BACKGROUND

Patients with lung cancer exhibit the poorest outcomes when infected with coronavirus disease 2019 (COVID-19). However, the potential impact of COVID-19 on the tumor microenvironment (TME) of lung adenocarcinoma (LUAD) remains unknown.

METHODS

Expression data and clinical information were sourced from the Cancer Genome Atlas (TCGA) and Gene Expression Omnibus (GEO) databases. Prognostic, differentially expressed circadian-related genes (CRGs) were identified using multivariate Cox regression and LASSO regression analyses to establish an immune-related gene signature. The clinical value, immune landscape, somatic mutations, and drug sensitivity of high- and low-risk groups were assessed using Kaplan-Meier curves and immunotherapy cohorts. Finally, in vitro and in vivo experiments were conducted to elucidate the molecular function of melatonin in regulating the immune microenvironment and therapeutic resistance.

RESULTS

Three circadian-related patterns and distinct CRGs clusters were identified based on the abnormal expression of 13 CRGs. Circadian genomic phenotypes were identified based on 13 circadian phenotype-related differentially expressed genes (DEGs). A CRGs risk signature was constructed; the high CRGs risk group displayed an immunosuppressive TME, poor survival, and therapy resistance. Melatonin reversed EGFR-tyrosine kinase inhibitor (EGFR-TKI) resistance by regulating immune cell infiltration into the TME, both in vitro and in vivo.

CONCLUSIONS

The investigation revealed crosstalk between CRGs signatures and immune infiltration patterns in LUAD and COVID-19. Melatonin acted as a promising agent to suppress the malignant features of lung cancer and enhance treatment sensitivity by modulating the TME.

A Protocol to Determine Circadian Phase by At-Home Salivary Dim Light Melatonin Onset Assessment

Internal circadian phase assessment is increasingly acknowledged as a critical clinical tool for the diagnosis, monitoring, and treatment of circadian rhythm sleep-wake disorders and for investigating circadian timing in other medical disorders. The widespread use of in-laboratory circadian phase assessments in routine practice has been limited, most likely because circadian phase assessment is not required by formal diagnostic nosologies, and is not generally covered by insurance. At-home assessment of salivary dim light melatonin onset (DLMO, a validated circadian phase marker) is an increasingly accepted approach to assess circadian phase. This approach may help meet the increased demand for assessments and has the advantages of lower cost and greater patient convenience. We reviewed the literature describing at-home salivary DLMO assessment methods and identified factors deemed to be important to successful implementation. Here, we provide specific protocol recommendations for conducting at-home salivary DLMO assessments to facilitate a standardized approach for clinical and research purposes. Key factors include control of lighting, sampling rate, and timing, and measures of patient compliance. We include findings from implementation of an optimization algorithm to determine the most efficient number and timing of samples in patients with Delayed Sleep-Wake Phase Disorder. We also provide recommendations for assay methods and interpretation. Providing definitive criteria for each factor, along with detailed instructions for protocol implementation, will enable more widespread adoption of at-home circadian phase assessments as a standardized clinical diagnostic, monitoring, and treatment tool.

Melatonin: A potential protective multifaceted force for sepsis-induced cardiomyopathy

Sepsis is a life-threatening condition manifested by organ dysfunction caused by a dysregulated host response to infection. Lung, brain, liver, kidney, and heart are among the affected organs. Sepsis-induced cardiomyopathy is a common cause of death among septic patients. Sepsis-induced cardiomyopathy is characterized by an acute and reversible significant decline in biventricular both systolic and diastolic function. This is accompanied by left ventricular dilatation. The pathogenesis underlying sepsis-induced cardiomyopathy is multifactorial. Hence, targeting an individual pathway may not be effective in halting the extensive dysregulated immune response. Despite major advances in sepsis management strategies, no effective pharmacological strategies have been shown to treat or even reverse sepsis-induced cardiomyopathy. Melatonin, namely, N-acetyl-5-methoxytryptamine, is synthesized in the pineal gland of mammals and can also be produced in many cells and tissues. Melatonin has cardioprotective, neuroprotective, and anti-tumor activity. Several literature reviews have explored the role of melatonin in preventing sepsis-induced organ failure. Melatonin was found to act on different pathways that are involved in the pathogenesis of sepsis-induced cardiomyopathy. Through its antimicrobial, anti-inflammatory, and antioxidant activity, it offers a potential role in sepsis-induced cardiomyopathy. Its antioxidant activity is through free radical scavenging against reactive oxygen and nitrogen species and modulating the expression and activity of antioxidant enzymes. Melatonin anti-inflammatory activities control the overactive immune system and mitigate cytokine storm. Also, it mitigates mitochondrial dysfunction, a major mechanism involved in sepsis-induced cardiomyopathy, and thus controls apoptosis. Therefore, this review discusses melatonin as a promising drug for the management of sepsis-induced cardiomyopathy.

Estimating dim light melatonin onset time in children using delta changes in melatonin

We aimed to establish a method for estimating dim light melatonin onset (DLMO) using mathematical slopes calculated from melatonin concentrations at three sampling points before and after sleep in children. The saliva of 30 children (mean age ± SD: 10.2 ± 1.3 years old) was collected under dim-light conditions up to six times every hour starting at 17:30 (t17), namely, 18:30 (t18), 19:30 (t19), 20:30 (t20), 21:30 (t21), 22:30 (t22), and 23:30 (t23), in the evening, and at 6:00 (t30) the following morning. We calculated SLOPE on (mathematical slope between melatonin concentrations at t18 and t20, t21 or t22), SLOPE off (the slope between t20, t21 or t22, and t30), and Δ S L O P E , which is generated by subtracting SLOPE on from SLOPE off . DLMO was estimated by multiple regression analysis with the leave-one-out cross-validation (LOOCV) method using SLOPE on and SLOPE off , and Δ S L O P E . The intraclass correlation coefficient (ICC) between the estimated and measured DLMOs was used as the index of estimation accuracy. DLMOs estimated using multiple regression equations with SLOPE on and SLOPE off yielded significant ICCs for the measured DLMOs, with the largest ICC at t20 (ICC = 0.634). Additionally, the ICC between the estimated and measured DLMOs using the equation with Δ S L O P E was significant, with a larger ICC at t20 (ICC = 0.726) than that of the equation with SLOPE on and SLOPE off . Our results showed that DLMO could be estimated with a certain level of accuracy from salivary melatonin levels at three time points before and after sleep in children.

Supplementary Information

The online version contains supplementary material available at 10.1007/s41105-023-00493-x.

