Melatonin and reproduction revisited

Melatonin influences on steroidogenic gene expression in the ovary of pinealectomized rats

OBJECTIVE

To analyze the expression of genes related to steroidogenesis in the ovary of pinealectomized rats.

DESIGN

Experimental research.

SETTING

University research laboratory.

ANIMAL(S)

Thirty female adult rats.

INTERVENTION(S)

Administration of vehicle (GI), pinealectomy with vehicle (GII), or pinealectomy with melatonin replacement (10 μg/night) for 60 consecutive days (GIII), then euthanasia after 2 months of treatment, ovary collection complementary DNA microarray analyses, confirmatory quantitative reverse-transcriptase polymerase chain reaction analyses, and immunohistochemical analyses for localizing steroidogenesis changes in the ovary.

MAIN OUTCOME MEASURE(S)

Biologic molecular study followed by immunohistochemical analysis.

RESULT(S)

The changes in the expression of CYP11A1, CYP17A1, and CYP19A1 after pinealectomy (GII) compared with control (GI) showed the Cyp17a1 expression level increased in the theca interna and interstitial cells in the GII rats compared with the other groups.

CONCLUSION(S)

Melatonin deprivation (pinealectomy) or administration may influence the ovarian CYP17A1 expression and steroidogenesis.

Melatonin improves the quality of in vitro produced (IVP) bovine embryos: implications for blastocyst development, cryotolerance, and modifications of relevant gene expression

To evaluate the potential effects of melatonin on the kinetics of embryo development and quality of blastocyst during the process of in vitro bovine embryo culture. Bovine cumulus–oocyte complexes (COCs) were fertilized after in vitro maturation. The presumed zygotes were cultured in in vitro culture medium supplemented with or without 10⁻⁷ M melatonin. The cleavage rate, 8-cell rate and blastocyst rate were examined to identify the kinetics of embryo development. The hatched blastocyst rate, mortality rate after thawing and the relevant transcript abundance were measured to evaluate the quality of blastocyst. The results showed that melatonin significantly promoted the cleavage rate and 8-cell embryo yield of in vitro produced bovine embryo. In addition, significantly more blastocysts were observed by Day 7 of embryo culture at the presence of melatonin. These results indicated that melatonin accelerated the development of in vitro produced bovine embryos. Following vitrification at Day 7 of embryo culture, melatonin (10⁻⁷ M) significantly increased the hatched blastocyst rate from 24 h to 72 h and decreased the mortality rate from 48 h to 72 h after thawing. The presence of melatonin during the embryo culture resulted in a significant increase in the gene expressions of DNMT3A, OCC, CDH1 and decrease in that of AQP3 after thawing. In conclusion, melatonin not only promoted blastocyst yield and accelerated in vitro bovine embryo development, but also improved the quality of blastocysts which was indexed by an elevated cryotolerance and the up-regulated expressions of developmentally important genes.

Proliferative effects of melatonin on Schwann cells: implication for nerve regeneration following peripheral nerve injury

Activation of proliferation of Schwann cells is crucial for axonal guidance and successful nerve regeneration following peripheral nerve injury (PNI). Considering melatonin plays an important role in proliferative regulation of central glial cells, the present study determined whether melatonin can effectively promote Schwann cell proliferation and improve nerve regeneration after PNI. The spontaneous immortalized rat Schwann cell line (RSC 96 cells) was first analyzed by quantitative polymerase chain reaction (QPCR) to detect the potential existence of melatonin receptors. The melatonin receptor-mediated signaling responsible for proliferation was examined by measuring the phosphorylation of extracellular signal-regulated kinases (ERK1/2) pathway. The in vivo model of PNI was performed by the end-to-side neurorrhaphy. The quantity of Schwann cells as well as the number of re-innervated motor end plates (MEP) on target muscles was examined to represent the functional recovery of injured nerves. QPCR results indicated that MT1 is the dominant receptor in Schwann cells. Immunoblotting and proliferation assay revealed an enhanced phosphorylation of ERK1/2 and increased number of RSC 96 cells following melatonin administration. Nonselective melatonin receptor antagonist (luzindole) treatment significantly suppressed all the above findings, suggesting that the proliferative effects of melatonin were mediated by a receptor-dependent pathway. In vivo results corresponded well with in vitro findings in which melatonin effectively increased the amount of proliferated Schwann cells and re-innervated MEP on target muscles following PNI. As melatonin successfully improves nerve regeneration by promoting Schwann cell proliferation, therapeutic use of melatonin may thus serve as a promising strategy to counteract the PNI-induced neuronal disability.

Melatonin prevents experimental preterm labor and increases offspring survival

Preterm delivery is the leading cause of neonatal mortality and contributes to delayed physical and cognitive development in children. At present, there is no efficient therapy to prevent preterm labor. A large body of evidence suggests that intra-amniotic infections may be a significant and potentially preventable cause of preterm birth. This work assessed the effect of melatonin in a murine model of inflammation-associated preterm delivery which mimics central features of preterm infection in humans. For this purpose, preterm labor was induced in BALB/c mice by intraperitoneal injections of bacterial lipopolysaccharide (LPS) at 10.00 hr (10 μg LPS) and 13.00 hr (20 μg LPS) on day 15 of pregnancy. On day 14 of pregnancy, a pellet of melatonin (25 mg) had been subcutaneously implanted into a group of animals. In the absence of melatonin, a 100% incidence of preterm birth was observed in LPS-treated animals, and the fetuses showed widespread damage. By comparison, treatment with melatonin prevented preterm birth in 50% of the cases, and all pups from melatonin-treated females were born alive and their body weight did not differ from control animals. Melatonin significantly prevented the LPS-induced rises in uterine prostaglandin (PG) E2 , PGF2α, and cyclooxygenase-2 protein levels. In addition, melatonin prevented the LPS-induced increase in uterine nitric oxide (NO) production, inducible NO synthase protein, and tumor necrosis factor-alpha (TNFα) levels. Collectively, our results suggest that melatonin could be a new therapeutic tool to prevent preterm labor and to increase offspring survival.

Synthetic melatoninergic ligands: achievements and prospects

Pineal hormone melatonin is widely used in the treatment of disorders of circadian rhythms. The presence of melatonin receptors in various animal tissues motivates the use of this hormone in some other diseases. For this reason, in recent years investigators continued the search for synthetic analogues of melatonin which are metabolically stable and selective to receptors. This review includes recent information about the most famous melatonin analogues, their structure, properties, and physiological features of the interaction with melatonin receptors.

