Effect of melatonin on nocturnal blood pressure: meta-analysis of randomized controlled trials

Melatonin and Vascular Function

The indolamine hormone melatonin, also known as N-acetyl-5-methoxytrypamine, is frequently associated with circadian rhythm regulation. Light can suppress melatonin secretion, and photoperiod regulates melatonin levels by promoting its production and secretion at night in response to darkness. This hormone is becoming more and more understood for its functions as an immune-modulatory, anti-inflammatory, and antioxidant hormone. Melatonin may have a major effect on several diabetes-related disturbances, such as hormonal imbalances, oxidative stress, sleep disturbances, and mood disorders, according to recent research. This has raised interest in investigating the possible therapeutic advantages of melatonin in the treatment of diabetic complications. In addition, several studies have described that melatonin has been linked to the development of diabetes, cancer, Alzheimer's disease, immune system disorders, and heart diseases. In this review, we will highlight some of the functions of melatonin regarding vascular biology.

Associations between actigraphy-derived rest-activity rhythm characteristics and hypertension in United States adults

People with disrupted circadian rhythms, such as shift workers, have shown a higher risk of hypertension. However, it is unclear whether more subtle differences in diurnal rest-activity rhythms in the population are associated with hypertension. Clarifying the association between the rest-activity rhythm, a modifiable behavioural factor, and hypertension could provide insight into preventing hypertension and possibly cardiovascular diseases. In this study, we investigated the association between rest-activity rhythm characteristics and hypertension in a large representative sample of United States adults. Cross-sectional data were obtained from the National Health and Nutrition Examination Survey 2011-2014 (N = 6726; mean [range] age 49 [20-79] years; 52% women). Five rest-activity rhythm parameters (i.e., pseudo F statistic, amplitude, mesor, amplitude:mesor ratio, and acrophase) were derived from 24-h actigraphy data using the extended cosine model. We performed multiple logistic regression to assess the associations between the rest-activity rhythm parameters and hypertension. Subgroup analysis stratified by age, gender, race/ethnicity, body mass index and diabetes status was also conducted. A weakened overall rest-activity rhythm, characterised by a lower F statistic, was associated with higher odds of hypertension (odds ratio quintile 1 versus quintile 5 [OR Q1vs.Q5 ] 1.61, 95% confidence interval [CI] 1.26-2.05; p trend < 0.001). Similar results were found for lower amplitude (OR Q1vs.Q5 1.51, 95% CI 1.13-2.03; p trend = 0.01) and amplitude:mesor ratio (OR Q1vs.Q5 1.34, 95% CI 1.01-1.78; p trend = 0.03). The results were robust to the adjustment of confounders, individual behaviours including physical activity levels and sleep duration and appeared consistent across subgroups. Possible interaction between the rest-activity rhythm and body mass index was found. Our results support an association between weakened rest-activity rhythms and higher odds of hypertension.

Melatonin, a natural antioxidant therapy in spinal cord injury

Spinal cord injury (SCI) is a sudden onset of disruption to the spinal neural tissue, leading to loss of motor control and sensory function of the body. Oxidative stress is considered a hallmark in SCI followed by a series of events, including inflammation and cellular apoptosis. Melatonin was originally discovered as a hormone produced by the pineal gland. The subcellular localization of melatonin has been identified in mitochondria, exhibiting specific onsite protection to excess mitochondrial reactive oxygen species and working as an antioxidant in diseases. The recent discovery regarding the molecular basis of ligand selectivity for melatonin receptors and the constant efforts on finding synthetic melatonin alternatives have drawn researchers' attention back to melatonin. This review outlines the application of melatonin in SCI, including 1) the relationship between the melatonin rhythm and SCI in clinic; 2) the neuroprotective role of melatonin in experimental traumatic and ischemia/reperfusion SCI, i.e., exhibiting anti-oxidative, anti-inflammatory, and anti-apoptosis effects, facilitating the integrity of the blood-spinal cord barrier, ameliorating edema, preventing neural death, reducing scar formation, and promoting axon regeneration and neuroplasticity; 3) protecting gut microbiota and peripheral organs; 4) synergizing with drugs, rehabilitation training, stem cell therapy, and biomedical material engineering; and 5) the potential side effects. This comprehensive review provides new insights on melatonin as a natural antioxidant therapy in facilitating rehabilitation in SCI.

Current Insights into the Risks of Using Melatonin as a Treatment for Sleep Disorders in Older Adults

Exogenous melatonin is commonly used for sleep disorders in older adults, and its use is increasing over time. It appears to have modest efficacy in treating insomnia and circadian rhythm sleep-wake disorders. Melatonin is commonly perceived to be a safe alternative to other hypnotics and is available without prescription in some jurisdictions. New evidence suggests that endogenous melatonin has pleomorphic effects on multiple organ systems, many of which are poorly understood. This narrative review summarizes the current evidence regarding the safety of melatonin in older adults (defined by age over 65 years). Melatonin appears to have a favorable safety profile in this population, however there is a dearth of evidence regarding the safety of prolonged use. There are several factors which increase the risk of adverse effects of melatonin in older adults, and these should be taken into consideration when prescribing to this population.

Hypotensive effects of melatonin in rats: Focus on the model, measurement, application, and main mechanisms

The hypotensive effects of melatonin are based on a negative correlation between melatonin levels and blood pressure in humans. However, there is a positive correlation in nocturnal animals that are often used as experimental models in cardiovascular research, and the hypotensive effects and mechanism of melatonin action are often investigated in rats and mice. In rats, the hypotensive effects of melatonin have been studied in normotensive and spontaneously or experimentally induced hypertensive strains. In experimental animals, blood pressure is often measured indirectly during the light (passive) phase of the day by tail-cuff plethysmography, which has limitations regarding data quality and animal well-being compared to telemetry. Melatonin is administered to rats in drinking water, subcutaneously, intraperitoneally, or microinjected into specific brain areas at different times. Experimental data show that the hypotensive effects of melatonin depend on the experimental animal model, blood pressure measurement technique, and the route, time and duration of melatonin administration. The hypotensive effects of melatonin may be mediated through specific membrane G-coupled receptors located in the heart and arteries. Due to melatonin's lipophilic nature, its potential hypotensive effects can interfere with various regulatory mechanisms, such as nitric oxide and reactive oxygen species production and activation of the autonomic nervous and circadian systems. Based on the research conducted on rats, the cardiovascular effects of melatonin are modulatory, delayed, and indirect.

Estrogen-dependent depressor response of melatonin via baroreflex afferent function and intensification of PKC-mediated Nav1.9 activation

Recent studies suggest that melatonin (Mel) plays an important role in the regulation of blood pressure (BP) via the aortic baroreflex pathway. In this study, we investigated the interaction between the baroreflex afferent pathway and Mel-mediated BP regulation in rats under physiological and hypertensive conditions. Mel (0.1, 0.3, and 1.0 mg/mL) was microinjected into the nodose ganglia (NG) of rats. We showed that Mel-induced reduction of mean arterial pressure in female rats was significantly greater than that in male and in ovariectomized rats under physiological condition. Consistently, the expression of Mel receptors (MTNRs) in the NG of female rats was significantly higher than that of males. In L-NAME-induced hypertensive and spontaneously hypertensive rat models, MTNRs were upregulated in males but downregulated in female models. Interestingly, Mel-induced BP reduction was found in male hypertensive models. In whole-cell recording from identified baroreceptor neurons (BRNs) in female rats, we found that Mel (0.1 μM) significantly increased the excitability of a female-specific subpopulation of Ah-type BRNs by increasing the Nav1.9 current density via a PKC-mediated pathway. Similar results were observed in baroreceptive neurons of the nucleus tractus solitarius, showing the facilitation of spontaneous and evoked excitatory post-synaptic currents in Ah-type neurons. Collectively, this study reveals the estrogen-dependent effect of Mel/MTNRs under physiological and hypertensive conditions is mainly mediated by Ah-type BRNs, which may provide new theoretical basis and strategies for the gender-specific anti-hypertensive treatment in clinical practice.