Power Analysis for Human Melatonin Suppression Experiments

In humans, the nocturnal secretion of melatonin by the pineal gland is suppressed by ocular exposure to light. In the laboratory, melatonin suppression is a biomarker for this neuroendocrine pathway. Recent work has found that individuals differ substantially in their melatonin-suppressive response to light, with the most sensitive individuals being up to 60 times more sensitive than the least sensitive individuals. Planning experiments with melatonin suppression as an outcome needs to incorporate these individual differences, particularly in common resource-limited scenarios where running within-subjects studies at multiple light levels is costly and resource-intensive and may not be feasible with respect to participant compliance. Here, we present a novel framework for virtual laboratory melatonin suppression experiments, incorporating a Bayesian statistical model. We provide a Shiny web app for power analyses that allows users to modify various experimental parameters (sample size, individual-level heterogeneity, statistical significance threshold, light levels), and simulate a systematic shift in sensitivity (e.g., due to a pharmacological or other intervention). Our framework helps experimenters to design compelling and robust studies, offering novel insights into the underlying biological variability in melatonin suppression relevant for practical applications.

Common Methods of Extraction and Determination of Phytomelatonin in Plants

The presence of melatonin in plants, called phytomelatonin, has gained great interest in recent years. The determination of phytomelatonin levels in plant extracts for both physiological and plant foodstuff studies requires sophisticated techniques due to the low endogenous levels of this indolic compound with hormonal nature. This chapter presents the most common and advanced techniques in the determination of phytomelatonin, with special emphasis on the techniques of extraction, cleaning, separation, detection, identification, and quantification. Multiple examples and recommendations are presented for a clear overview of the pros and cons of phytomelatonin determinations in plant tissues, seeds, and fruits, mainly.

Melatonin facts: Lack of evidence that melatonin is a radical scavenger in living systems

Melatonin is a small natural compound, so called a neuro-hormone that is synthesized mainly in pineal gland in animals. Its main role is to master the clock of the body, under the surveillance of light. In other words, it transfers the information concerning night and day to the peripheral organs which, without it, could not "know" which part of the circadian rhythm the body is in. Besides its main circadian and circannual rhythms mastering, melatonin is reported to be a radical scavenger and/or an antioxidant. Because radical scavengers are chemical species able to neutralize highly reactive and toxic species such as reactive oxygen species, one would like to transfer this property to living system, despite impossibilities already largely reported in the literature. In the present commentary, we refresh the memory of the readers with this notion of radical scavenger, and review the possible evidence that melatonin could be an in vivo radical scavenger, while we only marginally discuss here the fact that melatonin is a molecular antioxidant, a feature that merits a review on its own. We conclude four things: (i) the evidence that melatonin is a scavenger in acellular systems is overwhelming and could not be doubted; (ii) the transposition of this property in living (animal) systems is (a) theoretically impossible and (b) not proven in any system reported in the literature where most of the time, the delay of the action of melatonin is over several hours, thus signing a probable induction of cellular enzymatic antioxidant defenses; (iii) this last fact needs a confirmation through the discovery of a nuclear factor-a key relay in induction processes-that binds melatonin and is activated by it and (iv) we also gather the very important description of the radical scavenging capacity of melatonin in acellular systems that is now proven and shared by many other double bond-bearing molecules. We finally discussed briefly on the reason-scientific or else-that led this description, and the consequences of this claim, in research, in physiology, in pathology, but most disturbingly in therapeutics where a vast amount of money, hope, and patient bien-être are at stake.

Hypnotic effects of melatonin depend on the environmental lighting conditions in the rat

Acute effects of exogenous melatonin have been widely reported to promote sleep or induce drowsiness in human. However, testing of the hypnotic effects of melatonin in nocturnal rodents has yielded contradictory results. The latter may be associated with differences in concentration, lighting conditions, time of administration of melatonin, and possibly the type of analysis. In this study, electroencephalogram (EEG) and electromyogram were recorded in pigmented male Brown Norway rats under both light-dark (LD) and constant dark (DD) conditions. Melatonin was administered intraperitoneally at a moderate dose of 3 mg/kg, at either 1 h after lights on under LD condition or 1 h after the activity offset under DD condition. The dosage is known to be able to entrain nocturnal rodents in DD conditions, but does not change sleep in rodents in LD. Only the rats under DD conditions showed a significant reduction in nonrapid eye movement (NREM) sleep latency, while the NREM sleep power spectrum remained unaffected. Under LD condition, melatonin did not alter NREM and rapid eye movement (REM) sleep latency, and had only minor effects on the NREM sleep EEG. Regardless of lighting conditions, melatonin administration resulted in less, but longer episodes for all vigilance states suggesting increased vigilance state consolidation. In the discussion, we compare our results with a summary of previously published data concerning the hypnotic effects of melatonin in polysomnographic/EEG-confirmed sleep in humans and nocturnal rodents. In conclusion, the hypnotic effect of exogenous melatonin in nocturnal rodents not only depends on the time of day, and concentration, but is also influenced by the lighting conditions. Regardless of inducing sleep or not, melatonin may consolidate sleep and through that enhance sleep quality.

The evaluation of melatonin levels in chronic spontaneous urticaria: A case control study

Background: Although sleep disturbance is known to be common in patients with chronic spontaneous urticaria (CSU), sleep hormone levels in the blood have never before been studied in CSU. Objective: In this study, we aimed to evaluate the serum melatonin levels in patients with CSU. Methods: For the patient group, 80 patients with recently diagnosed CSU, and, for the control group, 75 healthy controls (HC) were included. The study participants' melatonin levels were measured by using the enzyme-linked immunosorbent assay method. CSU disease activity was evaluated by using the urticaria activity score-7 (UAS-7), and the quality of life was assessed with the chronic urticaria quality of life questionnaire (CU-Q2oL). The patients with concomitant diseases likely to affect the melatonin levels or those using related medications were excluded from the study. Results: The patient group consisted of 53 female subjects (67%); the median (interquartile range) age was 34 years (27-43 years). The levels of melatonin were lower in the patients with CSU when compared with the HCs (p < 0.03). The melatonin levels had no significant relationship between UAS-7 and the total scores in CU-Q2oL (p > 0.05). However, a significant negative correlation in the melatonin levels was observed with questions 7 (overall sleep assessment) and 11 (difficulty in falling into sleep) in the CU-Q2oL (r = -0.55 [p < 0.001] and r = -0.62 [p < 0.001], respectively). Conclusion: The presence of low melatonin levels in the patients with CSU suggests that melatonin has a key regulatory role in the CSU development in addition to the deterioration in sleep quality. A new treatment strategy to increase the melatonin levels in CSU may be pursued in further studies to confirm our findings.

