Melatonin seems to be a mediator that transfers the environmental stimuli to oocytes for inheritance of adaptive changes through epigenetic inheritance system

Toxicology of Blister Agents: Is Melatonin a Potential Therapeutic Option?

Blister or vesicant chemical warfare agents (CWAs) have been widely used in different military conflicts, including World War I and the Iran-Iraq War. However, their mechanism of action is not fully understood. Sulfur and nitrogen mustard exert toxic effects not only through the alkylation of thiol-bearing macromolecules, such as DNA and proteins, but also produce free radicals that can develop direct toxic effects in target organs such as the eyes, skin, and respiratory system. The lack of effective treatments against vesicant CWAs-induced injury makes us consider, in this complex scenario, the use and development of melatonin-based therapeutic strategies. This multifunctional indoleamine could facilitate neutralization of the oxidative stress, modulate the inflammatory response, and prevent the DNA damage, as well as the long-term health consequences mediated by vesicant CWAs-induced epigenetic mechanisms. In this context, it would be essential to develop new galenic formulations for the use of orally and/or topically applied melatonin for the prophylaxis against vesicant CWAs, as well as the development of post-exposure treatments in the near future.

Therapeutic targets of cancer drugs: Modulation by melatonin

The biological functions of melatonin range beyond the regulation of the circadian rhythm. With regard to cancer, melatonin's potential to suppress cancer initiation, progression, angiogenesis and metastasis as well as sensitizing malignant cells to conventional chemo- and radiotherapy are among its most interesting effects. The targets at which melatonin initiates its anti-cancer effects are in common with those of a majority of existing anti-cancer agents, giving rise to the notion that this molecule is a pleiotropic agent sharing many features with other antineoplastic drugs in terms of their mechanisms of action. Among these common mechanisms of action are the regulation of several major intracellular pathways including mitogen-activated protein kinase (MAPK), extracellular signal-regulated kinase (ERK) and protein kinase B (AKT/PKB) signaling. The important mediators affected by melatonin include cyclins, nuclear factor-κB (NF-κB), heat shock proteins (HSPs) and c-Myc, all of which can serve as potential targets for cancer drugs. Melatonin also exerts some of its anti-cancer effects via inducing epigenetic modifications, DNA damage and mitochondrial disruption in malignant cells. The regulation of these mediators by melatonin mitigates tumor growth and invasiveness via modulating their downstream responsive genes, housekeeping enzymes, telomerase reverse transcriptase, apoptotic gene expression, angiogenic factors and structural proteins involved in metastasis. Increasing our knowledge on how melatonin affects its target sites will help find ways of exploiting the beneficial effects of this ubiquitously-acting molecule in cancer therapy. Acknowledging this, here we reviewed the most studied target pathways attributed to the anti-cancer effects of melatonin, highlighting their therapeutic potential.

Advances in Characterizing Recently-Identified Molecular Actions of Melatonin: Clinical Implications

Melatonin, N-acetyl-5-methoxy-tryptamine, was discovered to be a product of serotonin metabolism in the mammalian pineal gland where its synthesis is under control of the light:dark cycle. Besides its regulatory pathway involving ganglion cells in the retina, the neural connections between the eyes and the pineal gland include the master circadian clock, the suprachiasmatic nuclei, and the central and peripheral nervous systems. Since pineal melatonin is released into the blood and into the cerebrospinal fluid, it has access to every cell in an organism and it mediates system-wide effects. Subsequently, melatonin was found in several extrapineal organs and, more recently, perhaps in every cell of every organ. In contrast to the pinealocytes, non-pineal cells do not discharge melatonin into the blood; rather it is used locally in an intracrine, autocrine, or paracrine manner. Melatonin levels in non-pineal cells do not exhibit a circadian rhythm and do not depend on circulating melatonin concentrations although when animals are treated with exogenous melatonin it is taken up by presumably all cells. Mitochondria are the presumed site of melatonin synthesis in all cells; the enzymatic machinery for melatonin synthesis has been identified in mitochondria. The association of melatonin with mitochondria, because of its ability to inhibit oxidative stress, is very fortuitous since these organelles are a major site of damaging reactive oxygen species generation. In this review, some of the actions of non-pineal-derived melatonin are discussed in terms of cellular and subcellular physiology.

