Does melatonin play a disease-promoting role in rheumatoid arthritis?

Progress towards understanding the effects of artificial light on the transmission of vector-borne diseases

Artificial light at night (ALAN) is a common form of light pollution worldwide, and the intensity, timing, duration, and wavelength of light exposure can affect biological rhythms, which can lead to metabolic, reproductive, and immune dysfunctions and consequently, host-pathogen interactions. Insect vector-borne diseases are a global problem that needs to be addressed, and ALAN plays an important role in disease transmission by affecting the habits and physiological functions of vector organisms. In this work, we describe the mechanisms by which ALAN affects host physiology and biochemistry, host-parasite interactions, and vector-borne viruses and propose preventive measures for related infectious diseases to minimize the effects of artificial light on vector-borne diseases.

Melatonin as a natural anti-inflammatory and anti-oxidant therapy in the testis: a focus on infertility and aging†

Melatonin is a pineal hormone that regulates testicular activity (i.e., steroidogenesis and spermatogenesis) through two complementary mechanisms, indirect effects exerted via the hypothalamic-adenohypophyseal axis and direct actions that take place on the different cell populations of the male gonad. The effects of increased age on the testis and the general mechanisms involved in testicular pathology leading to infertility are still only poorly understood. However, there is growing evidence that link testicular aging and idiopathic male infertility to local inflammatory and oxidative stress events. Because literature data strongly indicate that melatonin exhibits anti-inflammatory and anti-oxidant properties, this review focuses on the potential benefits exerted by this indoleamine at testicular level in male reproductive fertility and aging. Taking into account that the effects of melatonin supplementation on testicular function are currently being investigated, the overview covers not only promising prospects but also many questions concerning the future therapeutic value of this indoleamine as an anti-aging drug as well as in the management of cases of male infertility for which there are no medical treatments currently available.

Melatonin and regulation of miRNAs: novel targeted therapy for cancerous and noncancerous disease

miRNAs, small noncoding RNAs with crucial diagnostic and prognostic capabilities, play essential therapeutic roles in different human diseases. These biomarkers are involved in several biological mechanisms and are responsible for the regulation of multiple genes expressions in cells. miRNA-based therapy has shown a very bright future in the case of clinical interventions. Melatonin, the main product of the pineal gland, is a multifunctional neurohormone with numerous therapeutic potentials in human diseases. Melatonin is able to regulate miRNAs in different pathologies such as malignant and nonmalignant diseases, which can be considered as a novel kind of targeted therapy. Herein, this review discusses possible therapeutic utility of melatonin for the regulation of miRNAs in various pathological conditions.

Myasthenia gravis exacerbation after melatonin administration: case series from a tertiary referral centre

Background

Myasthenia gravis is an autoimmune disease mediated by antibodies against proteins associated with the postsynaptic membrane of the neuromuscular junction. Several drugs may trigger an exacerbation of the disease. Melatonin supplements are widely used for the treatment of insomnia as they are well tolerated with few side effects. The role of melatonin in the immune system and its effects in autoimmune disorders remain uncertain.

Case presentation

We identified three patients in our referral centre from 2014 to 2019 who presented a worsening within days or weeks of starting melatonin. Two of them stopped the treatment without clinical improvement in the next week. Increasing dose of corticosteroids did not lead to clinical improvement in the next month and one of the patients was finally administered intravenous immunoglobulins.

Conclusion

Melatonin may trigger exacerbations of myasthenia gravis, probably due to an upregulation of the adaptive immune system and an interaction with the corticosteroids and other immunosuppressant treatments. We consider that melatonin should be administered with caution in these patients.

Conditional Controlled Light/Dark Cycle Influences Exercise-Induced Benefits in a Rat Model with Osteoarthritis: In Vitro and In Vivo Study

Physical exercise has long been recommended as a treatment for osteoarthritis (OA), though its effects vary based on the exercise protocol. Here, we examined whether environmental lighting conditions influence the anti-inflammatory benefits of exercise in a rat model of OA. Moderate-intensity treadmill exercise (Ex) was performed for six weeks under a 12:12 h light/dark (L/D) cycle, and compared against rats housed in a 24 h continuous light (L/L) environment. L/L conditions were associated with serological changes shortly after OA induction, which exacerbated the inflammatory microenvironment in the joint. Differentiation capacity was also impaired in bone precursor cells isolated from normal rats maintained under L/L conditions, despite elevated inflammatory responses. Exercise training under L/L conditions led to increased corticosterone levels in the blood, which exacerbated the progression of cartilaginous and synovial lesions. Osteoporotic phenomena were also observed in exercise-trained rats maintained under L/L conditions, along with inflammation-induced catabolism in the gastrocnemius muscle. Aberrant light/dark cycle conditions were also found to be associated with suppression of splenic Cry1 expression in exercise-trained rats, leading to dysregulation of immune responses. Taken together, these data suggest that lighting condition may be an important environmental factor influencing the exercise-induced benefits on OA.