Determination of well-being-related markers in nails by liquid chromatography tandem mass spectrometry

Well-being is a multifactorial positive state that is highly influenced by some endogenous molecules that control happiness and euphoric feelings. These molecules, e.g., neurotransmitters, hormones and their derivatives, play a crucial role in metabolism and may be referred to as "well-being-related markers". The deregulation of well-being-related markers can lead to organism malfunctions and life-threatening states. In this research, we aimed to evaluate the potential of nails for the chronic production of several well-being-related markers. For this purpose, we developed an LCMS /MS-based method for the determination of 10 well-being-related markers, including melatonin, serotonin, cortisol, kynurenine and several precursors and metabolites. The method was optimized regarding different analytical steps: required sample amount, extraction time, number of required extractions, preconcentration, injection volume and MS conditions. Method validation was performed by two different approaches: (i) using surrogate nail matrix and (ii) using authentic nail samples by standard additions. The method was found to be linear in the expected endogenous range and sensitive enough to determine the low endogenous concentration levels in nails. Accuracy and precision were appropriate in both validation approaches. As proof of concept, the method was used (i) to correlate fingernail and toenail levels for all metabolites in 22 volunteers, (ii) to establish the endogenous concentration range of all metabolites in females (n = 50) and males (n = 34) and (iii) to correlate the metabolite levels with age. For some metabolites, the calculated ranges have been reported for the first time. In summary, the present strategy to evaluate well-being-related markers in nails may be a useful tool for the evaluation of the production of these important compounds with high potential for a wide range of clinical purposes.

A Cross-Sectional Study of Myopia and Morning Melatonin Status in Northern Irish Adolescent Children

Purpose

Previous studies have demonstrated an association between melatonin status and both refractive error and axial length in young adult myopes. This study aimed to determine if this relationship extends to a younger adolescent cohort.

Methods

Healthy children aged 12-15 years provided morning saliva samples before attending Ulster University (55°N) for cycloplegic autorefraction and axial length measures. Participants completed questionnaires describing recent sleep habits and physical activity. Salivary melatonin was quantified using high-performance liquid chromatography-tandem mass spectrometry. Data collection for all participants occurred over a 1-week period (April 2021).

Results

Seventy participants aged 14.3 (95% CI: 14.2-14.5) years were categorised by spherical equivalent refraction [SER] (range: -5.38DS to +1.88DS) into two groups; myopic SER ≤ -0.50DS (n = 22) or nonmyopic -0.50DS < SER ≤ +2.00DS (n = 48). Median morning salivary melatonin levels were 4.52 pg/ml (95% CI: 2.60-6.02) and 4.89 pg/ml (95% CI: 3.18-5.66) for myopic and nonmyopic subjects, respectively, and did not differ significantly between refractive groups (P = 0.91). Melatonin levels were not significantly correlated with SER, axial length, sleep, or activity scores (Spearman's rank, all P > 0.39). Higher levels of physical activity were associated with higher sleep quality (Spearman's rank, ρ = -0.28, P = 0.02).

Conclusion

The present study found no significant relationship between morning salivary melatonin levels and refractive error or axial length in young adolescents. This contrasts with outcomes from a previous study of adults with comparable methodology, season of data collection, and geographical location. Prospective studies are needed to understand the discrepancies between adult and childhood findings and evaluate whether melatonin levels in childhood are indicative of an increased risk for future onset of myopia and/or faster axial growth trajectories and myopia progression in established myopes. Future work should opt for a comprehensive dim-light melatonin onset protocol to determine circadian phase.

Potential Neuroprotective Role of Melatonin in Sepsis-Associated Encephalopathy Due to Its Scavenging and Anti-Oxidative Properties

Sepsis is defined as life-threatening organ dysfunction caused by a dysregulated host response to infection. The brain is one of the organs involved in sepsis, and sepsis-induced brain injury manifests as sepsis-associated encephalopathy (SAE). SAE may be present in up to 70% of septic patients. SAE has a very wide spectrum of clinical symptoms, ranging from mild behavioral changes through cognitive disorders to disorders of consciousness and coma. The presence of SAE increases mortality in the population of septic patients and may lead to chronic cognitive dysfunction in sepsis survivors. Therefore, therapeutic interventions with neuroprotective effects in sepsis are needed. Melatonin, a neurohormone responsible for the control of circadian rhythms, exerts many beneficial physiological effects. Its anti-inflammatory and antioxidant properties are well described. It is considered a potential therapeutic factor in sepsis, with positive results from studies on animal models and with encouraging results from the first human clinical trials. With its antioxidant and anti-inflammatory potential, it may also exert a neuroprotective effect in sepsis-associated encephalopathy. The review presents data on melatonin as a potential drug in SAE in the wider context of the pathophysiology of SAE and the specific actions of the pineal neurohormone.

Methylene blue molecularly imprinted polymer for melatonin determination in urine and saliva samples

A highly sensitive and rapid electrochemical sensor was developed for detecting melatonin using a molecularly imprinted polymer (MIP) with methylene blue as the functional monomer and melatonin as the template. The MIP was synthesized via a simple electropolymerization process that did not require an initiating reagent. The sensor demonstrated good selectivity for melatonin against common interferences such as lactate, cytosine, cytidine, urea, ascorbic acid, creatine, creatinine, serotonin, and tryptophan. Melatonin detection was achieved at a potential of 0.60 V vs. Ag/AgCl with a sensitivity of 138.8 ± 4.7 µA µM‒1 in the linear range 0.097 - 200 µM and a limit of detection of 29 nM (3SB/m). The sensor exhibited excellent reproducibility and repeatability for both within (intra) and between (inter) electrodes (%RSD < 3% for n = 3). The sensor was applied to authentic urine and saliva samples with recoveries of 103 ± 1% and 102 ± 1%, respectively.

Gut microbiota crosstalk mechanisms are key in pulmonary hypertension: The involvement of melatonin is instrumental too

The microbiota refers to a plethora of microorganisms with a gene pool of approximately three million, which inhabits the human gastrointestinal tract or gut. The latter, not only promotes the transport of nutrients, ions, and fluids from the lumen to the internal environment but is linked with the development of diseases including coronary artery disease, heart failure, and lung diseases. The exact mechanism of how the microbiota achieves crosstalk between itself and distant organs/tissues is not clear, but factors released to other organs may play a role, like inflammatory and genetic factors, and now we highlight melatonin as a novel mediator of the gut-lung crosstalk. Melatonin is present in high concentrations in the gut and the lung and has recently been linked to the pathogenesis of pulmonary hypertension (PH). In this comprehensive review of the literature, we suggest that melatonin is an important link between the gut microbiota and the development of PH (where suppressed melatonin-crosstalk between the gut and lungs could promote the development of PH). More studies are needed to investigate the link between the gut microbiota, melatonin and PH. Studies could also investigate whether microbiota genes play a role in the epigenetic aspects of PH. This is relevant because, for example, dysbiosis (caused by epigenetic factors) could reduce melatonin signaling between the gut and lungs, reduce subcellular melatonin concentrations in the gut/lungs, or reduce melatonin serum levels secondary to epigenetic factors. This area of research is largely unexplored and further studies are warranted.