Benefits and adverse events of melatonin use in the elderly (Review)

Melatonin is a hormone secreted by the pineal gland in accordance with the circadian rhythm when the light level decreases. Reduction of melatonin secretion with age may be associated with physiological aging in neurodegenerative diseases by affecting the suprachiasmatic nucleus or of the neuronal pathways of transmission to the pineal gland. A significant decrease in melatonin synthesis has been reported in various disorders and diseases, including cardiovascular diseases, metabolic disorders (particularly diabetes type 2), cancer and endocrine diseases. In addition to the fact, that melatonin is a sleep inducer, it also exerts cytoprotective properties as an antioxidant and free radical scavenger. The therapeutic role of melatonin has been demonstrated in sleep disorders, eye damage and cardiovascular disease. The association between melatonin and β-blockers has had a positive impact on sleep disorders in clinical trials. Previous studies have reported the anti-inflammatory effect of melatonin by adjusting levels of pro-inflammatory cytokines, including interleukin (IL)-6, IL-1β and tumor necrosis factor-α. Melatonin treatment has been demonstrated to decrease IL-6 and IL-10 expression levels and efficiently attenuate T-cell proliferation. Currently, there is an inconsistency of scientific data regarding the lowest optimal dose and safety of melatonin for long-term use. The aim of the present review was to summarize the evidence on the role of melatonin in various clinical conditions and highlight the future research in this area.

Melatonin Prevents T Lymphocyte Infiltration to the Kidneys of Hypertensive Rats, Induced by a High-Salt Diet, by Preventing the Expression of CXCR3 Ligand Chemokines

In a previous study, we demonstrated that melatonin prevents kidney damage in a salt-induced hypertension model by decreasing oxidative stress. We hypothesized that this effect involves melatonin’s immunomodulatory properties. In vivo Study-Dahl salt-sensitive (DSS) rats were fed normal chow, a high-salt diet (HSD), or a HSD and melatonin (30 mg/kg/day) in their water for eight weeks. Kidneys were harvested for immediate lymphocyte isolation and characterization by Flow cytometry (CD3+CD4+ and CD3+CD8+) and for lymphocyte chemoattractant (mainly CXCL chemokines) gene expression studies. In vitro study-rat mesangial cells (RMC) were cultured in a high-salt medium without and with melatonin. A HSD was associated with significant renal infiltration of CD4+ and CD8+ T lymphocytes compared to control. Melatonin significantly reduced renal lymphocyte infiltration. A HSD significantly increased mRNA expression of CXCL chemokines. Adding melatonin to the HSD abolished this effect. Treating RMC cells with salt increased the expression of CXCL10 and CXCL11 but not CXCL9. Adding melatonin to the culture media prevented this increase. Treating HSD-fed rats with melatonin decreased renal lymphocyte chemoattractant mRNA expression and is associated with significantly reducing renal T lymphocyte infiltration. Salt may have a direct effect on chemokine-producing renal cells, which is blunted by melatonin treatment.

Expression of Melatonin Receptor 1 in Rat Mesenteric Artery and Perivascular Adipose Tissue and Vasoactive Action of Melatonin

Melatonin is released by the pineal gland and can modulate cardiovascular system function via the G protein-coupled melatonin receptors MT1 and MT2. Most vessels are surrounded by perivascular adipose tissue (PVAT), which affects their contractility. The aim of our study was to evaluate mRNA and protein expression of MT1 and MT2 in the mesenteric artery (MA) and associated PVAT of male rats by RT-PCR and Western blot. Receptor localization was further studied by immunofluorescence microscopy. Effects of melatonin on neurogenic contractions were explored in isolated superior MA ex vivo by measurement of isometric contractile tension. MT1, but not MT2, was present in MA, and MT1 was localized mainly in vascular smooth muscle. Moreover, we proved the presence of MT1, but not MT2 receptors, in MA-associated PVAT. In isolated superior MA with intact PVAT, neuro-adrenergic contractile responses were significantly smaller when compared to arteries with removed PVAT. Pre-treatment with melatonin of PVAT-stripped arterial rings enhanced neurogenic contractions, while the potentiating effect of melatonin was not detected in preparations with preserved PVAT. We hypothesize that melatonin can stimulate the release of PVAT-derived relaxing factor(s) via MT1, which can override the direct pro-contractile effect of melatonin on vascular smooth muscle. Our results suggest that melatonin is involved in the control of vascular tone in a complex way, which is vessel specific and can reflect a sum of action on different layers of the vessel wall and surrounding PVAT.

Melatonin: From Neurobiology to Treatment

Melatonin, the major regulator of the sleep/wake cycle, also plays important physiological and pharmacological roles in the control of neuronal plasticity and neuroprotection. Accordingly, the secretion of this hormone reaches the maximal extent during brain development (childhood-adolescence) while it is greatly reduced during aging, a condition associated to altered sleep pattern and reduced neuronal plasticity. Altogether, these properties of melatonin have allowed us to demonstrate in both experimental models and clinical studies the great chronobiotic efficacy and sleep promoting effects of exogenous melatonin. Thus, the prolonged release formulation of melatonin, present as a drug in the pharmaceutical market, has been recently recommended for the treatment of insomnia in over 55 years old subjects.

Melatonin Supplementation for Six Weeks Had No Effect on Arterial Stiffness and Mitochondrial DNA in Women Aged 55 Years and Older with Insomnia: A Double-Blind Randomized Controlled Study

Melatonin is a hormone produced in the pineal gland that controls sleep and circadian rhythm. Some studies have reported antioxidant and anti-inflammatory effects of melatonin that could benefit cardiometabolic function; however, there is a lack of evidence to support these assertions. The aim of this study was to investigate whether melatonin has beneficial effects on arterial stiffness and mitochondrial deoxyribonucleic acid (DNA) in humans. Methods: This study was designed as a double-blind randomized controlled study. Thirty-eight healthy women aged 55 years and older were enrolled. All had insomnia (Pittsburgh Sleep Quality Index (PSQI) ≥ 5), not treated with any medications, for at least three months before enrollment. Subjects were divided into a melatonin and a placebo group according to melatonin supplementation. The melatonin group took 2 mg melatonin every night for six weeks. The cardio–ankle vascular index (CAVI) was used as an indicator of arterial stiffness. After six weeks, CAVI, mitochondrial DNA (mtDNA) copy number in white blood cells (WBCs), and other metabolic indices, such as homeostasis model assessment of insulin resistance (HOMA-IR), were checked. Results: Sleep quality index using PSQI was improved in the melatonin group from a score of 11 to 8 (p = 0.01), but did not change significantly in the control group. However, there was no significant intergroup difference in PSQI. Systolic blood pressure (SBP) decreased in the melatonin group from 135 to 128 mmHg (p = 0.015), while remaining stable in the placebo group. Right CAVI, mitochondrial DNA copy number, and HOMA-IR were not altered in either group. There were no intergroup differences in CAVI, mtDNA, HOMA-IR, or SBP between baseline and week six. Conclusions: We found no evidence that melatonin supplementation improved cardiometabolic parameters like arterial stiffness, mtDNA, or insulin resistance compared to the placebo between baseline and week six. Sleep quality was improved in the melatonin group. Further research, including longer-term studies with higher doses of melatonin, is warranted.

