Influence of cigarette smoking on melatonin levels in man

Comparative Pharmacokinetics of Sustained-Release versus Immediate-Release Melatonin Capsules in Fasting Healthy Adults: A Randomized, Open-Label, Cross-Over Study

Background: Exogenous melatonin, a nutraceutical for maintaining a healthy sleep-wake cycle and managing sleep disorders, requires large, repeated doses due to its low bioavailability and short half-life. This necessitates the development of a sustained-release formulation with a longer half-life and sustained plasma concentration. Therefore, exogenous novel 5 mg sustained-release melatonin capsules (Melatonin-SR, test product) were formulated. Methods: This open-label cross-over study compared the pharmacokinetics (maximum concentration [Cmax], time to reach Cmax [Tmax], area under the curve [AUC], and elimination half-life [t1/2]) and the safety of Melatonin-SR with 5 mg immediate-release melatonin capsules (Melatonin-IR, reference product) after single-dose oral administration in healthy fasting adults. Results: Sixteen participants (aged 18-45 years) were randomized (1:1) to receive either Melatonin-SR or Melatonin-IR in two periods with a 7-day washout period. Melatonin-SR reported a lower Cmax (11,446.87 pg/mL) compared to Melatonin-IR (22,786.30 pg/mL). The mean Tmax of Melatonin-SR and Melatonin-IR was 1.26 h and 0.87 h, respectively. The mean t1/2 of Melatonin-SR (5.10 h) was prolonged by five-fold compared to Melatonin-IR (1.01 h). One adverse event (vomiting) was reported following the administration of the Melatonin-IR. Conclusions: Melatonin-SR resulted in higher and sustained plasma melatonin concentrations for an extended period and was well-tolerated. Hence, Melatonin-SR may be a promising nutraceutical for maintaining healthy sleep.

PRECISE trial (Pain RElief Combination Intervention StratEgies): protocol for the clinical trial of a pregabalin-melatonin combination for fibromyalgia

INTRODUCTION

Fibromyalgia is associated with chronic widespread pain and disturbed sleep. Multidisciplinary, multimodal management often includes pharmacotherapy; however, current drugs used to treat fibromyalgia provide meaningful benefit to only 30-60% of treated individuals. Combining two or more different drugs is common in clinical practice with the expectation of better efficacy, tolerability or both; however, further research is needed to identify which combinations actually provide added benefit. Thus, we are planning a clinical trial to evaluate melatonin (MLT)-pregabalin (PGB) combination in participants with fibromyalgia.

METHODS AND ANALYSIS

This will be a single-centre, double-blind, randomised, double-dummy, three-period, crossover trial comparing a MLT-PGB combination to each monotherapy in 54 adult participants satisfying the 2016 American College of Rheumatology criteria for fibromyalgia. Participants will receive maximally tolerated doses of MLT, PGB and MLT-PGB combination for 6 weeks. The primary outcome will be daily pain intensity (0-10); secondary outcomes will include the Fibromyalgia Impact Questionnaire, SF-36 survey, Medical Outcomes Study Sleep Scale, Beck Depression Inventory (BDI-II), adverse events and other measures. Analysis of the primary and secondary outcomes will involve a linear mixed model with sequence, period, treatment, the first-order carryover and baseline pain score as fixed effects and participant as a random effect to test whether there are any treatment differences among three treatments and to estimate the least square mean of the mean daily pain intensity for each treatment, adjusting for carryover as well as period effects (ie, stability of pain levels).

ETHICS AND DISSEMINATION

This trial has been registered with the International Standard Randomised Controlled Trial Number Registry, ISRCTN #18278231, has been granted ethical approval by the Queen's University Health Sciences Research Ethics Board (Queen's HSREB Protocol #6040998) and is currently under review for a Clinical Trial Application to Health Canada Natural and Non-prescription Health Products Directorate. All participants will provide written informed consent prior to trial participation. Following trial completion, results will be disseminated in one or more biomedical journal publications and presented at one or more scientific meetings.

TRIAL REGISTRATION NUMBER

This trial has been registered with the International Standard Randomised Controlled Trial Number Registry, ISRCTN18278231.

Assessing the potential for drug interactions and long term safety of melatonin for the treatment of insomnia in children with autism spectrum disorder

INTRODUCTION

Melatonin preparations are emerging first-line pharmacotherapy for insomnia in children and adolescents with autism spectrum disorder (ASD), but quality, formulation, consistency, dosing, and limited long-term safety data are of concern. The recent approval of pediatric-appropriate prolonged-release melatonin (Ped-PRM) addresses these aspects.

AREAS COVERED

A systematic search of PubMed and web of science for prospective, randomized, and controlled trials (RCTs) of melatonin preparations vs placebo in children and adolescents with ASD and the European public assessment report on Ped-PRM was conducted.

EXPERT OPINION

Melatonin is rapidly absorbed and undergoes first pass hepatic metabolism by cytochrome CYP1A2; over 80% is excreted in the urine as 6-sulfatoxymelatonin (inactive). Immediate-release melatonin (IRM) is short-acting (3-4 h), whereas PRM provides therapeutic levels throughout the night. Drugs interacting with CYP1A2 are likely to slow-down melatonin metabolism. High variability in bioavailability among subjects calls for dose optimization. Melatonin was essentially safe for short-term use (up to 3 months). Long-term data available for Ped-PRM demonstrate fatigue (6.3%), somnolence (6.3%), and mood swings (4.2%) with no evidence of effects on height, BMI, or pubertal development, tolerance or withdrawal effects following long-term use of this product. Studies on long-term safety of IRM and oversight of melatonin supplement manufacture are warranted.