Melatonin: Facts, Extrapolations and Clinical Trials

Melatonin is a fascinating molecule that has captured the imagination of many scientists since its discovery in 1958. In recent times, the focus has changed from investigating its natural role as a transducer of biological time for physiological systems to hypothesized roles in virtually all clinical conditions. This goes along with the appearance of extensive literature claiming the (generally) positive benefits of high doses of melatonin in animal models and various clinical situations that would not be receptor-mediated. Based on the assumption that melatonin is safe, high doses have been administered to patients, including the elderly and children, in clinical trials. In this review, we critically review the corresponding literature, including the hypotheses that melatonin acts as a scavenger molecule, in particular in mitochondria, by trying not only to contextualize these interests but also by attempting to separate the wheat from the chaff (or the wishful thinking from the facts). We conclude that most claims remain hypotheses and that the experimental evidence used to promote them is limited and sometimes flawed. Our review will hopefully encourage clinical researchers to reflect on what melatonin can and cannot do and help move the field forward on a solid basis.

Development and Validation of an Ultrasensitive LC-MS/MS Method for the Quantification of Melatonin in Human Saliva

A growing body of literature describes the potential effects of circadian disruption on human health. Indeed, psychiatric diseases, metabolic syndrome, and cancers may be linked to disturbance of the circadian rhythm. Currently, the best practice to assess circadian rhythm is the measurement of melatonin levels. Our goal was thus to develop and validate a highly sensitive LC-MS/MS method to follow salivary melatonin levels throughout the day and night. Our method reached a lower limit of the measuring interval (LLMI) of 0.8 pg/mL. To our knowledge, it is the most sensitive method allowing quantitation of melatonin in saliva. Saliva, obtained from passive drooling or salivette, was extracted by an efficient and quick liquid-liquid extraction with no further cleanup needed. The method was validated according to the European Medicines Agency (EMA) guidelines and provided excellent results regarding accuracy, precision, linearity, selectivity, and specificity. Comparison between radioimmunoassay and our method was performed and showed differences at low levels, most likely due to cross-reactivity with other indols. To assess daytime melatonin levels in humans, salivary melatonin levels of ten volunteers were monitored throughout the day and showed lower daytime levels than reported in previous studies.

Structural properties and binding mechanism of DNA aptamers sensing saliva melatonin for diagnosis and monitoring of circadian clock and sleep disorders

Circadian desynchrony with the external light-dark cycle influences the rhythmic secretion of melatonin which is among the first signs of circadian rhythm sleep disorders. An accurate dim light melatonin onset (established indicator of circadian rhythm sleep disorders) measurement requires lengthy assays, and antibody affinities alterations, especially in patients with circadian rhythm disorders whose melatonin salivary levels vary significantly, making antibodies detection mostly inadequate. In contrast, aptamers with their numerous advantages (e.g., target selectivity, structural flexibility in tuning binding affinities, small size, etc.) can become preferable biorecognition molecules for salivary melatonin detection with high sensitivity and specificity. This study thoroughly characterizes the structural property and binding mechanism of a single-stranded DNA aptamer full sequence (MLT-C-1) and its truncated versions (MLT-A-2, MLT-A-4) to decipher its optimal characteristics for saliva melatonin detection. We use circular dichroism spectroscopy to determine aptamers' conformational changes under different ionic strengths and showed that aptamers display a hairpin loop structure where few base pairs in the stem play a significant role in melatonin binding and formation of aptamer stabilized structure. Through microscale thermophoresis, aptamers demonstrated a high binding affinity in saliva samples (MLT-C-1F K_d = 12.5 ± 1.7 nM; MLT-A-4F K_d = 11.2 ± 1.6 nM; MLT-A-2F K_d = 2.4 ± 2.8 nM; limit-of-detection achieved in pM, highest sensitivity attained for MLT-A-2F aptamer with the lowest detection limit of 1.35 pM). Our data suggest that aptamers are promising as biorecognition molecules and provide the baseline parameters for the development of an aptamer-based point-of-care diagnostic system for melatonin detection and accurate profiling of its fluctuations in saliva.

Desynchronizing the sleep---wake cycle from circadian timing to assess their separate contributions to physiology and behaviour and to estimate intrinsic circadian period

Circadian clocks drive cyclic variations in many aspects of physiology, but some daily variations are evoked by periodic changes in the environment or sleep-wake state and associated behaviors, such as changes in posture, light levels, fasting or eating, rest or activity and social interactions; thus, it is often important to quantify the relative contributions of these factors. Yet, circadian rhythms and these evoked effects cannot be separated under typical 24-h day conditions, because circadian phase and the length of time awake or asleep co-vary. Nathaniel Kleitman's forced desynchrony (FD) protocol was designed to assess endogenous circadian rhythmicity and to separate circadian from evoked components of daily rhythms in multiple parameters. Under FD protocol conditions, light intensity is kept low to minimize its impact on the circadian pacemaker, and participants have sleep-wake state and associated behaviors scheduled to an imposed non-24-h cycle. The period of this imposed cycle, Τ, is chosen so that the circadian pacemaker cannot entrain to it and therefore continues to oscillate at its intrinsic period (τ, ~24.15 h), ensuring circadian components are separated from evoked components of daily rhythms. Here we provide detailed instructions and troubleshooting techniques on how to design, implement and analyze the data from an FD protocol. We provide two procedures: one with general guidance for designing an FD study and another with more precise instructions for replicating one of our previous FD studies. We discuss estimating circadian parameters and quantifying the separate contributions of circadian rhythmicity and the sleep-wake cycle, including statistical analysis procedures and an R package for conducting the non-orthogonal spectral analysis method that enables an accurate estimation of period, amplitude and phase.