Diagnostic and Therapeutic Approach to Sleep Disorders, High Blood Pressure and Cardiovascular Diseases: A Consensus Document by the Italian Society of Hypertension (SIIA)

Hypertension is a major contributor to fatal/nonfatal cardiovascular diseases, and timely identification and appropriate management of factors affecting hypertension and its control are mandatory public health issues. By inducing neurohormonal alterations and metabolic impairment, sleep disorders have an impact on a variety of cardiovascular risk factors, including hypertension, and ultimately increase the risk of cardiovascular events. There is evidence that qualitative and quantitative sleep disorders are associated with resistant hypertension and with impaired circadian blood pressure variations. However, sleep disturbances are often unrecognized, or heterogeneity exists in their management by non-specialists in the field. This document by the Italian Society of Hypertension summarizes the updated evidence linking sleep disorders to hypertension and cardiovascular diseases, the major underlying mechanisms, and the possible management strategies. A simplified, evidence-based diagnostic and therapeutic algorithm for comorbid hypertension and common sleep disorders, namely obstructive sleep apnoea and insomnia, is proposed.

Thymosin β4: A Multi-Faceted Tissue Repair Stimulating Protein in Heart Injury

Thymosin Beta-4 (Tβ4) is known as a major pleiotropic actin-sequestering protein that is involved in tumorigenesis. Tβ4 is a water-soluble protein that has different promising clinical applications in the remodeling and ulcerated tissues repair following myocardial infarction, stroke, plasticity and neurovascular remodeling of the Peripheral Nervous System (PNS) and the Central Nervous System (CNS). On the other hand, similar effects have been observed for Tβ4 in other kinds of tissues, including cardiac muscle tissue. In recent reports, as it activates resident epicardial progenitor cells and modulates inflammatory-caused injuries, Tβ4 has been suggested as a promoter of the survival of cardiomyocytes. Furthermore, Tβ4 may act in skeletal muscle and different organs in association/synergism with numerous other tissue repair stimulating factors, including melatonin and C-fiber-derived peptides. For these reasons, the present review highlights the promising role of Tβ4 in cardiac healing.

Melatonin in Wine and Beer: Beneficial Effects

Melatonin is a hormone secreted in the pineal gland with several functions, especially regulation of circadian sleep cycle and the biological processes related to it. This review evaluates the bioavailability of melatonin and resulting metabolites, the presence of melatonin in wine and beer and factors that influence it, and finally the different benefits related to treatment with melatonin. When administered orally, melatonin is mainly absorbed in the rectum and the ileum; it has a half-life of about 0.45–1 h and is extensively inactivated in the liver by phase 2 enzymes. Melatonin (MEL) concentration varies from picograms to ng/mL in fermented beverages such as wine and beer, depending on the fermentation process. These low quantities, within a dietary intake, are enough to reach significant plasma concentrations of melatonin, and are thus able to exert beneficial effects. Melatonin has demonstrated antioxidant, anticarcinogenic, immunomodulatory and neuroprotective actions. These benefits are related to its free radical scavenging properties as well and the direct interaction with melatonin receptors, which are involved in complex intracellular signaling pathways, including inhibition of angiogenesis and cell proliferation, among others. In the present review, the current evidence on the effects of melatonin on different pathophysiological conditions is also discussed.

Associations Between Sleep Disorders and Hypertensive Disorders of Pregnancy and Materno-fetal Consequences

PURPOSE OF THE REVIEW

To review the data supporting the associations between sleep disorders and hypertensive disorders of pregnancy, their diagnosis, consequences, treatment, and potential mechanisms.

RECENT FINDINGS

The prevalence of sleep-disordered breathing, insomnia, and restless legs syndrome increases as pregnancy progresses secondary to physiologic changes associated with pregnancy. Sleep-disordered breathing is strongly associated with the development of gestational hypertension and preeclampsia, both of which are associated with increased risk of perinatal complications. Diagnosing sleep disorders in pregnant presents added challenges, but polysomnography remains the gold standard for diagnosing sleep-disordered breathing in this group. Sleep disorders, and especially sleep-disordered breathing, are highly prevalent among pregnant women and associated with hypertensive disorders of pregnancy. Clinicians should be mindful of this association and endeavor to identify at-risk women for further evaluation.

Cardioprotective Role of Melatonin in Acute Myocardial Infarction

Melatonin is a pleiotropic, indole secreted, and synthesized by the human pineal gland. Melatonin has biological effects including anti-apoptosis, protecting mitochondria, anti-oxidation, anti-inflammation, and stimulating target cells to secrete cytokines. Its protective effect on cardiomyocytes in acute myocardial infarction (AMI) has caused widespread interest in the actions of this molecule. The effects of melatonin against oxidative stress, promoting autophagic repair of cells, regulating immune and inflammatory responses, enhancing mitochondrial function, and relieving endoplasmic reticulum stress, play crucial roles in protecting cardiomyocytes from infarction. Mitochondrial apoptosis and dysfunction are common occurrence in cardiomyocyte injury after myocardial infarction. This review focuses on the targets of melatonin in protecting cardiomyocytes in AMI, the main molecular signaling pathways that melatonin influences in its endogenous protective role in myocardial infarction, and the developmental prospect of melatonin in myocardial infarction treatment.

[Hypertension and insomnia]

Insomnia is frequently detected in patients with arterial hypertension (AH): from 19% to 47.9% of all cases according to epidemiological studies. On the other hand, the frequency of hypertension in patients with insomnia ranges from 21.4% to 50.2%, whereas in patients without insomnia, from 11.0% to 41.8%. In single studies in which patients with insomnia underwent ambulatory blood pressure monitoring (ABPM), these patients showed higher nocturnal blood pressure levels. Recent data suggests that insomnia is also a risk factor for hypertension. Among the pathogenetic mechanisms explaining the relationship between hypertension and insomnia, an increase in the activity of the main neuroendocrine stress systems, sympatho - adrenal and hypothalamic - pituitary - adrenal, and the frequent presence of concomitant anxiety disorders are discussed. To determine the sleep quality in patients with insomnia, the Pittsburgh Sleep Quality Index (PSQI) is most often used, patients with hypertension in a number of studies had higher total PSQI score compared to individuals with normal blood pressure. PSQI score correlates with systolic and diastolic blood pressure level, as well as with the presence of non - dipper blood pressure profile. Both hypertension and insomnia are associated with impaired cognitive functions. However, the relationship between cognitive impairment and insomnia is rather contradictory, which is most associated with the methodology for assessing cognitive functions and differences in the initial clinical and demographic characteristics of the examined patient population.

Adverse Events Associated with Melatonin for the Treatment of Primary or Secondary Sleep Disorders: A Systematic Review

BACKGROUND

Melatonin is widely available either on prescription for the treatment of sleep disorders or as an over-the-counter dietary supplement. Melatonin has also recently been licensed in the UK for the short-term treatment of jetlag. Little is known about the potential for adverse events (AEs), in particular AEs resulting from long-term use. Concern has been raised over the possible risks of exposure in certain populations including pre-adolescent children and patients with epilepsy or asthma.

OBJECTIVES

The aim of this systematic review was to assess the evidence for AEs associated with short-term and longer-term melatonin treatment for sleep disorders.

METHODS

A literature search of the PubMed/Medline database and Google Scholar was conducted to identify randomised, placebo-controlled trials (RCTs) of exogenous melatonin administered for primary or secondary sleep disorders. Studies were included if they reported on both the types and frequencies of AEs. Studies of pre-term infants, studies of < 1 week in duration or involving single doses of melatonin and studies in languages other than English were excluded. Findings from open-label studies that raised concerns relating to AE reports in patients were also examined. Studies were assessed for quality of reporting against the Consolidated Standards of Reporting Trials (CONSORT) checklist and for risk of bias against the Cochrane Collaboration risk-of-bias criteria.