Drug Use in Night Owls May Increase the Risk for Mental Health Problems

Drugs of abuse are widely known to worsen mental health problems, but this relationship may not be a simple causational one. Whether or not a person is susceptible to the negative effects of drugs of abuse may not only be determined by their addictive properties, but also the users’ chronotype, which determines their daily activity patterns. The present study investigates the relationship between chronotype, drug use and mental health problems in a cross-sectional community sample. Participants (n = 209) completed a selection of questionnaires online, including the Munich Chronotype Questionnaire, the Depression Anxiety Stress Scale, the Alcohol Use Disorder Identification Test, the Cannabis Use Disorder Identification Test and the Fagerström Test for Nicotine Dependence. We conducted multiple regression models to determine relationships between participants’ chronotype and their reported mental health symptoms and then estimated mediation models to investigate the extent to which their drug consumption accounted for the identified associations. Chronotype was significantly associated with participants’ overall mental health (β = 0.16, p = 0.022) and their anxiety levels (β = 0.18, p = 0.009) but not with levels of depression or stress. However, both relationships were fully mediated by participants’ overall drug consumption. Thus, late chronotypes, so-called “night owls”, not only use more drugs but consequently have an increased risk for developing anxiety and deteriorating mental health status. This group may be particularly vulnerable to the negative psychological effects of drugs. Our results point toward the importance of considering chronotype in designing preventative and therapeutic innovations, specifically for anxiety, which at present has been largely neglected.

Pharmacological and philosophical considerations for the around-the-clock use of scheduled melatonin to promote sedation and reduce aggression in individuals with serious mental illness: a case report

Melatonin, the endogenous hormone that helps maintain circadian rhythm, has been used exogenously for both primary and secondary sleep disorders. While the effects of melatonin given prior to planned sleep and to restore normal circadian sleep phases have been well studied, there is little information on the use of melatonin as a pharmacotherapeutic intervention for around-the-clock sedation to prevent agitation and aggressive patient behaviors. This is the first case report to our knowledge of melatonin used throughout the day, as a scheduled dose for prolonged treatment duration, to reduce aggression in a patient with severe mental illness.

Third-hand smoke exposure is associated with abnormal serum melatonin level via hypomethylation of CYP1A2 promoter: Evidence from human and animal studies

This study aimed to examine whether and how third-hand smoke (THS) exposure would influence serum melatonin level. 1083 participants with or without exposure to THS were enrolled. Serum ROS, SOD, GSH-Px, and melatonin were measured by ELISA. Methylation microarrays detection and WGCNA were performed to identify hub methylated-sites. The methylation levels of hub-sites were validated in addtional samples. Moreover, mice were exposed to THS for 6 months mimicking exposure of human and the serum, liver, and pineal were collected. Oxidative stress-related indicators in serum, pineal, and liver were measured by ELISA. The expressions of mRNA and protein and methylation levels of hub-gene discovered in human data were further explored by RT-PCR, western-blot, and TBS. The results showed the participants exposed to THS had lower melatonin-level. 820 differentially methylated sites associated with THS were identified. And the hub-site located on the CYP1A2 promoter was identified, which mediated the association between THS and decreased melatonin-level. Decreased peak of serum melatonin, increased ROS and reduced SOD and GSH-Px in pineal and liver, and elevated CYP1A2 expression in liver was also found in the THS-exposed mice. Hypo-methylation of 7 CPG sites on the CYP1A2 promoter was identified, which accelerated the catabolism of melatonin. Overall, THS exposure is associated with abnormal melatonin catabolism through hypo-methylation of CYP1A2-promoter.

Potential Role of Melatonin as an Adjuvant for Atherosclerotic Carotid Arterial Stenosis

Carotid artery stenosis (CAS) is an atherosclerotic disease characterized by a narrowing of the artery lumen and a high risk of ischemic stroke. Risk factors of atherosclerosis, including smoking, hypertension, hyperglycemia, hyperlipidemia, aging, and disrupted circadian rhythm, may potentiate atherosclerosis in the carotid artery and further reduce the arterial lumen. Ischemic stroke due to severe CAS and cerebral ischemic/reperfusion (I/R) injury after the revascularization of CAS also adversely affect clinical outcomes. Melatonin is a pluripotent agent with potent anti-inflammatory, anti-oxidative, and neuroprotective properties. Although there is a shortage of direct clinical evidence demonstrating the benefits of melatonin in CAS patients, previous studies have shown that melatonin may be beneficial for patients with CAS in terms of reducing endothelial damage, stabilizing arterial plaque, mitigating the harm from CAS-related ischemic stroke and cerebral I/R injury, and alleviating the adverse effects of the related risk factors. Additional pre-clinical and clinical are required to confirm this speculation.