Melatonin inhibits voltage-sensitive Ca(2+) channel-mediated neurotransmitter release

Melatonin is involved in various neuronal functions such as circadian rhythmicity and thermoregulation. Melatonin has a wide range of pharmacologically effective concentration levels from the nanomolar to millimolar levels. Recently, the antiepileptic effect of high dose melatonin has been the focus of clinical studies; however, its detailed mechanism especially in relation to neurotransmitter release and synaptic transmission remains unclear. We studied the effect of melatonin at high concentrations on the neurotransmitter release by monitoring norepinephrine release in PC12 cells, and excitatory postsynaptic potential in rat hippocampal slices. Melatonin inhibits the 70mM K(+)-induced Ca(2+) increase at millimolar levels without effect on bradykinin-triggered Ca(2+) increase in PC12 cells. Melatonin (1mM) did not affect A2A adenosine receptor-evoked cAMP production, and classical melatonin receptor antagonists did not reverse the melatonin-induced inhibitory effect, suggesting G-protein coupled receptor independency. Melatonin inhibits the 70mM K(+)-induced norepinephrine release at a similar effective concentration range in PC12 cells. We confirmed that melatonin (100µM) inhibits excitatory synaptic transmission of the hippocampal Schaffer collateral pathway with the decrease in basal synaptic transmission and the increase in paired pulse ratio. These results show that melatonin inhibits neurotransmitter release through the blocking of voltage-sensitive Ca(2+) channels and suggest a possible mechanism for the antiepileptic effect of melatonin.

Role of melatonin on production and preservation of gametes and embryos: a brief review

The aim of this brief review is to clarify the role of melatonin in the production and preservation of mammalian gametes and embryos. Melatonin is an indoleamine synthesized from tryptophan in the pineal gland and other organs that operates as a hypothalamic-pituitary-gonadal axis modulator and regulates the waxing and waning of seasonal reproductive competence in photoperiodic mammals. A major function of the melatonin rhythm is to transmit information about the length of the daily photoperiod to the circadian and circannual systems in order to provide time-of-day and time-of-year information, respectively, to the organism. Melatonin is also a powerful antioxidant and anti-apoptotic agent, which is due to its direct scavenging of toxic oxygen derivatives and its ability to reduce the formation of reactive species. Mammalian gametes and embryos are highly vulnerable to oxidative stress due to the presence of high lipid levels; during artificial breeding procedures, these structures are exposed to dramatic changes in the microenvironment, which have a direct bearing on their function and viability. Free radicals influence the balance between oxidation-reduction reactions, disturb the transbilayer-phospholipid asymmetry of the plasma membrane and enhance lipid peroxidation. Melatonin, due to its amphiphilic nature, is undoubtedly useful in tissues by protecting them from free radical-mediated oxidative damage and cellular death. The supplementation of melatonin to semen extender or culture medium significantly improves sperm viability, oocyte competence and blastocyst development in vitro.

Clinical relevance of melatonin in ovarian and placental physiology: a review

Within the last decade, the synthesis of melatonin in and its functions at the level of the peripheral reproductive organs has come into better focus. Melatonin is produced at several reproductive organ sites, e.g., the oocyte, ovarian follicular cells and the placental cytotrophoblasts. Moreover, these cells also contain membrane receptors for this indoleamine. In addition, via the free radical scavenging activity of melatonin and its metabolites, oxidative stress is reduced in all reproductive organ cells ensuring their optimal function. Enhancement of oocyte maturation and preservation of oocyte quality may be major functions of melatonin. Oocyte damage reduces successful fertilization and the development of a healthy fetus. The findings that melatonin protects the oocyte from toxic oxygen species have implications for improving the outcome of in vitro fertilization-embryo transfer procedures, as already shown in two published reports. Some actions of melatonin in the placenta may be context specific. Thus, melatonin is believed to function in the maintenance of optimal placental homeostasis by deferring apoptosis of villous cytotrophoblasts, while protecting syncytiotrophoblasts from oxidative damage. Melatonin reduces oxidative damage in the placenta and may improve hemodynamics and nutrient transfer at the placental-uterine interface. The use of melatonin to treat preeclampsia should also be considered.

Cloning and expression of melatonin receptors in the mudskipper Boleophthalmus pectinirostris: their role in synchronizing its semilunar spawning rhythm

The mudskipper Boleophthalmus pectinirostris, a burrow-dwelling fish inhabiting intertidal mudflats, spawns only once during the spawning season around either the first or last lunar quarters. To understand the molecular mechanisms regulating this semilunar spawning rhythm, we cloned all melatonin receptor subtypes (mtnr1a1.4, mtnr1a1.7, mtnr1b, and mtnr1c). Expression of three melatonin receptor subtypes (except mtnr1c) was found in the ovaries. In contrast, the expression of all receptor subtypes was found in the diencephalon and the pituitary. In the fully-grown follicles, only mtnr1a1.7 mRNA was detected in both the isolated follicle layers and denuded oocytes. Interestingly, the transcript levels of both mtnr1a1.4 in the diencephalon and mtnr1a1.7 in the ovary displayed two cycles within one lunar month, and peaked around the first and last lunar quarters. We used 17α,20β-dihydroxy-4-pregnen-3-one (DHP), a maturation-inducing hormone, as a biomarker to examine the involvement of melatonin receptors in the control of the spawning cycle. Melatonin significantly increased the plasma DHP level 1h post intraperitoneal injection. Melatonin also directly stimulated ovarian fragments in vitro to produce a significantly higher amount of DHP. Taken together, these results provided the first evidence that melatonin receptors were involved in the synchronization of the semilunar spawning rhythm in the female mudskipper by acting through the HPG axis and/or directly on ovarian tissues to stimulate the production of DHP.

Melatonin: the watchdog of villous trophoblast homeostasis against hypoxia/reoxygenation-induced oxidative stress and apoptosis

Human placenta produces melatonin and expresses its receptors. We propose that melatonin, an antioxidant, protects the human placenta against hypoxia/reoxygenation (H/R)-induced damage. Primary term villous cytotrophoblasts were cultured under normoxia (8% O2) with or without 1mM melatonin for 72h to induce differentiation into the syncytiotrophoblast. The cells were then cultured for an additional 22h under normoxia or subjected to hypoxia (0.5% O2) for 4h followed by 18h reoxygenation (8% O2) with or without melatonin. H/R induced oxidative stress, which activated the Bax/Bcl-2 mitochondrial apoptosis pathway and the downstream fragmentation of DNA. Villous trophoblast treatment with melatonin reversed all the negative effects induced by H/R to normoxic levels. This study shows that melatonin protects the villous trophoblast against H/R-induced oxidative stress and apoptosis and suggests a potential preventive and therapeutic use of this indolamine in pregnancy complications characterized by syncytiotrophoblast survival alteration.

Serum Levels of Melatonin and Oxidative Stress Markers and Correlation between Them in Infertile Men

INTRODUCTION

Infertility is the problem of 15% of young couples in different societies. One of the factors that could affect fertility is oxidative stress. Therefore, the aim of the present study is to investigate the level of Melatonin, a free radical scavenger, and its correlation with oxidative biomarkers in infertile men.

METHODS

For this purpose, fertile and infertile men in 2 groups, 30 people in each group, were studied. The fertile men were selected from husbands of patients admitted to Alzahra obstetric and gynecology hospital, according to WHO standards. The infertile men were selected from patients referred to infertility ward. Blood sampling from the participants carried out at a specific time, sera collected and the levels of malondialdehyde, total antioxidant capacity and Melatonin were detected in the sera. The data were analyzed using t-test and Sperman's correlation method.

