Scientific basis for the potential use of melatonin in bone diseases: osteoporosis and adolescent idiopathic scoliosis

The melatonin contained in beer can provide health benefits, due to its antioxidant, anti-inflammatory and immunomodulatory properties

Beer is a fermented beverage with a low alcohol content originating from cereal fermentation (barley or wheat). It forms part of the diet for many people. It contains melatonin (N-acetyl-5-methoxytryptamine). Melatonin is a molecule with a wide range of antioxidant, oncostatic, immunomodulatory, and cytoprotective properties. The aim of this work was to review the data supporting the idea that a moderate consumption of beer, because of its melatonin content, is particularly useful in healthy diets and in other physiological situations (such as pregnancy, menopause, and old age). Data source: a) The MEDLINE /PubMed search was conducted from 1975 to April 2022, and b) Our own experience and published studies on melatonin, the immune system, and beer. We provide a review of research on the mechanisms of melatonin generation in beer, its concentrations, and its possible effects on health. The melatonin contained in beer, as part of a healthy diet and in some special physiological situations, could act as a protective factor and improve the quality of life of those who drink it in moderation. © 2022 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Reactive Oxygen Species Control Osteoblast Apoptosis through SIRT1/PGC-1α/P53Lys382 Signaling, Mediating the Onset of Cd-Induced Osteoporosis

The imbalance between osteogenesis and osteoclastogenesis is a feature of bone metabolic disease. Cadmium (Cd) exposure causes human bone loss and osteoporosis (OP) through bioaccumulation of the food chain. However, the impact of Cd on bone tissues and the underlying molecular mechanisms are not well-characterized. In the current study, we found that the Cd concentration in bone tissues of OP patients was higher than normal subjects; meanwhile, the nuclear silent information regulator of transcription 1 (SIRT1) protein expression level was significantly decreased, which is a new star molecule to treat OP. It is further revealed that SIRT1 activation markedly reprograms bone metabolic and stress-response pathways that incline with osteoblast (OB) apoptosis. Suppressing reactive oxygen species (ROS) release with N-acetyl-l-cysteine (NAC) abolished Cd-induced reduction of SIRT1 protein, deacetylation of P53, OB apoptosis, and attenuated OP. Conversely, overexpression of SIRT1 suppressed Cd-induced ROS release. SIRT1 overexpression in vivo and in vitro dampened PGC-1α protein, acetylation of P53 at lysine 382, and caspase-dependent apoptosis. These results reveal that ROS/SIRT1 controls P53 acetylation and coordinates OB apoptosis involved in the onset of OP.

SP7: from Bone Development to Skeletal Disease

PURPOSE OF REVIEW

The purpose of this review is to summarize the different roles of the transcription factor SP7 in regulating bone formation and remodeling, discuss current studies in investigating the causal relationship between SP7 mutations and human skeletal disease, and highlight potential therapeutic treatments that targeting SP7 and the gene networks that it controls.

RECENT FINDINGS

Cell-type and stage-specific functions of SP7 have been identified during bone formation and remodeling. Normal bone development regulated by SP7 is strongly associated with human bone health. Dysfunction of SP7 results in common or rare skeletal diseases, including osteoporosis and osteogenesis imperfecta with different inheritance patterns. SP7-associated signaling pathways, SP7-dependent target genes, and epigenetic regulations of SP7 serve as new therapeutic targets in the treatment of skeletal disorders. This review addresses the importance of SP7-regulated bone development in studying bone health and skeletal disease. Recent advances in whole genome and exome sequencing, GWAS, multi-omics, and CRISPR-mediated activation and inhibition have provided the approaches to investigate the gene-regulatory networks controlled by SP7 in bone and the therapeutic targets to treat skeletal disease.

Molecular basis of ligand selectivity for melatonin receptors

Sleep disorders in adults are related to adverse health effects such as reduced quality of life and increased mortality. About 30-40% of adults are suffering from different sleep disorders. The human melatonin receptors (MT1 and MT2) are family A G protein-coupled receptors that respond to the neurohormone melatonin MEL which regulates circadian rhythm and sleep. Many efforts have been made to develop drugs targeting melatonin receptors to treat insomnia, circadian rhythm disorders, and even cancer. However, designing subtype-selective melatonergic drugs remains challenging due to their high similarities in both sequences and structures. MEL (a function-selective compound with a bulky β-naphthyl group) behaves as an MT2-selective antagonist, whereas it is an agonist of MT1. Here, molecular dynamics simulations were used to investigate the ligand selectivity of MT receptors at the atomic level. We found that the binding conformation of MEL differs in different melatonin receptors. In MT1, the naphthalene ring of MEL forms a structure perpendicular to the membrane surface. In contrast, there is a 130° angle between the naphthalene ring of MEL and the membrane surface in MT2. Because of this conformational difference, the MEL leads to a constant water channel in MT1 which activates the receptor. However, MEL hinders the formation of continuous water channels, resulting in an inactive state of MT2. Furthermore, we found that A117^3.29 in MT2 is a crucial amino acid capable of hindering the conformational flip of the MEL molecule. These results, coupled with previous functional data, reveal that although MT1 and MT2 share highly similar orthosteric ligand-binding pockets, they also display distinctive features that could be used to design selective compounds. Our findings provide new insights into functionally selective melatonergic drug development for sleep disorders.

