The effects of melatonin on humoral immune responses of young and aged rats

Immunoregulatory properties of melatonin in the humoral immune system: A narrative review

Melatonin is the major product both synthesized and secreted by the pineal gland during the night period and it is the principal chronobiotic hormone that regulates the circadian rhythms and seasonal changes in vertebrate biology. Moreover, melatonin shows both a broad distribution along the phylogenetically distant organisms and a high functional versatility. At the present time, a significant amount of experimental evidence has been reported in scientific literature and has clearly shown a functional relationship between the endocrine, nervous, and immune systems. The biochemistry basis of the functional communication between these systems is the utilization of a common chemicals signals. In this framework, at present melatonin is considered to be a relevant member of the so-called neuro-endocrine-immunological network. Thus, both in vivo and in vitro investigations conducted in both experimental animals and humans, have clearly documented that melatonin has an important immunomodulatory role. However, most of the published results refer to information on T lymphocytes, i.e., cell-mediated immunity. On the contrary, fewer studies have been carried out on B lymphocytes, the cells responsible for the so-called humoral immunity. In this review, we have focused on the biological role of melatonin in the humoral immunity. More precisely, we report the actions of melatonin on B lymphocytes biology and on the production of different types of antibodies.

Associations between Melatonin, Neuroinflammation, and Brain Alterations in Depression

Pro-inflammatory systemic conditions that can cause neuroinflammation and subsequent alterations in brain regions involved in emotional regulation have been suggested as an underlying mechanism for the pathophysiology of major depressive disorder (MDD). A prominent feature of MDD is disruption of circadian rhythms, of which melatonin is considered a key moderator, and alterations in the melatonin system have been implicated in MDD. Melatonin is involved in immune system regulation and has been shown to possess anti-inflammatory properties in inflammatory conditions, through both immunological and non-immunological actions. Melatonin has been suggested as a highly cytoprotective and neuroprotective substance and shown to stimulate all stages of neuroplasticity in animal models. The ability of melatonin to suppress inflammatory responses through immunological and non-immunological actions, thus influencing neuroinflammation and neurotoxicity, along with subsequent alterations in brain regions that are implicated in depression, can be demonstrated by the antidepressant-like effects of melatonin. Further studies that investigate the associations between melatonin, immune markers, and alterations in the brain structure and function in patients with depression could identify potential MDD biomarkers.

COVID-19: Sleep, Circadian Rhythms and Immunity - Repurposing Drugs and Chronotherapeutics for SARS-CoV-2

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic has affected nearly 28 million people in the United States and has caused more than five hundred thousand deaths as of February 21, 2021. As the novel coronavirus continues to take its toll in the United States and all across the globe, particularly among the elderly (>65 years), clinicians and translational researchers are taking a closer look at the nexus of sleep, circadian rhythms and immunity that may contribute toward a more severe coronavirus disease-19 (COVID-19). SARS-CoV-2-induced multi-organ failure affects both central and peripheral organs, causing increased mortality in the elderly. However, whether differences in sleep, circadian rhythms, and immunity between older and younger individuals contribute to the age-related differences in systemic dysregulation of target organs observed in SARS-CoV-2 infection remain largely unknown. Current literature demonstrates the emerging role of sleep, circadian rhythms, and immunity in the development of chronic pulmonary diseases and respiratory infections in human and mouse models. The exact mechanism underlying acute respiratory distress syndrome (ARDS) and other cardiopulmonary complications in elderly patients in combination with associated comorbidities remain unclear. Nevertheless, understanding the critical role of sleep, circadian clock dysfunction in target organs, and immune status of patients with SARS-CoV-2 may provide novel insights into possible therapies. Chronotherapy is an emerging concept that is gaining attention in sleep medicine. Accumulating evidence suggests that nearly half of all physiological functions follow a strict daily rhythm. However, healthcare professionals rarely take implementing timed-administration of drugs into consideration. In this review, we summarize recent findings directly relating to the contributing roles of sleep, circadian rhythms and immune response in modulating infectious disease processes, and integrate chronotherapy in the discussion of the potential drugs that can be repurposed to improve the treatment and management of COVID-19.

Melatonin, aging, and COVID-19: Could melatonin be beneficial for COVID-19 treatment in the elderly?

