The decrease of pineal melatonin production with age. Causes and consequences

Melatonin and Phytomelatonin: Chemistry, Biosynthesis, Metabolism, Distribution and Bioactivity in Plants and Animals-An Overview

Melatonin is a ubiquitous indolamine, largely investigated for its key role in the regulation of several physiological processes in both animals and plants. In the last century, it was reported that this molecule may be produced in high concentrations by several species belonging to the plant kingdom and stored in specialized tissues. In this review, the main information related to the chemistry of melatonin and its metabolism has been summarized. Furthermore, the biosynthetic pathway characteristics of animal and plant cells have been compared, and the main differences between the two systems highlighted. Additionally, in order to investigate the distribution of this indolamine in the plant kingdom, distribution cluster analysis was performed using a database composed by 47 previously published articles reporting the content of melatonin in different plant families, species and tissues. Finally, the potential pharmacological and biostimulant benefits derived from the administration of exogenous melatonin on animals or plants via the intake of dietary supplements or the application of biostimulant formulation have been largely discussed.

Fluoride-Free Diet Stimulates Pineal Growth in Aged Male Rats

The pineal gland is a naturally calcifying endocrine organ which secretes the sleep-promoting hormone melatonin. Age-related changes of the pineal have been observed, including decreased pinealocyte numbers, increased calcification, and a reduction in melatonin production. Since fluoride is attracted to calcium within the pineal gland, this study sought to examine the effects of a fluoride-free diet on the morphology of the pineal gland of aged male rats (26 months old). All animals had previously been raised on standard fluoridated food and drinking water. These control animals were compared to other animals that were placed on a fluoride-free diet ("fluoride flush") for 4 or 8 weeks. At 4 weeks, pineal glands from fluoride-free animals showed a 96% increase in supporting cell numbers and at 8 weeks a 73% increase in the number of pinealocytes compared to control animals. In contrast, the number of pinealocytes and supporting cells in animals given an initial 4-week fluoride flush followed by a return to fluoridated drinking water (1.2 ppm NaF) for 4 weeks were not different from control animals. Our findings therefore demonstrate that a fluoride-free diet encouraged pinealocyte proliferation and pineal gland growth in aged animals and fluoride treatment inhibited gland growth. These findings suggest that dietary fluoride may be detrimental to the pineal gland.

Physiological and pharmacological effects of melatonin on remote ischemic perconditioning after myocardial ischemia-reperfusion injury in rats: Role of Cybb, Fas, NfκB, Irisin signaling pathway

It has been found that remote organ/limb temporary ischemia, known as remote ischemic conditioning, can provide protection against the formation of lethal ischemic outcome. Current evidence suggests that aging and age-releated comorbidities impair the cardioprotective effects of conditionings. In conjuction with aging, decrease in melatonin synthesis from pineal gland can have role in the pathogenesis of aging and age-related cardiovascular diseases. In this study, we investigated the effects of remote ischemic perconditioning (RIPerC) and physiological and pharmacological concentrations of melatonin on the infarct size, Fas gene, cytochrome b-245 beta chain (Cybb) gene, nuclear factor-kappa B (NfκB), and irisin using an in vivo model of myocardial ischemia/reperfusion (I/R) injury. Sprague-Dawley rats that were divided into two groups first as non-pinealectomized (Non-Px) and pinealectomized (Px), and then (a) Control; (b) I/R (30-minute ischemia, 120-minute reperfusion caused by left coronary artery ligation); (c) I/R + RIPerC (when myocardial ischemia initiated, three cycles of 5-minute occlusion followed by 5-minute reperfusion); (d) I/R + Mel; (e) Px; (f) Px + I/R; (g) Px + I/R + RIPerC; (h) Px + I/R + RIPerC + Mel groups. The infarct size was determined by TTC staining and analyzed by the ImageJ program. Molecular parameters were evaluated by qRT-PCR and Western blot. Results showed that increased infarct size in Non-Px groups decreased with RIPerC and melatonin. However, increased infarct size in Px groups was decreased minimally with RIPerC and significantly decreased with RIPerC + Melatonin. Fold change in Fas gene was associated with the infarct size. RIPerC and melatonin reduced expressions of Cybb, NfκB, and irisin genes. The physiological release and pharmacological concentration of melatonin may improve protective effect of RIPerC against I/R-induced infarct size by modulating Cybb, Fas, NfκB, Irisin signaling pathways.