RESULTS

Melatonin level in the sera from fertile men were 522 (39.32) ng/L and in infertile men were 511.78 (34.6) ng/L. MDA level in fertile and infertile men were 2.26 (0.34) vs 2.99 (0.44) nmol/ml which was significantly different. The level of TAC in the sera from fertile men were significantly higher than in infertile men. The result obtained for correlation coefficient Spearman's test revealed a significant, strong and direct correlation between Melatonin and TAC and a significant and reverse correlation between melatonin and MDA.

CONCLUSION

It is concluded that melatonin could be involved in infertility. In other word, melatonin treatment and antioxidant-rich nutrition could help fertility by combating oxidative stress.

Melatonin: its possible role in the management of viral infections--a brief review

Melatonin, a versatile molecule, is synthesized by the pineal gland but also by other organs, including gastrointestinal tract, retina, thymus, bone marrow, and by leukocytes. Besides playing an important role in various functions of the body, including sleep and circadian rhythm regulation, melatonin also shows immunoregulatory, free radical scavenger and antioxidant functions. Because of these latter characteristics melatonin has also been found to be effective in fighting viral infections in a variety of experimental animal and in vitro studies. These data suggest a possible therapeutic potential of melatonin in human virus-induced disorders.

Melatonin promotes the in vitro development of pronuclear embryos and increases the efficiency of blastocyst implantation in murine

When a defect occurs in the in vitro development of a pronuclear embryo, the interruption of the subsequent implantation limits the success of assisted conception. This common problem remains to be solved. In this study, we observed that melatonin at its physiological concentration (10(-7)  m) significantly promoted the in vitro development of murine pronuclear embryos. This was indicated by the increased blastocyst rate, hatching blastocyst rate, and blastocyst cell number with melatonin treatment. In addition, when these blastocysts were implanted into female recipient mice, the pregnancy rates (95.0% versus control 67.8%), litter sizes (4.1 pups/litter versus control 2.7 pups/litter), and postnatal survival rates of offspring (96.84% versus control 81.24%) were significantly improved compared with their non-melatonin-treated counterparts. Mechanistic studies revealed that melatonin treatment upregulates gene expression of the antioxidant enzyme, superoxide dismutase (SOD), and the anti-apoptotic factor bcl-2 while downregulating the expression of pro-apoptotic genes p53 and caspase-3. Due to these changes, melatonin treatment reduces ROS production and cellular apoptosis during in vitro embryo development and improves the quality of blastocysts. The implantation of blastocysts with higher quality leads to more healthy offspring and increased pup survival.

Potency of melatonin in living beings

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

Melatonin mediates protective effects on inflammatory response induced by interleukin-1 beta in human mesenchymal stem cells

Joint diseases like osteoarthritis usually are accompanied with inflammatory processes, in which pro-inflammatory cytokines mediate the generation of intracellular reactive oxygen species (ROS) and compromise survival of subchondral osteoblasts. Melatonin is capable of manipulating bone formation and osteogenic differentiation of mesenchymal stem cells (MSCs). The aim of this work was to investigate the anti-inflammatory effect of melatonin on MSC proliferation and osteogenic differentiation in the absence or presence of interleukin-1 beta (IL-1β), which was used to induce inflammation. Our data showed that melatonin improved cell viability and reduced ROS generation in MSCs in a dose-dependent manner. When exposed to 10 ng/mL IL-1β, various concentrations of melatonin resulted in significant reduction of ROS by 34.9% averagely. Luzindole as a melatonin receptor antagonist reversed the anti-oxidant effect of melatonin in MSCs with co-exposure to IL-1β. Real-time RT-PCR data suggested that melatonin treatment up-regulated the expression of CuZnSOD and MnSOD, while down-regulated the expression of Bax. To investigate the effect of melatonin on osteogenesis, MSCs were cultured in osteogenic differentiation medium supplemented with IL-1β, melatonin, or luzindole. After exposed to IL-1β for 21 days, 1 μm melatonin treatment significantly increased the levels of type I collagen, ALP, and osteocalcin, and 100 μm melatonin treatment yielded the highest level of osteopontin. Our study demonstrated that melatonin maintained MSC survival and promoted osteogenic differentiation in inflammatory environment induced by IL-1β, suggesting melatonin treatment could be a promising method for bone regenerative engineering in future studies.

Molecular mechanisms of melatonin's inhibitory actions on breast cancers

Melatonin is involved in many physiological functions and it plays an important role in many pathological processes as well. Melatonin has been shown to reduce the incidence of experimentally induced cancers and can significantly inhibit the growth of some human tumors, namely hormone-dependent cancers. The anticancer effects of melatonin have been observed in breast cancer, both in in vivo with models of chemically induced rat mammary tumors, and in vitro studies on human breast cancer cell lines. Melatonin acts at different physiological levels and its antitumoral properties are supported by a set of complex, different mechanisms of action, involving apoptosis activation, inhibition of proliferation, and cell differentiation.

Peripheral reproductive organ health and melatonin: ready for prime time

Melatonin has a wide variety of beneficial actions at the level of the gonads and their adnexa. Some actions are mediated via its classic membrane melatonin receptors while others seem to be receptor-independent. This review summarizes many of the published reports which confirm that melatonin, which is produced in the ovary, aids in advancing follicular maturation and preserving the integrity of the ovum prior to and at the time of ovulation. Likewise, when ova are collected for in vitro fertilization-embryo transfer, treating them with melatonin improves implantation and pregnancy rates. Melatonin synthesis as well as its receptors have also been identified in the placenta. In this organ, melatonin seems to be of particular importance for the maintenance of the optimal turnover of cells in the villous trophoblast via its ability to regulate apoptosis. For male gametes, melatonin has also proven useful in protecting them from oxidative damage and preserving their viability. Incubation of ejaculated animal sperm improves their motility and prolongs their viability. For human sperm as well, melatonin is also a valuable agent for protecting them from free radical damage. In general, the direct actions of melatonin on the gonads and adnexa of mammals indicate it is an important agent for maintaining optimal reproductive physiology.

Protective effect of melatonin against Adriamycin-induced cardiotoxicity

The aim of this in vivo study was to explore the protective properties of melatonin against Adriamycin-induced myocardial toxicity. A rat model of breast cancer was established and the rats were randomly divided into the blank group (Blank), the solvent group [Diss; dehydrated alcohol: physiological saline (1:9)], the Adriamycin group (ADM), the melatonin group (MLT) and the melatonin + Adriamycin group (M+A). The concentrations of lipid peroxide (LPO), superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) in myocardial tissues were detected, the changes in myocardial tissues were observed using light microscopy and electron microscopy, and the 1-month survival rates of each group of rats were compared. Breast cancer was established in 116 rats. In the ADM group, the concentration of LPO was higher and the concentrations of SOD and GSH-Px were significantly lower than those in the blank group. In the M+A group, compared with the ADM group, the concentration of LPO was lower (P<0.05) and the concentrations of SOD and GSH-Px were higher (P<0.05). It was observed using light and electron microscopy that the myocardial injuries to the M+A group were significantly alleviated in comparison with those in the ADM group; the 1-month survival rate in the M+A group was higher than that in the ADM group. Melatonin may have a protective role in the myocardium by reducing Adriamycin-induced myocardial oxidative damage.