Melatonin in different food samples: Recent update on distribution, bioactivities, pretreatment and analysis techniques

Melatonin (MLT) plays a significant role on maintaining the basic physiological functions and regulating various metabolic processes in plentiful organisms. Recent years have witnessed an increase in MLT's share in global market with its affluent functions. However, the worrisome quality issues and inappropriate or excessive application of MLT take place inevitably. In addition, its photosensitive properties, oxidation, complex substrate concentration and trace levels leave exact detection of MLT doubly difficult. Therefore, it is essential to exploit precise, sensitive and stable extraction and detection methods to resolve above questions. In this study, we reviewed the distribution and bioactivities of MLT and conducted a comprehensive overview of the developments of pretreatment and analysis methods for MLT in food samples since 2010. Commonly used pretreatment methods for MLT include not only traditional techniques, but also novel ones, such as solid-phase extraction, QuEChERS, microextraction by packed sorbent, solid phase microextraction, liquid phase microextraction, and so on. Analysis methods include liquid chromatography coupled with different detectors, GC methods, capillary electrophoresis, sensors, and so on. The advantages and disadvantages of different techniques have been compared and the development tendency was prospected.

Melatonin: Emerging Player in the Management of Oral Cancer

Oral cancer (OC) has emerged as a major medical and social issue in many industrialized nations due to the high death rate. It is becoming increasingly common in people under the age of 45, although the underlying causes and mechanisms of this increase remain unclear. Melatonin, as a pleiotropic hormone, plays a pivotal role in a wide variety of cellular and physiological functions. Mounting evidence supports melatonin's ability to modify/influence oral carcinogenesis, help in the reduction of the incidence of OC, and increase chemo- and radiosensitivity. Despite its potential anti-carcinogenic effects, the precise function of melatonin in the management of OC is not well understood. This review summarizes the current knowledge regarding melatonin function in anti-carcinogenesis mechanisms for OC. In addition, clinical assessment and the potential therapeutic utility of melatonin in OC are discussed. This review will provide a basis for researchers to create new melatonin-based personalized medicines for treating and preventing OC.

Circadian phase advances in children during camping life according to the natural light-dark cycle

BACKGROUND

It is known that the circadian rhythm phase in adults can be advanced in a natural light-dark cycle without electrical lighting. However, the effect of advanced sleep-wake timing according to the natural light-dark cycle on children's circadian phase is unclear. We investigated the effects of approximately 2 weeks of camping life with little access to artificial lighting on children's circadian phases. We also conducted an exploratory examination on the effects of wake time according to natural sunrise time on the manner of the advance of their circadian phases.

METHODS

Twenty-one healthy children (mean ± SD age, 10.6 ± 1.4 years) participated in a camping program with wake time (4:00) being earlier than sunrise time (EW condition), and 21 healthy children (10.4 ± 1.1 years) participated in a camping program with wake time (5:00) being almost matched to sunrise time (SW condition). Salivary dim light melatonin onset (DLMO) before the camping program and that after approximately 2 weeks of camping were compared.

RESULTS

DLMO was advanced by approximately 2 h after the camping program compared with the circadian phase in daily life in both conditions. In addition, the advances in DLMO were significantly correlated with mid-sleep points before the camp in both conditions (EW: r = 0.72, p < 0.01, SW: r = 0.70, p < 0.01). These correlations mean that the phase advance was greater for the children with delayed sleep habits in daily life. Furthermore, in the EW condition, mean DLMO after the camp (18:09 ± 0:33 h) was earlier than natural sunset time and there was no significant decrease in interindividual variability in DLMO. On the other hand, in the SW condition, mean DLMO after the camp (18:43 ± 0:20 h) matched natural sunset time and interindividual variability in DLMO was significantly lower than that before the camp.

CONCLUSIONS

Camping with advanced sleep and wake timing under natural sunlight advances children's circadian phases. However, DLMO earlier than sunset in an early waking condition may lead to large interindividual variability in the circadian rhythm phase.

Dim light melatonin onset following simulated eastward travel is earlier in young males genotyped as PER35/5 than PER34/4

Inter-individual variability exists in recovery from jetlag following travel across time zones. Part of this variation may be due to genetic differences at the variable number tandem repeat (VNTR) polymorphism of the PERIOD3 (PER3) gene as this polymorphism has been associated with chronotype and sleep, as well as sensitivity to blue light on melatonin suppression. To test this hypothesis we conducted a laboratory-based study to compare re-entrainment in males genotyped as PER3^4/4 (n = 8) and PER3^5/5 (n = 8) following simulated eastward travel across six time zones. The recovery strategy included morning blue-enriched light exposure and appropriately-timed meals during the first 24 h after simulated travel. Dim light melatonin onset (DLMO), sleep characteristics, perceived sleepiness levels (Stanford Sleepiness Scale), and resting metabolic parameters were measured during constant routine periods before and after simulated travel. While DLMO time was similar between the two groups prior to simulated eastward travel (p = .223), it was earlier in the PER3^5/5 group (17h23 (17h15; 17h37)) than the PER3^4/4 group (18h05 (17h53; 18h12)) afterwards (p = .046). During resynchronisation, perceived sleepiness and metabolic parameters were similar to pre-travel in both groups but sleep was more disturbed in the PER3^5/5 group (total sleep time: p = .008, sleep efficiency: p = .008, wake after sleep onset: p = .023). The PER3 VNTR genotype may influence the efficacy of re-entrainment following trans-meridian travel when blue-enriched light exposure is incorporated into the recovery strategy on the first day following travel.

Melatonin as an Antioxidant Agent in Stroke: An Updated Review

Stroke is a devastating disease associated with high mortality and disability worldwide, and is generally classified as ischemic or hemorrhagic, which share certain similar pathophysiological processes. Oxidative stress is a critical factor involved in stroke-induced injury, which not only directly damages brain tissue, but also enhances a series of pathological signaling cascades, contributing to inflammation, brain edema, and neuronal death. To alleviate these serious secondary brain injuries, neuroprotective agents targeting oxidative stress inhibition may serve as a promising treatment strategy. Melatonin is a hormone secreted by the pineal gland, and has various properties, such as antioxidation, anti-inflammation, circadian rhythm modulation, and promotion of tissue regeneration. Numerous animal experiments studying stroke have confirmed that melatonin exerts considerable neuroprotective effects, partially via anti-oxidative stress. In this review, we introduce the possible role of melatonin as an antioxidant in the treatment of stroke based on the latest published studies of animal experiments and clinical research.

