Interactions between melatonin and estrogen may regulate cerebrovascular function in women: clinical implications for the effective use of HRT during menopause and aging

The Heterogeneity of Post-Menopausal Disease Risk: Could the Basis for Why Only Subsets of Females Are Affected Be Due to a Reversible Epigenetic Modification System Associated with Puberty, Menstrual Cycles, Pregnancy and Lactation, and, Ultimately, Menopause?

For much of human evolution, the average lifespan was <40 years, due in part to disease, infant mortality, predators, food insecurity, and, for females, complications of childbirth. Thus, for much of evolution, many females did not reach the age of menopause (45-50 years of age) and it is mainly in the past several hundred years that the lifespan has been extended to >75 years, primarily due to public health advances, medical interventions, antibiotics, and nutrition. Therefore, the underlying biological mechanisms responsible for disease risk following menopause must have evolved during the complex processes leading to Homo sapiens to serve functions in the pre-menopausal state. Furthermore, as a primary function for the survival of the species is effective reproduction, it is likely that most of the advantages of having such post-menopausal risks relate to reproduction and the ability to address environmental stresses. This opinion/perspective will be discussed in the context of how such post-menopausal risks could enhance reproduction, with improved survival of offspring, and perhaps why such risks are preserved. Not all post-menopausal females exhibit risk for this set of diseases, and those who do develop such diseases do not have all of the conditions. The diseases of the post-menopausal state do not operate as a unified complex, but as independent variables, with the potential for some overlap. The how and why there would be such heterogeneity if the risk factors serve essential functions during the reproductive years is also discussed and the concept of sets of reversible epigenetic changes associated with puberty, pregnancy, and lactation is offered to explain the observations regarding the distribution of post-menopausal conditions and their potential roles in reproduction. While the involvement of an epigenetic system with a dynamic "modification-demodification-remodification" paradigm contributing to disease risk is a hypothesis at this point, validation of it could lead to a better understanding of post-menopausal disease risk in the context of reproduction with commonalities may also lead to future improved interventions to control such risk after menopause.

Melatonin and oestrogen treatments were able to improve neuroinflammation and apoptotic processes in dentate gyrus of old ovariectomized female rats

The aim of this study was to determine the outcomes of oestrogen and melatonin treatments following long-term ovarian hormone depletion on neuroinflammation and apoptotic processes in dentate gyrus of hippocampi. Forty-six female Wistar rats of 22 months of age were used. Twelve of them remained intact, and the other 34 were ovariectomized at 12 months of age. Ovariectomized animals were divided into three groups and treated for 10 weeks with oestrogens, melatonin or saline. All rats were killed by decapitation at 24 months of age, and dentate gyri were collected. A group of 2 month-old intact female rats was used as young control. The levels of pro-inflammatory cytokines and heat shock protein 70 (HSP 70) were analysed by ELISA. The expressions of TNFα, IL1β, GFAP, nNOS, iNOS, HO-1, NFκB, Bax, Bad, AIF, Bcl2 and SIRT1 genes were detected by real-time (RT)-PCR. Western blots were used to measure the protein expression of NFκB p65, NFκB p50/105, IκBα, IκBβ, p38 MAPK, MAP-2 and synapsin I. We have assessed the ability of 17β-oestradiol and melatonin administration to downregulate markers of neuroinflammation in the dentate gyrus of ovariectomized female rats. Results indicated that 17β-oestradiol and melatonin treatments were able to significantly decrease expression of pro-inflammatory cytokines, iNOS and HO-1 in the hippocampus when compared to non-treated animals. A similar age- and long-term ovarian hormone depletion- related increase in GFAP was also attenuated after both melatonin and oestradiol treatments. In a similar way to oestradiol, melatonin decreased the activation of p38 MAPK and NFκB pathways. The treatments enhanced the levels of synaptic molecules synapsin I and MAP-2 and have been shown to modulate the pro-antiapoptotic ratio favouring the second and to increase SIRT1 expression. These findings support the potential therapeutic role of melatonin and oestradiol as protective anti-inflammatory agents for the central nervous system during menopause.