The aim of this review is to summarize current studies on the relationship between melatonin and aging. Nowadays, age-related diseases come into prominence, and identifying age-related changes and developing proper therapeutic approaches are counted as some of the major issues regarding community health. Melatonin is the main hormone of the pineal gland. Melatonin is known to influence many biological processes in the body, including circadian rhythms, the immune system, and neuroendocrine and cardiovascular functions.Melatoninrhythms also reflect the biological process of aging. Aging is an extremely complex and multifactorial process. Melatonin levels decline considerably with aging and its decline is associated with several age-related diseases. Aging is closely associated with oxidative damage and mitochondrial dysfunction. Free radical reactions initiated by the mitochondria constitute the inherent aging process. Melatonin plays a pivotal role in preventing age-related oxidative stress. Coronavirus disease 2019 (COVID-19) fatality rates increase with chronic diseases and age, where melatonin levels decrease. For this reason, melatonin supplementation in elderly could be beneficial in COVID-19 treatment. Therefore, studies on the usage of melatonin in COVID-19 treatment are needed.

T. cruzi infection among aged rats: Melatonin as a promising therapeutic molecule

Although T. cruzi was identified as the cause of Chagas disease more than 100 years ago, satisfactory treatments still do not exist, especially for chronic disease. Here we review work suggesting that melatonin could have promise as a Chagas therapeutic. Melatonin has remarkably diverse actions. It is an immunomodulator, an anti-inflammatory, an antioxidant, a free radical scavenger, and has antiapoptotic and anti-aging effects. The elderly (aged 60 years or more) as a group are growing faster than any other age group. Here we discuss the major effects and the mechanisms of action of melatonin on aged T. cruzi-infected rats. Melatonin's protective effects may be consequences of its cooperative antioxidant and immunomodulatory actions. Melatonin modulates oxidative damage, inducing an antioxidant response and reversing age-related thymus regression. Its protective actions could be the result of its anti-apoptotic activity, and by its counteracting the excessive production of corticosterone. This review describes our work showing that host age plays an important and variable influence on the progression of systemic T. cruzi infection and supporting the hypothesis that melatonin should be considered as a powerful therapeutic compound with multiple activities that can improve host homeostasis during experimental T. cruzi infection.

Effects of Photoperiod Change on Melatonin Secretion, Immune Function and Antioxidant Status of Cashmere Goats

The photoperiod affects animals' secretion of hormones, especially melatonin (MLT), which is involved in the regulation of the immune function and antioxidant status. The present experiment was conducted to study the effects of the photoperiod on MLT secretion, immune function, antioxidant status and related gene expression in goats. Eighteen adult female cashmere goats were randomly divided into three photoperiod groups: the control group (CG: natural photoperiod); the short-day photoperiod group (SDPP group: 8 h light; 16 h dark) and the shortening-day photoperiod group (SIPP group: lighting time shortened gradually from 16 h/d to 8 h/d). The experiment lasted for 60 days. The results showed that SDPP increased MLT concentration in serum at day 30 of the experiment (p < 0.05), but SIPP increased it at day 60 (p < 0.05). The activity of total superoxide dismutase (T-SOD), glutathione peroxidase (GPx) and catalase (CAT) increased (p < 0.05), and malondialdehyde (MDA) concentration decreased (p < 0.05) at day 30 in SDPP; no significant effects of SIPP were observed at day 30. Both SDPP and SIPP goats had higher activities of T-SOD, GPx and CAT (p < 0.05) at day 60. The concentration of immunoglobulin G (IgG), interleukin 1β (IL-1β) and interleukin 2 (IL-2) increased in SDPP (p < 0.05) at day 30. Both SDPP and SIPP raised the concentration of IgG, IL-1β and IL-2 at day 60 (p < 0.05). For the relative gene expression, the SDPP improved the gene expression of SOD1, CAT, GPx4, nuclear factor erythroid-2-related factor 2(Nrf2), IL-1β, IL-2 and tumor necrosis factor-α (TNF-α) (p < 0.05) in blood leukocytes at day 30. In addition, at day 60, goats in the SDPP group had a higher gene expression of CAT, GPx4, IL-1β and IL-2 (p < 0.05). Goats in SIPP had significantly higher gene expression of SOD1, CAT, GPx4, Nrf2, TNFα, IL-1β and IL-2 (p < 0.05) than those in CG. These results indicated that SDPP and SIPP could secrete more MLT and then improve the immune function and antioxidant status of the goats.