Nucleic acid methylation and orofacial morphogenesis

In this review, we highlight the current state of knowledge of the diverse roles nucleic acid methylation plays in the embryonic development of the orofacial region and how aberrant methylation may contribute to orofacial clefts. We also consider the role of methylation in the regulation of neural crest cell function as it pertains to orofacial ontogeny. Changes in DNA methylation, as a consequence of environmental effects, have been observed in the regulatory regions of several genes, potentially identifying new candidate genes for orofacial clefting and opening promising new avenues for further research. While the focus of this review is primarily on the nonsyndromic forms of orofacial clefting, syndromic forms are briefly discussed in the context of aberrant nucleic acid methylation.

Melatonin-induced demethylation of antioxidant genes increases antioxidant capacity through RORα in cumulus cells of prepubertal lambs

Physical damage and oxidative stress may occur in prepubertal cumulus cells, due to insufficient glutathione synthesis. To determine potential epigenetic mechanisms related to antioxidant effects of melatonin on ovine prepubertal cumulus cells, 30 lambs, 4-wk-old were randomly allocated into two groups: a control (C, n = 20) group and a melatonin (M, n = 10) group given a subcutaneous implant containing 18 mg melatonin. All lambs were superovulated (250 IU FSH and 250 IU eCG). Cumulus cells from germinal vesicle stage cumulus oocyte complexes (COCs) were collected by ovarian follicular aspiration and dissociated with hyaluronidase. Compared to the C group, the M group had greater superovulation, better antioxidant capacity, a higher proportion of fully expanded COCs and a lower proportion of apoptotic cumulus cells (P < 0.05). Melatonin up-regulated mRNA expression of genes for melatonin receptors MT1 and nuclear binding site RORα, antioxidants (SOD1, GPx4 and CAT) and cumulus cell expansion (PTX3, HAS2 and PTGS2), as well as Bcl2, but down-regulated expression of Bax (P < 0.05). Regarding epigenetics, there were less methylation at five CpG sites of SOD1, three CpG sites of GPx4 and two CpG sites of CAT in M versus C groups (P <  0.05), leading to lower total methylation of SOD1, GPx4 and CAT promoters region on M group (P < 0.05). In a mechanistic study, addition of MT1 or RORα antagonist increased ROS and MDA concentrations, but decreased T-AOC, GPx, CAT and T-SOD concentrations (P < 0.05), whereas there were no significant difference between the melatonin and MT2 antagonist treatment groups for T-AOC, GPx, CAT and T-SOD concentrations. Furthermore, addition of RORα agonist decreased total DNA methylation of SOD1, GPx4 and CAT, with no significant difference after MT1 agonist treatment. These studies provided new information regarding epigenetic mechanisms by which melatonin promoted ovine prepubertal cumulus cells antioxidant through RORα, both in vitro and in vivo.

Updated View on the Relation of the Pineal Gland to Autism Spectrum Disorders

Identification of the biological features of autism is essential for designing an efficient treatment and for prevention of the disorder. Though the subject of extensive research, the neurophysiological features of autism remain unclear. One of the proposed biological causes of autism is malfunction of the pineal gland and deficiency of its principal hormone, melatonin. The main function of melatonin is to link and synchronize the body's homeostasis processes to the circadian and seasonal rhythms, and to regulate the sleep-wake cycle. Therefore, pineal dysfunction has been implicated based on the common observation of low melatonin levels and sleep disorders associated with autism. In this perspective, we highlight several recent findings that support the hypothesis of pineal gland/melatonin involvement in autism. Another common symptom of autism is abnormal neuroplasticity, such as cortical overgrowth and dendritic spine dysgenesis. Here, we synthesize recent information and speculate on the possibility that this abnormal neuroplasticity is caused by hyperactivity of endogenous N,N-dimethyltryptamine (DMT). The pineal gland was proposed as the source of DMT in the brain and therefore, our assumption is that besides melatonin deficiency, pineal dysfunction might also play a part in the development of autism through abnormal metabolism of DMT. We hope that this manuscript will encourage future research of the DMT hypothesis and reexamination of several observations that were previously attributed to other factors, to see if they could be related to pineal gland/melatonin malfunction. Such research could contribute to the development of autism treatment by exogenous melatonin and monitored light exposure.