Pineal gland calcification under hypoxic conditions

The pineal gland (glandula pinealis) is neuroendocrine gland located at the epithalamus of the brain secreting melatonin. The aim of this study was to explore effects of prenatal hypoxia in rats at the age of 33 weeks on the occurrence of pineal gland calcification. Distribution and chemical composition of calcerous material by light, scanning and transmission electron microscopy was investigated. Melatonin concentrations in blood plasma by direct radioimmunoassay were measured. Rats were exposed to prenatal hypoxia for 12 h at day 20 of development and second group to prenatal hypoxia for 2x8 h at days 19 and 20 of development. Vacuoles of intracellular edema in the pineal samples after 12 h hypoxia were found. Their size ranges up to 30 µm. Some of them were filled with the flocculent and fibrous material. Samples of pineal glands after 2 x 8 h hypoxia revealed the pericellular edema of pinealocytes. The amount of calcium rich particles in 2 x 8 h hypoxia group was lower than in 12 h hypoxia group. Plasma melatonin levels did not differ between control and both hypoxia groups. We concluded that calcification is a process induced by osteoblasts and osteocytes with melatonin as a promotor and it is favored under hypoxic conditions.

The Potential of Phytomelatonin as a Nutraceutical

Phytomelatonin (plant melatonin) is chemically related to the amino acid tryptophan and has many diverse properties. Phytomelatonin is an interesting compound due to its outstanding actions at the cellular and physiological level, especially its protective effect in plants exposed to diverse stress situations, while its vegetable origin offers many opportunities because it is a natural compound. We present an overview of its origin, its action in plants in general (particularly in plant species with high levels of phytomelatonin), and its possibilities for use as a nutraceutical with particular attention paid to the beneficial effects that it may have in human health. The differences between synthetic melatonin and phytomelatonin, according to its origin and purity, are presented. Finally, the current market for phytomelatonin and its limits and potentials are discussed.

Assessment of Pineal Gland Volume and Calcification in Healthy Subjects: Is it Related to Aging?

Purpose:

The human pineal gland is a small neuroendocrine organ which produces melatonin. The main goal of this study was to provide a reference range for pineal volume in all age groups and to determine calcified and noncalcified tissue and their proportions, which may be a reflection of melatonin production in all age groups, by using very thin computerized tomography (CT) slices.

Materials and methods:

A total of 167 outpatients had undergone cranial CT. Each of the subject’s total pineal volume (TPV), calcified pineal volume (CPV) and noncalcified pineal volume (NPV) according to age groups were calculated in cubic millimeters. Also, proportion of calcification (POC) was noted.

Results:

The median values were 88.5 mm³ (12.3 mm³–411mm³) for TPV, 74.3 mm³ (12.3 mm³–298 mm³) for NPV, and 3.9 mm³ (0 mm³–141 mm³) for CPV. POC showed a gradual increase from 0–49 years. In the ≥70 group, when compared with the 60–69 age group, CPV and POC values were significantly lower (P: 0.036, P: 0.034, respectively).

Conclusion:

This study brings a radiological point of view to the distribution of pineal calcification according to age that has a link with melatonin secretion.

Age-related changes in the incidence of pineal gland calcification in Turkey: A prospective multicenter CT study

The goal of this cross-sectional observational study was to determine the incidence of pineal gland calcification (PGC), to investigate the interaction of PGC and aging, and to compare the incidence of PGC among the populations living in Turkey. In a prospective study the rate of PGC on CT scans of 1376 individuals in six referral centers from different regions of Turkey was investigated, with emphasis on effects of climatological parameters and aging on PGC. It was found that the incidence of PGC increased rapidly after first decade and the increase remains gradual thereafter, higher in males than in females for all age groups. There was a significant difference for incidence and degree of PGC between different clinics and between both sexes (p<0.001). In addition, there was a significant difference for the degree of PGC between the clinics in low altitude group and those in high altitude group (p<0.001 for each). Logistic regression analysis revealed that age, sex, altitude and intensity of sunlight exposure significantly affected the risk of PGC (odds ratios (OR) 1.335, 95% confidence intervals (CI) 1.261-1.414, p<0.001; OR 1.900, 95% CI 1.486-2.428, p<0.001; OR 0.715, 95% CI 0.517-0.990, p<0.05; OR 0.997, 95% CI 0.994-0.999, p<0.01, respectively). Furthermore, by multiple linear regression analysis, high altitude and increased intensity of sunlight exposure were found to affect the degree of PGC (beta=0.003, p<0.001). It is concluded that there is a close relationship between PGC and the aforementioned parameters, supporting a link between the development of PGC and these. This study provides some reference data for new clinical studies on the putative role of pineal gland in future.