Physiological consequences of space flight, including abnormal bone metabolism, space radiation injury, and circadian clock dysregulation: Implications of melatonin use and regulation as a countermeasure

Exposure to the space environment induces a number of pathophysiological outcomes in astronauts, including bone demineralization, sleep disorders, circadian clock dysregulation, cardiovascular and metabolic dysfunction, and reduced immune system function. A recent report describing experiments aboard the Space Shuttle mission, STS-132, showed that the level of melatonin, a hormone that provides the biochemical signal of darkness, was decreased during microgravity in an in vitro culture model. Additionally, abnormal lighting conditions in outer space, such as low light intensity in orbital spacecraft and the altered 24-h light-dark cycles, may result in the dysregulation of melatonin rhythms and the misalignment of the circadian clock from sleep and work schedules in astronauts. Studies on Earth have demonstrated that melatonin regulates various physiological functions including bone metabolism. These data suggest that the abnormal regulation of melatonin in outer space may contribute to pathophysiological conditions of astronauts. In addition, experiments with high-linear energy transfer radiation, a ground-based model of space radiation, showed that melatonin may serve as a protectant against space radiation. Gene expression profiling using an in vitro culture model exposed to space flight during the STS-132 mission, showed that space radiation alters the expression of DNA repair and oxidative stress response genes, indicating that melatonin counteracts the expression of these genes responsive to space radiation to promote cell survival. These findings implicate the use of exogenous melatonin and the regulation of endogenous melatonin as countermeasures for the physiological consequences of space flight.

Adolescent idiopathic scoliosis : a review of aetiological theories of a multifactorial disease

Adolescent idiopathic scoliosis (AIS), defined by an age at presentation of 11 to 18 years, has a prevalence of 0.47% and accounts for approximately 90% of all cases of idiopathic scoliosis. Despite decades of research, the exact aetiology of AIS remains unknown. It is becoming evident that it is the result of a complex interplay of genetic, internal, and environmental factors. It has been hypothesized that genetic variants act as the initial trigger that allow epigenetic factors to propagate AIS, which could also explain the wide phenotypic variation in the presentation of the disorder. A better understanding of the underlying aetiological mechanisms could help to establish the diagnosis earlier and allow a more accurate prediction of deformity progression. This, in turn, would prompt imaging and therapeutic intervention at the appropriate time, thereby achieving the best clinical outcome for this group of patients. Cite this article: Bone Joint J 2022;104-B(8):915-921.

Melatonin Attenuates RANKL-Induced Osteoclastogenesis via Inhibition of Atp6v0d2 and DC-STAMP through MAPK and NFATc1 Signaling Pathways

Melatonin is a hormone secreted by the pineal gland that is involved in the biorhythm of reproductive activities. The present study investigated the inhibitory effects of melatonin on osteoclastogenesis in RAW 264.7 cells according to changes in V-ATPase and the corresponding inhibition of the MAPK and NFATc1 signaling processes. Methods: the cytotoxic effect of melatonin was investigated by MTT assay. Osteoclast differentiation and gene expression of osteoclast-related factors were confirmed via TRAP staining, pit formation assay, immunofluorescence imaging, western blot, and real-time PCR. Results: melatonin was found to inactivate the p38 and JNK of MAP kinase in RAW264.7 cells treated with RANKL and treated with a combination RANKL and melatonin for 1, 3, and 5 days. The melatonin treatment group showed a reduction in osteoclastogenesis transcription factors and ATP6v0d2 gene expression. Conclusions: melatonin inhibits osteoclast differentiation and cell fusion by inhibiting the expression of Atp6v0d2 through the inactivation of MAPK and NFATc1 signaling in RANKL-stimulated RAW264.7 macrophages. The findings of the present study suggest that melatonin could be a suitable therapy for bone loss and imply a potential role of melatonin in bone health.

Single-cell RNA Seq reveals cellular landscape-specific characteristics and potential etiologies for adolescent idiopathic scoliosis

BACKGROUNDS

Abnormal vertebral growth and development have been found in adolescent idiopathic scoliosis (AIS) patients, and the proliferation and differentiation of bone development-related cells play important roles in its pathogenesis. However, a comprehensive single-cell-level differentiation roadmap in AIS has not been achieved.