Melatonin and the theories of aging: a critical appraisal of melatonin's role in antiaging mechanisms

The classic theories of aging such as the free radical theory, including its mitochondria-related versions, have largely focused on a few specific processes of senescence. Meanwhile, numerous interconnections have become apparent between age-dependent changes previously thought to proceed more or less independently. Increased damage by free radicals is not only linked to impairments of mitochondrial function, but also to inflammaging as it occurs during immune remodeling and by release of proinflammatory cytokines from mitotically arrested, DNA-damaged cells that exhibit the senescence-associated secretory phenotype (SASP). Among other effects, SASP can cause mutations in stem cells that reduce the capacity for tissue regeneration or, in worst case, lead to cancer stem cells. Oxidative stress has also been shown to promote telomere attrition. Moreover, damage by free radicals is connected to impaired circadian rhythmicity. Another nexus exists between cellular oscillators and metabolic sensing, in particular to the aging-suppressor SIRT1, which acts as an accessory clock protein. Melatonin, being a highly pleiotropic regulator molecule, interacts directly or indirectly with all the processes mentioned. These influences are critically reviewed, with emphasis on data from aged organisms and senescence-accelerated animals. The sometimes-controversial findings obtained either in a nongerontological context or in comparisons of tumor with nontumor cells are discussed in light of evidence obtained in senescent organisms. Although, in mammals, lifetime extension by melatonin has been rarely documented in a fully conclusive way, a support of healthy aging has been observed in rodents and is highly likely in humans.

Melatonin protects against transient focal cerebral ischemia in both reproductively active and estrogen-deficient female rats: the impact of circulating estrogen on its hormetic dose-response

Melatonin (5-15 mg/kg) protects male animals against ischemic stroke. We explored the potential interactions and synergistic neuroprotection of melatonin and estrogen using a panel of lipid peroxidation and radical-scavenging assays, primary neuronal cultures subjected to oxygen-glucose deprivation (OGD), and lipopolysaccharide (LPS)-stimulated RAW 264.7 cells. Neuroprotective efficacy of melatonin was also evaluated in both reproductively active and ovariectomized female rats subjected to transient focal cerebral ischemia. Relative to melatonin or estradiol (E2) alone, a combination of the two agents exhibited robust, synergistic antioxidant and radical-scavenging actions (P<0.05, respectively). Additionally, the two agents, when combined at large doses, showed synergistic inhibition in the production of tumor necrosis factor alpha (TNF-α) and interleukin-6 (IL-6) in the LPS-stimulated RAW 264.7 cells (P<0.05, respectively). Alternatively, co-treatment with melatonin and E2 independently, but not combined, showed a U-shaped dose-responsive (hormetic) cytoprotection for neuronal cultures subjected to OGD. When combined at a dosage either positively or negatively skewed from each optimal dosage, however, co-treatment caused synergistic neuroprotection. Relative to vehicle-injected controls, melatonin given intravenously at 1-5 mg/kg, but not 0.1 or 15 mg/kg, significantly reduced brain infarction and improved neurobehavioral outcomes (P<0.05, respectively) in reproductively active female rats. In ovariectomized stroke rats, melatonin was only effective at a large dosage (15-50 mg/kg). These results demonstrate complex interactions and synergistic antioxidant, radical-scavenging, and anti-inflammatory actions between estradiol and melatonin, and highlight the potential need to rectify the melatonin's hormetic dose-response by the level of circulating estradiol in the treatment of female stroke patients.

Melatonin-induced estrogen receptor alpha-mediated calbindin-D9k expression plays a role in H2O2-mediated cell death in rat pituitary GH3 cells

Calbindin-D9k (CaBP-9k) is a 9-kDa polypeptide possessing two calcium-binding sites that is expressed in the mammalian intestine, uterus, and pituitary gland. The factors regulating the expression of the estrogen receptor (ER) and CaBP-9k in the pituitary gland are currently unknown. In this study, we investigated whether the ER and CaBP-9k expression are regulated by melatonin during H(2)O(2)-induced cell death in rat pituitary GH3 cells. Cell survival increased by approximately 27-36% in H(2)O(2) plus melatonin compared to H(2)O(2) alone, and CaBP-9k expression was augmented by treatment with H(2)O(2) plus melatonin. These results suggest that the increase in cell survival and the melatonin-induced CaBP-9k expression may play a role in protecting cells against H(2)O(2)-mediated cell death. This result is also consistent with the increase in CaBP-9k expression leading to rises in p-ERK and p-Bad (S112). Over-expression of CaBP-9k caused an increase in p-ERK. ERalpha expression was higher in H(2)O(2) plus melatonin-treated cells compared to those treated with H(2)O(2) alone, while ERbeta expression was not. Also, ERalpha in the nuclear fraction increased in the presence of melatonin and decreased in the presence of ICI 182 780 or ICI 182 780 plus melatonin. The relative binding affinity of ERalpha for melatonin was higher than that of ERbeta, suggesting that melatonin has the potential to preferentially bind ERalpha. In conclusion, these results indicate that melatonin may increase CaBP-9k expression through ERalpha.