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

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

Aging, Melatonin, and the Pro- and Anti-Inflammatory Networks

Aging and various age-related diseases are associated with reductions in melatonin secretion, proinflammatory changes in the immune system, a deteriorating circadian system, and reductions in sirtuin-1 (SIRT1) activity. In non-tumor cells, several effects of melatonin are abolished by inhibiting SIRT1, indicating mediation by SIRT1. Melatonin is, in addition to its circadian and antioxidant roles, an immune stimulatory agent. However, it can act as either a pro- or anti-inflammatory regulator in a context-dependent way. Melatonin can stimulate the release of proinflammatory cytokines and other mediators, but also, under different conditions, it can suppress inflammation-promoting processes such as NO release, activation of cyclooxygenase-2, inflammasome NLRP3, gasdermin D, toll-like receptor-4 and mTOR signaling, and cytokine release by SASP (senescence-associated secretory phenotype), and amyloid-β toxicity. It also activates processes in an anti-inflammatory network, in which SIRT1 activation, upregulation of Nrf2 and downregulation of NF-κB, and release of the anti-inflammatory cytokines IL-4 and IL-10 are involved. A perhaps crucial action may be the promotion of macrophage or microglia polarization in favor of the anti-inflammatory phenotype M2. In addition, many factors of the pro- and anti-inflammatory networks are subject to regulation by microRNAs that either target mRNAs of the respective factors or upregulate them by targeting mRNAs of their inhibitor proteins.

Melatonin in macrophage biology: Current understanding and future perspectives

Melatonin is a ubiquitous hormone found in various organisms and highly affects the function of immune cells. In this review, we summarize the current understanding of the significance of melatonin in macrophage biology and the beneficial effects of melatonin in macrophage-associated diseases. Enzymes associated with synthesis of melatonin, as well as membrane receptors for melatonin, are found in macrophages. Indeed, melatonin influences the phenotype polarization of macrophages. Mechanistically, the roles of melatonin in macrophages are related to several cellular signaling pathways, such as NF-κB, STATs, and NLRP3/caspase-1. Notably, miRNAs (eg, miR-155/-34a/-23a), cellular metabolic pathways (eg, α-KG, HIF-1α, and ROS), and mitochondrial dynamics and mitophagy are also involved. Thus, melatonin modulates the development and progression of various macrophage-associated diseases, such as cancer and rheumatoid arthritis. This review provides a better understanding about the importance of melatonin in macrophage biology and macrophage-associated diseases.

Melatonin and inflammation-Story of a double-edged blade

Melatonin is an immune modulator that displays both pro- and anti-inflammatory properties. Proinflammatory actions, which are well documented by many studies in isolated cells or leukocyte-derived cell lines, can be assumed to enhance the resistance against pathogens. However, they can be detrimental in autoimmune diseases. Anti-inflammatory actions are of particular medicinal interest, because they are observed in high-grade inflammation such as sepsis, ischemia/reperfusion, and brain injury, and also in low-grade inflammation during aging and in neurodegenerative diseases. The mechanisms contributing to anti-inflammatory effects are manifold and comprise various pathways of secondary signaling. These include numerous antioxidant effects, downregulation of inducible and inhibition of neuronal NO synthases, downregulation of cyclooxygenase-2, inhibition of high-mobility group box-1 signaling and toll-like receptor-4 activation, prevention of inflammasome NLRP3 activation, inhibition of NF-κB activation and upregulation of nuclear factor erythroid 2-related factor 2 (Nrf2). These effects are also reflected by downregulation of proinflammatory and upregulation of anti-inflammatory cytokines. Proinflammatory actions of amyloid-β peptides are reduced by enhancing α-secretase and inhibition of β- and γ-secretases. A particular role in melatonin's actions seems to be associated with the upregulation of sirtuin-1 (SIRT1), which shares various effects known from melatonin and additionally interferes with the signaling by the mechanistic target of rapamycin (mTOR) and Notch, and reduces the expression of the proinflammatory lncRNA-CCL2. The conclusion on a partial mediation by SIRT1 is supported by repeatedly observed inhibitions of melatonin effects by sirtuin inhibitors or knockdown.