Melatonin: From Pharmacokinetics to Clinical Use in Autism Spectrum Disorder

The role of melatonin has been extensively investigated in pathophysiological conditions, including autism spectrum disorder (ASD). Reduced melatonin secretion has been reported in ASD and led to many clinical trials using immediate-release and prolonged-release oral formulations of melatonin. However, melatonin’s effects in ASD and the choice of formulation type require further study. Therapeutic benefits of melatonin on sleep disorders in ASD were observed, notably on sleep latency and sleep quality. Importantly, melatonin may also have a role in improving autistic behavioral impairments. The objective of this article is to review factors influencing treatment response and possible side effects following melatonin administration. It appears that the effects of exposure to exogenous melatonin are dependent on age, sex, route and time of administration, formulation type, dose, and association with several substances (such as tobacco or contraceptive pills). In addition, no major melatonin-related adverse effect was described in typical development and ASD. In conclusion, melatonin represents currently a well-validated and tolerated treatment for sleep disorders in children and adolescents with ASD. A more thorough consideration of factors influencing melatonin pharmacokinetics could illuminate the best use of melatonin in this population. Future studies are required in ASD to explore further dose-effect relationships of melatonin on sleep problems and autistic behavioral impairments.

Systematic review of melatonin levels in individuals with complete cervical spinal cord injury

Context: Pineal melatonin production is mediated by afferent signaling pathways that navigate through the cervicothoracic spinal cord. Melatonin profiles in individuals with complete cervical spinal cord injury (SCI) have not been systematically reviewed despite this proposed pathway. Objectives: The primary objective was to understand melatonin profiles in individuals with complete cervical SCI, as compared to healthy controls and those with thoracolumbar and incomplete cervical SCI. Secondary objectives were to understand the impact of injury chronicity and melatonin supplementation on melatonin values in adults with complete cervical SCI. Methods: This review (PROSPERO ID: CRD42017073767) searched several databases and gray literature sources from January 1978 to August 2017. Studies were eligible if they evaluated melatonin levels (blood, saliva or urinary metabolite measurements) in adults with complete cervical SCI. 390 studies were screened and 12 studies met final selection criteria. Given the heterogeneity in study designs, a narrative analysis was performed. Results: There is evidence that adults with complete cervical SCI have absent diurnal melatonin rhythms as compared to healthy controls and individuals with thoracolumbar SCI below T3. There is limited evidence comparing levels in individuals with incomplete tetraplegia. There is insufficient evidence describing profiles immediately (<2 weeks) after cervical SCI. Based on a limited number of studies, melatonin supplementation does not appear to improve sleep outcomes in adults with long-standing complete cervical SCI. Conclusions: Future research should explore melatonin levels acutely after cervical SCI and the impact of supplementation on non-sleep outcomes.

Tobacco smoking and its drug interactions with comedications involving CYP and UGT enzymes and nicotine

Tobacco smoking is a global public health threat causing several illnesses including cardiovascular disease (Myocardial infarction), cerebrovascular disease (Stroke), peripheral vascular disease (Claudication), chronic obstructive pulmonary disease, asthma, reduced female infertility, sexual dysfunction in men, different types of cancer and many other diseases. It has been estimated in 2015 that approximately 1.3 billion people smoke, around the globe. Use of medications among smokers is more common, nowadays. This review is aimed to identify the medications affected by smoking, involving Cytochrome P450 (CYP) and uridine diphosphate-glucuronosyltransferases (UGTs) enzymes and Nicotine. Polycyclic aromatic hydrocarbons (PAHs) of tobacco smoke have been associated with the induction of CYP enzymes such as CYP1A1, CYP1A2 and possibly CYP2E1 and UGT enzymes. The drugs metabolized by CYP1A1, CYP1A2, CYP2E1 and UGT enzymes might be affected by tobacco smoking and the smokers taking medications metabolized by those enzymes, may need higher doses due to decreased plasma concentrations through enhanced induction by PAHs of tobacco smoke. The prescribers and the pharmacists are required to be aware of medications affected by tobacco smoking to prevent the toxicity-associated complications during smoking cessation.

The neuroprotective role of melatonin in neurological disorders

Melatonin is a neurohormone secreted from the pineal gland and has a wide-ranging regulatory and neuroprotective role. It has been reported that melatonin level is disturbed in some neurological conditions such as stroke, Alzheimer's disease, and Parkinson's disease, which indicates its involvement in the pathophysiology of these diseases. Its properties qualify it to be a promising potential therapeutic neuroprotective agent, with no side effects, for some neurological disorders. This review discusses and localizes the effect of melatonin in the pathophysiology of some diseases.

Long-Term Melatonin Therapy for Adolescents and Young Adults with Chronic Sleep Onset Insomnia and Late Melatonin Onset: Evaluation of Sleep Quality, Chronotype, and Lifestyle Factors Compared to Age-Related Randomly Selected Population Cohorts

The extent of continuance of melatonin therapy initiated in pre-pubertal children with chronic sleep onset insomnia (CSOI) was investigated in young adult life. Sleep timing, sleep quality, adverse events, reasons for cessation of therapy, and patient characteristics with regard to therapy regimen, chronotype and lifestyle factors possibly influencing sleeping behavior were assessed. With an online survey using questionnaires (Pittsburgh Sleep Quality Index, Insomnia Severity Index, Morningness-Eveningness Questionnaire, and Munich Chronotype Questionnaire), outcomes were measured and compared with age-related controls. These controls were extracted from published epidemiological research programs applying the same questionnaires. At the moment of the survey, melatonin was still continued by 27.3% of the patients, with a mean treatment duration of 10.8 years. The overall average treatment duration was 7.1 years. Sleep quality of both discontinued and persistent melatonin users did not deviate from controls. Sleep timing and chronotype scores indicated evening type preference in all responders. Adverse events were scarce but the perceived timing of pubertal development suggested a tendency towards delayed puberty in former and current users of melatonin. This study may underestimate the number of children that are able to stop using melatonin due to the response rate (47.8%) and appeal for continuing users. Sleep timing parameters were based on self-reported estimates. Control populations were predominantly students and were of varying nationalities. The statistical power of this study is low due to the limited sample size. Melatonin therapy sustained for 7.1 years does not result in substantial deviations of sleep quality as compared to controls and appears to be safe. The evening type preference suggests a causal relation with CSOI. This study shows that ten years after initiation of treatment with melatonin for CSOI, approximately 75% of the patients will have normal sleep quality without medication.