Roles of melatonin in fetal programming in compromised pregnancies

Compromised pregnancies such as those associated with gestational diabetes mellitus, intrauterine growth retardation, preeclampsia, maternal undernutrition, and maternal stress may negatively affect fetal development. Such pregnancies may induce oxidative stress to the fetus and alter fetal development through the epigenetic process that may affect development at a later stage. Melatonin is an oxidant scavenger that reverses oxidative stress during the prenatal period. Moreover, the role of melatonin in epigenetic modifications in the field of developmental programming has been studied extensively. Here, we describe the physiological function of melatonin in pregnancy and discuss the roles of melatonin in fetal programming in compromised pregnancies, focusing on its involvement in redox and epigenetic mechanisms.

Physiological crosstalk between melatonin and glucocorticoid receptor modulates T-cell mediated immune responses in a wild tropical rodent, Funambulus pennanti

Immunoenhancing attributes of melatonin (Mel) on the immunocompromised state induced by glucocorticoid is well known, but the involvement of their receptors in the modulation of immunity has never been studied in any rodent. The present study explores the role of Mel and its receptors (MT1 and MT2) in amelioration of immunocompromised state induced by a synthetic glucocorticoid, dexamethasone (Dex) in a tropical rodent Funambulus pennanti. Immune parameters viz. DTH response, Lymphocyte proliferation, cytokine (IL-2) and antibody production were assessed following pretreatment of Mel and Dex alone or in combination. Mel enhanced the IL-2 production, thymic and splenic lymphocyte proliferation thereby increasing T helper cell associated immune responses and anti-KLH-IgG production. MT1 and MT2 receptor expression was downregulated following Dex treatment while glucocorticoid receptors (GR) expression was downregulated in Mel treated groups suggesting that the immunomodulatory effects of glucocorticoids and Mel are mediated via their receptors. To gain further insights on the role of Mel receptors, we used nonselective melatonin receptor antagonist luzindole which resulted in reversal of most of the immunomodulatory actions of Mel. Therefore, it may be suggested that a physiological cross talk exist between Mel and GR which is of high adaptive significance in wild animals for balancing the immunity during ecologically stressful conditions.

Melatonin: a potent candidate in the regulation of fish oocyte growth and maturation

Recent studies on several fish species, especially carp, implicated pineal hormone melatonin (N-acetyl-5-methoxytryptamine) as a potent candidate in the regulatory mechanism of seasonal reproduction. Under natural conditions, the temporal pattern of serum melatonin varied with daily light-dark cycle and the reproductive status of the fish as well. Carefully controlled study revealed that exogenous administration of melatonin may result in stimulation or inhibition or no influences at all on the gonadal functions depending on the reproductive status of fish. Cross-talk between the melatonin and ovarian steroid has been evident from in vitro study, in which melatonin accelerated the action of 17α,20β-dihydroxy-4-pregnen-3-one or maturation inducing hormone (MIH) on meiotic cell cycle resumption in carp oocytes by formation of maturation promoting factor (MPF) - a complex of two proteins, cyclin B and cyclin dependant kinase Cdk1. While several lines of evidence suggest melatonin effects on hypothalamo-hypophyseal-gonadal axis, localization and dynamics of a 37-kDa melatonin receptor protein in carp oocytes argued in favor of extra-hypothalamic direct action of melatonin on fish reproduction. A recent study in carp indicated that influences of an identical regimen of photoperiods in different parts of annual cycle on ovarian functions vary in relation to the profiles of serum melatonin, but not to any rhythm parameters of MT1 or MT2 receptors on the gonad or brain. The purpose of this short review is to bring together the current knowledge on the biological effects of melatonin on fish reproduction mainly focusing the recent findings on carp.

Phenotypic changes caused by melatonin increased sensitivity of prostate cancer cells to cytokine-induced apoptosis

Melatonin has antiproliferative properties in prostate cancer cells. Melatonin reduces proliferation without increasing apoptosis, and it promotes cell differentiation into a neuroendocrine phenotype. Because neuroendocrine cells displayed an androgen-independent growth and high resistance to radiotherapy and chemotherapy, the role of molecules that induce neuroendocrine differentiation was questioned in terms of their usefulness as oncostatic agents. By using human epithelial androgen-dependent and androgen-independent prostate cancer cells, the role of melatonin in drug-induced apoptosis was studied after acute treatments. In addition to cytokines such as hrTNF-alpha and TRAIL, chemotherapeutic compounds, including doxorubicin, docetaxel, or etoposide, were employed in combination with melatonin to promote cell death. Melatonin promotes cell toxicity caused by cytokines without influencing the actions of chemotherapeutic agents. In addition, antioxidant properties of melatonin were confirmed in prostate cancer cells. However, its ability to increase cell death caused by cytokines was independent of the redox changes. Finally, phenotypic changes caused by chronic treatment with the indole, that is, neuroendocrine differentiation, make cells significantly more sensitive to cytokines and slightly more sensitive to some chemotherapeutic compounds. Thus, melatonin is a good inhibitor of the proliferation of prostate cancer cells, promoting phenotypic changes that do not increase survival mechanisms and make cells more sensitive to cytokines such as TNF-alpha or TRAIL.

Melatonin distribution reveals clues to its biological significance in basal metazoans

Although nearly ubiquitous in nature, the precise biological significance of endogenous melatonin is poorly understood in phylogenetically basal taxa. In the present work, we describe insights into the functional role of melatonin at the most “basal” level of metazoan evolution. Hitherto unknown morphological determinants of melatonin distribution were evaluated in Nematostella vectensis by detecting melatonin immunoreactivity and examining the spatial gene expression patterns of putative melatonin biosynthetic and receptor elements that are located at opposing ends of the melatonin signaling pathway. Immuno-melatonin profiling indicated an elaborate interaction with reproductive tissues, reinforcing previous conjectures of a melatonin-responsive component in anthozoan reproduction. In situ hybridization (ISH) to putative melatonin receptor elements highlighted the possibility that the bioregulatory effects of melatonin in anthozoan reproduction may be mediated by interactions with membrane receptors, as in higher vertebrates. Another intriguing finding of the present study pertains to the prevalence of melatonin in centralized nervous structures. This pattern may be of great significance given that it 1) identifies an ancestral association between melatonin and key neuronal components and 2) potentially implies that certain effects of melatonin in basal species may be spread widely by regionalized nerve centers.