From Implantation to Birth: Insight into Molecular Melatonin Functions

Melatonin is a lipophilic hormone synthesized and secreted mainly in the pineal gland, acting as a neuroendocrine transducer of photoperiodic information during the night. In addition to this activity, melatonin has shown an antioxidant function and a key role as regulator of physiological processes related to human reproduction. Melatonin is involved in the normal outcome of pregnancy, beginning with the oocyte quality, continuing with embryo implantation, and finishing with fetal development and parturition. Melatonin has been shown to act directly on several reproductive events, including folliculogenesis, oocyte maturation, and corpus luteum (CL) formation. The molecular mechanism of action has been investigated through several studies which provide solid evidence on the connections between maternal melatonin secretion and embryonic and fetal development. Melatonin administration, reducing oxidative stress and directly acting on its membrane receptors, melatonin thyroid hormone receptors (MT1 and MT2), displays effects on the earliest phases of pregnancy and during the whole gestational period. In addition, considering the reported positive effects on the outcomes of compromised pregnancies, melatonin supplementation should be considered as an important tool for supporting fetal development, opening new opportunities for the management of several reproductive and gestational pathologies.

Melatonin, adolescence, and the brain: An insight into the period-specific influences of a multifunctional signaling molecule

Melatonin is a neurohormone that is involved in the modulation of a wide range of physiological processes, including maintenance of the circadian rhythm, mediation of photoperiodic information, regulation of the sleep-wake cycle, synchronization of cell physiology, antioxidant defense, and immune-modulation. Although there are reports of increasing use of melatonin in the management of a number of health conditions, evidence exists that is suggestive of deleterious effects of melatonin administration on brain and reproductive development in the prepubertal and pubertal periods that are within the teenage years. In this review, we examine the influences of endogenous and exogenous melatonin on the adolescent brain, with specific reference to its involvement in the evolution of brain functions, brain structure, sleep regulation, and modulation of behaviors in health or disease.

Melatonin protects against defects induced by deoxynivalenol during mouse oocyte maturation

Deoxynivalenol (DON) is one of the most prevalent fusarium mycotoxins in feedstuff and food. DON causes detrimental effects on human and animal reproductive systems by inducing oxidative stress and apoptosis. However, melatonin is a multifunctional endogenous hormone that plays crucial roles in the development of animal germ cells and embryos as a robust deoxidizer. In this study, we explored the effects of melatonin on the DON exposure mouse oocytes. Our in vitro and in vivo results showed that DON adversely affected mouse oocyte maturation and early embryo cleavage, while melatonin administration ameliorated the toxic effects of DON. DON exposure disrupted the meiotic spindle formation and kinetochore-microtubule attachment, which induced aneuploidy in oocytes. This might be through DON effects on the acetylated tubulin level. Moreover, we found that DON exposure caused the alteration of DNA and histone methylation level, which might affect early embryo cleavage. The toxic effects of DON on oocytes might be through its induction of oxidative stress-mediated early apoptosis, while the treatment with melatonin significantly ameliorated these phenotypes in DON-exposed mouse oocytes. Collectively, our results indicated the protection effects of melatonin against defects induced by DON during mouse oocyte meiotic maturation.

