Endogenous Melatonin Synthesis Research Articles

A Crosstalk Between Pineal and Major Extra-Pineal Sources of Melatonin and its Role in Ovarian Growth and Maturation in Fish

Pinealocytes of the pineal gland in vertebrates mainly synthesize melatonin (5-methoxy-N-acetyl-tryptamine). Moreover, melatonin is synthesized in several extra-pineal cells, including the photoreceptor cells of the retina, the cells of the gut, and the hepatocytes of the liver in different vertebrates, including fish species. One of the remarkable features of pineal and retinal melatonin is that it is produced rhythmically in synchronization with the environmental Light-Dark (LD) cycle, with a daily nighttime peak. However, the melatonin synthesis in tissue/cells from the extra-pineal and extra-retinal origin(s) may not always undergo photoperiod-regulated daily variations but is also dependent on the environmental food entrainment factors (in the gut), acting as the most reliable synchronizer(s) in its daily rhythm features. Moreover, the regulation of the liver and ovary (important for fish reproduction) is unclear. In this review, we attempt a comparative account of the nature and regulation of endogenous melatonin synthesis between a source like the pineal gland and many other nonpineal origins, which have gained serious attention in the last ten years. We also review the functions of melatonin in regulating fish ovarian growth and maturation. The physiological melatonin levels, manipulated either endogenously (by photoperiodic modulations) or exogenously (by injections or by feeds), have tremendous effects on reproductive events in fish at the age of its first maturity, as revealed in recent findings. Characterization and identification of the importance of pineal gland melatonin in the growth of the oocytes via the hypothalamic-pituitary-gonadal axis have been explored several years back. The identification of melatonin receptors about fourteen years back on the wall of developing oocyte spurt the breakthrough, which introduced the concept of direct control of melatonin on developing oocytes. Thus, this review gains uniqueness by addressing the latest developments recorded in the field of melatonin and fish reproduction, particularly in improving oocyte maturation. Nonetheless, an attempt has been made to underline approaches that need to be developed to apply the molecule in large-scale aquaculture.

Fetal malnutrition is associated with impairment of endogenous melatonin synthesis in pineal via hypermethylation of promoters of protein kinase C alpha and cAMP response element-binding.

This study investigated whether and how fetal malnutrition would influence endogenous melatonin synthesis, and whether such effect of fetal malnutrition would transmit to the next generation. We enrolled 2466 participants and 1313 of their offspring. The urine 6-hydroxymelatonin sulfate and serum melatonin rhythm were measured. Methylationmicroarray detection and bioinformatics analysis were performed to identify hub methylated sites. Additionally, rat experiment was performed to elucidate mechanisms. The participants with fetal malnutrition had lower 6-hydroxymelatonin sulfate (16.59±10.12μg/24hours vs 24.29±11.99μg/24hours, P<.001) and arear under curve of melatonin rhythm (67.11±8.16pg/mL vs 77.11±8.04pg/mL, P<.001). We identified 961 differentially methylated sites, in which the hub methylated sites were locating on protein kinase C alpha (PRKCA) and cAMP response element-binding protein (CREB1) promoters, mediating the association of fetal malnutrition with impaired melatonin secretion. However, such effects were not observed in the offspring (all P>.05). Impaired histomorphology of pineal, decreased melatonin in serum, pineal, and pinealocyte were also found in the in vivo and in vitro experiments (P<.05 for the differences of the indicators). Hypermethylation of 10 CpG sites on the PRKCA promoter and 8 CpG sites on the CREB1 promoter were identified (all P<.05), which down-regulated PRKCA and CREB1 expressions, leading to decreased expression of AANAT, and then resulting in the impaired melatonin synthesis. Collectively, fetal malnutrition can impair melatonin synthesis through hypermethylation of PRKCA and CREB1 promoters, and such effects cannot be transmitted to the next generation.

The effect of long-term beta-blockers on melatonin secretion, sleep quality, and vascular brain damage