METHODS

The present study compared the single-cell level cellular landscapes of spinal cancellous bone tissues between AIS patients and healthy subjects using high throughput single-cell RNA sequencing (scRNA-seq), which covers multiple cellular lineages including osteoblast, chondrocyte, osteoclast and related immunocytes. We constructed the differentiation trajectories of bone development-related cell lineages through pseudotime analysis, and the intercellular-communication networks between bone development-related cells and immunocytes were further developed.

RESULTS

A total of 11 distinct cell clusters were identified according to the genome-wide transcriptome profiles. t-Distributed stochastic neighbor embedding (t-SNE) analysis showed that mesenchymal stem cells (MSC) were classified into three subtypes: MSC-LOXL2, MSC-IGFBP5, and MSC-GJA1. Gene ontology (GO) analysis showed that MSC-GJA1 might possess greater osteoblast differentiation potential than the others. MSC-IGFBP5 was the specific MSC subtype observed only in AIS. There were two distinct gene expression clusters: OB-DPT and OB-OLFML2B, and the counts of osteoblasts derived from AIS was significantly less than that of non-AIS subjects. In AIS patients, MSC-IGFBP5 failed to differentiate into osteoblasts and exhibited negative regulation of cell proliferation and enhanced cell death. CPC-PCNA was found to be the specific chondrocyte progenitor cell (CPC) subtype observed only in AIS patients. The cell counts of OC-BIRC3 in AIS were less than those in controls. Pseudotime analysis suggested two possible distinct osteoclast differentiation patterns in AIS and control subjects. Monocytes in AIS mainly differentiated into OC-CRISP3.

CONCLUSIONS

Our single-cell analysis first revealed differences existed in the cellular states between AIS patients and healthy subjects and found the differentiation disruption of specific MSC and CPC clusters in AIS. Cell communication analysis provided the possible pathogenesis of osteoblast and chondrocyte differentiation dysfunction in AIS.

Melatonin effects on bone: Implications for use as a therapy for managing bone loss

Melatonin is the primary circadian output signal from the brain and is mainly synthesized in pinealocytes. The rhythm and secretion of melatonin are under the control of an endogenous oscillator located in the SCN or the master biological clock. Disruptions in circadian rhythms by shift work, aging, or light at night are associated with bone loss and increased fracture risk. Restoration of nocturnal melatonin peaks to normal levels or therapeutic levels through timed melatonin supplementation has been demonstrated to provide bone-protective actions in various models. Melatonin is a unique molecule with diverse molecular actions targeting melatonin receptors located on the plasma membrane or mitochondria or acting independently of receptors through its actions as an antioxidant or free radical scavenger to stimulate osteoblastogenesis, inhibit osteoclastogenesis, and improve bone density. Its additional actions on entraining circadian rhythms and improving quality of life in an aging population coupled with its safety profile make it an ideal therapeutic candidate for protecting against bone loss in susceptible populations. The intent of this review is to provide a focused discussion on bone loss and disorders of the bone as it relates to melatonin and conditions that modify melatonin levels with the hope that future therapies include those that include melatonin and correct those factors that modify melatonin levels like circadian disruption.

A Decade in Review after Idiopathic Scoliosis Was First Called a Complex Trait-A Tribute to the Late Dr. Yves Cotrel for His Support in Studies of Etiology of Scoliosis

Adolescent Idiopathic Scoliosis (AIS) is a prevalent and important spine disorder in the pediatric age group. An increased family tendency was observed for a long time, but the underlying genetic mechanism was uncertain. In 1999, Dr. Yves Cotrel founded the Cotrel Foundation in the Institut de France, which supported collaboration of international researchers to work together to better understand the etiology of AIS. This new concept of AIS as a complex trait evolved in this setting among researchers who joined the annual Cotrel meetings. It is now over a decade since the first proposal of the complex trait genetic model for AIS. Here, we review in detail the vast information about the genetic and environmental factors in AIS pathogenesis gathered to date. More importantly, new insights into AIS etiology were brought to us through new research data under the perspective of a complex trait. Hopefully, future research directions may lead to better management of AIS, which has a tremendous impact on affected adolescents in terms of both physical growth and psychological development.

Melatonin inhibits RANKL‑induced osteoclastogenesis through the miR‑882/Rev‑erbα axis in Raw264.7 cells