Behavioral and molecular effects of prenatal continuous light exposure in the adult rat

Disruption of the maternal environment during pregnancy leads to behavioral changes and diseases in the adult offspring. To explore the influence of prenatal continuous light exposure (PCLE) on the adult offspring, we exposed pregnant Wistar rats to constant light during late gestation. Adult PCLE offspring showed an anxiety-like behavior and impairment of short-term memory in different tests. Measurements in the whole brain homogenates from newborn and adult offspring indicated decreased melatonin and serotonin levels and increased reactive oxygen species level in PCLE offspring. Further, we determined melatonin-, serotonin-, oxidative stress-, apoptosis-, and circadian system-related genes expression in different brain areas of adult offspring. The serotonin reuptaker Slc6a4 displayed a decreased expression in the prefrontal cortex of PCLE group. The circadian rhythm-related gene Rora was upregulated in the amygdala of PCLE offspring. Our results point to adverse behavioral effects of PCLE on adult offspring, involving serotonin and melatonin signaling dysregulation, increased chronic oxidative stress, and altered gene expression.

Daily differential expression of melatonin-related genes and clock genes in rat cumulus-oocyte complex: changes after pinealectomy

This study investigated the maturational stage (immature and mature ovaries) differences of mRNA expression of melatonin-forming enzymes (Aanat and Asmt), melatonin membrane receptors (Mt1 and Mt2) and putative nuclear (Rorα) receptors, and clock genes (Clock, Bmal1, Per1, Per2, Cry1, Cry2) in cumulus-oocyte complexes (COC) from weaning Wistar rats. We also examined the effects of pinealectomy and of melatonin pharmacological replacement on the daily expression of these genes in COC. qRT-PCR analysis revealed that in oocytes, the mRNA expression of Asmt, Mt2, Clock, Bmal1, Per2, and Cry1 were higher (P < 0.05) in immature ovaries than in the mature ones. In cumulus cells, the same pattern of mRNA expression for Asmt, Aanat, Rorα, Clock, Per1, Cry1, and Cry2 genes was observed. In oocytes, pinealectomy altered the daily mRNA expression profiles of Asmt, Mt1, Mt2, Clock, Per1, Cry1, and Cry2 genes. In cumulus cells, removal of the pineal altered the mRNA expression profiles of Mt1, Mt2, Rorα, Aanat, Asmt, Clock, Bmal1, Per2, Cry1, and Cry2 genes. Melatonin treatment partially or completely re-established the daily mRNA expression profiles of most genes studied. The mRNA expression of melatonin-related genes and clock genes in rat COC varies with the maturational stage of the meiotic cellular cycle in addition to the hour of the day. This suggests that melatonin might act differentially in accordance with the maturational stage of cumulus/oocyte complex. In addition, it seems that circulating pineal melatonin is very important in the design of the daily profile of mRNA expression of COC clock genes and genes related to melatonin synthesis and action.

Melatonin, noncoding RNAs, messenger RNA stability and epigenetics--evidence, hints, gaps and perspectives

Melatonin is a highly pleiotropic regulator molecule, which influences numerous functions in almost every organ and, thus, up- or down-regulates many genes, frequently in a circadian manner. Our understanding of the mechanisms controlling gene expression is actually now expanding to a previously unforeseen extent. In addition to classic actions of transcription factors, gene expression is induced, suppressed or modulated by a number of RNAs and proteins, such as miRNAs, lncRNAs, piRNAs, antisense transcripts, deadenylases, DNA methyltransferases, histone methylation complexes, histone demethylases, histone acetyltransferases and histone deacetylases. Direct or indirect evidence for involvement of melatonin in this network of players has originated in different fields, including studies on central and peripheral circadian oscillators, shift work, cancer, inflammation, oxidative stress, aging, energy expenditure/obesity, diabetes type 2, neuropsychiatric disorders, and neurogenesis. Some of the novel modulators have also been shown to participate in the control of melatonin biosynthesis and melatonin receptor expression. Future work will need to augment the body of evidence on direct epigenetic actions of melatonin and to systematically investigate its role within the network of oscillating epigenetic factors. Moreover, it will be necessary to discriminate between effects observed under conditions of well-operating and deregulated circadian clocks, and to explore the possibilities of correcting epigenetic malprogramming by melatonin.