Depressive disorders: Processes leading to neurogeneration and potential novel treatments

Mood disorders are wide spread with estimates that one in seven of the population are affected at some time in their life (Kessler et al., 2012). Many of those affected with severe depressive disorders have cognitive deficits which may progress to frank neurodegeneration. There are several peripheral markers shown by patients who have cognitive deficits that could represent causative factors and could potentially serve as guides to the prevention or even treatment of neurodegeneration. Circadian rhythm misalignment, immune dysfunction and oxidative stress are key pathologic processes implicated in neurodegeneration and cognitive dysfunction in depressive disorders. Novel treatments targeting these pathways may therefore potentially improve patient outcomes whereby the primary mechanism of action is outside of the monoaminergic system. Moreover, targeting immune dysfunction, oxidative stress and circadian rhythm misalignment (rather than primarily the monoaminergic system) may hold promise for truly disease modifying treatments that may prevent neurodegeneration rather than simply alleviating symptoms with no curative intent. Further research is required to more comprehensively understand the contributions of these pathways to the pathophysiology of depressive disorders to allow for disease modifying treatments to be discovered.

Melatonin, the Hormone of Darkness: From Sleep Promotion to Ebola Treatment

Melatonin is a hormone secreted by the enigmatic pineal gland in response to darkness, hence the name hormone of darkness. It has generated a great deal of interest as a therapeutic modality for various diseases particularly sleep disorders. This pleiotropic molecule has anti-inflammatory, antioxidant and anticoagulopathic properties in addition to its endothelial protective effects. In this article we discuss melatonin secretion and mechanisms of action as well as therapeutic rationale. We also highlight the potential utility of melatonin in the deadly modern-day Ebola epidemic.

Melatonin: shedding light on infertility?--A review of the recent literature

In recent years, the negative impact of oxidative stress on fertility has become widely recognised. Several studies have demonstrated its negative effect on the number and quality of retrieved oocytes and embryos following in-vitro fertilisation (IVF). Melatonin, a pineal hormone that regulates circadian rhythms, has also been shown to exhibit unique oxygen scavenging abilities. Some studies have suggested a role for melatonin in gamete biology. Clinical studies also suggest that melatonin supplementation in IVF may lead to better pregnancy rates. Here we present a critical review and summary of the current literature and provide suggestions for future well designed clinical trials.

Morning melatonin serum values do not correlate with disease activity in rheumatoid arthritis: a cross-sectional study

Rheumatoid arthritis (RA), the most prevalent autoimmune arthritis worldwide, usually presents with a circannual manner and, meanwhile, follows a circadian rhythm for symptoms like morning stiffness. Therefore, association between RA and some hormones such as melatonin (MLT) and vitamin D, whose serum values are related to body circadian rhythms or seasonal variations, has become more noticeable recently. Since some studies proposed that RA patients show altered MLT circadian rhythms, especially in concordance with symptoms, in this research, we present the correlation between MLT serum values and RA disease activity score (DAS28ESR). The current cross-sectional study was carried out on 80 volunteers (60 patients and 20 healthy controls). Fifty percent of the participants in each group were sampled in cold, and the same percentage were sampled in warm seasons at 8 a.m. Disease activity was estimated utilizing DAS28ESR. Patients with possible known confounders of MLT secretion were excluded. A commercial MLT ELISA kit was employed to measure MLT. Statistical analysis was conducted by SPSS-11 software. This study outlined higher serum values of MLT in RA patients compared with controls (P = 0.006, z = -2.73). However, MLT did not correlate with DAS in patients (P = 0.45, r = -0.09). GLM analysis demonstrated that DAS28ESR, age, disease duration, medications, gender, and season of sampling had no influence on serum MLT. However, newly diagnosed RA patients presented higher MLT values than established ones (P = 0.03, t = -2.2). A cutoff point value of 23 pg/mL (63.3 % sensitivity and 90 % specificity) for MLT was computed between patients and controls. This study denoted that morning MLT serum values are higher in RA patients than in healthy volunteers. However, MLT and RA disease activity or other disease characteristics do not correlate. MLT serum values were higher in newly diagnosed RA patients than established ones.

Could agomelatine be the ideal antidepressant?