Geographical distribution of adolescent body height with respect to effective day length in Japan: an ecological analysis

The height of Japanese youth raised in the northern region tends to be greater than that of youth raised in the southern region; therefore, a geographical gradient in youth body height exists. Although this gradient has existed for about 100 years, the reasons for it remain unclear. Consideration of the nutritional improvement, economic growth, and intense migration that has occurred in this period indicates that it is probably the result of environmental rather than nutritional or genetic factors. To identify possible environmental factors, ecological analysis of prefecture-level data on the body size of 8- to 17-year-old youth averaged over a 13-year period (1996 to 2008) and Japanese mesh climatic data on the climatic variables of temperature, solar radiation, and effective day length (duration of photoperiod exceeding the threshold of light intensity) was performed. The geographical distribution of the standardized height of Japanese adolescents was found to be inversely correlated to a great extent with the distribution of effective day length at a light intensity greater than 4000 lx. The results of multiple regression analysis of effective day length, temperature, and weight (as an index of food intake) indicated that a combination of effective day length and weight was statistically significant as predictors of height in early adolescence; however, only effective day length was statistically significant as a predictor of height in late adolescence. Day length may affect height by affecting the secretion of melatonin, a hormone that inhibits sexual and skeletal maturation, which in turn induces increases in height. By affecting melatonin production, regional differences in the duration of the photoperiod may lead to regional differences in height. Exposure to light intensity greater than 4000 lx appears to be the threshold at which light intensity begins to affect the melatonin secretion of humans who spend much of their time indoors.

Effects and side effects associated with the non-nutritional use of tryptophan by humans

The daily nutritional requirement for L-tryptophan (Trp) is modest (5 mg/kg). However, many adults choose to consume much more, up to 4-5 g/d (60-70 mg/kg), typically to improve mood or sleep. Ingesting L-Trp raises brain tryptophan levels and stimulates its conversion to serotonin in neurons, which is thought to mediate its actions. Are there side effects from Trp supplementation? Some consider drowsiness a side effect, but not those who use it to improve sleep. Though the literature is thin, occasional side effects, seen mainly at higher doses (70-200 mg/kg), include tremor, nausea, and dizziness, and may occur when Trp is taken alone or with a drug that enhances serotonin function (e.g., antidepressants). In rare cases, the "serotonin syndrome" occurs, the result of too much serotonin stimulation when Trp is combined with serotonin drugs. Symptoms include delirium, myoclonus, hyperthermia, and coma. In 1989 a new syndrome appeared, dubbed eosinophilia myalgia syndrome (EMS), and was quickly linked to supplemental Trp use. Key symptoms included debilitating myalgia (muscle pain) and a high peripheral eosinophil count. The cause was shown not to be Trp but a contaminant in certain production batches. This is not surprising, because side effects long associated with Trp use were not those associated with the EMS. Over 5 decades, Trp has been taken as a supplement and as an adjunct to medications with occasional modest, short-lived side effects. Still, the database is small and largely anecdotal. A thorough, dose-related assessment of side effects remains to be conducted.

Melatonin inhibits cell proliferation and induces caspase activation and apoptosis in human malignant lymphoid cell lines

Melatonin exerts strong anti-tumour activity via several mechanisms, including anti-proliferative and pro-apoptotic effects in addition to its potent antioxidant activity. Several studies have investigated the effects of melatonin on haematological malignancies. However, the previous studies investigating lymphoid malignancies have been largely restricted to a single type of malignancy, Burkitt's lymphoma (BL). Thus, we examined the actions of melatonin on the growth and apoptosis in a small panel of cell lines representing different human lymphoid malignancies including Ramos (Epstein-Barr virus-negative BL), SU-DHL-4 (diffuse large B cell lymphoma), DoHH2 (follicular B non-Hodgkin lymphoma) and JURKAT (acute T cell leukaemia). We showed that melatonin promotes cell cycle arrest and apoptosis in all these cells, although there was marked variations in responses among different cell lines (sensitivity; Ramos/DoHH2 > SU-DHL-4 > JURKAT). Melatonin-induced apoptosis was relatively rapid, with increased caspase 3 and PARP cleavage detected within 0.5-1 h following melatonin addition. Moreover, there was evidence for rapid processing of both caspase 9, as well as a breakdown of the mitochondrial inner transmembrane potential. On the contrary, caspase activation was detected only in SU-DHL-4 and Ramos cells following melatonin treatment suggesting that the extrinsic pathway does not make a consistent contribution to melatonin-induced apoptosis in malignant lymphocytes. Although all cell lines expressed the high-affinity melatonin receptors, MT1 and MT2, melatonin-induced caspase activation appeared to be independent these receptors. Our findings confirm that melatonin could be a potential chemotherapeutic/preventive agent for malignant lymphocytes. However, it is necessary to take into account that different lymphoid malignancies may differ in their response to melatonin.

Temporal and histological evaluation of melatonin patterns in a 'basal' metazoan

While recent advances suggest functional pleiotropy of melatonin in higher organisms, an understanding of the biological significance of this ancient molecule in early evolutionary groups is lacking. Here, endogenous melatonin production was identified for the first time in the sea anemone Actinia equina, a nonsymbiotic hexacorallian cnidarian. Day/night activity profiles of melatonin in this anemone indicated that melatonin levels oscillate with significant nocturnal peaks. However, dynamic changes in melatonin concentration did not persist under constant dark conditions and therefore were not circadian in nature. Thus, the oscillating pattern of melatonin in A. equina is presumed to be the result of alternative, simpler melatonin control mechanism that likely involves direct regulation by the daily photocycle. As nocturnal melatonin signals still potentially provide 'time-of-day' information and can illustrate the seasonally changing length of the biological night, we hypothesize that melatonin may be relevant to temporal coordination of timed processes also in anthozoans. Spatial patterns of melatonin distribution found in this study indicate abundant melatonin distribution in the endodermal filaments wrapped around gametes. This finding supports the possibility that one of the melatonin-responsive processes in this basal metazoan species may involve reproductive functions.

Melatonin supplementation decreases prolactin synthesis and release in rat adenohypophysis: correlation with anterior pituitary redox state and circadian clock mechanisms