RESULTS

37 RCTs met criteria for inclusion. Daily melatonin doses ranged from 0.15 mg to 12 mg. Subjects were monitored for up to 29 weeks, but most studies were of much shorter duration (4 weeks or less). The most frequently reported AEs were daytime sleepiness (1.66%), headache (0.74%), other sleep-related AEs (0.74%), dizziness (0.74%) and hypothermia (0.62%). Very few AEs considered to be serious or of clinical significance were reported. These included agitation, fatigue, mood swings, nightmares, skin irritation and palpitations. Most AEs either resolved spontaneously within a few days with no adjustment in melatonin, or immediately upon withdrawal of treatment. Melatonin was generally regarded as safe and well tolerated. Many studies predated publication of the CONSORT checklist and consequently did not conform closely to the guidelines. Similarly, only eight studies were judged 'good' overall with respect to the Cochrane risk-of-bias criteria. Of the remaining papers, 16 were considered 'fair' and 13 'poor' but publication of almost half of the papers preceded that of the earliest version of the guidelines.

CONCLUSION

Few, generally mild to moderate, AEs were associated with exogenous melatonin. No AEs that were life threatening or of major clinical significance were identified. The scarcity of evidence from long-term RCTs, however, limits the conclusions regarding the safety of continuous melatonin therapy over extended periods. There are insufficient robust data to allow a meaningful appraisal of concerns that melatonin may result in more clinically significant adverse effects in potentially at-risk populations. Future studies should be designed to comply with appropriate quality standards for RCTs, which most past studies have not.

Cardioprotective Melatonin: Translating from Proof-of-Concept Studies to Therapeutic Use

In this review we summarized the actual clinical data for a cardioprotective therapeutic role of melatonin, listed melatonin and its agonists in different stages of development, and evaluated the melatonin cardiovascular target tractability and prediction using machine learning on ChEMBL. To date, most clinical trials investigating a cardioprotective therapeutic role of melatonin are in phase 2a. Selective melatonin receptor agonists Tasimelteon, Ramelteon, and combined melatonergic-serotonin Agomelatine, and other agonists with registered structures in CHEMBL were not yet investigated as cardioprotective or cardiovascular drugs. As drug-able for these therapeutic targets, melatonin receptor agonists have the benefit over melatonin of well-characterized pharmacologic profiles and extensive safety data. Recent reports of the X-ray crystal structures of MT1 and MT2 receptors shall lead to the development of highly selective melatonin receptor agonists. Predictive models using machine learning could help to identify cardiovascular targets for melatonin. Selecting ChEMBL scores > 4.5 in cardiovascular assays, and melatonin scores > 4, we obtained 284 records from 162 cardiovascular assays carried out with 80 molecules with predicted or measured melatonin activity. Melatonin activities (agonistic or antagonistic) found in these experimental cardiovascular assays and models include arrhythmias, coronary and large vessel contractility, and hypertension. Preclinical proof-of-concept and early clinical studies (phase 2a) suggest a cardioprotective benefit from melatonin in various heart diseases. However, larger phase 3 randomized interventional studies are necessary to establish melatonin and its agonists’ actions as cardioprotective therapeutic agents.

Genetic polymorphisms associated with reactive oxygen species and blood pressure regulation

Hypertension is the most prevalent cause of cardiovascular disease and kidney failure, but only about 50% of patients achieve adequate blood pressure control, in part, due to inter-individual genetic variations in the response to antihypertensive medication. Significant strides have been made toward the understanding of the role of reactive oxygen species (ROS) in the regulation of the cardiovascular system. However, the role of ROS in human hypertension is still unclear. Polymorphisms of some genes involved in the regulation of ROS production are associated with hypertension, suggesting their potential influence on blood pressure control and response to antihypertensive medication. This review provides an update on the genes associated with the regulation of ROS production in hypertension and discusses the controversies on the use of antioxidants in the treatment of hypertension, including the antioxidant effects of antihypertensive drugs.

The effects of melatonin supplementation on blood pressure in patients with metabolic disorders: a systematic review and meta-analysis of randomized controlled trials

The current systematic review and meta-analysis of randomized controlled trials (RCTs) was conducted to evaluate the potential effect of melatonin supplementation on blood pressure in patients with metabolic disorders. The following databases were searched until June 2018: PubMed, MEDLINE, EMBASE, Web of Science, and Cochrane Central Register of Controlled Trials. Two reviewers independently assessed the eligibility of retrieved studies, extracted data from included trials, and evaluated the risk of bias of included studies. Statistical heterogeneity was tested using Cochran's Q test and I-square (I²) statistic. Data were pooled using random-effect models and standardized mean difference (SMD) was considered as the effect size. Eight RCTs, out of 743 potential citations, were eligible to be included in the current meta-analysis. The pooled findings indicated a significant reduction in systolic (SBP) (SMD = -0.87; 95% CI, -1.36, -0.38; P = 0.001; I²: 84.3) and diastolic blood pressure (DBP) (SMD = -0.85; 95% CI, -1.20, -0.51; P = 0.001; I²: 68.7) following melatonin supplementation in individuals with metabolic disorders. In summary, the current meta-analysis demonstrated that melatonin supplementation significantly decreased SBP and DBP in patients with metabolic disorders. Additional prospective studies are recommended using higher supplementation doses and longer intervention periods to confirm our findings.

Role of the Circadian Clock in the Metabolic Syndrome and Nonalcoholic Fatty Liver Disease

Nonalcoholic fatty liver disease (NAFLD) is the most common chronic liver disease in industrialized nations and is strongly associated with the metabolic syndrome. The prevalence of NAFLD continues to rise along with the epidemic of the metabolic syndrome. Metabolic homeostasis is linked to the circadian clock (rhythm), with multiple signaling pathways in organs regulated by circadian clock genes, and recent studies of circadian clock gene functions suggest that disruption of the circadian rhythm is associated with significant morbidity and mortality, including the metabolic syndrome. In the industrialized world, various human behaviors and activities such as work and eating patterns, jet lag, and sleep deprivation interfere with the circadian rhythm, leading to perturbations in metabolism and development of the metabolic syndrome. In this review, we discuss how disruption of the circadian rhythm is associated with various metabolic conditions that comprise the metabolic syndrome and NAFLD.

New perspectives on the role of melatonin in human sleep, circadian rhythms and their regulation

In mammals, a central circadian clock, located in the suprachiasmatic nuclei (SCN) of the hypothalamus, tunes the innate circadian physiological rhythms to the ambient 24 h light-dark cycle to invigorate and optimize the internal temporal order. The SCN-activated, light-inhibited production of melatonin conveys the message of darkness to the clock and induces night-state physiological functions, for example, sleep/wake blood pressure and metabolism. Clinically meaningful effects of melatonin treatment have been demonstrated in placebo-controlled trials in humans, particularly in disorders associated with diminished or misaligned melatonin rhythms, for example, circadian rhythm-related sleep disorders, jet lag and shift work, insomnia in children with neurodevelopmental disorders, poor (non-restorative) sleep quality, non-dipping nocturnal blood pressure (nocturnal hypertension) and Alzheimer's disease (AD). The diminished production of melatonin at the very early stages of AD, the role of melatonin in the restorative value of sleep (perceived sleep quality) and its sleep-anticipating effects resulting in attenuated activation of certain brain networks are gaining a new perspective as the role of poor sleep quality in the build-up of β amyloid, particularly in the precuneus, is unravelled. As a result of the recently discovered relationship between circadian clock, sleep and neurodegeneration, new prospects of using melatonin for early intervention, to promote healthy physical and mental ageing, are of prime interest in view of the emerging link to the aetiology of Alzheimer's disease. LINKED ARTICLES: This article is part of a themed section on Recent Developments in Research of Melatonin and its Potential Therapeutic Applications. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v175.16/issuetoc.