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

Melatonin and the theories of aging: a critical appraisal of melatonin's role in antiaging mechanisms

The classic theories of aging such as the free radical theory, including its mitochondria-related versions, have largely focused on a few specific processes of senescence. Meanwhile, numerous interconnections have become apparent between age-dependent changes previously thought to proceed more or less independently. Increased damage by free radicals is not only linked to impairments of mitochondrial function, but also to inflammaging as it occurs during immune remodeling and by release of proinflammatory cytokines from mitotically arrested, DNA-damaged cells that exhibit the senescence-associated secretory phenotype (SASP). Among other effects, SASP can cause mutations in stem cells that reduce the capacity for tissue regeneration or, in worst case, lead to cancer stem cells. Oxidative stress has also been shown to promote telomere attrition. Moreover, damage by free radicals is connected to impaired circadian rhythmicity. Another nexus exists between cellular oscillators and metabolic sensing, in particular to the aging-suppressor SIRT1, which acts as an accessory clock protein. Melatonin, being a highly pleiotropic regulator molecule, interacts directly or indirectly with all the processes mentioned. These influences are critically reviewed, with emphasis on data from aged organisms and senescence-accelerated animals. The sometimes-controversial findings obtained either in a nongerontological context or in comparisons of tumor with nontumor cells are discussed in light of evidence obtained in senescent organisms. Although, in mammals, lifetime extension by melatonin has been rarely documented in a fully conclusive way, a support of healthy aging has been observed in rodents and is highly likely in humans.

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.

Acute allograft rejection and immunosuppression: influence on endogenous melatonin secretion

Melatonin displays a dose-dependent immunoregulatory effect in vitro and in vivo. Exogenous high-dose melatonin therapy exerted an immunosuppressive effect, abrogating acute rejection (AR), significantly prolonging transplant survival. Endogenous melatonin secretion, in response to heterotopic rat cardiac allograft transplantation (Tx), was investigated during the AR response and under standardized immunosuppressive maintenance therapy with cyclosporin A (CsA) and rapamycin (RPM). Recipients of syngeneic transplants, and recipients of allogeneic grafts, either untreated or receiving immunosuppressive therapy constituted the experimental groups. Endogenous circadian melatonin levels were measured at 07:00, 19:00, and 24:00 hr, using a novel radioimmunoassay (RIA) procedure, under standardized 12-hr-light/dark-conditions (light off: 19:00 hr; light on: 07:00 hr), before and after Tx. Neither the operative trauma, nor the challenge with a perfused allograft or the AR response influenced endogenous melatonin peak secretion. Immunosuppressive therapy with CsA led to a significant increase in peak secretion, measured for days 7 (212 +/- 40.7 pg/mL; P < 0.05), 14 (255 +/- 13.9 pg/mL; P < 0.001), and 21 (219 +/- 34 pg/mL; P < 0.01) after Tx, as compared with naïve animals (155 +/- 25.8 pg/mL). In contrast, treatment with RPM significantly decreased the melatonin peak post-Tx up to day 7 (87 +/- 25.2 pg/mL; P < 0.001), compared with naïve animals (155 +/- 25.8 pg/mL). These findings imply a robust nature of the endogenous circadian melatonin secretion kinetics, even against the background of profound allogeneic stimuli. Immunosuppressive maintenance therapy with CsA and RPM modulated early melatonin secretion, indicating a specific secondary action of these drugs. Further studies are necessary to disclose the long-term effect of immunosuppressive therapy on circadian melatonin secretion in transplant recipients.

Role of the melatonin system in the control of sleep: therapeutic implications

The circadian rhythm of pineal melatonin secretion, which is controlled by the suprachiasmatic nucleus (SCN), is reflective of mechanisms that are involved in the control of the sleep/wake cycle. Melatonin can influence sleep-promoting and sleep/wake rhythm-regulating actions through the specific activation of MT(1) (melatonin 1a) and MT(2) (melatonin 1b) receptors, the two major melatonin receptor subtypes found in mammals. Both receptors are highly concentrated in the SCN. In diurnal animals, exogenous melatonin induces sleep over a wide range of doses. In healthy humans, melatonin also induces sleep, although its maximum hypnotic effectiveness, as shown by studies of the timing of dose administration, is influenced by the circadian phase. In both young and elderly individuals with primary insomnia, nocturnal plasma melatonin levels tend to be lower than those in healthy controls. There are data indicating that, in affected individuals, melatonin therapy may be beneficial for ameliorating insomnia symptoms. Melatonin has been successfully used to treat insomnia in children with attention-deficit hyperactivity disorder or autism, as well as in other neurodevelopmental disorders in which sleep disturbance is commonly reported. In circadian rhythm sleep disorders, such as delayed sleep-phase syndrome, melatonin can significantly advance the phase of the sleep/wake rhythm. Similarly, among shift workers or individuals experiencing jet lag, melatonin is beneficial for promoting adjustment to work schedules and improving sleep quality. The hypnotic and rhythm-regulating properties of melatonin and its agonists (ramelteon, agomelatine) make them an important addition to the armamentarium of drugs for treating primary and secondary insomnia and circadian rhythm sleep disorders.