Sini powder with paroxetine ameliorates major depressive disorder by modulating circadian rhythm: A randomized, double-blind, placebo-controlled trial

Circadian rhythm disorder is a significant risk factor for mental diseases, and the recovery of circadian rhythm function has gradually become a signal of effective antidepressant therapy. Sini powder (SNP) is a classical, traditional Chinese formula for depression treatment. However, few clinical reports have been recorded. This randomized, double-blinded, controlled trial (ChiCTR1900022700) aimed to explore the efficacy of SNP on depression via regulating circadian rhythm. In total, 36 patients with major depressive disorder (MDD) were enrolled for 4-weeks medication and 6-weeks follow-up. HAMD-24 score and circadian rhythm index, including dim light melatonin onset (DLMO) and phase angle difference (PAD), were included in the assessment. DLMO and PAD were statistically significant in the SNP group after 4 weeks of treatment (p < .05) and with greater improvement in DLMO (p = .03). In addition, DLMO and the HAMD-24 score showed a positive correlation (p < .05); the HAMD-24 score degree decreased significantly over time (p < .001). Similarly, interaction effects were shown significantly between group and time (p = .049). The duration of SNP supplementation was relatively short, and the sample size was relatively small. SNP granules combined with paroxetine tablets have definite efficacy in improving the circadian rhythms of MDD patients, reflecting the therapeutic advantages of traditional Chinese medicine as antidepressants.

Quantification of serotonin and eight of its metabolites in plasma of healthy volunteers by mass spectrometry

Serotonin is transformed into melatonin under the control of the light/dark cycle, representing a cornerstone of circadian rhythmicity. Serotonin also undergoes extensive metabolism to produce 5-hydroxyindoleacetic acid (5-HIAA), a biomarker for the diagnosis and monitoring of serotonin secreting neuroendocrine tumors (NETs). While serotonin, melatonin and their metabolites are part of an integrated comprehensive system, human observations about their respective plasma concentrations are still limited. We report here for the first time a multiplex UHPLC-MS/MS assay for the quantification of serotonin, 5-HIAA, 5-hydroxytryptophol (5-HTPL), N-acetyl-serotonin (NAS), Mel, 6-OH-Mel, 5-methoxytryptamine (5-MT), 5-methoxytryptophol (5-MTPL), and 5-methoxyindoleacetic acid (5-MIAA) in human plasma. Analytes were extracted by protein precipitation and solid phase extraction. Plasma concentrations for these analytes were determined in 102 healthy volunteers. The LLOQ of the assay ranges from 2.2 nM for serotonin to 1.0 pM for 6-OH-Mel. This sensitivity enables the quantification of circulating serotonin, 5-HIAA, NAS, Mel, and 5-MIAA, even at their lowest diurnal concentrations. This assay will enable specific, precise and accurate measurement of serotonin, Mel and their metabolites to draw a detailed picture of this complex pineal metabolism, allowing a dynamic understanding of these pathways and providing promising biomarkers and a metabolic signature for serotonin-secreting NETs.

Melatonin and andrographolide synergize to inhibit the colospheroid phenotype by targeting Wnt/beta-catenin signaling

β-catenin signaling, and angiogenesis are associated with colospheroid (CSC), development. CSCs, spheroids derived from colon cancer cells, are responsible for metastasis, drug resistance, and disease recurrence. Whether dysregulating β-catenin and inhibiting angiogenesis reduce CSC growth is unknown. In this study, the molecular mechanism of CSC growth inhibition was evaluated using a novel combination of melatonin (MLT) and andrographolide (AGP). These drugs have anticarcinogenic, antioxidant, and antimetastatic properties. CSCs were obtained from two metastatic colon cancer cell lines (HT29 and HCT-15). The viability and stemness were monitored (FDA propidium iodide staining and immunoblot for CD44, CD133, Nanog, Sox2, and Oct4). The drug combination synergistically diminished stemness via increased reactive oxygen species (ROS) levels, reduced mitochondrial membrane potential and ATP level. MLT + AGP induced cell death by inhibiting β-catenin expression and its downregulatory signals, Cyclin D1, c-Myc. MLT + AGP treated cells exhibited translocation of phospho-β-catenin to the nucleus and dephosphorylated-β-catenin. Downregulation of β-catenin activation and its transcription factors (TCF4 and LEF1) and GTP binding/G-protein related activity were found in the dual therapy. Angiogenic inhibition is consistent with downregulation of VEGF messenger RNA transcripts (VEGF189), phosphorylated VEGF receptor protein expression, matrigel invasion, and capillary tube inhibition. In vivo, the intravenous injection of MLT + AGP slowed HT29 metastatic colon cancer. Histopathology indicated significant reduction in microvascular density and tumor index. Immunohistochemistry for caspase 7, and β-catenin found increased apoptosis and downregulation of β-catenin signals. The mechanism(s) of decreased colospheroids growth were the inhibition of the Wnt/β-catenin pathway. Our results provide a rationale for using MLT in combination with AGP for the inhibition of CRCs.

A validated method for the rapid quantification of melatonin in over-the-counter hypnotics by the atmospheric pressure solid analysis probe (ASAP)

Melatonin is a hormone that regulates the biological day and night cycle. It is mainly produced by the pineal gland during the night. People suffering from insomnia use it as a soporific drug. The aim of this study was to develop a method for the rapid quantification of melatonin in hypnotics. For that purpose, atmospheric pressure solid analysis probe-assisted mass spectrometry was applied, where no chromatographic separation is needed. Thereby, one single analysis takes less than 1 min. Reference measurements were performed with ultra-high-performance liquid chromatography coupled with a quadrupole-time-of-flight mass spectrometer. Both methods were validated and real sample extracts were tested. The coefficients of determination were above 0.97 for both methods. The limits of detection and quantification were below 1 mg kg^-1. Both methods gave comparable results. Moreover, the content of melatonin differed from the specified value in many samples. The highest and lowest observed deviations were 78% and 1%, respectively.

Beneficial effects of melatonin on liver fibrosis: A systematic review of current biological evidence

Hepatic fibrosis is a reversible response to either acute or chronic cellular injury from a wide variety of etiologies, characterized by excessive deposition of extracellular matrix resulting in liver dysfunction and cirrhosis. Melatonin (N‐acetyl‐5‐methoxytryptamine), the main product secreted by the pineal gland, is a multitasking indolamine with important physiological functions such as anti‐inflammatory and antioxidant actions, modulation of circadian rhythms, and immune system enhancement. Among the numerous biological activities of melatonin, its antifibrotic effects have received increasingly more attention. In this study, we performed a systematic review of publications of the last 10 years evaluating the mechanisms of action of melatonin against liver fibrosis. The study protocol was registered at PROSPERO (CRD42022304744). Literature research was performed employing PubMed, Scopus, and Web of Science (WOS) databases, and after screening, 29 articles were included. Results from the selected studies provided denoted the useful actions of melatonin on the development, progression, and evolution of liver fibrosis. Melatonin antifibrotic effects in the liver involved the reduction of profibrogenic markers and modulation of several cellular processes and molecular pathways, mainly acting as an antioxidant and anti‐inflammatory agent. In addition, the indolamine influenced different molecular processes, such as hepatocyte apoptosis, modulation of autophagy and mitophagy, restoration of circadian rhythms, and modulation of microRNAs, among others. Although some limitations have been found regarding variability in the study design, the findings here summarized display the potential role of melatonin in ameliorating the development of liver fibrosis and its possible progression to liver cirrhosis and hepatocarcinoma.