In the laboratory rat, a number of physiological parameters display seasonal changes even under constant conditions of temperature, lighting, and food availability. Since there is evidence that prolactin (PRL) is, among the endocrine signals, a major mediator of seasonal adaptations, the authors aimed to examine whether melatonin administration in drinking water resembling in length the exposure to a winter photoperiod could affect accordingly the 24-h pattern of PRL synthesis and release and some of their anterior pituitary redox state and circadian clock modulatory mechanisms. Melatonin (3 µg/mL drinking water) or vehicle was given for 1 mo, and rats were euthanized at six time intervals during a 24-h cycle. High concentrations of melatonin (>2000 pg/mL) were detected in melatonin-treated rats from beginning of scotophase (at 21:00 h) to early photophase (at 09:00 h) as compared with a considerably narrower high-melatonin phase observed in controls. By cosinor analysis, melatonin-treated rats had significantly decreased MESOR (24-h time-series average) values of anterior pituitary PRL gene expression and circulating PRL, with acrophases (peak time) located in the middle of the scotophase, as in the control group. Melatonin treatment disrupted the 24-h pattern of anterior pituitary gene expression of nitric oxide synthase (NOS)-1 and -2, heme oxygenase-1 and -2, glutathione peroxidase, glutathione reductase, Cu/Zn- and Mn-superoxide dismutase, and catalase by shifting their acrophases to early/middle scotophase or amplifying the maxima. Only the inhibitory effect of melatonin on pituitary NOS-2 gene expression correlated temporally with inhibition of PRL production. Gene expression of metallothionein-1 and -3 showed maxima at early/middle photophase after melatonin treatment. The 24-h pattern of anterior pituitary lipid peroxidation did not vary after treatment. In vehicle-treated rats, Clock and Bmal1 expression peaked in the anterior pituitary at middle scotophase, whereas that of Per1 and Per2 and of Cry1 and Cry2 peaked at the middle and late photophase, respectively. Treatment with melatonin raised mean expression of anterior pituitary Per2, Cry1, and Cry2. In the case of Per1, decreased MESOR was observed, although the single significant difference found between the experimental groups when analyzed at individual time intervals was increase at early scotophase in the anterior pituitary of melatonin-treated rats. Melatonin significantly phase-delayed expression of Per1, Per2, and Cry1, also phase-delayed the plasma corticosterone circadian rhythm, and increased the amplitude of plasma corticosterone and thyrotropin rhythms. The results indicate that under prolonged duration of a daily melatonin signal, rat anterior pituitary PRL synthesis and release are depressed, together with significant changes in the redox and circadian mechanisms controlling them.

Melatonin osteoporosis prevention study (MOPS): a randomized, double-blind, placebo-controlled study examining the effects of melatonin on bone health and quality of life in perimenopausal women

The purpose of this double-blind study was to assess the effects of nightly melatonin supplementation on bone health and quality of life in perimenopausal women. A total of 18 women (ages 45-54) were randomized to receive melatonin (3mg, p.o., n=13) or placebo (n=5) nightly for 6months. Bone density was measured by calcaneal ultrasound. Bone turnover marker (osteocalcin, OC for bone formation and NTX for bone resorption) levels were measured bimonthly in serum. Participants completed Menopause-Specific Quality of Life-Intervention (MENQOL) and Pittsburgh Sleep Quality Index (PSQI) questionnaires before and after treatment. Subjects also kept daily diaries recording menstrual cycling, well-being, and sleep patterns. The results from this study showed no significant change (6-month-baseline) in bone density, NTX, or OC between groups; however, the ratio of NTX:OC trended downward over time toward a ratio of 1:1 in the melatonin group. Melatonin had no effect on vasomotor, psychosocial, or sexual MENQOL domain scores; however, it did improve physical domain scores compared to placebo (mean change melatonin: -0.6 versus placebo: 0.1, P<0.05). Menstrual cycling was reduced in women taking melatonin (mean cycles melatonin: 4.3 versus placebo: 6.5, P<0.05), and days between cycles were longer (mean days melatonin: 51.2 versus placebo: 24.1, P<0.05). No differences in duration of menses occurred between groups. The overall PSQI score and average number of hours slept were similar between groups. These findings show that melatonin supplementation was well tolerated, improved physical symptoms associated with perimenopause, and may restore imbalances in bone remodeling to prevent bone loss. Further investigation is warranted.

Beneficial actions of melatonin in the management of viral infections: a new use for this "molecular handyman"?

Melatonin (N‐acetyl‐5‐methoxytryptamine) is a multifunctional signaling molecule that has a variety of important functions. Numerous clinical trials have examined the therapeutic usefulness of melatonin in different fields of medicine. Clinical trials have shown that melatonin is efficient in preventing cell damage under acute (sepsis, asphyxia in newborns) and chronic states (metabolic and neurodegenerative diseases, cancer, inflammation, aging). The beneficial effects of melatonin can be explained by its properties as a potent antioxidant and antioxidant enzyme inducer, a regulator of apoptosis and a stimulator of immune functions. These effects support the use of melatonin in viral infections, which are often associated with inflammatory injury and increases in oxidative stress. In fact, melatonin has been used recently to treat several viral infections, which are summarized in this review. The role of melatonin in infections is also discussed herein. Copyright © 2012 John Wiley & Sons, Ltd.

Melatonin, the circadian multioscillator system and health: the need for detailed analyses of peripheral melatonin signaling

Evidence is accumulating regarding the importance of circadian core oscillators, several associated factors, and melatonin signaling in the maintenance of health. Dysfunction of endogenous clocks, melatonin receptor polymorphisms, age- and disease-associated declines of melatonin likely contribute to numerous diseases including cancer, metabolic syndrome, diabetes type 2, hypertension, and several mood and cognitive disorders. Consequences of gene silencing, overexpression, gene polymorphisms, and deviant expression levels in diseases are summarized. The circadian system is a complex network of central and peripheral oscillators, some of them being relatively independent of the pacemaker, the suprachiasmatic nucleus. Actions of melatonin on peripheral oscillators are poorly understood. Various lines of evidence indicate that these clocks are also influenced or phase-reset by melatonin. This includes phase differences of core oscillator gene expression under impaired melatonin signaling, effects of melatonin and melatonin receptor knockouts on oscillator mRNAs or proteins. Cross-connections between melatonin signaling pathways and oscillator proteins, including associated factors, are discussed in this review. The high complexity of the multioscillator system comprises alternate or parallel oscillators based on orthologs and paralogs of the core components and a high number of associated factors with varying tissue-specific importance, which offers numerous possibilities for interactions with melatonin. It is an aim of this review to stimulate research on melatonin signaling in peripheral tissues. This should not be restricted to primary signal molecules but rather include various secondarily connected pathways and discriminate between direct effects of the pineal indoleamine at the target organ and others mediated by modulation of oscillators.

Melatonin synergistically enhances cisplatin-induced apoptosis via the dephosphorylation of ERK/p90 ribosomal S6 kinase/heat shock protein 27 in SK-OV-3 cells

To evaluate melatonin's ability to enhance ovarian cancer cells to cisplatin treatment for ovarian cancer, this study was performed. Melatonin by itself had no significant cytotoxicity against SK-OV-3 cells, while cisplatin suppressed the cell viability in a dose-dependent manner. Combined treatment with cisplatin and melatonin synergistically inhibited the viability of SK-OV-3 cells with the synergism between two drugs (1 > combination index). In contrast, melatonin revealed the protective effect against cisplatin-induced cytotoxicity in OSEN normal ovarian epithelial cells. Cotreatment with cisplatin and melatonin increased the sub-G1 DNA contents and TdT-mediated dUTP nick end-labeling (TUNEL)-positive cells compared with cisplatin control in SK-OV-3 cells, suggesting that melatonin augments cisplatin-induced apoptosis. Consistently, combined treatment of cisplatin and melatonin increased the cleavage of caspase-3 and poly-(ADP-ribose) polymerase (PARP). Importantly, melatonin synergistically inhibited the phosphorylation of extracellular signal-regulated kinase (ERK) along with dephosphorylation of 90-kDa ribosomal S6 kinase (p90RSK) and heat shock protein 27 (HSP27) induced by cisplatin. Furthermore, melatonin remarkably blocked the expression and colocalization of p90RSK and HSP27 by combination treatment with cisplatin. Taken together, our findings demonstrate that melatonin enhances cisplatin-induced apoptosis via the inactivation of ERK/p90RSK/HSP27 cascade in SK-OV-3 cells as a potent synergist to cisplatin treatment.