Melatonin as pharmacologic support in burn patients: a proposed solution to thermal injury-related lymphocytopenia and oxidative damage

OBJECTIVE

To review the data that support the clinical use of melatonin in the treatment of burn patients, with special emphasis on the stimulation of the oxidative defense system, the immune system, circadian rhythm of sleep/wakefulness, and the reduction in the toxicity of therapeutic agents used in the treatment of burn victims.

DATA SOURCE

A MEDLINE/PubMed search from 1975 to July 2006 was conducted.

STUDY SELECTION

The screening of the literature was examined using the key words: burn patients, lymphocytopenia, skin oxidative stress, antioxidant, melatonin, and free radicals.

DATA EXTRACTION AND SYNTHESIS

Thermal injury often causes damage to multiple organs remote from the original burn wound and may lead to multiple organ failure. Animal models and burn patients exhibit elevated free radical generation that may be causative in the local wound response and in the development of burn shock and distant organ injury. The suppression of nonspecific resistance and the disturbance in the adaptive immune system makes burn patients vulnerable to infections. Moreover, there is loss of sleep and the toxicity produced by drugs habitually used in the clinic for burn patients. Melatonin is a powerful antioxidant and is a potent protective agent against damage after experimental thermal injury. Some actions of melatonin as a potential supportive pharmacologic agent in burn patients include its: role as a scavenger of both oxygen and nitrogen-based reactants, stimulation of the activities of a variety of antioxidative enzymes, reduction in proinflammatory cytokines, inhibition of adhesion molecules, chronobiotic effects, and reduction in the toxicity of the drugs used in protocols to treat thermal injury patients.

CONCLUSIONS

These combined actions of melatonin, along with its low toxicity and its ability to penetrate all morphophysiologic membranes, could make it a ubiquitously acting and highly beneficial molecule in burn patients.

Serum melatonin in juvenile rheumatoid arthritis: correlation with disease activity

The study was conducted to investigate the abnormalities in early morning serum melatonin among patients with Juvenile Rheumatoid Arthritis (JRA) and to outline its relation to disease activity and severity. Twenty one patients with JRA and twenty healthy age and sex matched controls were enrolled in the study. Fifteen patients had polyarticular JRA, 3 had oligoarticular and 3 had systemic onset JRA. Evaluation was carried out clinically, functionally and radiologically by using disease activity score, Juvenile Arthritis Functional Assessment Report for Children (JAFAR-C score) and modified Larsen score, respectively. Laboratory investigations included Complete Blood Picture (CBC), The Erythrocyte Sedimentation Rate (ESR), C-Reactive Protein (CRP), classic IgM Rheumatoid Factor (RF), Anti-nuclear Antibodies (ANA) and melatonin estimation in serum. The serum levels of melatonin were significantly increased in JRA patients (mean +/- SD = 13.9 +/- 8 pg mL(-1)) as compared to healthy controls (mean +/- SD = 8.1 +/- 2.7 pg mL(-1), p < 0.01). A significant positive correlation could link serum melatonin levels to disease activity scores and ESR (r = 0.91, p < 0.001 and r = 0.55, p < 0.01, respectively). No significant correlation was found between melatonin and either Larsen or JAFAR scores (r = 0.19, r = 0.15, respectively). According to melatonin levels, there were 2 groups of patients: Group I with elevated melatonin level (more than 11 pg mL(-1)) (n = 15) and group II with normal melatonin level (less than 11 pg mL(-1)) (n = 6). Patients with elevated melatonin levels had higher ESR (p < 0.05), higher disease activity scores (p < 0.01) and Larsen scores (p < 0.05), than the group of patients with normal serum melatonin. The results of GAFAR scores were comparable between the two groups (p > 0.05). Hence the study conclude that the elevated melatonin levels among JRA patients with active synovitis and its close relation to disease activity rather than disease severity suggests that melatonin might play a promoting role in rheumatoid arthritis. Hence, inhibition of its synthesis and/or action by specific antagonists may be of therapeutic value.

Melatonin: therapeutic and clinical utilization

Melatonin, acting through melatonin receptors, is involved in numerous physiological processes including circadian entrainment, blood pressure regulation, oncogenesis, retinal physiology, seasonal reproduction, ovarian physiology, immune function and most recently in inducing osteoblast differentiation. Moreover, melatonin was proved to be a potent-free radical scavenger and a broad-spectrum antioxidant. More research is required into the effects of therapeutically modulating the melatoninergic system on circadian haemodynamics and rhythm under varying physiopathological conditions and the possible impact on morbidity and mortality in humans.