Bioinspired fabrication of bifunctional antibody-enzyme co-assembled nanocomposites for chemiluminescence immunoassays of E. coli O157:H7

Immunoassays based on enzyme-labeled antibodies have been widely used in the food safety field. However, the production process of enzyme-labeled antibodies is complicated and the low storage stability limits their application. Herein, antibody-horseradish peroxidase (HRP) co-assembled nanocomposites (AHC NCs) with outstanding advantages such as enhanced stability, lower cost, and substrate affinity were successfully prepared via a one-pot green method. Then the AHC NCs were employed as an alternative to traditional enzyme-labeled antibodies to develop a chemiluminescence enzyme immunoassay (CLEIA) toward Escherichia coli (E. coli) O157:H7. Under optimal conditions, E. coli O157:H7 can be detected in a linear range from 1 × 10³ CFU mL^-1 to 5 × 10⁶ CFU mL^-1, while the limit of detection (LOD) is as low as 2.2 × 10² CFU mL^-1 (3σ). A series of repeatability studies showed reproducible results with a coefficient of variation of less than 7%. In addition, the proposed CLEIA was successfully applied to the analysis of spiked samples (tap water) and gave quantitative recoveries from 93.72% to 100.72%. This work demonstrates that the developed CLEIA can be applied as a universal platform for specific detection of diversified analytes.

Effects of different light incident angles via a head-mounted device on the magnitude of nocturnal melatonin suppression in healthy young subjects

Bright light is a primary zeitgeber (synchronizer) for the central circadian pacemaker in humans. Recently, head-mounted devices for light therapy have been developed to treat patients suffering from circadian rhythm sleep disorders. In this study, to evaluate the influence of the light incident angle of head-mounted devices on the human circadian pacemaker, we examined the effects of bright light (ca.10000 lx) from two different angles (55° vs. 28°) on the suppression of melatonin secretion at night. Twenty-nine subjects (25.1 ± 6.3 SD years) participated in the present study. The subjects were kept under dim light conditions (< 5 lx) from 4 h before their habitual bedtime, followed by exposure to 1 h of bright light at two different angles during their habitual bedtime. Saliva samples were collected every hour under dim light conditions and then collected every 30 min during the bright light exposure. To assess the effect of the light incident angle on ipRGCs mediating light-evoked pupillary constriction, pupil size was measured in before and after exposure to bright light. Melatonin suppression in the group exposed to light at 28° was significantly higher than that in the group with light at 55° (p < 0.001). The pupillary constriction was significantly greater in the group exposed to light at 28° than that in the group with light at 55° (p < 0.001). The present findings suggest that the light incident angle is an important factor for bright light therapy and should be considered to effectively use head-mounted devices in home and clinical settings.

Use of Melatonin in Cancer Treatment: Where Are We?

Cancer represents a large group of diseases accounting for nearly 10 million deaths each year. Various treatment strategies, including surgical resection combined with chemotherapy, radiotherapy, and immunotherapy, have been applied for cancer treatment. However, the outcomes remain largely unsatisfying. Melatonin, as an endogenous hormone, is associated with the circadian rhythm moderation. Many physiological functions of melatonin besides sleep–wake cycle control have been identified, such as antioxidant, immunomodulation, and anti-inflammation. In recent years, an increasing number of studies have described the anticancer effects of melatonin. This has drawn our attention to the potential usage of melatonin for cancer treatment in the clinical setting, although huge obstacles still exist before its wide clinical administration is accepted. The exact mechanisms behind its anticancer effects remain unclear, and the specific characters impede its in vivo investigation. In this review, we will summarize the latest advances in melatonin studies, including its chemical properties, the possible mechanisms for its anticancer effects, and the ongoing clinical trials. Importantly, challenges for the clinical application of melatonin will be discussed, accompanied with our perspectives on its future development. Finally, obstacles and perspectives of using melatonin for cancer treatment will be proposed. The present article will provide a comprehensive foundation for applying melatonin as a preventive and therapeutic agent for cancer treatment.

[Melatonin: A short clarification for the over-enthusiasts]

Melatonin is a naturally occurring molecule derived from tryptophan. Melatonin is a key player in relaying the circadian rhythm between our environment and our body. It has also a key role in rhythming the seasons (more production during long nights and less during short ones) as well as in the reproduction cycles of the mammals. Melatonin is often and surprisingly presented as a molecule with multiple therapeutic properties that can fix (or help to fix) many health issues, such as diseases (cancer, ageing, virus-induced affections including COVID-19, etc…) or toxicological situations (metals, venoms, chemical such as adriamycin [doxorubicin], methotrexate or paclitaxel). The mechanistics behind those wonders is still missing and this is puzzling. In the present commentary, the main well-established biological properties are presented and briefly discussed with the aim of delineating the borders between facts and wishful thinking.

Detection of Melatonin in Tissue Samples

Melatonin is present in higher quantity in brain during the night. The variation of its quantity is not only a matter of day/night cycle but also a matter of organ and tissues' sublocalization. It is of the highest importance to be able to precisely measure these quantities, and thus, these variations, particularly to better understand the way melatonin signals its presence and the variation thereof through many putative targets. In this chapter, we detail the way these measures can be performed.

Measuring Dim Light Melatonin Onset in Humans

The pineal melatonin rhythm provides a robust reference signal for the timing of the endogenous human circadian system. Dim light melatonin onset (DLMO) time is considered a gold-standard marker of the central circadian clock when measured from plasma or saliva. In this chapter, we describe the appropriate conditions for collecting plasma and salivary melatonin and the threshold method to calculate the DLMO.