The influence of long-term administration of beta-blockers to melatonin synthesis, sleep quality and vascular brain damage. The main study group included 114 patients, aged 47-83, with cardiovascular diseases, who were under a complex therapy with long-term administration of beta-blockers. The comparison group included 110 patients with cardiovascular diseases, similar in age and sex, who did not receive beta-blockers in their complex therapy. The circadian dynamics of melatonin synthesis was observed by excretion of 6-sulfatoxymelatonin (6-SM), the major metabolite of melatonin, in three urinary samples (day, evening, night). All the patients underwent night polysomnography to assess the severity of sleep disorders. The severity of vascular brain damage was assessed using magnetic resonance imaging. The analyses showed large variability in individual values of 6-SM circadian excretion of patients with cardiovascular diseases (from 0.9 to 133 μg/24h with a mid-point 16.8 μg/24h). A considerable decrease of 6-SM circadian excretion is detected in the group of patients taking beta-blockers comparing to those not Me [q 25; q 75]: 12.8 [6.2; 21.1] and 24.0 [12.5; 41.5] μg/24h, respectively (p<0.001), with no differences in sleep values and severity of vascular brain damage. Comparing subgroups of patients with 6-SM circadian excretion lower and higher than 16.8 μg/24h showed a significant increase of sleep latency, decrease of rapid eye movement sleep (REM sleep), increasing number of gliosis foci in white matter of the brain with higher values of leptin, leptin/adiponectin ratio and glycohemoglobin in the group of patients with 6-SM circadian excretion ≤16.8 μg/24h. A low level of endogenous melatonin is a risk factor for development of sleep structure and quality disorders, vascular white matter brain damages with a higher risk for metabolic disorders. Long-term beta-blockers administration decrease endogenous melatonin synthesis to 50% increasing the risk for insomnia and vascular brain damage, mostly in patients with lower initial level of 6-SM circadian excretion.: melatonin, 6-sulfatoxymelatonin, beta-blockers, insomnia, vascular white matter brain damage, leptin, adiponectin.

TLR2-Melatonin Feedback Loop Regulates the Activation of NLRP3 Inflammasome in Murine Allergic Airway Inflammation.

Toll-like receptor 2 (TLR2) is suggested to initiate the activation of NLRP3 inflammasome, and considered to be involved in asthma. The findings that melatonin modulates TLRs-mediated immune responses, together with the suppressing effect of TLRs on endogenous melatonin synthesis, support the possibility that a feedback loop exists between TLRs system and endogenous melatonin synthesis. To determine whether TLR2-melatonin feedback loop exists in allergic airway disease and regulates NLRP3 inflammasome activity, wild-type (WT) and TLR2−/− mice were challenged with OVA to establish allergic airway disease model. Following OVA challenge, WT mice exhibited increased-expression of TLR2, activation of NLRP3 inflammasome and marked airway inflammation, which were all effectively inhibited in the TLR2−/− mice, indicating that TLR2-NLRP3 mediated airway inflammation. Meanwhile, melatonin biosynthesis was reduced in OVA-challenged WT mice, while such reduction was notably rescued by TLR2 deficiency, suggesting that TLR2-NLRP3-mediated allergic airway inflammation was associated with decreased endogenous melatonin biosynthesis. Furthermore, addition of melatonin to OVA-challenged WT mice pronouncedly ameliorated airway inflammation, decreased TLR2 expression and NLRP3 inflammasome activation, further implying that melatonin in turn inhibited airway inflammation via suppressing TLR2-NLRP3 signal. Most interestingly, although melatonin receptor antagonist luzindole significantly reduced the protein expressions of ASMT, AANAT and subsequent level of melatonin in OVA-challenged TLR2−/− mice, it exhibited null effect on leukocytes infiltration, Th2-cytokines production and NLRP3 activity. These results indicate that a TLR2-melatonin feedback loop regulates NLRP3 inflammasome activity in allergic airway inflammation, and melatonin may be a promising therapeutic medicine for airway inflammatory diseases such as asthma.

Nano-ZnO-Induced Drought Tolerance Is Associated with Melatonin Synthesis and Metabolism in Maize.

The applications of ZnO nanoparticles in agriculture have largely contributed to crop growth regulation, quality enhancement, and induction of stress tolerance, while the underlying mechanisms remain elusive. Herein, the involvement of melatonin synthesis and metabolism in the process of nano-ZnO induced drought tolerance was investigated in maize. Drought stress resulted in the changes of subcellular ultrastructure, the accumulation of malondialdehyde and osmolytes in leaf. The nano-ZnO (100 mg L−1) application promoted the melatonin synthesis and activated the antioxidant enzyme system, which alleviated drought-induced damage to mitochondria and chloroplast. These changes were associated with upregulation of the relative transcript abundance of Fe/Mn SOD, Cu/Zn SOD, APX, CAT, TDC, SNAT, COMT, and ASMT induced by nano-ZnO application. It was suggested that modifications in endogenous melatonin synthesis were involved in the nano-ZnO induced drought tolerance in maize.