Melatonin

Melatonin is a ubiquitous molecule and widely distributed in nature, with functional activity occurring in unicellular organisms, plants, fungi and animals. In most vertebrates, including humans, melatonin is synthesized primarily in the pineal gland and is regulated by the environmental light/dark cycle via the suprachiasmatic nucleus. Pinealocytes function as 'neuroendocrine transducers' to secrete melatonin during the dark phase of the light/dark cycle and, consequently, melatonin is often called the 'hormone of darkness'. Melatonin is principally secreted at night and is centrally involved in sleep regulation, as well as in a number of other cyclical bodily activities. Melatonin is exclusively involved in signaling the 'time of day' and 'time of year' (hence considered to help both clock and calendar functions) to all tissues and is thus considered to be the body's chronological pacemaker or 'Zeitgeber'. Synthesis of melatonin also occurs in other areas of the body, including the retina, the gastrointestinal tract, skin, bone marrow and in lymphocytes, from which it may influence other physiological functions through paracrine signaling. Melatonin has also been extracted from the seeds and leaves of a number of plants and its concentration in some of this material is several orders of magnitude higher than its night-time plasma value in humans. Melatonin participates in diverse physiological functions. In addition to its timekeeping functions, melatonin is an effective antioxidant which scavenges free radicals and up-regulates several antioxidant enzymes. It also has a strong antiapoptotic signaling function, an effect which it exerts even during ischemia. Melatonin's cytoprotective properties have practical implications in the treatment of neurodegenerative diseases. Melatonin also has immune-enhancing and oncostatic properties. Its 'chronobiotic' properties have been shown to have value in treating various circadian rhythm sleep disorders, such as jet lag or shift-work sleep disorder. Melatonin acting as an 'internal sleep facilitator' promotes sleep, and melatonin's sleep-facilitating properties have been found to be useful for treating insomnia symptoms in elderly and depressive patients. A recently introduced melatonin analog, agomelatine, is also efficient for the treatment of major depressive disorder and bipolar affective disorder. Melatonin's role as a 'photoperiodic molecule' in seasonal reproduction has been established in photoperiodic species, although its regulatory influence in humans remains under investigation. Taken together, this evidence implicates melatonin in a broad range of effects with a significant regulatory influence over many of the body's physiological functions.

The role of melatonin in immuno-enhancement: potential application in cancer

Melatonin, a neurohormone produced mainly by the pineal gland, is a modulator of haemopoiesis and of immune cell production and function, both in vivo and in vitro. Physiologically, melatonin is associated with T-helper 1 (Th1) cytokines, and its administration favours Th1 priming. In both normal and leukaemic mice, melatonin administration results in quantitative and functional enhancement of natural killer (NK) cells, whose role is to mediate defenses against virus-infected and cancer cells. Melatonin appears to regulate cell dynamics, including the proliferative and maturational stages of virtually all haemopoietic and immune cells lineages involved in host defense - not only NK cells but also T and B lymphocytes, granulocytes and monocytes - in both bone marrow and tissues. In particular, melatonin is a powerful antiapoptotic signal promoting the survival of normal granulocytes and B lymphocytes. In mice bearing mid-stage leukaemia, daily administration of melatonin results in a survival index of 30-40% vs. 0% in untreated mice. Thus, melatonin seems to have a fundamental role as a system regulator in haemopoiesis and immuno-enhancement, appears to be closely involved in several fundamental aspects of host defense and has the potential to be useful as an adjuvant tumour immunotherapeutic agent.

Sex-dependent effect of melatonin on systemic erythematosus lupus developed in Mrl/Mpj-Faslpr mice: it ameliorates the disease course in females, whereas it exacerbates it in males

In this study, the effect of chronic administration of melatonin on MRL/MpJ-Fas(lpr) mice has been studied. These mice spontaneously develop an autoimmune disease that has many features resembling human systemic lupus erythematosus. In fact, histological studies showed that all female mice and most male mice exhibited glomerular abnormalities, arteritic lesions, and cellular interstitial inflammatory infiltrate ranging from mild to severe patterns. Treatment with melatonin improved the histological pattern in females and worsened it in males. Moreover, female mice treated with melatonin showed a diminution of titers of total serum IgG, IgM, and anti-double-stranded DNA and anti-CII autoantibodies; a decrease in proinflammatory cytokines (IL-2, IL-6, interferon-gamma, TNF-alpha, and IL-1beta), an increase in antiinflammatory cytokines (IL-10), and a decrease in nitrite/nitrate. In male mice, treatment with melatonin exhibited the opposite effect, worsening all the immunological parameters with an elevation of titers of autoantibodies and a prevalence of proinflammatory vs. antiinflammatory cytokines. Similar results were obtained when lymphocytes from spleen and lymph nodes were cultured. Again, melatonin treatment in females decreased proinflammatory cytokines and increased antiinflammatory cytokines produced by lymphocytes; in males, the effect was the opposite. These findings suggest that melatonin action in MRL/MpJ-Fas(lpr) mice is gender dependent, probably through modulation and inhibition of sex hormones.