Evaluation of different internal standardization approaches for the quantification of melatonin in cell culture samples by multiple heart-cutting two dimensional liquid chromatography tandem mass spectrometry

We evaluate here different analytical strategies for the chromatographic separation and determination of N-acetyl-5-methoxytryptamine (MEL) and its oxidative metabolites N1-acetyl-N2-formyl-5-methoxykynuramine (AFMK), N1-acetyl-5-methoxykynuramine (AMK) and cyclic 3-hydroxymelatonin (c3OHM) in cell culture samples. Two dimensional liquid chromatography (2D-LC) in the multiple heart-cutting mode was compared with regular 1D chromatographic separations of MEL and its oxidative metabolites. Our results showed that the use of trifluoroacetic acid (TFA) as mobile phase modifier was required to obtain a satisfactory resolution and peak shapes particularly for c3OHM. As TFA is not compatible with ESI ionization the application of the MHC mode was mandatory for a proper chromatographic separation. We evaluate also different internal standardization approaches based on the combined use of a surrogate standard (5-methoxytryptophol) and an internal standard (6-methoxytryptamine) for MEL quantification in cell culture samples obtaining unsatisfactory results both by 1D- and 2D-LC-ESI-MS/MS (from 9 ± 2 to 186 ± 38%). We demonstrate that only the application of isotope dilution Mass Spectrometry through the use of an in house synthesized ¹³C isotopically labelled analogue provided quantitative MEL recoveries both by using 1D- and 2D-LC-ESI-MS/MS (99±1 and 98±1. Respectively) in androgen-insensitive human prostate carcinoma PC3 cells.

Supplemental light exposure improves sleep architecture in people with type 2 diabetes

AIMS

People with type 2 diabetes (T2D) suffer from sleep disorders, with the mechanism not clearly understood. In T2D, the light transducing retinal photoreceptors that regulate sleep behaviours are dysfunctional; hence, we determine here whether supplemental light exposure ameliorates sleep quality and daytime sleepiness in T2D.

METHODS

Supplemental light (10,000 Lux, polychromatic) was self-administered for 30 min every morning for 14 days by ten participants with T2D with no diabetic retinopathy (DR). The effectiveness of supplemental light was assessed by comparing subjective sleep questionnaire (PSQI and ESS) scores and salivary dim light melatonin onset (DLMO) before and after the light exposure as well as with a self-maintained sleep diary during the light exposure.

RESULTS

Compared to the baseline, supplemental light significantly improved the excessive daytime sleepiness score (p = 0.004) and phase-advanced the DLMO on average by ~ 23 min. Sleep diary analyses showed that afternoon nap duration significantly shortened over the first week of supplemental light exposure (p = 0.019). Afternoon naps and midnight awakening were significantly longer in diabetic participants with thinner perifoveal retina.

CONCLUSIONS

In this case series, we provide initial evidence that supplemental bright light improves daytime sleepiness in T2D with no DR, with the critical period of light exposure showing a beneficial effect after one week. We infer that supplemental light augments photoreceptor signalling in T2D and therefore optimises circadian photoentrainment leading to improved sleep. Our findings inform the development of tailored light therapy protocols in future clinical trials for improving sleep architecture in diabetes.

Serum Daytime Melatonin Levels Reflect Cerebrospinal Fluid Melatonin Levels in Alzheimer's Disease but Are Not Correlated with Cognitive Decline

Background:

Nocturnal cerebrospinal fluid (CSF) and blood melatonin levels are altered in Alzheimer’s disease (AD). However, literature remains inconclusive on daytime blood melatonin levels. A positive correlation between melatonin levels and Mini-Mental State Examination (MMSE) scores in AD subjects has been evidenced following cross-sectional analyses. Whereas a correlation between serum and spinal CSF melatonin has been shown in healthy volunteers, an equal investigation in AD patients still has to be undertaken.

Objective:

1) To evaluate whether serum melatonin levels correlate with spinal CSF melatonin levels in AD. 2) To compare daytime CSF and serum melatonin levels between patients with AD dementia, mild cognitive impairment due to AD, and healthy controls, and to evaluate whether melatonin can affect cognitive decline in AD.

Methods:

Subjects with AD and healthy controls included in two existing cohorts, of whom a CSF and serum sample was available at the neurobiobank and had at least 6 months of neuropsychological follow-up, were included in the present study. Melatonin concentrations were measured with liquid chromatography-mass spectrometry.

Results:

Daytime serum melatonin levels correlated with spinal CSF melatonin levels in AD (r = 0.751, p < 0.001). No significant differences regarding daytime melatonin levels were found between patients and controls. No correlations were observed between daytime melatonin levels and MMSE score changes.

Conclusion:

Daytime serum melatonin accurately reflects CSF melatonin levels in AD, raising the possibility to assess melatonin alterations by solely performing blood sampling if also confirmed for night-time values. However, daytime melatonin levels are not associated with changes of cognitive impairment.

Melatonin controversies, an update

Melatonin was discovered more than 60 years ago. Since then, several seminal discoveries have allowed us to define its function as a neuroendocrine hormone and its molecular targets in mammals and many other species. However, many fundamental issues have not yet been solved such as the subcellular localization of melatonin synthesis and the full spectrum of its molecular targets. In addition, a considerable number of controversies persist in the field, mainly concerning how many functions melatonin has. Altogether, this illustrates how "immature" the field still is. The intention of this opinion article is to note the controversies and limitations in the field, to initiate a discussion and to make proposals/guidelines to overcome them and move the field forward.

Journal of pineal research guideline for authors: Defining and characterizing melatonin targets

A multitude of effects has been attributed to melatonin at pmol/L to mmol/L concentrations. More than fifteen targets have been proposed for melatonin but only few of them are well characterized. The current guidelines intend to provide a framework to improve and rationalize the characterization of melatonin targets and effects. They should be considered as mandatory guidelines and minimum requirements for manuscripts submitted to the Journal of Pineal Research.

Nail Melatonin Content: A Suitable Non-Invasive Marker of Melatonin Production

Melatonin plays multiple physiological roles in the human body. Evaluation of melatonin production by the determination of urinary 6-sulfatoxymelatonin in 24-h samples has important drawbacks which hinder the successful evaluation of melatonin production in large cohorts. Here, we evaluated the potential of nail analysis for estimating melatonin production. Firstly, mass spectrometry methodology for the determination of melatonin in nails was optimized and successfully validated. The method was found to be linear in the range 6.5-830 fg/mg with intraday and interday accuracy in the range 100-104 %, precision below 15 % and a LOD of 3.5 fg/mg. Secondly, nail melatonin concentrations from 84 volunteers (age 5-96) were determined. The expected correlation between melatonin and age was obtained (correlation coefficient -0.615; p < 0.001). Additionally, we showed that fingernails are preferable to toenails to determine nail melatonin content. Finally, fingernails collected for 180 days after melatonin administration (two volunteers, 1.9 mg/night during 5 days) were analyzed. Nail melatonin concentrations immediately rose after administration and went back to pre-administration values after ≈100 days in both volunteers. Our results suggest that melatonin determination in nails is a suitable non-invasive tool for the estimation of global melatonin production. Due to the easy collection and storage of nails, the long-term information obtained and the multiple functions of melatonin, nail melatonin content might complement dim light melatonin onset, which is commonly measured from plasma/saliva samples, paving the way for melatonin research.