МОРФО-ФУНКЦІОНАЛЬНИЙ СТАН ЕПІФІЗА ТА СУПРАХІАЗМАТИЧНОГО ЯДРА ГІПОТАЛАМУСА ЩУРІВ ЗА РІЗНИХ РЕЖИМІВ УВЕДЕННЯ ЕКЗОГЕННОГО МЕЛАТОНІНУ

In modern society increase of digitalization associated with grown exceed level of light at night – a new type of pollution. Presence of light at night inhibited endogenous melatonin synthesis by pineal gland, that influence on circadian system work cycles, so organism oftenbroken regime of wake/sleep, meals, physical activity. Also, a lack of melatonin in some certain time of dayand low melatonin concentration both, were shown take some intervention in diseases development through incorrect regulation of clock-depended genes expression. In connect with this, some latest clinical protocol in therapy or clinical trials of many different pathologies (for example, insomnia, metabolic syndrome, cardiovascular diseases, central nervous and immune system trouble, cancer, viral infection, etc.) include exogenous melatonin usage. As melatonin perform his function via endocrine and paracrine ways in variety types of cell, his application take place in wide range of doses and in different time of day (chronotherapeutic approach). Therefore, important to control state of circadian system central elements – pineal gland (main producer of endogenous melatonin) and suprachiasmatic nucleus (SCN) of hypothalamus (central pacemaker of circadian rhythm) in conditionsof exogenous melatonin treatment. Thus, the main goal of our research were analysis of rats pineal gland and hypothalamic SCN morpho-functional state after different time (morning, evening and continuously with drinking water) melatonin daily administration. Melatonin was administered by gavage for 7 weeks in dose 30 mg/kg 1 h before lights-off (M ZT11, evening), or 1 h after lights-on (M ZT01, morning), or continuously with drinking water during day-night period (MW). After melatonin use only in MW group pineal gland demonstrates changes in morphology (pinealocytes nucleus had mild basophilic color) and morphometric (increased cross-sectional area of the pinealocytes nucleus in compare with control group) analysis data. Besides, some similar changes were observed in SCN: the cross-sectional area of the SCN neurons nucleus grown in case of usage each of regime melatonin administration, while morphology characteristic remains without any alteration. In general, it suggesting about having by melatonin non-inhibiting features in context of circadian system feedback loop and supposing wide potential for melatonin use with absent huge side effect on central elements of above mentioned system.

Melatonin modulates autophagy and inflammation protecting human placental trophoblast from hypoxia/reoxygenation.

Melatonin has been proposed as a possible treatment for the deleterious effects of hypoxia/reoxygenation (H/R), such as autophagy, inflammation, and apoptosis. Pathological pregnancies, such as preeclampsia, are associated with placental H/R, and decreased placental melatonin synthesis as well as lower melatonin levels in the placenta and maternal plasma. However, the effects of exogenous melatonin on inflammation and autophagy induced by pregnancy complications associated with H/R await investigation. This study aimed to determine as to whether melatonin protects human primary villous trophoblasts against H/R-induced autophagy, inflammation, and apoptosis. Human primary villous cytotrophoblasts were isolated and immunopurified from normal term placentas. These cells were then exposed or not to 1mmol/L melatonin for 72hour in normoxia (8% O2 ), thereby inducing differentiation into syncytiotrophoblast that was then exposed to H/R (0.5% O2 , for 4hour) or normoxia. H/R decreased endogenous melatonin synthesis (by 68%) and interleukin (IL)-10 levels (by 72%), coupled to increased tumor necrosis factor (TNF) (by 114%), IL-6 (by 55%), and NFκB (by 399%), compared to normoxia. Melatonin treatment reversed the H/R effect, restoring IL-10, TNF, and IL-6 levels to those of the normoxia condition. Melatonin, as well as NFκB inhibition, enhanced autophagy activation, consequently increasing syncytiotrophoblast survival in H/R conditions. This study suggests that H/R, which is present in pregnancy complications, inhibits endogenous melatonin production, thereby contributing to reduced syncytiotrophoblast viability. Results indicate that exogenous melatonin treatment may afford protection against H/R-induced damage, thereby enhancing placental cell survival, and contributing to improved fetal outcomes.

Disturbances in melatonin secretion and the efficacy of replacement therapy in sleep disorders

The review presents data on the dependence of endogenous melatonin synthesis on the time of day, age, pineal gland size, lighting conditions, administration of beta-blockers and a number of other medications. The results of studies on parasecretion and efficacy of exogenous melatonin use in sleep-wake cycle disturbances, insomnia, neurodegeneration, diabetes mellitus and oncological diseases are discussed.