Acutely administered melatonin is beneficial while chronic melatonin treatment aggravates the evolution of TNBS-induced colitis

The aim of this study was to evaluate the effects of melatonin on the inflammatory response and hydroxyproline production in an experimental acute and chronic model of trinitrobenzene sulfonic (TNBS) acid-induced colitis in Wistar rats. In the acute model, melatonin (0.5, 1, and 2 mg/kg, i.p.) was applied 48, 24, and 1 hr prior to the induction of colitis and 24 and 48 hr after; the severity of colitis was less evident in melatonin-treated animals with significant response in the group treated with 2 mg/kg. All doses investigated significantly reduced the myeloperoxidase activity (MPO). In the chronic studies, melatonin (1 and 2 mg/kg, i.p.) was administered daily 24 hr before hapten instillation and for 7 or 21 days after TNBS; melatonin (2 mg/kg) worsened colitis evolution in the 21-day study with a significant increase in MPO activity and tumor necrosis factor-alpha production with respect to TNBS group. Histological slides were in concordance with macroscopic data where areas of extensive necrosis and edema, fibrosis, and absence of regenerated epithelium were observed. Moreover, the hydroxyproline determination, used as indicator of collagen production and fibrosis, also showed a marker increase. The results obtained in this experimental model showed that short-term administration is protective while in the long term it negatively influences evolution of inflammatory colitis; therefore, the immunostimulatory effect of melatonin in some situations when given chronically, such as during inflammatory bowel disease, might lead to negative consequences.

Melatonin treatment counteracts the hyperthermic effect of lipopolysaccharide injection in the Syrian hamster

The present study examined the acute response in body temperature to lipopolysaccharide (LPS) injection to Syrian hamsters at two time intervals during the light-dark cycle. Its modification by melatonin (MT) administration in the drinking water was also assessed. Hamsters were intraperitoneally (i.p.) implanted with a transmitter to measure core body temperature. MT was administered from day 8 post-surgery until the end of experiment. On day 16 after surgery, LPS or saline was injected i.p. at the beginning of the light phase (ZT 0) or of the scotophase (ZT 14). At ZT 0, LPS increased core body temperature, an effect that persisted for at least 5h and that was blunted by MT administration. At ZT 14, the hyperthermic effect of LPS was absent. Rather, at ZT 14 the animals showed increases in core body temperature following saline or LPS during the first 2h after injection only, which were significantly less intense in LPS-treated animals. MT administration blunted this difference. Five days after injection, hamsters that had received LPS at ZT 0 showed an increase in the mesor of core body temperature rhythm as compared to saline. This effect was suppressed by MT administration. The results demonstrate that MT prevents body temperature increase after LPS at ZT 0.

Melatonin, immune function and aging

Aging is associated with a decline in immune function (immunosenescence), a situation known to correlate with increased incidence of cancer, infectious and degenerative diseases. Innate, cellular and humoral immunity all exhibit increased deterioration with age. A decrease in functional competence of individual natural killer (NK) cells is found with advancing age. Macrophages and granulocytes show functional decline in aging as evidenced by their diminished phagocytic activity and impairment of superoxide generation. There is also marked shift in cytokine profile as age advances, e.g., CD3+ and CD4+ cells decline in number whereas CD8+ cells increase in elderly individuals. A decline in organ specific antibodies occurs causing reduced humoral responsiveness. Circulating melatonin decreases with age and in recent years much interest has been focused on its immunomodulatory effect. Melatonin stimulates the production of progenitor cells for granulocytes-macrophages. It also stimulates the production of NK cells and CD4+ cells and inhibits CD8+ cells. The production and release of various cytokines from NK cells and T-helper lymphocytes also are enhanced by melatonin. Melatonin presumably regulates immune function by acting on the immune-opioid network, by affecting G protein-cAMP signal pathway and by regulating intracellular glutathione levels. Melatonin has the potential therapeutic value to enhance immune function in aged individuals and in patients in an immunocompromised state.