Transgenerational epigenetic inheritance: focus on soma to germline information transfer

In trangenerational epigenetic inheritance, phenotypic information not encoded in DNA sequence is transmitted across generations. In germline-dependent mode, memory of environmental exposure in parental generation is transmitted through gametes, leading to appearance of phenotypes in the unexposed future generations. The memory is considered to be encoded in epigenetic factors like DNA methylation, histone modifications and regulatory RNAs. Environmental exposure may cause epigenetic modifications in the germline either directly or indirectly through primarily affecting the soma. The latter possibility is most intriguing because it contradicts the established dogma that hereditary information flows only from germline to soma, not in reverse. As such, identification of the factor(s) mediating soma to germline information transfer in transgenerational epigenetic inheritance would be pathbreaking. Regulatory RNAs and hormone have previously been implicated or proposed to play a role in soma to germline communication in epigenetic inheritance. This review examines the recent examples of gametogenic transgenerational inheritance in plants and animals in order to assess if evidence of regulatory RNAs and hormones as mediators of information transfer is supported. Overall, direct evidence for both mobile regulatory RNAs and hormones is found to exist in plants. In animals, although involvement of mobile RNAs seems imminent, direct evidence of RNA-mediated soma to germline information transfer in transgenerational epigenetic inheritance is yet to be obtained. Direct evidence is also lacking for hormones in animals. However, detailed examination of recently reported examples of transgenerational inheritance reveals circumstantial evidence supporting a role of hormones in information transmission.

MT3 melatonin binding site, MT1 and MT2 melatonin receptors are present in oocyte, but only MT1 is present in bovine blastocyst produced in vitro

BACKGROUND

Melatonin inclusion into in vitro oocyte maturation (IVM) protocols has been suggested because it possesses a powerful free radical scavenger capability that improves the quality of the oocyte used in in vitro embryo production (IVP). The aim of our study was to investigate the presence of melatonin membrane receptors (MT1and MT2) and MT3, which is the melatonin binding site of NQO2 enzyme, in both oocytes and hatched blastocysts to consider an additional subcellular mechanism responsible for the effects of melatonin on IVP.

METHODS

The presence of the high affinity melatonin receptors was investigated through an autoradiographic binding assay, using the non-permeable ligand [125I]-iodomelatonin (17 pM) in embryos. The kind of melatonin site was investigated in oocytes and embryos by immunocytochemistry. In vitro fertilized bovine embryos produced from in vitro maturated oocytes supplemented with melatonin (0.0001 to 1000 nM) were analysed to determine their cleavage and blastocyst formation rates.

RESULTS

The [125I]-iodomelatonin (17 pM) binding in blastocysts was blocked by pre-incubation with melatonin (30000 nM), showing the presence of the high affinity melatonin receptors. MT1, MT2 and NQO2 immunoreactivity was observed in oocytes. MT1 immunoreactivity was observed in hatched blastocysts, however MT2 and NQO2 were not observed in this embryonic stage. Melatonin (pM) triggered significant difference in both cleavage and blastocysts formation rates.

CONCLUSIONS

The high affinity MT1 melatonin receptor must be taking part in IVM events; furthermore it is the first melatonin receptor to appear during bovine embryo development in vitro.

Influence of photoperiod on hormones, behavior, and immune function

Photoperiodism is the ability of plants and animals to measure environmental day length to ascertain time of year. Central to the evolution of photoperiodism in animals is the adaptive distribution of energetically challenging activities across the year to optimize reproductive fitness while balancing the energetic tradeoffs necessary for seasonally-appropriate survival strategies. The ability to accurately predict future events requires endogenous mechanisms to permit physiological anticipation of annual conditions. Day length provides a virtually noise free environmental signal to monitor and accurately predict time of the year. In mammals, melatonin provides the hormonal signal transducing day length. Duration of pineal melatonin is inversely related to day length and its secretion drives enduring changes in many physiological systems, including the HPA, HPG, and brain-gut axes, the autonomic nervous system, and the immune system. Thus, melatonin is the fulcrum mediating redistribution of energetic investment among physiological processes to maximize fitness and survival.