Adrenoceptor expression and diurnal rhythms of melatonin and its precursors in the pineal gland of type 2 diabetic goto-kakizaki rats

A decrease in the nighttime release of the pineal hormone melatonin is associated with aging and chronic diseases in animals an humans. Melatonin has a protective role in type 2 diabetes; however, its synthesis itself is affected in the disease. The aim of this study was to detect crucially impaired steps in the pineal melatonin synthesis of type 2 diabetic Goto-Kakizaki (GK) rats. Therefore, plasma melatonin concentrations and the pineal content of melatonin and its precursors (tryptophan, 5-hydroxytryptophan, serotonin, and N-acetylserotonin) were quantified in GK rats compared with Wistar rats (each group 8 and 50 wk old) in a diurnal manner (four animals per group and per time point). Additionally, the expression of pineal adrenoceptor subtype mRNA was investigated. We found that in diabetic GK rats, 1) inhibitory alpha-2-adrenoceptors are significantly more strongly expressed than in Wistar rats, 2) the formation of 5-hydroxytryptophan is crucially impaired, and 3) the pineal gland protein content is significantly reduced compared with that in Wistar rats. This is the first time that melatonin synthesis is examined in a type 2 diabetic rat model in a diurnal manner. The present data unveil several reasons for a reduced melatonin secretion in diabetic animals and present an important link in the interaction between melatonin and insulin.

Neuroprotection by radical avoidance: search for suitable agents

Neurodegeneration is frequently associated with damage by free radicals. However, increases in reactive oxygen and nitrogen species, which may ultimately lead to neuronal cell death, do not necessarily reflect its primary cause, but can be a consequence of otherwise induced cellular dysfunction. Detrimental processes which promote free radical formation are initiated, e.g., by disturbances in calcium homeostasis, mitochondrial malfunction, and an age-related decline in the circadian oscillator system. Free radicals generated at high rates under pathophysiological conditions are insufficiently detoxified by scavengers. Interventions at the primary causes of dysfunction, which avoid secondary rises in radical formation, may be more efficient. The aim of such approaches should be to prevent calcium overload, to reduce mitochondrial electron dissipation, to support electron transport capacity, and to avoid circadian perturbations. L-theanine and several amphiphilic nitrones are capable of counteracting excitotoxicity and/or mitochondrial radical formation. Resveratrol seems to promote mitochondrial biogenesis. Mitochondrial effects of leptin include attenuation of electron leakage. Melatonin combines all the requirements mentioned, additionally regulates anti- and pro-oxidant enzymes and is, with few exceptions, very well tolerated. In this review, the perspectives, problems and limits of drugs are compared which may be suitable for reducing the formation of free radicals.

The physiological function of melatonin in plants

Melatonin (N-acetyl-5-methoxytryptamine), a well-known animal hormone, was discovered in plants in 1995 but very little research into it has been carried out since. It is present in different parts of all the plant species studied, including leaves, stems, roots, fruits and seeds. This brief review will attempt to provide an overview of melatonin (its discovery, presence and functions in different organisms, biosynthetic route, etc.) and to compile a practically complete bibliography on this compound in plants. The common biosynthetic pathways shared by the auxin, indole-3-acetic, and melatonin suggest a possible coordinated regulation in plants. More specifically, our knowledge to date of the role of melatonin in the vegetative and reproductive physiology of plants is presented in detail. The most interesting aspects for future physiological studies are presented.