Pharmacokinetics of Melatonin: The Missing Link in Clinical Efficacy?

Despite widespread clinical application of melatonin, several unanswered questions remain regarding the pharmacokinetics of this drug. This lack of knowledge may contribute to the inconsistency of results in previous clinical studies. Currently, a t max value of 30-45 min and a t ½elimination of 45 min are well established. Several questions relate to what constitutes a clinically effective plasma concentration, the choice of ideal administration route, and the optimal method of analysis. Furthermore, investigations of melatonin metabolites in humans are urgently needed in order to characterize their biological functions and the metabolic fates of these derivatives. Finally, pharmacokinetics in patients should be investigated further in order to reduce the risk of potential adverse effects, such as daytime sleepiness or unintended sedation.

Pharmacokinetic Drug Interactions with Tobacco, Cannabinoids and Smoking Cessation Products

Tobacco smoke contains a large number of compounds in the form of metals, volatile gases and insoluble particles, as well as nicotine, a highly addictive alkaloid. Marijuana is the most widely used illicit drug of abuse in the world, with a significant increase in the USA due to the increasing number of states that allow medical and recreational use. Of the over 70 phytocannabinoids in marijuana, Δ9-tetrahydrocannabinol (Δ9THC), cannabidiol (CBD) and cannibinol are the three main constituents. Both marijuana and tobacco smoking induce cytochrome P450 (CYP) 1A2 through activation of the aromatic hydrocarbon receptor, and the induction effect between the two products is additive. Smoking cessation is associated with rapid downregulation of CYP1A enzymes. On the basis of the estimated half-life of CYP1A2, dose reduction of CYP1A drugs may be necessary as early as the first few days after smoking cessation to prevent toxicity, especially for drugs with a narrow therapeutic index. Nicotine is a substrate of CYP2A6, which is induced by oestrogen, resulting in lower concentrations of nicotine in females than in males, especially in females taking oral contraceptives. The significant effects of CYP3A4 inducers and inhibitors on the pharmacokinetics of Δ9THC/CBD oromucosal spray suggest that CYP3A4 is the primary enzyme responsible for the metabolism of Δ9THC and CBD. Limited data also suggest that CBD may significantly inhibit CYP2C19. With the increasing use of marijuana and cannabis products, clinical studies are needed in order to determine the effects of other drugs on pharmacokinetics and pharmacodynamics.

Inhibition of melatonin metabolism in humans induced by chemical components from herbs and effective prediction of this risk using a computational model

BACKGROUND AND PURPOSE

Herbs which are widely used as food and medicine, are involved in many physiopathological processes. Melatonin is a human hormone, synthesized and secreted by the pineal gland, with a range of biological functions. Here, we have evaluated the potential influences of components extracted from common herbs on melatonin metabolism in humans.

EXPERIMENTAL APPROACH

An in vivo pharmacokinetic study involving 12 healthy subjects, in vitro incubations with human liver microsomes (HLMs) and recombinant human cytochrome P (CYP) isoenzymes and an in silico quantitative structure-activity relationship (QSAR) model analysis using comparative molecular field analysis and comparative molecular similarity indices analysis methods were employed to explore these interactions.

KEY RESULTS

After systematic screening of 66 common herbs, Angelica dahurica exhibited the most potent inhibition of melatonin metabolism in vitro. The in vivo pharmacokinetic study indicated inhibition of melatonin metabolism, with approximately 12- and 4-fold increases in the AUC and C_max of melatonin in human subjects. Coumarins from A. dahurica, including imperatorin, isoimperatorin, phellopterin, 5-methoxypsoralen and 8-methoxypsoralen, markedly inhibited melatonin metabolism with K_i values of 14.5 nM, 38.8 nM, 6.34 nM, 5.34 nM and 18 nM respectively, through inhibition of CYP 1A2, 1A1 and 1B1 in HLMs. A QSAR model was established and satisfactorily predicted the potential risk of coumarins for inhibition of melatonin metabolism in vivo.

CONCLUSION AND IMPLICATIONS

Coumarins from A. dahurica inhibited melatonin metabolism in vivo and in vitro. Our findings provide vital guidance for the clinical use of melatonin.

Pharmacokinetics of oral and intravenous melatonin in healthy volunteers

BACKGROUND

The aim was to investigate the pharmacokinetics of oral and iv melatonin in healthy volunteers.