Melatonin: Antioxidant and modulatory properties in age-related changes during Trypanosoma cruzi infection

The purpose of this study was to investigate the effects of melatonin on selected biomarkers of innate and humoral immune response as well as the antioxidant/oxidant status (superoxide dismutase-SOD and reduced glutathione levels (GSH) to understand whether age-related changes would influence the development of acute Trypanosoma cruzi (T. cruzi) infection. Young- (5 weeks) and middle-aged (18 months) Wistar rats were orally treated with melatonin (gavage) (05 mg/kg/day), 9 days after infection. A significant increase in both SOD activity and GSH levels was found in plasma from all middle-aged melatonin-treated animals. Melatonin triggered enhanced expression of major histocompatibility class II (MHC-II) antigens on antigen-presenting cell (APC) and peritoneal macrophages in all treated animals. High levels of CD4⁺ CD28-negative T cells (*P<.05) were detected in middle-aged control animals. Melatonin induced a significant reduction (***P<.001) in CD28-negative in CD4⁺ and CD8⁺ T cells in middle-aged control animals. Contrarily, the same group displayed upregulated CD4⁺ CD28⁺ T and CD8⁺ CD28⁺ T cells. Melatonin also triggered an upregulation of CD80 and CD86 expression in all young-treated groups. Significant percentages of B and spleen dendritic cells in middle-aged infected and treated animals were observed. Our data reveal new features of melatonin action in inhibiting membrane lipid peroxidation, through the reduction in 8-isoprostane, upregulating the antioxidant defenses and triggering an effective balance in the antioxidant/oxidant status during acute infection. The ability of melatonin to counteract the immune alterations induced by aging added further support to its use as a potential therapeutic target not only for T. cruzi infection but also for other immunocompromised states.

Exogenous melatonin reduces somatic cell count of milk in Holstein cows

High somatic cell counts in milk caused by mastitis significantly influence the quality of milk and result in substantial annual economic loss. This study evaluated the beneficial effects of melatonin (MT) on milk somatic cell count (SCC) in cows. To examine the effects of melatonin on SCC, one hundred twenty cows were divided into four groups based on milk SCC. In each group, half of the cows were treated with melatonin (S.C.). Melatonin treatment significantly reduced milk SCC. To explore the potential mechanism, 20 cows with relatively high SCC were selected to evaluate the biochemical and immunological profiles of their blood after melatonin treatment. Treatment with MT significantly reduced SCC in milk, lowered serum cortisol concentrations and increased the levels of albumin, alanine transaminase and lactate dehydrogenase. Following treatment with MT, the concentration of IgG and IgM rose transiently then decreased significantly, similar to changes observed for white blood cells and lymphocytes. In conclusion, MT treatment improved the quality of milk by reducing SCC. This may be due to melatonin improving immune activity in cows.

Immune stimulation by exogenous melatonin during experimental endotoxemia

Melatonin has been shown to enhance the immune response under immune-compromised conditions. However, its immune-modulatory effects under inflammatory conditions are unclear at present. Both pro- and anti-inflammation has been reported. To study time-dependent effects of melatonin on the general immune response during endotoxemia in more detail, we used two models in male rats: per-acute endotoxemia was induced by lipopolysaccharide (LPS) bolus injection (2.5 mg/kg), sub-acute endotoxemia by LPS infusion (2.5 mg/kg × h). Melatonin was applied directly before and 2 h after LPS administration (3 mg/kg, each). The LPS-induced formation of the pro-inflammatory cytokines tumor necrosis factor alpha, interferon-gamma, interleukin (IL)-1α/β, IL-5, and IL-6 and of the anti-inflammatory cytokine IL-10 was further amplified by melatonin, although it was only significant during per-acute endotoxemia. In both models, melatonin had no effect on the LPS-induced nitric oxide release. These findings show that exogenous melatonin is capable of enhancing the general immune response under inflammatory conditions.