Melatonin in Heart Failure: A Promising Therapeutic Strategy?

Heart failure is a multifactorial clinical syndrome characterized by the inability of the heart to pump sufficient blood to the body. Despite recent advances in medical management, poor outcomes in patients with heart failure remain very high. This highlights a need for novel paradigms for effective, preventive and curative strategies. Substantial evidence supports the importance of endogenous melatonin in cardiovascular health and the benefits of melatonin supplementation in various cardiac pathologies and cardiometabolic disorders. Melatonin plays a crucial role in major pathological processes associated with heart failure including ischemic injury, oxidative stress, apoptosis, and cardiac remodeling. In this review, available evidence for the role of melatonin in heart failure is discussed. Current challenges and possible limitations of using melatonin in heart failure are also addressed. While few clinical studies have investigated the role of melatonin in the context of heart failure, current findings from experimental studies support the potential use of melatonin as preventive and adjunctive curative therapy in heart failure.

Cardiovascular Benefits of Dietary Melatonin: A Myth or a Reality?

The role of the diet as well as the impact of the dietary habits on human health and disease is well established. Apart from its sleep regulatory effect, the indoleamine melatonin is a well-established antioxidant molecule with multiple health benefits. Convincing evidence supports the presence of melatonin in plants and foods with the intake of such foods affecting circulating melatonin levels in humans. While numerous actions of both endogenous melatonin and melatonin supplementation are well described, little is known about the influence of the dietary melatonin intake on human health. In the present review, evidence for the cardiovascular health benefits of melatonin supplementation and dietary melatonin is discussed. Current knowledge on the biological significance as well as the underlying physiological mechanism of action of the dietary melatonin is also summarized. Whether dietary melatonin constitutes an alternative preventive treatment for cardiovascular disease is addressed.

Relationship between autonomic cardiovascular control and obstructive sleep apnoea in persons with spinal cord injury: a retrospective study

Study design

Retrospective study.

Objective

To determine if there is an association between obstructive sleep apnoea (OSA) and blood pressure (BP) pattern or heart rate variability (HRV) in people with spinal cord injury (SCI).

Setting

A state-based spinal cord service in Victoria, Australia.

Methods

We identified 42 subjects who had ambulatory BP monitoring (ABPM) within 6 months of a diagnostic sleep study at Austin Hospital between 2009 and 2014. Markers for autonomic function, including circadian BP pattern and HRV were extracted from the ABPM study database. Apnoea/hypopnoea index (AHI), arousals/hour and oxygen desaturation index were extracted from the sleep study database. Subjects with a nocturnal systolic BP dipping more than 10% of daytime value were defined as dippers, between 10 and 0% were non-dippers and those with a higher night than day systolic BP were reverse dippers. Severity of OSA is classified as non-OSA (AHI < 5), mild (AHI 5-15), moderate (AHI 15-30) and severe (AHI > 30).

Results

Subjects (n = 42) were predominantly male (85.7%), aged 44 ± 15.4 (mean ± SD), with a BMI of 24.4 ± 5.7 (mean ± SD) and mainly tetraplegic (92.9%). There was no difference in AHI, oxygen desaturation index or arousals/hour between dippers, non-dippers and reverse dippers. None of the HRV parameters differed between dippers, non-dippers and reverse dippers. No differences were found in 24 h, night-time, daytime or nocturnal dip in BP between subjects with non-OSA, mild, moderate and severe OSA.

Conclusion

We found no relationship between BP pattern or HRV and the severity of OSA in persons with SCI.

Melatonin for Atypical Antipsychotic-Induced Metabolic Adverse Effects: A Meta-Analysis of Randomized Controlled Trials

The objective of our study was to determine the effect of melatonin administration on atypical antipsychotic-induced metabolic adverse effects in patients with psychiatric disorders. A systematic search was performed in PUBMED, Cochrane Library, Scopus, Web of Science, and EBSCOhost electronic databases. Randomized controlled trials studying the effect of melatonin on antipsychotic-induced metabolic adverse effects were identified and subjected to meta-analysis. Four studies were included in the meta-analysis, including 57 patients on melatonin and 61 patients on placebo. Melatonin produced a significant decrease in the diastolic blood pressure compared with placebo (mean difference = −4.44 [95% CI, −7.00 to −1.88]; p = 0.0007; I² = 13%), but not the systolic blood pressure (mean difference = −4.23 [95% CI, −8.11 to −0.36]; p = 0.03; I² = 0%). Although a decrease in the body mass index was seen in the melatonin group, the difference was not significant in the random-effects analysis model. To conclude, in patients on atypical antipsychotics, melatonin at a dose of up to 5 mg/day for a treatment duration of up to 12 weeks attenuated the rise in diastolic blood pressure compared with placebo but had no significant effects on other metabolic parameters.

Melatonin and health: an umbrella review of health outcomes and biological mechanisms of action

BACKGROUND

Our aims were to evaluate critically the evidence from systematic reviews as well as narrative reviews of the effects of melatonin (MLT) on health and to identify the potential mechanisms of action involved.

METHODS

An umbrella review of the evidence across systematic reviews and narrative reviews of endogenous and exogenous (supplementation) MLT was undertaken. The Oxman checklist for assessing the methodological quality of the included systematic reviews was utilised. The following databases were searched: MEDLINE, EMBASE, Web of Science, CENTRAL, PsycINFO and CINAHL. In addition, reference lists were screened. We included reviews of the effects of MLT on any type of health-related outcome measure.

RESULTS

Altogether, 195 reviews met the inclusion criteria. Most were of low methodological quality (mean -4.5, standard deviation 6.7). Of those, 164 did not pool the data and were synthesised narratively (qualitatively) whereas the remaining 31 used meta-analytic techniques and were synthesised quantitatively. Seven meta-analyses were significant with P values less than 0.001 under the random-effects model. These pertained to sleep latency, pre-operative anxiety, prevention of agitation and risk of breast cancer.

CONCLUSIONS

There is an abundance of reviews evaluating the effects of exogenous and endogenous MLT on health. In general, MLT has been shown to be associated with a wide variety of health outcomes in clinically and methodologically heterogeneous populations. Many reviews stressed the need for more high-quality randomised clinical trials to reduce the existing uncertainties.

Melatonin, mitochondria, and the metabolic syndrome

A number of risk factors for cardiovascular disease including hyperinsulinemia, glucose intolerance, dyslipidemia, obesity, and elevated blood pressure are collectively known as metabolic syndrome (MS). Since mitochondrial activity is modulated by the availability of energy in cells, the disruption of key regulators of metabolism in MS not only affects the activity of mitochondria but also their dynamics and turnover. Therefore, a link of MS with mitochondrial dysfunction has been suspected since long. As a chronobiotic/cytoprotective agent, melatonin has a special place in prevention and treatment of MS. Melatonin levels are reduced in diseases associated with insulin resistance like MS. Melatonin improves sleep efficiency and has antioxidant and anti-inflammatory properties, partly for its role as a metabolic regulator and mitochondrial protector. We discuss in the present review the several cytoprotective melatonin actions that attenuate inflammatory responses in MS. The clinical data that support the potential therapeutical value of melatonin in human MS are reviewed.