METHODS

The study was performed as a cohort crossover study. The volunteers received either 10 mg oral melatonin or 10 mg intravenous melatonin on two separate study days. Blood samples were collected at different time points following oral administration and short iv infusion, respectively. Plasma melatonin concentrations were determined by RIA technique. Pharmacokinetic analyses were performed by "the method of residuals" and compartmental analysis. The pharmacokinetic variables: k a, t 1/2 absorption, t max, C max, t 1/2 elimination, AUC 0-∞, and bioavailability were determined for oral melatonin. C max, t 1/2 elimination, V d, CL and AUC 0-∞ were determined for intravenous melatonin.

RESULTS

Twelve male volunteers completed the study. Baseline melatonin plasma levels did not differ significantly between the study days (P = 0.067). Mean (SD) t 1/2 absorption of oral melatonin was 6.0 (3.1) min. Mean t max was 40.8 (17.8) min with a median (IQR) C max of 3550.5 (2500.5-8057.5) pg ml(-1). Mean t 1/2 elimination was 53.7 (7.0) min. Median absolute bioavailability was 2.5 (1.7-4.7) %. Median C max after short iv infusion of melatonin was 389,875.0 (174,775.0-440,362.5) pg ml(-1). Mean t 1/2 elimination was 39.4 (3.6) min, mean V d 1.2 (0.6) l kg(-1) and mean CL 0.0218 (0.0102) l min(-1) kg(-1).

CONCLUSIONS

This cohort crossover study estimated pharmacokinetics of oral and iv melatonin, respectively in healthy volunteers. Bioavailability of oral melatonin was only 3 %.

TRIAL REGISTRATION

Eudra-CT number: 2013-000205-23 (initial registration 27.03.2013). Clinicaltrials.gov Identifier: NCT01923974 (initial registration 08.08.2013).

Melatonin: Physiological effects in humans

Melatonin is a methoxyindole synthesized and secreted principally by the pineal gland at night under normal light/dark conditions. The endogenous rhythm of secretion is generated by the suprachiasmatic nuclei and entrained to the light/dark cycle. Light is able to either suppress or synchronize melatonin production according to the light schedule. The nycthohemeral rhythm of this hormone can be evaluated by repeated measurement of plasma or saliva melatonin or urine sulfatoxymelatonin, the main hepatic metabolite. The primary physiological function of melatonin, whose secretion adjusts to night length, is to convey information concerning the daily cycle of light and darkness to body structures. This information is used for the organisation of functions, which respond to changes in the photoperiod such as the seasonal rhythms. Seasonal rhythmicity of physiological functions in humans related to possible alteration of the melatonin message remains, however, of limited evidence in temperate areas under field conditions. Also, the daily melatonin secretion, which is a very robust biochemical signal of night, can be used for the organisation of circadian rhythms. Although functions of this hormone in humans are mainly based on correlations between clinical observations and melatonin secretion, there is some evidence that melatonin stabilises and strengthens coupling of circadian rhythms, especially of core temperature and sleep-wake rhythms. The circadian organisation of other physiological functions depend also on the melatonin signal, for instance immune, antioxidant defences, haemostasis and glucose regulation. The difference between physiological and pharmacological effects of melatonin is not always clear but is based upon consideration of dose and not of duration of the hormone message. It is admitted that a "physiological" dose provides plasma melatonin levels in the same order of magnitude as a nocturnal peak. Since the regulating system of melatonin secretion is complex, following central and autonomic pathways, there are many pathophysiological situations where melatonin secretion can be disturbed. The resulting alteration could increase the predisposition to disease, add to the severity of symptoms or modify the course and outcome of the disorder. Since melatonin receptors display a very wide distribution in the body, putative therapeutic indications of this compound are multiple. Great advances in this field could be achieved by developing multicentre trials in a large series of patients, in order to establish efficacy of melatonin and absence of long-term toxicity.

Potential drug interactions with melatonin

Possible interactions of melatonin with concurrently administered drugs were investigated in in vitro studies utilising human hepatic post-mitochondrial preparations; similar studies were conducted with rat preparations to ascertain whether rat is a suitable surrogate for human. Drugs were selected based not only on the knowledge that the 6-hydroxylation of exogenous melatonin, its principal pathway of metabolism, is mainly mediated by hepatic CYP1A2, but also on the likelihood of the drug being concurrently administered with melatonin. Hepatic preparations were incubated with either melatonin or 6-hydroxymelatonin in the presence and absence of a range of concentrations of interacting drug, and the production of 6-sulphatoxymelatonin monitored using a radioimmunoassay procedure. Of the drugs screened, only the potent CYP1A2 inhibitor 5-methoxypsoralen impaired the 6-melatonin hydroxylation at pharmacologically relevant concentrations, and is likely to lead to clinical interactions; diazepam, tamoxifen and acetaminophen (paracetamol) did not impair the metabolic conversion of melatonin to 6-sulphatoxymelatonin at concentrations attained following therapeutic administration. 17-Ethinhyloestradiol appeared not to suppress the 6-hydroxylation of melatonin but inhibited the sulphation of 6-hydroxymelatonin, but this is unlikely to result in an interaction following therapeutic intake of the steroid. Species differences in the inhibition of melatonin metabolism in human and rat hepatic post-mitochondrial preparations were evident implying that the rat may not be an appropriate surrogate of human in such studies.