Altered circadian rhythms in rheumatoid arthritis patients play a role in the disease's symptoms

The circadian changes in the metabolism or nocturnal secretion of endogenous corticosteroids (reduction) observed in rheumatoid arthritis (RA) patients are responsible, in part, for the time-dependent changes that are observed in the inflammatory response and related early morning clinical symptoms of the disease. Melatonin (MLT), another circadian nocturnal hormone that is the secretory product of the pineal gland, has been implicated in the time-dependent RA inflammatory reaction with effects that are opposite to those of corticosteroids. As a consequence, altered functioning of the HPA axis (early morning reduced corticosteroid production) and of the pineal gland (night increased MLT production) found in RA patients, seem to be important factors in the appearance and perpetuation of the clinical circadian symptoms of the disease. Consistently, human proinflammatory Th1-type cytokine production (related to MLT stimulation) exhibits a diurnal rhythmicity with peak levels during the night and early morning, at a time when plasma cortisol (inducing the Th2-type cytokine production) is lowest and MLT is highest. Reduced daily light exposure as observed in northern Europe (Estonia), at least during the winter, might explain the higher and more prolonged serum MLT concentrations that were observed in northern RA patients, as well as some epidemiological features versus southern Europe patients.

Positive relationship between melatonin receptor type 1B polymorphism and rheumatoid factor in rheumatoid arthritis patients in the Korean population

Melatonin is reported to be an anti-inflammatory agent. No genetic study concerning the association between melatonin and inflammatory disease has yet been reported. Here we performed a polymorphism study on the melatonin receptor type 1B (MTNR1B) in Korean rheumatoid arthritis (RA) patients and controls. The polymorphism of MTNR1B located in 3'-untranslated region (rs 1562444) was selected for its higher rate of heterozygosity among other single nucleotide polymorphisms (SNPs) in both MTNR1A and MTNR1B genes and investigated in RA patients (n = 173) and healthy controls (n = 195) by polymerase chain reaction-restriction fragment length polymorphism assay using NlaIII restriction enzyme. No statistically significant difference in either genotype distribution or allele frequency was observed between RA patients and controls. The genotype distributions and allele frequencies of rheumatoid factor negative [RF(-)] patients were similar to those of controls. However, statistical analysis of genotype revealed a significant association (chi2 = 6.42, P = 0.04) is present between RF(+) and MTNR1B SNP (rs 1562444). Although no statistically significant difference in allele frequency between RF(+) and controls was observed (chi2 = 2.75, P = 0.10), the results might suggest that MTNR1B SNP (rs 1562444) is associated with the presence of RF in RA. This is the first study, to our knowledge, to report a positive genetic relationship between melatonin and RA.

A review of the multiple actions of melatonin on the immune system

This review summarizes the numerous observations published in recent years which have shown that one of the most significant of melatonin's pleiotropic effects is the regulation of the immune system. The overview summarizes the immune effects of pinealectomy and the association between rhythmic melatonin production and adjustments in the immune system as markers of melatonin's immunomodulatory actions. The effects of both in vivo and in vitromelatonin administration on non-specific, humoral, and cellular immune responses as well as on cellular proliferation and immune mediator production are presented. One of the main features that distinguishes melatonin from the classical hormones is its synthesis by a number of non-endocrine extrapineal organs, including the immune system. Herein, we summarize the presence of immune system-synthesized melatonin, its direct immunomodulatory effects on cytokine production, and its masking effects on exogenous melatonin action. The mechanisms of action of melatonin in the immune system are also discussed, focusing attention on the presence of membrane and nuclear receptors and the characterization of several physiological roles mediated by some receptor analogs in immune cells. The review focuses on melatonin's actions in several immune pathologies including infection, inflammation, and autoimmunity together with the relation between melatonin, immunity, and cancer.

Nocturnal Hormones and Clinical Rhythms in Rheumatoid Arthritis

It is well known that some clinical signs and symptoms of rheumatoid arthritis (RA) vary within a day and between days; the morning stiffness that is observed in patients who have RA has become one of the diagnostic criteria of the disease. The circadian changes in the metabolism or nocturnal secretion of endogenous corticosteroids is certainly responsible, in part, for the time-dependent changes that are observed in the inflammatory response and related clinical symptoms. More recently, melatonin (mLT), another circadian nocturnal hormone that is the secretory product of the pineal gland, has been implicated in time-dependent inflammatory reactions, with effects that are opposite of those of corticosteroids. Therefore, altered functioning of the hypothalamic-pituitary-adrenocortical axis (reduced corticosteroid production) and of the pineal gland (increased mLT production) found in RA patients seem to be important factors in the perpetuation and clinical circadian symptoms of the disease. Consistently, human proinflammatory Th1-type cytokine production (related to mLT stimulation) exhibits a diurnal rhythmicity, with peak levels during the night and early morning, at a time when plasma cortisol (inducing Th2-type cytokine production) is lowest and mLT is highest. Reduced daily light exposure as observed in northern Europe (Estonia), at least during the winter, might explain the higher and more prolonged mLT concentrations as well as some epidemiological features that are observed in northern European patients with RA versus southern European patients.