Epigenetic regulation: a new research area for melatonin?

Epigenetic, modifications of DNA and histones, i.e. heritable alterations in gene expression that do not involve changes in DNA sequences, are known to be involved in disease. Two important epigenetic changes that contribute to disease are abnormal methylation patterns of DNA and modifications of histones in chromatin. Epimutations, such as the hypermethylation and epigenetic silencing of tumor suppressor genes, have revealed a new area for cancer treatment. Studies using DNA methyltransferase inhibitors such as procaine, hydralazine, and RG108 have had promising outcomes against cancer therapy. Melatonin, one of the most versatile molecules in nature, may hypothetically be involved in epigenetic regulation. In this review, the potential role of melatonin in inhibiting DNA methyltransferase and epigenetic regulation is discussed.

Association between adolescent idiopathic scoliosis prevalence and age at menarche in different geographic latitudes

BACKGROUND

Age at menarche is considered a reliable prognostic factor for idiopathic scoliosis and varies in different geographic latitudes. Adolescent idiopathic scoliosis prevalence has also been reported to be different in various latitudes and demonstrates higher values in northern countries. A study on epidemiological reports from the literature was conducted to investigate a possible association between prevalence of adolescent idiopathic scoliosis and age at menarche among normal girls in various geographic latitudes. An attempt is also made to implicate a possible role of melatonin in the above association.

MATERIAL-METHODS

20 peer-reviewed published papers reporting adolescent idiopathic scoliosis prevalence and 33 peer-reviewed papers reporting age at menarche in normal girls from most geographic areas of the northern hemisphere were retrieved from the literature. The geographic latitude of each centre where a particular study was originated was documented. The statistical analysis included regression of the adolescent idiopathic scoliosis prevalence and age at menarche by latitude.

RESULTS

The regression of prevalence of adolescent idiopathic scoliosis and age at menarche by latitude is statistically significant (p < 0.001) and are following a parallel declining course of their regression curves, especially in latitudes northern than 25 degrees.

CONCLUSION

Late age at menarche is parallel with higher prevalence of adolescent idiopathic scoliosis. Pubarche appears later in girls that live in northern latitudes and thus prolongs the period of spine vulnerability while other pre-existing or aetiological factors are contributing to the development of adolescent idiopathic scoliosis. A possible role of geography in the pathogenesis of idiopathic scoliosis is discussed, as it appears that latitude which differentiates the sunlight influences melatonin secretion and modifies age at menarche, which is associated to the prevalence of idiopathic scoliosis.

Essential hypertension seems to result from melatonin-induced epigenetic modifications in area postrema

Essential hypertension is a complex multifactorial disorder with epigenetic and environmental factors contributing to its prevalence. Epigenetic system is a genetic regulatory mechanism that allows humans to maintain extraordinarily stable patterns of gene expression over many generations. Sympathetic nervous system plays a major role in the maintenance of hypertension and the rostral ventrolateral medulla is the main source of this sympathetic activation. A possible mechanism to explain the sympathetic hyperactivity in the rostral ventrolateral medulla is an action of the area postrema. Area postrema seems to be the region where a shift of the set-point to a higher operating pressure occurs resulting in hypertension. But, how can a shift occur in the area postrema. We propose that melatonin-induced epigenetic modifications in the neurons of area postrema plays a role in this shift. Area postrema is reported to contain high levels of melatonin receptors that play a role in the epigenetic modifications in certain cells. Environmental stressors cause epigenetic modifications in the neurons of area postrema via the pineal hormone melatonin and these changes lead to a shift in the set-point to a higher operating pressure. This signal is then sent via efferent projections to key medullary sympathetic nuclei in rostral ventrolateral medulla resulting in increases in sympathetic nerve activity. This model may explain the long-term alterations in sympathetic activity in essential hypertension.