On the mechanisms of melatonin in protection of aluminum phosphide cardiotoxicity

Aluminum phosphide (AlP), one of the most commonly used pesticides worldwide, has been the leading cause of self-poisoning mortalities among many Asian countries. The heart is the main organ affected in AlP poisoning. Melatonin has been previously shown to be beneficial in reversing toxic changes in the heart. The present study reveals evidence on the probable protective effects of melatonin on AlP-induced cardiotoxicity in rats. The study groups included a control (almond oil only), ethanol 5% (solvent), sole melatonin (50 mg/kg), AlP (16.7 mg/kg), and 4 AlP + melatonin groups which received 20, 30, 40 and 50 mg/kg of melatonin by intraperitoneal injections following AlP treatment. An electronic cardiovascular monitoring device was used to record the electrocardiographic (ECG) parameters. Heart tissues were studied in terms of oxidative stress biomarkers, mitochondrial complexes activities, ADP/ATP ratio and apoptosis. Abnormal ECG records as well as declined heart rate and blood pressure were found to be related to AlP administration. Based on the results, melatonin was highly effective in controlling AlP-induced changes in the study groups. Significant improvements were observed in the activities of mitochondrial complexes, oxidative stress biomarkers, the activities of caspases 3 and 9, and ADP/ATP ratio following treatment with melatonin at doses of 40 and 50 mg/kg. Our results indicate that melatonin can counteract the AlP-induced oxidative damage in the heart. This is mainly done by maintaining the normal balance of intracellular ATP as well as the prevention of oxidative damage. Further research is warranted to evaluate the possibility of using melatonin as an antidote in AlP poisoning.

Effects of exercise and stress management training on nighttime blood pressure dipping in patients with coronary heart disease: A randomized, controlled trial

INTRODUCTION

Blunted nighttime blood pressure (BP) dipping is prognostic of cardiovascular morbidity and mortality. Patients with coronary heart disease (CHD) are often characterized by a blunted nighttime BP dipping pattern. The present study compared the effects of 2 behavioral intervention programs, aerobic exercise (EX) and stress management (SM) training, with a usual care (UC) control group on BP dipping in a sample of CHD patients.

METHODS

This was a secondary analysis of a randomized, controlled trial with allocation concealment and blinded outcome assessment in 134 patients with stable CHD and exercise-induced myocardial ischemia. Nighttime BP dipping was assessed by 24-hour ambulatory BP monitoring, at prerandomization baseline and after 16 weeks of one of the following treatments: usual medical care; UC plus supervised aerobic EX for 35 minutes, 3 times per week; UC plus weekly 1.5-hour sessions of SM training.

RESULTS

The EX and SM groups exhibited greater improvements in systolic BP dipping (P=.052) and diastolic BP dipping (P=.031) compared with UC. Postintervention systolic BP percent-dipping means were 12.9% (SE=1.5) for SM, 11.1% (SE=1.4) for EX, and 8.6% (SE=1.4) for UC. Postintervention diastolic BP percent-dipping means were 13.3% (SE=1.9) for SM, 14.1% (SE=1.8) for EX, and 8.8% (1.8) for UC.

CONCLUSIONS

For patients with stable CHD, EX or SM training resulted in improved nighttime BP dipping compared with usual medical care. These favorable effects of healthy lifestyle modifications may help reduce the risk of adverse clinical events.

Administration of Melatonin and Metformin Prevents Deleterious Effects of Circadian Disruption and Obesity in Male Rats

Circadian disruption and obesity synergize to predispose to development of type 2 diabetes mellitus (T2DM), signifying that therapeutic targeting of both circadian and metabolic dysfunctions should be considered as a potential treatment approach. To address this hypothesis, we studied rats concomitantly exposed to circadian disruption and diet-induced obesity (CDO), a rat model recently shown to recapitulate phenotypical aspects of obese T2DM (eg, circadian disruption, obesity, insulin resistance, and islet failure). CDO rats were subsequently treated daily (for 12 wk) by timed oral gavage with vehicle, melatonin (a known chronobiotic), metformin, or combination treatment of both therapeutics. Melatonin treatment alone improved circadian activity rhythms, attenuated induction of β-cell failure, and enhanced glucose tolerance. Metformin alone did not modify circadian activity but enhanced insulin sensitivity and glucose tolerance. Importantly, the combination of melatonin and metformin had synergistic actions to modify progression of metabolic dysfunction in CDO rats through improved adiposity, circadian activity, insulin sensitivity, and islet cell failure. This study suggests that management of both circadian and metabolic dysfunctions should be considered as a potential preventative and therapeutic option for treatment of obesity and T2DM.

Short-term administration of melatonin or ghrelin on diabetic rats: effects on angiotensin II and vasopressin-induced uterine contractility

The aim of the present study was to investigate the effects of Angiotensin II (Ang II) and Arginin-Vasopressin (AVP) on contractility of non-pregnant uterus in diabetic Wistar rats and to explore whether one-week administration of Melatonin (MLT) or Ghrelin (GHR) will change the response of diabetic uterine muscle to AngII and AVP. Uterine horns, prepared by the method of isolated tissues were investigated as well as glycemic profile, blood pressure and body weight. The research of smooth muscle contractions was made by a new method of analysis, characterizing in detail the various phases of the myometrial activity. Differences in the development of the peptide-mediated smooth muscle contractions depending on the phase of the estrous cycle were observed. Experimental diabetes had a pronounced negative effect on force and time-parameters of AngII and AVP-stimulated uterine contractions. Administration of GHR or MLT had a beneficial effect on the glycemic status of diabetic rats and partially improved the response of uterine preparations to the peptides. The application of MLT increased both force and time-parameters of Ang II-and AVP-stimulated uterine contractions while treatment with GHR increased power characteristics and shortened contraction and relaxation of the smooth muscle process.

Nutraceuticals with a clinically detectable blood pressure-lowering effect: a review of available randomized clinical trials and their meta-analyses

AIMS

The aim of the present study was to review and comment on the available evidence on nutraceuticals with a clinically demonstrable blood pressure (BP)-lowering effect.

METHODS

We reviewed studies published in the English language from 1990 to 2015 on dietary supplements or nutraceuticals claiming to show an effect on human BP. An initial list of possibly effective agents and studies was obtained from the online reference, the Natural Medicine Comprehensive Database. Using PubMed, we searched agents identified from this list using the MeSH terms 'hypertension', 'blood pressure', 'dietary supplement' and 'nutraceuticals', alone and in combination. We then focused our attention on meta-analyses and randomized clinical trials.

RESULTS

Beyond the well-known effects on BP of the Dietary Approaches to Stop Hypertension (DASH) and the Mediterranean diet, a large number of studies have investigated the possible BP-lowering effect of different dietary supplements and nutraceuticals, most of which are antioxidant agents with a high tolerability and safety profile. In particular, a relatively large body of evidence supports the use of potassium, magnesium, L-arginine, vitamin C, cocoa flavonoids, beetroot juice, coenzyme Q10, controlled-release melatonin and aged garlic extract. The antihypertensive effect of all these nutraceuticals seems to be dose related and the overall tolerability is good.

CONCLUSION

Some nutraceuticals might have a positive impact on BP in humans. Further clinical research is needed, to identify from the available active nutraceuticals those with the best cost-effectiveness and risk-benefit ratio for widespread and long-term use in the general population with a low-added cardiovascular risk related to uncomplicated hypertension.