Melatonin Application to Pisum sativum L. Seeds Positively Influences the Function of the Photosynthetic Apparatus in Growing Seedlings during Paraquat-Induced Oxidative Stress.

Melatonin, due to its pleiotropic effects plays an important role improving tolerance to stresses. Plants increase endogenous melatonin synthesis when faced with harsh environments as well as exogenously applied melatonin limits stress injuries. Presented work demonstrated that single melatonin application into the seeds during pre-sowing priming improved oxidative stress tolerance of growing seedlings exposed to paraquat (PQ). PQ is a powerful herbicide which blocks the process of photosynthesis under light conditions due to free radicals excess production, when O2 is rapidly converted to and subsequently to other reactive oxygen species. The parameters of chlorophyll fluorescence [Fv/Fm, Fv/Fo, Rfd, ΦPSII, qP, and non-photochemical quenching (NPQ)] in all variants of pea leaves (derived from control non-treated seeds – C, and those hydroprimed with water – H, and hydroprimed with melatonin water solution 50 or 200 μM – H-MEL50 and H-MEL200, respectively) were analyzed as a tool for photosynthetic efficacy testing. Moreover stability of the photosynthetic pigments (chlorophylls a, b, and carotenoids) was also monitored under oxidative stress conditions. The results suggest that melatonin applied into the seed significantly enhances oxidative stress tolerance in growing seedlings. This beneficial effect was reflected in reduced accumulation of in leaf tissues, preservation of photosynthetic pigments, improved functioning of the photosynthetic apparatus and higher water content in the tissues during PQ-mediated stress. Our findings provide evidence for the physiological role of this molecule and serve as a platform for its possible applications in agricultural or related areas of research.

Melatonin synthesis follows a daily cycle in Daphnia

In freshwater systems, Daphnia has been demonstrated to show adaptive responses following the light-dark cycle. The adjustment of these responses to the change of day and night is probably transmitted via the hormone melatonin. The rate-limiting enzyme in melatonin synthesis is the arylalkylamine N-transferase (AANAT). We identified three genes coding for insect-like AANATs in Daphnia, of which we measured the gene expression in an ecologically relevant light-dark cycle. We demonstrated that Daphnia's insect-like AANAT gene expression oscillated in a daily manner, and that the highest peak of expression after the onset of darkness was followed by a peak of melatonin production at midnight. Moreover, we could show an oscillation of endogenous melatonin synthesis in Daphnia. In most organisms, melatonin synthesis is due to rhythmic expression of genes of the circadian clock, since transcription of aanats is directly linked to a circadian transcription factor. We could demonstrate that putative clock genes and insect-like AANAT genes of Daphnia were equally expressed. Therefore, we propose that melatonin synthesis is coupled to the expression of Daphnia clock genes, and that insect-like AANATs of crustaceans have a similar function as AANATs of vertebrates: The initiation of melatonin synthesis. In future studies with Daphnia, it will be necessary to take the time of day into account since melatonin concentrations might influence stress responses.

Potential role of melatonin in DNA damage caused by nitrosourea-induced mammary carcinogenesis

Mammary carcinogenesis was induced in female Sprague-Dawley rats by exposure to N-methyl-N-nitrosourea (NMU). Animals were kept under constant light conditions to arrest endogenous melatonin synthesis and were fed the same melatonin dosage, since nitrosourea exposure may also induce cellular injury, especially with extensive proliferative activity. The pro-apoptotic effects of the biogenic amine, melatonin, on rat whole blood leukocytes were assessed by alkaline single cell gel electrophoresis (comet) assay. Potential induction of stress due to animal immobilization and its additional effect on DNA damage was studied. The parameters relevant to the degree of DNA damage in groups with chemocarcinogen treatment demonstrated no significant effects as a result of the immobilization. A significant increase in DNA damage after melatonin treatment in NMU-induced carcinogenesis confirms its involvement in the activation of apoptosis.

Melatonin biosynthesis in the thymus of humans and rats.

Melatonin is an indoleamine widely distributed in the evolution that shows a great functional versatility, playing an important role as a transmitter of photoperiodic information and exhibiting antioxidant, oncostatic, anti-aging and immunomodulatory properties. In vertebrates, this molecule is produced by the pineal gland and other extrapineal sites. The present study was carried out to investigate the presence of melatonin in thymus and the possibility of an endogenous melatonin synthesis in this organ, in which T cells are matured. In this work, we demonstrate in humans and rats that thymus contains melatonin, expresses the mRNAs encoding N-acetyltransferase and hydroxyindol-O-methyltransferase, the two key enzymes of the melatonin synthesis, and has this biosynthetic machinery activated. In addition, rat thymocytes cultured for 24 h exhibited high levels of melatonin. The results presented here suggest that human and rat thymuses are able to synthesize melatonin, which could have intracrine, autocrine and paracrine functions.