Oral Administration of Melatonin to Old Ring Doves (Streptopelia risoria) Increases Plasma Levels of Melatonin and Heterophil Phagocytic Activity

We analyzed the effect of oral melatonin (23 microg/0.1 ml/animal/d; 1 h before dark on 12 consecutive days) in old birds, in natural photoperiods, on the hormone's plasma levels, and phagocytosis. Blood collections were performed daily at 2:00 am and 4:00 pm until 5 days after the treatment. From day 1, the melatonin levels were significantly higher than basal levels at both times. Values at 2:00 am were significantly higher than the 4:00 pm values. After treatment, the melatonin levels declined, returning from day 14 to basal values at both hours. At 2:00 am, phagocytosis was significantly greater than that obtained at 4:00 pm and greater than basal values. The 4:00 pm values were only significantly greater than basal on days 6 and 8, parallel to a decline in superoxide anion levels, which were lowest at 2:00 am. Melatonin administered to old ring doves increases the differences between nocturnal and diurnal plasma levels, and, in parallel, increases phagocytosis and reduces superoxide radical levels in heterophils.

Melatonin or a melatonin agonist corrects age-related changes in circadian response to environmental stimulus

The effects of a melatonin agonist, S-20098, included in the diet were tested on a specific effect of aging in hamsters: the marked decline in the phase shifting effects of a 6-h pulse of darkness on a background of constant light. In contrast to young hamsters, old hamsters fed with the control diet showed little or no phase shifts in response to a dark pulse presented in the middle of their inactive or active period. Old hamsters fed with S-20098 showed phase shifts that were ~70% of the ones in young animals and significantly greater than those in old controls. The phase advancing response to a dark pulse presented during the inactive period was dose dependent and reversed after S-20098 discontinuation. Melatonin included in the diet showed comparable restorative effects on the phase shifting response to a dark pulse in old hamsters. Replacement therapy with melatonin or melatonin-related compounds could prove useful in treating, preventing, or delaying disturbances of circadian rhythmicity and/or sleep in older people.

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

The pineal gland with its effects on immune system and free radicals may have a role on aging process. In this study, we investigated the effects of melatonin (10 mg/kg/d, s.c. for 7 days), the main secretion of the pineal gland, on the humoral immune responses of aged and young male Wistar rats. Eighteen aged (28 months old; 6 in control group and 12 in melatonin group) and 25 young (9 months old; 10 in control group and 15 in melatonin group) rats were given 4 x 10(8) sheep erythrocytes i.p. in order to evoke humoral immune responses. After a booster injection at the end of a period of three-weeks following the last melatonin injection, IgM and IgG1 levels were measured. Melatonin was found to increase IgG1 and IgM responses of aged rats when compared to controls (p = 0.049 and p = 0.007), respectively. In the young rats, while the IgG1 levels of control group were significantly higher than that of the melatonin group (p =0.021), IgM levels were not significantly different (p = 0.563). It is concluded that exogenous melatonin may augment the depressed humoral immune responses seen aged rats.

Antioxidant properties of melatonin--an emerging mystery

Over three centuries ago, the French philosopher René Descartes described the pineal gland as "the seat of the soul." However, it was not until the late 1950s that the chemical identity and biosynthesis of melatonin, the principal hormone secreted by the pineal body, were revealed. Melatonin, named from the Greek melanos, meaning black, and tonos, meaning color, is a biogenic amine with structural similarities to serotonin. The mechanisms mediating the synthesis of melatonin are transcriptionally regulated by the photoperiodic environment. Once synthesized, the neurohormone is a biologic modulator of mood, sleep, sexual behavior, reproductive alterations, immunologic function, and circadian rhythms. Moreover, melatonin exerts its regulatory roles through high-affinity, pertussis toxin-sensitive, G-protein (or guanine nucleotide binding protein) coupled receptors that reside primarily in the eye, kidney, gastrointestinal tract, blood vessels, and brain. Additional evidence also indicates a role for melatonin in aging and age-related diseases, probably related to its efficient free radical scavenger (or antioxidant) activity. The potential clinical benefit of melatonin as an antioxidant is remarkable, suggesting that it may be of use in the treatment of many pathophysiological disease states including various cancers, hypertension, pulmonary diseases, and a variety of neurodegenerative diseases such as Alzheimer's disease. This review summarizes the biosynthesis of melatonin and its many endocrine and physiological functions, including its therapeutic potential in human disease states. Emphasis is placed on the recent speculations indicating that this pineal hormone serves as an endogenous antioxidant agent with proficient free radical scavenging activity.