Molecular clocks and the human condition: approaching their characterization in human physiology and disease

Molecular clockworks knit together diverse biological networks and compelling evidence from model systems infers their importance in metabolism, immunological and cardiovascular function. Despite this and the diurnal variation in many aspects of human physiology and the phenotypic expression of disease, our understanding of the role and importance of clock function and dysfunction in humans is modest. There are tantalizing hints of connection across the translational divide and some correlative evidence of gene variation and human disease but most of what we know derives from forced desynchrony protocols in controlled environments. We now have the ability to monitor quantitatively ex vivo or in vivo the genome, metabolome, proteome and microbiome of humans in the wild. Combining this capability, with the power of mobile telephony and the evolution of remote sensing, affords a new opportunity for deep phenotyping, including the characterization of diurnal behaviour and the assessment of the impact of the clock on approved drug function.

Evaluating the Potential Effect of Melatonin on the post-Cardiac Surgery Sleep Disorder

BACKGROUND

Postoperative neurological injuries, including cognitive dysfunction, sleep disorder, delirium, and anxiety, are the important consequences of coronary artery bypass graft surgery (CABG). Evidence has shown that postoperative sleep disturbance is partly due to disturbed melatonin secretion in the perioperative period. The aim of this study was to evaluate the effect of melatonin on postoperative sleep disorder in patients undergoing CABG.

METHOD

One hundred forty-five elective CABG patients participated in a randomized double-blind study during the preoperative period. The patients were randomized to receive either 3 mg of melatonin or 10 mg of Oxazepam one hour before sleep time. Each group received the medication from 3 days before surgery until the time of discharge. Sleep quality was evaluated using the Groningen Sleep Quality Score (GSQS), and the incidence of delirium was evaluated by nursing records. Sleep quality and anxiety scores were compared before and after surgery through the Wilcoxon signed-rank test. The analysis of covariance (ANCOVA) and independent t-test were used to compare the sleep and anxiety scores between the groups. P values ≤ 0.05 were considered statistically significant.

RESULTS

Totally, 137 patients at a mean age of 60 years completed the study (76% male). The analysis of the data showed that sleep was significantly disturbed after surgery in both groups. The patients in the Oxazepam group demonstrated significantly higher disturbance in their mean postoperative GSQS score than did their counterparts in the melatonin group (p value < 0.001). A smaller proportion of the participants experienced delirium in the melatonin group (0.06%) than in the Oxazepam group (0.12%); however, this difference was not statistically significant.

CONCLUSION

The result of the present study revealed that melatonin improved sleep in post-cardiac surgery patients more than what was observed with Oxazepam. Therefore, melatonin may be considered an effective alternative for Benzodiazepines in the management of postoperative sleep disorder.

Nutraceuticals and Blood Pressure Control: Results from Clinical Trials and Meta-Analyses

Beyond the well-known effects on blood pressure (BP) of the dietary approaches to stop hypertension (DASH) and the Mediterranean diets, a large number of studies has investigated the possible BP lowering effect of different dietary supplements and nutraceuticals, the most part of them being antioxidant agents with a high tolerability and safety profile. In particular relatively large body of evidence support the use of potassium, L-arginine, vitamin C, cocoa flavonoids, beetroot juice, coenzyme Q10, controlled-release melatonin, and aged garlic extract. However there is a need for data about the long-term safety of a large part of the above discussed products. Moreover further clinical research is advisable to identify between the available active nutraceuticals those with the best cost-effectiveness and risk-benefit ratio for a large use in general population with low-added cardiovascular risk related to uncomplicated hypertension.

Therapeutic effects of melatonin receptor agonists on sleep and comorbid disorders

Several melatonin receptors agonists (ramelteon, prolonged-release melatonin, agomelatine and tasimelteon) have recently become available for the treatment of insomnia, depression and circadian rhythms sleep-wake disorders. The efficacy and safety profiles of these compounds in the treatment of the indicated disorders are reviewed. Accumulating evidence indicates that sleep-wake disorders and co-existing medical conditions are mutually exacerbating. This understanding has now been incorporated into the new Diagnostic and Statistical Manual of Mental Disorders, 5th Edition (DSM-5). Therefore, when evaluating the risk/benefit ratio of sleep drugs, it is pertinent to also evaluate their effects on wake and comorbid condition. Beneficial effects of melatonin receptor agonists on comorbid neurological, psychiatric, cardiovascular and metabolic symptomatology beyond sleep regulation are also described. The review underlines the beneficial value of enhancing physiological sleep in comorbid conditions.

Effect of captopril and melatonin on fibrotic rebuilding of the aorta in 24 hour light-induced hypertension

Chronic continuous light exposure leads to melatonin deficiency along with complex neurohumoral activation resulting in hypertension development in rats. The aim of this study was to show, whether continuous light induces fibrotic rebuilding of the aorta and whether the treatment with melatonin or angiotensin converting enzyme inhibitor captopril can prevent these potential alterations. In a six-week experiment, 3-month-old Wistar rats were divided into 4 groups (ten per group): controls, rats exposed to continuous light, exposed to continuous light plus treated with captopril (100 mg/kg/24 h) and exposed to continuous light plus treated with melatonin (10 mg/kg/24 h). Systolic blood pressure (SBP) and collagen type I and III in the media of thoracic aorta were measured. Continuous light induced hypertension and fibrotic rebuilding of the aorta in terms of enhancement of collagen I and III concentration in the aortic media. Both captopril and melatonin prevented SBP rise and reduced collagen III concentration in the aorta. However, only melatonin reduced collagen I and the sum of collagen I and III in the aortic tissue. We conclude that in continuous light-induced hypertension, administration of melatonin, along with SBP reduction, decreases collagen I and III concentration in the aorta. It is suggested that antifibrotic effect of melatonin may reduce the stiffness of the aorta and small arteries and beneficially influence the nature of the pulse wave and peripheral vascular resistance.

Impact of Maternal Melatonin Suppression on Amount and Functionality of Brown Adipose Tissue (BAT) in the Newborn Sheep

In human and sheep newborns, brown adipose tissue (BAT) accrued during fetal development is used for newborn thermogenesis. Here, we explored the role of maternal melatonin during gestation on the amount and functionality of BAT in the neonate. We studied BAT from six lambs gestated by ewes exposed to constant light from 63% gestation until delivery to suppress melatonin (LL), six lambs gestated by ewes exposed to LL but receiving daily oral melatonin (12 mg at 1700 h, LL + Mel) and another six control lambs gestated by ewes maintained in 12 h light:12 h dark (LD). Lambs were instrumented at 2 days of age. At 4-6 days of age, they were exposed to 24°C (thermal neutrality conditions) for 1 h, 4°C for 1 h, and 24°C for 1 h. Afterward, lambs were euthanized and BAT was dissected for mRNA measurement, histology, and ex vivo experiments. LL newborns had lower central BAT and skin temperature under thermal neutrality and at 4°C, and higher plasma norepinephrine concentration than LD newborns. In response to 4°C, they had a pronounced decrease in skin temperature and did not increase plasma glycerol. BAT weight in LL newborns was about half of that of LD newborns. Ex vivo, BAT from LL newborns showed increased basal lipolysis and did not respond to NE. In addition, expression of adipogenic/thermogenic genes (UCP1, ADBR3, PPARγ, PPARα, PGC1α, C/EBPβ, and perilipin) and of the clock genes Bmal1, Clock, and Per2 was increased. Remarkably, the effects observed in LL newborns were absent in LL + Mel newborns. Thus, our results support that maternal melatonin during gestation is important in determining amount and normal functionality of BAT in the neonate.

Melatonin supplementation to treat the metabolic syndrome: a randomized controlled trial

BACKGROUND

Supplemental melatonin may ameliorate metabolic syndrome (MetS) components, but data from placebo-controlled trials are lacking.