The pineal regulation of the immune system: 40 years since the discovery

The first observation on the relationship between the pineal gland and the immune system was done by the author of this paper in the late sixties and early seventies of the last century. After neonatal pinealectomy the thymus has been destroyed and wasting disease developed. Since that time a flood of experiments justified the observation and pointed to the prominent role of pineal in the regulation of the immune system. Melatonin, the hormone of the pineal gland stimulates immune processes acting to the immune cells' cytokine production, the haemopoiesis, and immune cell-target cell interactions. Melatonin receptors have been demonstrated and their localization and function were justified. Melatonin production by and melatonin receptors on (and in) the immune cells was proved. Melatonin agonists have been synthesized and the use of melatonin as adjuvant in the therapy of diseases connected to the immune system (cancers included) has been started. The paper summarizes the most important studies and discusses the interrelations of the data. The discussion points to the possibility of packed transport of the pineal hormone by the immune cells and to the adventages of local regulation by this transport.

Melatonin: buffering the immune system

Melatonin modulates a wide range of physiological functions with pleiotropic effects on the immune system. Despite the large number of reports implicating melatonin as an immunomodulatory compound, it still remains unclear how melatonin regulates immunity. While some authors argue that melatonin is an immunostimulant, many studies have also described anti-inflammatory properties. The data reviewed in this paper support the idea of melatonin as an immune buffer, acting as a stimulant under basal or immunosuppressive conditions or as an anti-inflammatory compound in the presence of exacerbated immune responses, such as acute inflammation. The clinical relevance of the multiple functions of melatonin under different immune conditions, such as infection, autoimmunity, vaccination and immunosenescence, is also reviewed.

The role of melatonin on gastric mucosal cell proliferation and telomerase activity in ageing

Despite antiproliferative effects of melatonin on cultured tumor cells, its effects on normal cells are less clear. The action of melatonin on telomerase activity in ageing of gastric mucosal tissues also is not known. In this study, we investigated the age-related changes in telomerase activity and cellular proliferation rate of gastric mucosa and the effect of melatonin. A total of 37 young (4 months old), and aged (20 months old) Wistar rats, kept under equal periods of light and dark, were divided into control [(PBS), i.p. for 21 days] and melatonin-treated (10 mg/kg melatonin, i.p. for 21 days) groups. Telomerase activity, cell proliferation rate, malondialdehyde (MDA) and glutathione (GSH) levels of the stomach were determined. Melatonin significantly inhibited the gastric mucosal proliferation rate of both young and aged rats. Telomerase activity was significantly reduced in aged rats compared to young animals. Melatonin significantly increased the telomerase activity of both young and aged rats. The MDA levels of gastric mucosa in the aged rats were significantly higher than those of the younger rats. On the contrary, the GSH levels of gastric mucosa of the aged group were significantly lower than that of the young rats. While melatonin had no effect on GSH levels of either young or aged rats, it significantly decreased the MDA levels in aged animals. In conclusion, melatonin may delay the ageing of gastric mucosa by inhibiting the replicative cellular senescence via its stimulatory effect on telomerase activity and suppressive effect on cellular proliferation and lipid peroxidation.

Effect of melatonin and tryptophan on humoral immunity in young and old ringdoves (Streptopelia risoria)

Melatonin is involved in the regulation of both cellular and humoral immunity. In the present study we have evaluated the effect of the oral administration of melatonin and its precursor, the amino acid tryptophan, on humoral immune response in ringdoves (Streptopelia risoria) from different age groups. Male and female ringdoves of 4-5years of age (young) and 12-14years of age (old) were used in this study. The animals received a single capsule of 300mg/kg b.w. of tryptophan (old animals) for 3 consecutive days 1h after lights on or a single oral dose (0.25 or 2.5mg/kg body weight/0.1ml per animal/day, young and old animals, respectively) of melatonin, for 3 consecutive days 1h before lights off. Blood samples were taken before beginning the treatment (basal values) and at the end of the treatment. Immunoglobulins, bactericidal and haemolytic activity were measured. Our results show that in old animals the humoral immune response was reduced with respect to the young. Both melatonin and tryptophan treatment increased the immunoglobulin concentration, with the nocturnal values being significantly higher than diurnal values and with a major effect in old animals. The bactericidal activity of the S. risoria serum against Staphylococcus aureus, after the treatment with melatonin or tryptophan, was increased at night with a greater effect in old animals. No significant differences were observed in the haemolytic activity of the serum in young animals, but there was an increase in old animals, with higher values at night after treatment with melatonin. In general, the oral administration of melatonin or tryptophan produced a stimulation of humoral immune response with greater effects in old ringdoves.