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

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

Melatonin: comprehensive profile

This chapter includes the aspects of melatonin. The drug is synthesized in the pineal gland starting from tryptophane or synthetically by using indole as starting material. Melatonin has been used as an adjunct to interleukin-2 therapy for malignant neoplasms, as contraceptive, in the management of various forms of insomnia, to alleviate jet lag following long flights, and finally as free radical scavenger and hence as an antioxidant and an anti-inflammatory. The chapter discusses the drug metabolism and pharmacokinetics and presents various method of analysis of this drug such as biological analysis, spectroscopic analysis, and chromatographic techniques of separation. It also discusses its physical properties such as solubility characteristics, X-ray powder diffraction pattern, and thermal methods of analysis. The chapter is concluded with a discussion on its biological properties such as activity, toxicity, and safety.

Associations of urinary 6-sulfatoxymelatonin with demographics, body mass, sex steroids, and lifestyle factors in preschool Japanese children

PURPOSE

We aimed to assess the associations of sex, age, body mass, sex steroid hormones, and lifestyle factors with the levels of melatonin in young children.

METHODS

This study followed a cross-sectional design and was conducted two preschools in Japan. Subjects were 235 boys and 203 girls, aged 3-6 years. Information related to demographics, body mass, and lifestyle factors was obtained from parent-administered questionnaires. The levels of 6-sulfatoxymelatonin and dehydroepiandrosterone in first-void morning urine were measured by radioimmunoassay. Urinary estrone, estradiol, testosterone, and 5-androstene-3β, 17α diol levels were measured by liquid chromatography-electrospray ionization tandem mass spectrometry.

RESULTS

The creatinine-corrected 6-sulfatoxymelatonin levels and the estimated value of 6-sulfatoxymelatonin excretion were higher in girls than in boys. After adjustments for age, the creatinine-corrected 6-sulfatoxymelatonin was negatively associated with weight and body mass index among boys and with weight and height among girls. However, the estimated value of 6-sulfatoxymelatonin excretion was not associated with any indices of body mass. No significant relationships of urinary sex steroids, light exposure at night, sleep time, sedentary lifestyles, or passive smoking with urinary 6-sulfatoxymelatonin were observed.

CONCLUSIONS

Our findings suggest that melatonin levels depend on sex and body size among young healthy children. Our results should be confirmed in future researches.

Melatonin pharmacokinetics following two different oral surge-sustained release doses in older adults

Melatonin is increasingly used for the treatment of sleep disorders. Surge-sustained formulations consisting of combined immediate release and controlled release dosing may mimic the endogenous melatonin physiologic profile. However, relatively little is known about the pharmacokinetic properties of low-dose (<0.5mg) and high-dose (>2mg) melatonin in a combined immediate release/controlled release dose, especially in older adults who may also exhibit altered melatonin disposition. To assess this, we conducted a randomized, double-blind, placebo-controlled study of low-dose (0.4mg) and high-dose (4.0mg) melatonin (25% immediate release+75% controlled release) in 27 older adults with insomnia complaints and low endogenous melatonin levels to determine whether melatonin pharmacokinetic properties differ between these two doses. The time to maximum level (1.3hrs versus 1.5hrs), elimination half-life (1.8hrs versus 2.1hrs), and apparent total clearance (379L/hr versus 478L/hr) did not differ significantly between the low- and high-dose arms, respectively. The maximum concentration was 405 ±93pg/mL for the low-dose arm and 3999±700pg/mL for the high-dose arm, both of which are substantially higher than physiologic melatonin levels for this age group. In addition, subjects in the high-dose arm maintained melatonin levels >50pg/mL for an average of 10hrs, which could result in elevated melatonin levels beyond the typical sleep period. Renal and liver function parameters remained stable after 6wks of treatment. The linear pharmacokinetic behavior of melatonin observed in the elderly can form the basis for future studies exploring a wider range of dosing scenarios to establish exposure-response relationships for melatonin-mediated sleep outcomes.

Melatonin: a multitasking molecule

Melatonin (N-acetyl-5-methoxytryptamine) has revealed itself as an ubiquitously distributed and functionally diverse molecule. The mechanisms that control its synthesis within the pineal gland have been well characterized and the retinal and biological clock processes that modulate the circadian production of melatonin in the pineal gland are rapidly being unravelled. A feature that characterizes melatonin is the variety of mechanisms it employs to modulate the physiology and molecular biology of cells. While many of these actions are mediated by well-characterized, G-protein coupled melatonin receptors in cellular membranes, other actions of the indole seem to involve its interaction with orphan nuclear receptors and with molecules, for example calmodulin, in the cytosol. Additionally, by virtue of its ability to detoxify free radicals and related oxygen derivatives, melatonin influences the molecular physiology of cells via receptor-independent means. These uncommonly complex processes often make it difficult to determine specifically how melatonin functions to exert its obvious actions. What is apparent, however, is that the actions of melatonin contribute to improved cellular and organismal physiology. In view of this and its virtual absence of toxicity, melatonin may well find applications in both human and veterinary medicine.