Changes with age in daytime and nighttime contents of melatonin, indoleamines, and catecholamines in the pineal gland: a comparative study in rat and Syrian hamster

Previous studies in rodents showed a severe deterioration of pineal physiology with aging. The present study investigated the age-related changes in the content of monoamines and metabolites in rat and Syrian hamster pineal gland. In addition to melatonin, the levels of 5-hydroxytryptophan (5HTP), serotonin (5HT), 5-hydroxyindoleacetic acid (5HIAA), N-acetylserotonin (N-Ac-SHT), dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC), and noradrenaline (NA) were measured by HPLC. Pronounced reductions were found in 5HT and 5HIAA contents during daytime in rats of 24 months, which had not been observed in animals of 12 months. In addition, nighttime pineal 5HIAA, N-Ac-5HT, and melatonin contents were decreased in the old rats, although a significant day:night variation persisted. Also a diurnal fluctuation in NA, DA, and DOPAC contents was present in young and middle-aged rats but not for NA and DOPAC in the oldest rats due to a decrease in the nighttime levels. Pineal DA levels were also reduced in 24-month-old rats during the night, although a marked day:night change was still found. In the Syrian hamster pineal, significant reductions in daytime 5HT and 5HIAA were found respectively at 12 and 18 months, while nighttime levels of these compounds were decreased from 18 months. The nocturnal content of N-Ac-5HT dropped gradually from 12 months, and melatonin was reduced by 74% and 86% in hamsters of 18 and 24 months, respectively. In all these compounds, a significant day:night variation was observed irrespective of age. However, neither a day:night variation nor an effect of aging was found in terms of pineal NA content. In contrast, pineal DA and DOPAC levels displayed a diurnal variation in hamsters of 1.5 and 6 months, but not in animals of 12 and 18 months due a reduced nighttime content. These data suggest that the decline of pineal melatonin with age is a consequence of a deficit in the pathway of serotonin utilization. This probably is explained by a reduced N-acetyltransferase activity, which may be linked to impaired pineal catecholaminergic neurotransmission.

Electron probe X-ray microanalysis of the elemental composition of the pineal gland of young adults and aged rats

Fractures of deep-frozen and freeze-dried pineal glands were analysed for elemental composition by means of X-ray microanalysis with a scanning electron microscope. The results from young adults (3 months old) were compared with those from aged animals (24 months old); significant increases in S, Ca, Al, Si, and Fe were observed in aged animals when compared to young adults. There were no significant differences with Na, Mg, Cl, K, Ti, Cr, Mn, Ni, Cu, Zn, whereas a decrease of P was observed in aged animals when compared to young adults. Whether the changes observed in elemental composition have a direct effect on the activity and production of metalloenzymes and the overall physiology of the pineal gland are discussed.

Age-related changes of neuronal responsiveness to melatonin in the striatum of sham-operated and pinealectomized rats

The age-related changes and the acute effects of intravenous melatonin on the activity of striatal neurons of 1-, 3-, 6-, 12-, and 18-month-old sham-operated and pinealectomized rats were investigated. There was a decline in responsiveness from 3- to 18-months of age, although in sham-pinealectomized rats the responses were similar at 12 and 18 months; in pinealectomized rats, the neuronal responses were quite stable at early ages. In all age groups of sham-pinealectomized rats, neuronal firing decreased in most cells, and increased in only a small percentage of cells after intravenous melatonin injection (100 ng/kg). However, in pinealectomized rats, the injection of melatonin at the same doses significantly increased the firing rate of most neurons compared to that in sham-operated animals at all age-groups, while the number of neurons showing an inhibitory response decreased. These results indicate that melatonin may be involved in the modulation of the activity of striatal neurons and demonstrates an age-dependent reduction in striatal sensitivity to melatonin. They also suggest that other compounds of pineal origin may modulate the activity of motor control centers.