METHODS

We conducted a double-blind, placebo-controlled, crossover, Phase II randomized pilot clinical trial to estimate the effects of melatonin supplementation on MetS components and the overall prevalence of MetS. We randomized 39 subjects with MetS to receive 8.0 mg oral melatonin or matching placebo nightly for 10 weeks. After a 6-week washout, subjects received the other treatment for 10 more weeks. We measured waist circumference, triglycerides, HDL cholesterol, fasting glucose, and blood pressure (BP) in each subject at the beginning and end of both 10-week treatment periods. The primary outcome was the mean 10-week change in each MetS component, and a secondary outcome was the proportion of subjects free from MetS, after melatonin versus placebo.

RESULTS

The mean 10-week change for most MetS components favored melatonin over placebo (except fasting glucose): waist circumference -0.9 vs. +1.0 cm (p = 0.15); triglycerides -66.3 vs. -4.2 mg/dL (p = 0.17); HDL cholesterol -0.2 vs. -1.1 mg/dL (p = 0.59); fasting glucose +0.3 vs. -3.1 mg/dL (p = 0.29); systolic BP -2.7 vs. +4.7 mmHg (p = 0.013); and diastolic BP -1.1 vs. +1.1 mmHg (p = 0.24). Freedom from MetS tended to be more common following melatonin versus placebo treatment (after the first 10 weeks, 35.3% vs. 15.0%, p = 0.25; after the second 10 weeks, 45.0% vs. 23.5%, p = 0.30). Melatonin was well-tolerated.

CONCLUSIONS

Melatonin supplementation modestly improved most individual MetS components compared with placebo, and tended to increase the proportion of subjects free from MetS after treatment.

TRIAL REGISTRATION

NCT01038921, clinicaltrials.gov.

Evidence of clinically relevant efficacy for dietary supplements and nutraceuticals

Beyond the well-known effects on blood pressure (BP) of the DASH and the Mediterranean diets, a large number of studies have investigated the possible a BP-lowering effect from different dietary supplements and nutraceuticals, mostly antioxidant agents with a high tolerability and safety profile. In particular, a relatively large body of evidence support the use of potassium, L-arginine, vitamin C, cocoa flavonoids, coenzyme Q10, controlled-release melatonin, and aged garlic extract. However there is a need for data about the long-term safety of a large part of these products. Moreover, further clinical research is advisable to identify between the available active nutraceuticals and those with the best cost-effectiveness and risk-benefit ratio for widespread use in a general population with low added cardiovascular risk related to uncomplicated hypertension.

Melatonin and the skeleton

Melatonin may affect bone metabolism through bone anabolic as well as antiresorptive effects. An age-related decrease in peak melatonin levels at nighttime is well documented, which may increase bone resorption and bone loss in the elderly. In vitro, melatonin reduces oxidative stress on bone cells by acting as an antioxidant. Furthermore, melatonin improves bone formation by promoting differentiation of human mesenchymal stem cell (hMSC) into the osteoblastic cell linage. Bone resorption is reduced by increased synthesis of osteoprogeterin (OPG), a decoy receptor that prevents receptor activator of NK-κB ligand (RANKL) in binding to its receptor. Moreover, melatonin is believed to reduce the synthesis of RANKL preventing further bone resorption. In ovariectomized as well as nonovariectomized rodents, melatonin has shown beneficial effects on bone as assessed by biochemical bone turnover markers, DXA, and μCT scans. Furthermore, in pinealectomized animals, bone mineral density (BMD) is significantly decreased compared to controls, supporting the importance of sufficient melatonin levels. In humans, dysfunction of the melatonin signaling pathway may be involved in idiopathic scoliosis, and the increased fracture risk in nighttime workers may be related to changes in the circadian rhythm of melatonin. In the so-far only randomized study on melatonin treatment, no effects were, however, found on bone turnover markers. In conclusion, melatonin may have beneficial effects on the skeleton, but more studies on humans are warranted in order to find out whether supplementation with melatonin at bedtime may preserve bone mass and improve bone biomechanical competence.

Potency of melatonin in living beings

Living beings are surrounded by various changes exhibiting periodical rhythms in environment. The environmental changes are imprinted in organisms in various pattern. The phenomena are believed to match the external signal with organisms in order to increase their survival rate. The signals are categorized into circadian, seasonal, and annual cycles. Among the cycles, the circadian rhythm is regarded as the most important factor because its periodicity is in harmony with the levels of melatonin secreted from pineal gland. Melatonin is produced by the absence of light and its presence displays darkness. Melatonin plays various roles in creatures. Therefore, this review is to introduce the diverse potential ability of melatonin in manifold aspects in living organism.

Melatonin modulates baroreflex control via area postrema

Pineal gland and its hormone melatonin have been implicated in modulation of cardiovascular system. We aimed at studying the effects of melatonin on baroreflex sensitivity and the role of area postrema, as a component modulator of baroreflex arch. Mean arterial pressure (MAP) and heart rate (HR) were recorded in conscious freely moving rats. Baroreceptor reflex sensitivity was assessed by determining the HR responses to ramped infusions of phenylephrine (PE) and sodium nitroprusside (SNP)-induced MAP changes. Melatonin bolus (0.11 mg/kg) immediately followed by its continuous infusion (0.43 × 10(-9) mol/L at a rate of 0.65 mL/h for 30 min) in healthy normotensive rats produced a downward shift of baroreceptor reflex control with a substantial inhibition of reflex tachycardia (-32%) and potentiation of reflex bradycardia (+20%). Ablation of area postrema (APX group) induced a sustained decrease of MAP (101 ± 3 vs. 116 ± 3 mmHg, P < 0.05 in comparison with sham rats, respectively). The melatonin-induced alterations of baroreflex function observed in the sham group were abolished in the APX group. We conclude that circulating melatonin can modulate baroreceptor reflex control of HR, thus resetting it toward lower HR values. The modulatory effects of melatonin may be mediated via melatonin receptors in the area postrema, located outside the blood-brain barrier.

Efficacy and safety of prolonged-release melatonin for insomnia in middle-aged and elderly patients with hypertension: a combined analysis of controlled clinical trials

BACKGROUND

Add-on prolonged-release melatonin (PRM) in antihypertensive therapy has been shown to ameliorate nocturnal hypertension. Hypertension is a major comorbidity among insomnia patients. The efficacy and safety of PRM for primary insomnia in patients aged 55 years and older who are treated with antihypertensive drugs were evaluated.

METHODS

Post hoc analysis of pooled antihypertensive drug-treated subpopulations from four randomized, double-blind trials of PRM and placebo for 3 weeks (N[PRM] = 195; N[placebo] = 197) or 28 weeks (N[PRM] = 157; N[placebo] = 40). Efficacy measurements included Leeds Sleep Evaluation Questionnaire scores of quality of sleep and alertness and behavioral integrity the following morning after 3 weeks, and sleep latency (daily sleep diary) and Clinical Global Impression of Improvement (CGI-I) after 6 months of treatment. Safety measures included antihypertensive drug-treated subpopulations from these four and three additional single-blind and open-label PRM studies of up to 1 year (N[PRM] = 650; N[placebo] = 632).

RESULTS

Quality of sleep and behavior following wakening improved significantly with PRM compared with placebo (P < 0.0001 and P < 0.0008, respectively). Sleep latency (P = 0.02) and CGI-I (P = 0.0003) also improved significantly. No differences were observed between PRM and placebo groups in vital signs, including daytime blood pressure at baseline and treatment phases. The rate of adverse events normalized per 100 patient-weeks was lower for PRM (3.66) than for placebo (8.53).

CONCLUSIONS

The findings demonstrate substantive and sustained efficacy of PRM in primary insomnia patients treated with antihypertensive drugs. PRM appears to be safe for insomnia in patients with cardiovascular comorbidity.