Inhibition of procarcinogen-bioactivating human CYP1A1, CYP1A2 and CYP1B1 enzymes by melatonin

Administration of melatonin to rodents decreases the incidence of tumorigenesis initiated by benzo[a]pyrene or 7,12-dimethylbenz[a]anthracene, which requires bioactivation by cytochrome P450 enzymes, such as CYP1A1, CYP1A2 and CYP1B1, to produce carcinogenic metabolites. The present study tested the hypothesis that melatonin is a modulator of human CYP1 catalytic activity and gene expression. As a comparison, we also investigated the effect of melatonin on the catalytic activity of CYP2A6, which is also a procarcinogen-bioactivating enzyme. Melatonin (3-300 microm) decreased 7-ethoxyresorufin O-dealkylation catalyzed by human hepatic microsomes and recombinant CYP1A1, CYP1A2 and CYP1B1, whereas it did not affect coumarin 7-hydroxylation catalyzed by hepatic microsomes or recombinant CYP2A6. Melatonin inhibited CYP1 enzymes by mixed inhibition, with apparent K(i) values (mean +/- S.E.M.) of 59 +/- 1 (CYP1A1), 12 +/- 1 (CYP1A2), 14 +/- 2 (CYP1B1) and 46 +/- 8 microm (hepatic microsomes). Additional experiments indicated that melatonin decreased benzo[a]pyrene hydroxylation catalyzed by hepatic microsomes and CYP1A2 but not by CYP1A1 or CYP1B1. Treatment of MCF-10A human mammary epithelial cells with melatonin (up to 300 microm) did not affect basal or benzo[a]pyrene-inducible CYP1A1 or CYP1B1 gene expression. Consistent with this finding, melatonin did not influence reporter activity in aryl hydrocarbon receptor-dependent pGudluc6.1-transfected MCF-10A cells treated with or without benzo[a]pyrene, as assessed in an in vitro cell-based luciferase reporter gene assay. Overall, melatonin is an in vitro inhibitor of human CYP1 catalytic activity, and it may be useful to develop potent analogues of melatonin as potential cancer chemopreventive agents that block CYP1-mediated chemical carcinogenesis.

Variation in CYP1A2 activity and its clinical implications: influence of environmental factors and genetic polymorphisms

CYP1A2 is involved in the metabolism of several widely used drugs and endogenous compounds, and in the activation of procarcinogens. Both genetic and environmental factors influence the activity of this enzyme. The current knowledge regarding factors influencing the activity of CYP1A2 is summarized in this review. Substrates, inhibitors and inducers of CYP1A2 activity, as well as phenotyping probes, are discussed. The functional significance and clinical importance of CYP1A2 gene polymorphisms are reviewed and interethnic differences in the distribution of CYP1A2 variant alleles and haplotypes are summarized. Finally, future perspectives for the possible clinical applications of CYP1A2 genotyping are discussed.

Consumption of vegetables alters morning urinary 6-sulfatoxymelatonin concentration

Melatonin, which is contained in certain vegetables, may have an influence on circulatory melatonin concentrations. This study examined the effects of the consumption of vegetables on 6-sulfatoxymelatonin concentrations in morning urine. Ninety-four healthy women aged 24-55 were recruited through a city public health center in Japan. The women randomly allocated to the intervention group were requested to consume high amounts of six selected vegetables, with a target of 350 g/day for 65 days, while those in the control group were asked to avoid the same six vegetables during the same period. First-void morning urine was collected before and at the end of the intervention period, and creatinine-adjusted 6-sulfatoxymelatonin concentrations were measured. At the end of the intervention period, daily mean intake of melatonin from the six vegetables was 1288.0 ng in the intervention group and 5.3 ng in the control group. In the intervention group, the mean concentration of 6-sulfatoxymelatonin changed from 48.1 [95% confidence interval (CI): 40.4-57.2] ng/mg creatinine to 49.6 (95% CI: 42.8-57.3) ng/mg creatinine across the intervention period. In the control group, the mean concentration of 6-sulfatoxymelatonin changed from 55.5 (95% CI: 48.7-63.2) ng/mg creatinine to 50.8 (95% CI: 44.0-58.7) ng/mg creatinine across the intervention period. A comparison of the two groups with regard to the changes in the 6-sulfatoxymelatonin concentrations across the intervention period showed a significant difference (P = 0.03). The results indicate that increased consumption of vegetables raises circulatory melatonin concentrations.

Effects of gender and moderate smoking on the pharmacokinetics and effects of the CYP1A2 substrate tizanidine

OBJECTIVE

We studied the effects of gender and smoking on the pharmacokinetics and effects of the cytochrome P450 (CYP) 1A2 substrate tizanidine.

METHODS

Seventy-one healthy young volunteers (male and female nonsmokers, male smokers) ingested 4 mg tizanidine. Plasma concentrations and pharmacodynamics of tizanidine were measured, and a caffeine test was performed.

RESULTS

Among nonsmokers, the peak concentration (C(max)) and area under concentration-time curve from 0 to infinity [AUC(0-infinity)] of tizanidine did not differ significantly between females and males. However, the half-life (t(1/2)) was 9% shorter in female nonsmokers than in male nonsmokers (P < 0.05). In male smokers, the t(1/2) was 10% shorter and the weight-adjusted AUC(0-infinity) 33% smaller than in male nonsmokers (P < 0.05). The caffeine/paraxanthine ratio was 35-40% smaller (P = 0.001) in male smokers than in nonsmoking males or females, but did not differ between males and females. Tizanidine lowered blood pressure and caused drowsiness significantly (P < 0.05) more in females than in either male groups. The effects on blood pressure were smallest in male smokers (P < 0.05).

CONCLUSIONS

Gender by itself seems to have no clinically significant effect on the pharmacokinetics of tizanidine, whereas smoking reduces plasma concentrations and effects of tizanidine. Any possible effect of gender and smoking is largely outweighed by individual variability in CYP1A2 activity due to genetic and environmental factors and in body weight. Careful dosing of tizanidine is warranted in small females, whereas male smokers can require higher than average doses.