Melatonin provides neuroprotection by reducing oxidative stress and HSP70 expression during chronic cerebral hypoperfusion in ovariectomized rats

Oxidative stress is believed to contribute to functional and histopathologic disturbances associated with chronic cerebral hypoperfusion (CCH) in rats. Melatonin has protective effects against cerebral ischemia/reperfusion injury. This effect has mainly been attributed to its antioxidant properties. In the present study, we evaluate the effects of melatonin on chronic cerebral hypoperfused rats and examined its possible influence on oxidative stress, superoxide dismutase (SOD) activity, reduced glutathione (GSH) levels, and heat shock protein (HSP) 70 induction. CCH was induced by permanent bilateral common carotid artery occlusion in ovariectomized female rats. Extensive neuronal loss in the hippocampus at day 14 following CCH was observed. The ischemic changes were preceded by increases in malondialdehyde (MDA) concentration and HSP70 induction as well as reductions in GSH and SOD. Melatonin treatment restored the levels of MDA, SOD, GSH, and HSP70 induction as compared to the ischemic group. Histopathologic analysis confirmed the protective effect of melatonin against CCH-induced morphologic alterations. Taken together, our results document that melatonin provides neuroprotective effects in CCH by attenuating oxidative stress and stress protein expression in neurons. This suggests melatonin may be helpful for the treatment of vascular dementia and cerebrovascular insufficiency.

Intracellular signaling pathways involved in cell growth inhibition of human umbilical vein endothelial cells by melatonin

Melatonin, an indolamine mainly produced in the pineal gland, has received a great deal of attention in the last decade because of its oncostatic effects, which are due to its immunomodulatory, antiproliferative, antioxidant and its possible antiangiogenesis properties. Herein, we document its antiproliferative action on human umbilical vein endothelial cells (HUVECs). Moreover, the possible cell signaling pathways when melatonin inhibited HUVEC proliferation were explored in this study. Primary HUVECs were isolated, cultured, purified and identified before the studies were performed. HUVECs were found to possess G-protein-coupled membrane receptors for melatonin (MT1 and MT2) and also nuclear melatonin receptors (RORalpha and RORbeta, especially RORbeta). No obvious expression of RORgamma was found. We investigated the membrane receptors and several intracellular signaling pathways including mitogen-activated protein kinases (MAPK)/extracellular signal-related kinases (ERK), phosphoinositol-3-kinase (PI3K)/Akt and protein kinases C (PKC) involved in antiproliferative action of melatonin on HUVECs. The blockade of these pathways using special inhibitors decreased cell growth. Furthermore, the constitutive activation of nuclear factor kappa B (NF-kappaB) contributed to the proliferation of HUVECs. High concentrations of melatonin inhibited both NF-kappaB expression and its binding ability to DNA, possibly through inactivation of ERK/Akt /PKC pathways. Taken together, high concentrations of melatonin markedly reduced HUVEC proliferation; the antiproliferative action of melatonin was closely correlated with following pathway: melatonin receptors/ERK/PI3K/Akt/PKC/ NF-kappaB.

Therapeutic treatments potentially mediated by melatonin receptors: potential clinical uses in the prevention of osteoporosis, cancer and as an adjuvant therapy

Melatonin's therapeutic potential is grossly underestimated because its functional roles are diverse and its mechanism(s) of action are complex and varied. Melatonin produces cellular effects via a variety of mechanisms in a receptor independent and dependent manner. In addition, melatonin is a chronobiotic agent secreted from the pineal gland during the hours of darkness. This diurnal release of melatonin impacts the sensitivity of melatonin receptors throughout a 24-hr period. This changing sensitivity probably contributes to the narrow therapeutic window for use of melatonin in treating sleep disorders, that is, at the light-to-dark (dusk) or dark-to-light (dawn) transition states. In addition to the cyclic changes in melatonin receptors, many genes cycle over the 24-hr period, independent or dependent upon the light/dark cycle. Interestingly, many of these genes support a role for melatonin in modulating metabolic and cardiovascular physiology as well as bone metabolism and immune function and detoxification of chemical agents and cancer reduction. Melatonin also enhances the actions of a variety of drugs or hormones; however, the role of melatonin receptors in modulating these processes is not known. The goal of this review is to summarize the evidence related to the utility of melatonin as a therapeutic agent by focusing on its other potential uses besides sleep disorders. In particular, its use in cancer prevention, osteoporosis and, as an adjuvant to other therapies are discussed. Also, the role that melatonin and, particularly, its receptors play in these processes are highlighted.