Alzheimer's disease: pathological mechanisms and the beneficial role of melatonin

Alzheimer's disease (AD) is a highly complex neurodegenerative disorder of the aged that has multiple factors which contribute to its etiology in terms of initiation and progression. This review summarizes these diverse aspects of this form of dementia. Several hypotheses, often with overlapping features, have been formulated to explain this debilitating condition. Perhaps the best-known hypothesis to explain AD is that which involves the role of the accumulation of amyloid-β peptide in the brain. Other theories that have been invoked to explain AD and summarized in this review include the cholinergic hypothesis, the role of neuroinflammation, the calcium hypothesis, the insulin resistance hypothesis, and the association of AD with peroxidation of brain lipids. In addition to summarizing each of the theories that have been used to explain the structural neural changes and the pathophysiology of AD, the potential role of melatonin in influencing each of the theoretical processes involved is discussed. Melatonin is an endogenously produced and multifunctioning molecule that could theoretically intervene at any of a number of sites to abate the changes associated with the development of AD. Production of this indoleamine diminishes with increasing age, coincident with the onset of AD. In addition to its potent antioxidant and anti-inflammatory activities, melatonin has a multitude of other functions that could assist in explaining each of the hypotheses summarized above. The intent of this review is to stimulate interest in melatonin as a potentially useful agent in attenuating and/or delaying AD.

The role of melatonin as an antioxidant in the follicle

Melatonin (N-acetyl-5-methoxytryptamine) is secreted during the dark hours at night by pineal gland, and it regulates a variety of important central and peripheral actions related to circadian rhythms and reproduction. It has been believed that melatonin regulates ovarian function by the regulation of gonadotropin release in the hypothalamus-pituitary gland axis via its specific receptors. In addition to the receptor mediated action, the discovery of melatonin as a direct free radical scavenger has greatly broadened the understanding of melatonin's mechanisms which benefit reproductive physiology. Higher concentrations of melatonin have been found in human preovulatory follicular fluid compared to serum, and there is growing evidence of the direct effects of melatonin on ovarian function especially oocyte maturation and embryo development. Many scientists have focused on the direct role of melatonin on oocyte maturation and embryo development as an anti-oxidant to reduce oxidative stress induced by reactive oxygen species, which are produced during ovulation process. The beneficial effects of melatonin administration on oocyte maturation and embryo development have been confirmed by in vitro and in vivo experiments in animals. This review also discusses the first application of melatonin to the clinical treatment of infertile women and confirms that melatonin administration reduces intrafollicular oxidative damage and increase fertilization rates. This review summarizes our recent works and new findings related to the reported beneficial effects of melatonin on reproductive physiology in its role as a reducer of oxidative stress, especially on oocyte maturation and embryo development.

Melatonin: the smart killer: the human trophoblast as a model

Melatonin has both the ability to induce intrinsic apoptosis in tumor cells while it inhibits it in non-tumor cells. Melatonin kills tumor cells through induction of reactive oxygen species generation and activation of pro-apoptotic pathways. In contrast, melatonin promotes the survival of non-tumor cells due to its antioxidant properties and the inhibition of pro-apoptotic pathways. In primary human villous trophoblast, a known pseudo-tumorigenic tissue, melatonin promotes the survival through inhibition of the Bax/Bcl-2 pathway while in BeWo choriocarcinoma cell line melatonin induces permeabilization of the mitochondrial membrane leading to cellular death. These findings suggest that the trophoblast is a good model to study the differential effects of melatonin on the intrinsic apoptosis pathway. This review describes the differential effects of melatonin on the intrinsic apoptosis pathway in tumor and non-tumor cells and presents the trophoblast as a novel model system in which to study these effects of melatonin.

Follicular fluid supplementation during in vitro maturation promotes sperm penetration in bovine oocytes by enhancing cumulus expansion and increasing mitochondrial activity in oocytes

The aim of this study was to examine the effects of bovine follicular fluid (bFF) on mitochondrial activity in in vitro-matured (IVM) oocytes and to assess its importance for fertilisation and embryo development. Bovine follicular oocytes were subjected to IVM in medium supplemented either with polyvinylpyrrolidone, bovine serum albumin, calf serum or bFF. Nuclear maturation, cumulus expansion, mitochondrial distribution and ATP content in oocytes were compared between groups along with subsequent in vitro fertilisation (IVF) and embryo development. Compared with other supplements, bFF generated significantly enhanced re-distribution of active mitochondria in oocytes and this effect was associated with elevated intracellular ATP content. Furthermore, bFF significantly improved cumulus expansion, which was associated with improved fertilisation rates when cumulus-enclosed oocytes were subjected to IVF; however, its promoting effect was neutralised when denuded oocytes were inseminated. Elevating ATP content in oocytes by bFF did not affect maturation or embryo development but promoted fertilisation when mitochondrial electron transport was blocked in oocytes before IVF by Rotenone. In conclusion, supplementation of IVM medium with bFF promotes sperm penetration both by the improvement of cumulus expansion and by enhancing ATP levels in oocytes, which maintains their ability to be fertilised after mitochondrial stress.

Melatonin inhibits insulin secretion in rat insulinoma β-cells (INS-1) heterologously expressing the human melatonin receptor isoform MT2

Melatonin exerts some of its effects via G-protein-coupled membrane receptors. Two membrane receptor isoforms, MT1 and MT2, have been described. The MT1 receptor is known to inhibit second messenger cyclic adenosine monophosphate (cAMP) signaling through receptor-coupling to inhibitory G-proteins (G(i) ). Much less is known about the MT2 receptor, but it has also been implicated in signaling via G(i) -proteins. In rat pancreatic β-cells, it has recently been reported that the MT2 receptor plays an inhibitory role in the cyclic guanosine monophosphate (cGMP) pathway. This study addresses the signaling features of the constitutively expressed human recombinant MT2 receptor (hMT2) and its impact on insulin secretion, using a rat insulinoma β-cell line (INS-1). On the basis of a specific radioimmunoassay, insulin secretion was found to be more strongly reduced in the clones expressing hMT2 than in INS-1 controls, when incubated with 1 or 100 nm melatonin. Similarly, cAMP and cGMP levels, measured by specific enzyme-linked immunosorbent assays (ELISAs), were reduced to a greater extent in hMT2 clones after melatonin treatment. In hMT2-expressing cells, the inhibitory effect of melatonin on insulin secretion was blocked by pretreatment with pertussis toxin, demonstrating the coupling of the hMT2 to G(i) -proteins. These results indicate that functional hMT2 expression leads to the inhibition of cyclic nucleotide signaling and a reduction in insulin release. Because genetic variants of the hMT2 receptor are considered to be risk factors in the development of type 2 diabetes, our results are potentially significant in explaining and preventing the pathogenesis of this disease.