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.

Effects of Hatha Yoga and Omkar Meditation on Cardiorespiratory Performance, Psychologic Profile, and Melatonin Secretion

OBJECTIVES

To evaluate effects of Hatha yoga and Omkar meditation on cardiorespiratory performance, psychologic profile, and melatonin secretion.

SUBJECTS AND METHODS

Thirty healthy men in the age group of 25-35 years volunteered for the study. They were randomly divided in two groups of 15 each. Group 1 subjects served as controls and performed body flexibility exercises for 40 minutes and slow running for 20 minutes during morning hours and played games for 60 minutes during evening hours daily for 3 months. Group 2 subjects practiced selected yogic asanas (postures) for 45 minutes and pranayama for 15 minutes during the morning, whereas during the evening hours these subjects performed preparatory yogic postures for 15 minutes, pranayama for 15 minutes, and meditation for 30 minutes daily, for 3 months. Orthostatic tolerance, heart rate, blood pressure, respiratory rate, dynamic lung function (such as forced vital capacity, forced expiratory volume in 1 second, forced expiratory volume percentage, peak expiratory flow rate, and maximum voluntary ventilation), and psychologic profile were measured before and after 3 months of yogic practices. Serial blood samples were drawn at various time intervals to study effects of these yogic practices and Omkar meditation on melatonin levels.

RESULTS

Yogic practices for 3 months resulted in an improvement in cardiorespiratory performance and psychologic profile. The plasma melatonin also showed an increase after three months of yogic practices. The systolic blood pressure, diastolic blood pressure, mean arterial pressure, and orthostatic tolerance did not show any significant correlation with plasma melatonin. However, the maximum night time melatonin levels in yoga group showed a significant correlation (r = 0.71, p < 0.05) with well-being score.

CONCLUSION

These observations suggest that yogic practices can be used as psychophysiologic stimuli to increase endogenous secretion of melatonin, which, in turn, might be responsible for improved sense of well-being.

Melatonin rejuvenates degenerated thymus and redresses peripheral immune functions in aged mice

The effect of melatonin on age-related thymic involution and peripheral immune dysfunctions was investigated. Exogenous melatonin was administered through the drinking water (15 microg/ml) of 22-month-old female C57BL mice for 60 consecutive days. Our results show that melatonin distinctly reversed the age-related thymic involution as revealed by the notable increase of thymus weight, total number of thymocytes and percentage of thymocytes at G2+S phases. More strikingly, spleen weight, total number of splenocytes and some peripheral immune capacity such as mitogen responsiveness and NK cell activity were also significantly recovered by 60 days of melatonin application in aged mice. Our findings demonstrate that even when the melatonin supplementation begins late in life, the age-related thymic involution and peripheral immune dysfunctions can be restored at least partially in old mice.

Exposure to short days, but not short-term melatonin, enhances humoral immunity of male Syrian hamsters (Mesocricetus auratus)

Many non-tropical rodent species rely on photoperiod as the primary cue to co-ordinate seasonally appropriate changes in physiology and behavior. Among these seasonal changes, several rodent species (e.g. deer mice, prairie voles, Siberian hamsters) adjust immune function in response to changes in ambient day lengths. The goals of the present study were to examine the effects of photoperiod on immune function of Syrian hamsters (Mesocricetus auratus), and to determine the role of melatonin in mediating photoperiodic changes in immunity. In Experiment 1, male Syrian hamsters were housed in long (LD 14:10) or short days (LD 10:14) for 10 wk. In Experiment 2, hamsters were housed in long days and half of the animals were given 10 consecutive days of i.p. melatonin injections (15 microg) in the early evening, while the remaining animals received injections of the vehicle alone. After the respective experimental manipulations, animals were injected with the antigen, keyhole limpet hemocyanin (KLH), blood samples were obtained and anti-KLH IgG antibody production was assessed. In Experiment 1, short-day hamsters underwent gonadal regression and reduced serum testosterone as well as displayed increased humoral immune function compared with long-day animals. In Experiment 2, short-term melatonin treatment did not affect gonadal mass, testosterone or humoral immune function. These results confirm previous findings of photoperiodic changes in immunity in rodents and suggest that changes in humoral immunity are not due to short-term changes in melatonin.