Nutritional and lifestyle correlates of the cancer-protective hormone melatonin

CONTEXT

Despite growing support for melatonin as a promising agent for cancer treatment and possibly cancer prevention, few studies have elucidated factors that influence endogenous melatonin. This overview summarizes dietary and lifestyle factors that have been shown to affect circulating melatonin levels.

BIOLOGICAL MECHANISMS

To date, many animal studies and in vitro experiments have illustrated that melatonin possesses oncostatic activity. Mechanisms that are currently being studied include melatonin's activity as an indirect antioxidant and free radical scavenger; its action on the immune system; suppression of fatty acid uptake and metabolism; and its ability to increase the degradation of calmoduline and to induce apoptosis. Studies further suggest that melatonin reduces local estrogen synthesis, through down-regulation of the hypothalamic-pituitary reproductive axis and direct actions of melatonin at the tumor cell level, thus behaving as a SERM.

THERAPEUTIC APPLICATIONS

Several small clinical trials have demonstrated that melatonin has some potential, either alone or in combination with standard cancer therapy, to yield favorable responses. Melatonin or its precursor tryptophan have been found in numerous edible plants, but more studies are needed to evaluate the influence of diets rich in tryptophan and melatonin on circulating melatonin levels in humans. Age, BMI, parity, and the use of certain drugs remain the factors that have been associated most consistently with aMT6s levels.

DISCUSSION

Further insights into the effects of dietary and lifestyle factors that modulate circulating melatonin levels may provide the basis for novel interventions to exploit melatonin for the prevention and treatment of human diseases.

Effect of Caffeine Intake 12 or 24 Hours Prior to Melatonin Intake and CYP1A2*1F Polymorphism on CYP1A2 Phenotyping by Melatonin

Earlier evidence suggests that melatonin is almost exclusively metabolised by CYP1A2 and could serve as a probe drug for CYP1A2 phenotyping. However, caffeine inhibits the metabolism of melatonin by CYP1A2 and dietary caffeine could be a potential confounder for the measurement of CYP1A2 activity with melatonin. We undertook a 3-phase cross-over study in 12 healthy volunteers to examine whether caffeine (200 mg single dose), taken 12 hr or 24 hr prior to melatonin intake, would affect the results of CYP1A2 phenotyping results as assessed by a spot sample melatonin concentration 1.5 hr after intake of 6 mg of melatonin orally. In addition we examined the influence of the CYP1A2*1F polymorphism on the phenotyping results by combining the present material with another 12 persons from a previous study. Caffeine, co-administered 12 or 24 hr prior to melatonin intake, did not have any significant effect on the 1.5 hr melatonin concentration (P=0.086 for ANOVA), but in two volunteers about 4 times increase in melatonin concentration was observed after caffeine intake 12 hr (but not 24 hr) before phenotyping with melatonin. Also, individuals homozygous for the CYP1A2*1A allele had clearly higher 1.5 hr melatonin concentration compared with the *1F/*1F or the *1F/*1A genotypes. Abstinence from caffeine for 24 hr prior to melatonin intake should be enough to overcome the possible confounding effect of caffeine on the CYP1A2 phenotyping with melatonin. Also, melatonin may be a sensitive probe to detect phenotypic differences with regard to CYP1A2*1F polymorphism. Melatonin might be, thus, advantageous for CYP1A2 phenotyping compared to the standard probe caffeine.

Effects of melatonin on the oxidant/antioxidant status and lung histopathology in rabbits exposed to cigarette smoke

OBJECTIVES AND BACKGROUND

To evaluate the effects of cigarette smoking on the histopathology and the oxidant/antioxidant status of the lungs and to test the potential antioxidant benefits of melatonin on these induced changes.

METHODOLOGY

Rabbits were exposed to cigarette smoke in a glass chamber for 1 h daily for 1 month with or without intraperitoneal melatonin injection. A melatonin control group was given intraperitoneal melatonin only. A control group was exposed to clean air only. At the end of 1 month, animals were sacrificed and lung tissues were examined histopathologically. Blood levels of protein sulphydryls, carbonyls, prostaglandin F2alpha (PGF2alpha), malondialdehyde (MDA), glutathione peroxidase and superoxide dismutase (SOD) were measured.

RESULTS

Intraparenchymal vascular congestion and thrombosis, intraparenchymal haemorrhage, respiratory epithelial proliferation, number of macrophages in the alveolar and bronchial lumen, alveolar destruction, emphysematous changes and bronchoalveolar haemorrhage scores were significantly increased in rabbits exposed to cigarette smoke compared with the control group. Protein sulphydryls and SOD levels were significantly decreased; carbonyls, PGF2alpha and MDA levels were significantly increased in the smoke exposed rabbits. Administration of melatonin to rabbits exposed to cigarette smoke caused a reduction in the bronchoalveolar haemorrhage score and blood carbonyls levels. Other parameters were unaffected by melatonin.

CONCLUSION

Exposure to cigarette smoke causes severe histopathological changes and negatively affects the oxidant/antioxidant status in the lungs of rabbits. A low daily dose of melatonin has some protective effects on histopathological changes and oxidant/antioxidant status of the lungs in smoke exposed rabbits.