Effect of combined lignan phytoestrogen and melatonin treatment on secretion of steroid hormones by adrenal carcinoma cells

OBJECTIVE

To investigate the in vitro effect of the combination of lignan enterolactone (ENL) or lignan enterodiol (END) with melatonin on steroid hormone secretion and cellular aromatase content in human adrenal carcinoma cells.

SAMPLE

Human adrenocortical carcinoma cells.

PROCEDURES

Melatonin plus ENL or END was added to cell culture medium along with cAMP (100μM); control cells received cAMP alone. Medium and cell lysates were collected after 24 and 48 hours of cultivation. Samples of medium were analyzed for progesterone, 17-hydroxyprogesterone, androstenedione, aldosterone, estradiol, and cortisol concentration by use of radioimmunoassays. Cell lysates were used for western blot analysis of aromatase content.

RESULTS

The addition of ENL or END with melatonin to cAMP-stimulated cells (treated cells) resulted in significant decreases in estradiol, androstenedione, and cortisol concentrations at 24 and 48 hours, compared with concentrations in cells stimulated with cAMP alone (cAMP control cells). The addition of these compounds to cAMP-stimulated cells also resulted in higher progesterone and 17-hydroxyprogesterone concentrations than in cAMP control cells; aldosterone concentration was not affected by treatments. Compared with the content in cAMP control cells, aromatase content in treated cells was significantly lower.

CONCLUSIONS AND CLINICAL RELEVANCE

The combination of lignan and melatonin affected steroid hormone secretion by acting directly on adrenal tumor cells. Results supported the concept that this combination may yield similar effects on steroid hormone secretion by the adrenal glands in dogs with typical and atypical hyperadrenocorticism.

Melatonin promotes osteoblastic differentiation through the BMP/ERK/Wnt signaling pathways

Although melatonin has a variety of biological actions such as antitumor, antiangiogenic, and antioxidant activities, the osteogenic mechanism of melatonin still remains unclear. Thus, in the present study, the molecular mechanism of melatonin was elucidated in the differentiation of mouse osteoblastic MC3T3-E1 cells. Melatonin enhanced osteoblastic differentiation and mineralization compared to untreated controls in preosteoblastic MC3T3-E1 cells. Also, melatonin increased wound healing and dose-dependently activated osteogenesis markers such as runt-related transcription factor 2 (Runx2), osteocalcin (OCN), bone morphogenic protein (BMP)-2 and -4 in MC3T3-E1 cells. Of note, melatonin activated Wnt 5 α/β, β-catenin and the phosphorylation of c-Jun N-terminal kinase (JNK), and extracellular signal-regulated kinase (ERK) in a time-dependent manner while it attenuated phosphorylation of glycogen synthase kinase 3 beta (GSK-3β) in MC3T3-E1 cells. Consistently, confocal microscope observation revealed that BMP inhibitor Noggin blocked melatonin-induced nuclear localization of β-catenin. Furthermore, Western blotting showed that Noggin reversed activation of β-catenin and Wnt5 α/β and suppression of GSK-3β induced by melatonin in MC3T3-E1 cells, which was similarly induced by ERK inhibitor PD98059. Overall, these findings demonstrate that melatonin promotes osteoblastic differentiation and mineralization in MC3T3-E1 cells via the BMP/ERK/Wnt pathways.

Melatonin reduces lipid peroxidation and apoptotic-like changes in stallion spermatozoa

Lipid peroxidation (LPO) has been claimed as a major factor involved in stallion damage during storage or cryopreservation. Because melatonin is a well-known potent antioxidant, the aim of the present study was to investigate the effect of melatonin during in vitro incubation. Furthermore, we investigated the presence of specific melatonin receptors (MT1 and MT2) using specific polyclonal antibodies and western blotting. Stallion spermatozoa were incubated up to 3 hr at 37°C in the presence of different concentrations of melatonin (0, 50 pm, 100 pm, 200 pm, or 1 μm). At the beginning and at the end of the incubation period, sperm motility (using computer-assisted sperm analysis), membrane integrity and permeability, fluidity of the sperm membrane, LPO, and mitochondrial membrane potential (Δψm) were flow cytometrically evaluated. Melatonin reduced changes in the spermatozoa related to apoptosis (increased sperm membrane permeability and lowered Δψm) (P < 0.05). Furthermore, LPO was dramatically reduced (P < 0.01) while no effect was observed on sperm motility or kinematics. Interestingly, melatonin helped maintain a more fluid sperm plasmalemma (P < 0.05). Our results clearly show the absence of MT1 and MT2 receptors in the stallion spermatozoa. It is concluded that melatonin is a useful tool to improve the quality of stored stallion sperm, increasing their life span and reducing premature aging, this likely relates to melatonin's antioxidant properties.

Protective effect of melatonin against human leukocyte apoptosis induced by intracellular calcium overload: relation with its antioxidant actions

Apoptosis or programmed cell death plays a critical role in both inflammatory and immune responses. Recent evidence demonstrates that control of leukocyte apoptosis is one of the most striking immune system-related roles of melatonin. For this reason, this study evaluated the protective effects of melatonin on human leukocyte apoptosis induced by sustained cytosolic calcium increases. Such protective effects are likely mediated by melatonin's free-radical scavenging actions. Treatments with the specific inhibitor of cytosolic calcium re-uptake, thapsigargin (TG), and/or the calcium-mobilizing agonist, N-formyl-methionyl-leucyl-phenylalanine (FMLP), induced intracellular reactive oxygen species (ROS) production, caspase activation as well as DNA fragmentation in human leukocytes. Also, TG- and/or FMLP-induced apoptosis was dependent on both cytosolic calcium increases and calcium uptake into mitochondria, because when cells were preincubated with the cytosolic calcium chelator, dimethyl BAPTA, and the inhibitor of mitochondrial calcium uptake, Ru360, TG- and FMLP-induced apoptosis was largely inhibited. Importantly, melatonin treatment substantially prevented intracellular ROS production, reversed caspase activation, and forestalled DNA fragmentation induced by TG and FMLP. Similar results were obtained by preincubating the cells with another well-known antioxidant, i.e., N-acetyl-L-cysteine. To sum up, depletion of intracellular calcium stores induced by TG and/or FMLP triggers different apoptotic events in human leukocytes that are dependent on calcium signaling. The protective effects resulting from melatonin administration on leukocyte apoptosis likely depend on melatonin's antioxidant action because we proved that this protection is melatonin receptor independent. These findings help to understand how melatonin controls apoptosis in cells of immune/inflammatory relevance.