Deficiencies in estrogen-mediated regulation of cerebrovascular homeostasis may contribute to an increased risk of cerebral aneurysm pathogenesis and rupture in menopausal and postmenopausal women

Despite the catastrophic consequence of ruptured intracranial aneurysms, very little is understood regarding their pathogenesis, and there are no reliable predictive markers for identifying at-risk individuals. Few studies have addressed the molecular pathological basis and mechanisms of intracranial aneurysm formation, growth, and rupture. The pathogenesis and rupture of cerebral aneurysms have been associated with inflammatory processes, and these have been implicated in the digestion and breakdown of vascular wall matrix. Epidemiological data indicate that the risk of cerebral aneurysm pathogenesis and rupture in women rises during and after menopause as compared to premenopausal women, and has been attributed to hormonal factors. Moreover, experimental evidence supports a role for estrogen in the modulation of each phase of the inflammatory response implicated in cerebral aneurysm pathogenesis and rupture. While the risk of aneurysm rupture in men also increases with age, this increased risk has been attributed to other recognized risk factors including cigarette smoking, use of alcohol, and history of hypertension, all of which are more common in men than women. We hypothesize, therefore, that decreases in both circulating estrogen levels and cerebrovascular estrogen receptor density may contribute to an increased risk of cerebral aneurysm pathogenesis and rupture in women during and after menopause. To test our hypothesis, experiments are needed to identify genes regulated by estrogen and to evaluate gene expression and intracellular mechanisms in cells/tissues exposed to varying concentrations and duration of treatment with estrogen, metabolites of estrogen, and selective estrogen receptor modulators (SERMs). Furthermore, it is not likely that the regulation of cerebrovascular homeostasis is due to the actions of estrogen alone, but rather the interplay of estrogen and other hormones and their associated receptor expression. The potential interactions of these hormones in the maintenance of normal cerebrovascular tone need to be elucidated. Additional studies are needed to define the role that estrogen and other sex hormones may play in the cerebrovascular circulation and the pathogenesis and rupture of cerebral aneurysms. Efforts directed at understanding the basic pathophysiological mechanisms of aneurysm pathogenesis and rupture promise to yield dividends that may have important therapeutic and clinical implications. The development of non-invasive tools such as molecular MRI for the detection of specific cells, molecular markers, and tissues may facilitate early diagnosis of initial pathophysiological changes that are undetectable by clinical examination or other diagnostic tools, and can also be used to evaluate the state of activity of cerebral aneurysm pathogenesis before, during, and after treatment.

Melatonin and sleep in aging population

The neurohormone melatonin is released from the pineal gland in close association with the light-dark cycle. There is a temporal relationship between the nocturnal rise in melatonin secretion and the 'opening of the sleep gate' at night. This association, as well as the sleep promoting effect of exogenous melatonin, implicates the pineal product in the physiological regulation of sleep. Aging is associated with a significant reduction in sleep continuity and quality. A decreased production of melatonin with age is documented in a majority of studies. Diminished nocturnal melatonin secretion with severe disturbances in sleep/wake rhythm has been consistently reported in Alzheimer's disease (AD). A recent survey on the effects of melatonin in sleep disturbances, including all age groups, failed to document significant and clinically meaningful effects of exogenous melatonin on sleep quality, efficiency and latency. However, in clinical trials involving elderly insomniacs and AD patients suffering from sleep disturbances exogenous melatonin has repeatedly been found to be effective in improving sleep. The results indicate that exogenous melatonin is more effective to promote sleep in the presence of a diminished production of endogenous melatonin. A MT1/MT2 receptor analog of melatonin (ramelteon) has recently been introduced as a new type of hypnotics with no evidence of abuse or dependence.

Endocrinology of menopausal transition and its brain implications

The central nervous system is one of the main target tissues for sex steroid hormones, which act on both through genomic mechanisms, modulating synthesis, release, and metabolism of many neuropeptides and neurotransmitters, and through non-genomic mechanisms, influencing electrical excitability, synaptic function, morphological features, and neuron-glia interactions. During the climacteric period, sex steroid deficiency causes many neuroendocrine changes. At the hypothalamic level, estrogen withdrawal gives rise to vasomotor symptoms, to eating behavior disorders, and altered blood pressure control. On the other hand, at the limbic level, the changes in serotoninergic, noradrenergic, and opioidergic tones contribute to the modifications in mood, behavior, and nociception. Hormone replacement therapy (HRT) positively affects climateric depression throughout a direct effect on neural activity and on the modulation of adrenergic and serotoninergic tones and may modulate the decrease in cognitive efficiency observed in climaterium. The identification of the brain as a de novo source of neurosteroids, suggests that the modifications in mood and cognitive performances occurring in postmenopausal women may also be related to a change in the levels of neurosteroids. These findings open new perspectives in the study of the effects of sex steroids on the central nervous system and on the possible use of alternative and/or auxiliary HRT.