Novel rhythms of N 1 ‐acetyl‐N 2 ‐formyl‐5‐methoxykynuramine and its precursor melatonin in water hyacinth: importance for phytoremediation

N1-acetyl-N2-formyl-5-methoxykynuramine (AMFK) is a major metabolite of melatonin in mammals. To investigate whether AFMK exists in plants, an aquatic plant, water hyacinth, was used. To achieve this, LC/MS/MS with a deuterated standard was employed. AFMK was identified in any plant for the first time. Both it and its precursor, melatonin, were rhythmic with peaks during the late light phase. These novel rhythms indicate that these molecules do not serve as the chemical signal of darkness as in animals but may relate to processes of photosynthesis or photoprotection. These possibilities are supported by higher production of melatonin and AFMK in plants grown in sunlight (10,000-15,000 microW/cm2) compared to those grown under artificial light (400-450 microW/cm2). Melatonin and AFMK, as potent free radical scavengers, may assist plants in coping with harsh environmental insults, including soil and water pollutants. High levels of melatonin and AFMK in water hyacinth may explain why this plant more easily tolerates environmental pollutants, including toxic chemicals and heavy metals and is successfully used in phytoremediation. These novel findings could lead to improvements in the phytoremediative capacity of plants by either stimulating endogenous melatonin synthesis or by adding melatonin to water/soil in which they are grown.

Melatonin Regulates the mRNA Expression of the mt1 Melatonin Receptor in the Rat Pars tuberalis

The pars tuberalis (PT) of the pituitary is a major neuroendocrine target site for melatonin as it contains a large number of high-affinity melatonin receptors. We have previously shown that melatonin autoregulates the density of its own receptors in the PT. However, whether melatonin regulation includes mRNA expression in vivo is unclear. In the present study we have used quantitative in situ hybridization to (1) follow the daily profile of mt₁ mRNA expression in the rat PT and (2) investigate whether mt₁ mRNA expression could be regulated in vivo by melatonin. We found clear diurnal variations of mt₁ mRNA expression that persist in constant darkness. We also showed, on pinealectomized animals, that the rhythmic pineal melatonin secretion is necessary for the expression of these daily variations. In a second step, we studied the effect of an acute suppression of endogenous melatonin synthesis on mt₁ melatonin receptors by applying a 1-hour light pulse during the night. We found that light induced a dramatic increase in mt₁ mRNA which was totally prevented by a melatonin injection showing that the acute effect of melatonin on the receptor mRNA is strongly inhibitory. A light pulse applied to animals with a chronic absence of melatonin was ineffective showing that light only affects melatonin receptors via the light-induced plasma melatonin suppression. Altogether our results show that melatonin regulates mt₁ melatonin receptor mRNA expression. However, this regulation seems to be complex: acute changes in plasma melatonin concentration regulate negatively the gene transcription, even if the daily endogenous nocturnal melatonin peak seems a prerequisite for variations in its receptor expression.

Methylcobalamin amplifies melatonin-induced circadian phase shifts by facilitation of melatonin synthesis in the rat pineal gland

Effects of methylcobalamin (methyl-B 12), a putative drug for treating human circadian rhythm disorders, on the melatonin-induced circadian phase shifts were examined in the rat. An intraperitoneal injection of 1–100 μg/kg melatonin 2-h before the activity onset time (CT 10) induced phase advances of free-running activity rhythms in a dose-dependent manner (ED 50=1.3 μg/kg). Injection of methyl-B 12 (500 μg/kg) prior to melatonin (1 μg/kg) injection induced larger phase advances than saline preinjected controls, while the injection of methyl-B 12 in combination with saline did not induce a phase advance. These results indicate amplification of melatonin-induced phase advances by methyl-B 12. Pinealectomy abolished the phase alternating effect of methyl-B 12, suggesting a site of action within the pineal gland. In fact, methyl-B 12 significantly increased the content of melatonin in the pineal collected 2-h after activity onset (CT 14). In contrast, no difference in melatonin content was found at CT 10, indicating that the effect of methyl-B 12 may be gated after the activity onset time when endogenous melatonin synthesis is known to increase. These results suggest that methyl-B 12 amplifies melatonin-induced phase advances via an increase in melatonin synthesis during the early subjective night at a point downstream from the clock regulation.