Melatonin, secreted in a typical diurnal rhythm pattern, has been reported to prevent osteoporosis; however, its role in osteoclastogenesis remains unclear. In the present study, the ability of melatonin to inhibit receptor activator of nuclear factor‑κB ligand (RANKL)‑induced osteoclastogenesis and the associated mechanism were investigated. Raw264.7 cells were cultured with RANKL (100 ng/ml) and macrophage colony‑stimulating factor (M‑CSF; 30 ng/ml) for 7 days, and tartrate‑resistant acid phosphatase (TRAP) staining was used to detect osteoclastogenesis following treatment with melatonin. In addition, the effect of melatonin on cathepsin K and microRNA (miR)‑882 expression was investigated via western blotting and reverse transcription‑quantitative PCR. Melatonin significantly inhibited RANKL‑induced osteoclastogenesis in Raw264.7 cells. From bioinformatics analysis, it was inferred that nuclear receptor subfamily 1 group D member 1 (NR1D1/Rev‑erbα) may be a target of miR‑882. In vitro, melatonin upregulated Rev‑erbα expression and downregulated miR‑882 expression in the osteoclastogenesis model. Rev‑erbα overexpression boosted the anti‑osteoclastogenesis effects of melatonin, whereas miR‑882 partially diminished these effects. The present results indicated that the miR‑882/Rev‑erbα axis may serve a vital role in inhibiting osteoclastogenesis following RANKL and M‑CSF treatment, indicating that Rev‑erbα agonism or miR‑882 inhibition may represent mechanisms through which melatonin prevents osteoporosis.

Research progress on the etiology and pathogenesis of adolescent idiopathic scoliosis

Etiology of adolescent idiopathic scoliosis (AIS), a complicated three-dimensional spinal deformity with early-onset, receives continuous attention but remains unclear. To gain an insight into AIS pathogenesis, this review searched PubMed database up to June 2019, using key words or medical subject headings terms including "adolescent idiopathic scoliosis," "scoliosis," "pathogenesis," "etiology," "genetics," "mesenchymal stem cells," and their combinations, summarized existing literatures and categorized the theories or hypothesis into nine aspects. These aspects include bone marrow mesenchymal stem cell studies, genetic studies, tissue analysis, spine biomechanics measurements, neurologic analysis, hormone studies, biochemical analysis, environmental factor analysis, and lifestyle explorations. These categories could be a guidance for further etiology or treatment researches to gain inspiration.

Advances in Sensing Technologies for Monitoring of Bone Health

: Changing lifestyle and food habits are responsible for health problems, especially those related to bone in an aging population. Poor bone health has now become a serious matter of concern for many of us. In order to avoid serious consequences, the early prediction of symptoms and diagnosis of bone diseases have become the need of the hour. From this inspiration, the evolution of different bone health monitoring techniques and measurement methods practiced by researchers and healthcare companies has been discussed. This paper focuses on various types of bone diseases along with the modeling and remodeling phenomena of bones. The evolution of various diagnosis tests for bone health monitoring has been also discussed. Various types of bone turnover markers, their assessment techniques, and recent developments for the monitoring of biochemical markers to diagnose the bone conditions are highlighted. Then, the paper focuses on the potential assessment of the recent sensing techniques (physical sensors and biosensors) that are currently available for bone health monitoring. Considering the importance of electrochemical biosensors in terms of high sensitivity and reliability, specific attention has been given to the recent development of electrochemical biosensors and significance in real-time monitoring of bone health.

Selenomethionine exposure affects chondrogenic differentiation and bone formation in Japanese medaka (Oryzias latipes)

Excess selenium entering the aquatic environment from anthropogenic activities has been associated with developmental abnormalities in fish including skeletal deformities of the head and spine. However, mechanisms of this developmental toxicity have not been well-characterized. In this study, Japanese medaka (Oryzias latipes) embryos were exposed to seleno-l-methionine (Se-Met) in a range of concentrations. Gene expression was evaluated for sex-determining region Y (SRY)-related box (Sox9a and Sox9b), runt-related transcription factor 2 (Runx2), and melatonin receptor (Mtr). Alterations in the length of Meckel's cartilage, tail curvature, and decreased calcification were observed in skeletal stains at 10- and 22-days post-fertilization (dpf). Embryonic exposure of Osterix-mCherry transgenic medaka resulted in fewer teeth. Sox9a and Sox9b were up-regulated, while Runx2 and Mtr were down-regulated by Se-Met prior to hatch. Whole mount in situ hybridization (WISH) localized gene expression to areas observed to be affected in vivo. In addition, Se-Met exposures of a Mtr morpholino (Mtr-MO) as well as Luzindole exposed embryos developed similar skeletal malformations, supporting involvement of Mtr. These findings demonstrate that Se-Met modulates expression of key genes involved in chondrogenic differentiation and bone formation during development.

Melatonin as an Agent for Direct Pulp-Capping Treatment

Melatonin plays an essential role in the regulation of bone growth. The actions that melatonin exerts on odontoblasts may be similar to its action on osteoblasts. This research aimed to evaluate the pulp response to melatonin used for direct pulp capping to evaluate the antioxidant effect of melatonin administered orally and its influence on dental pulp. Direct pulp capping was performed on the upper molars of Sprague Dawley rats using melatonin or Mineral Trioxide Aggregate (MTA). The study groups were: MTA; Melatonin; MTA + Melatonin administered orally; and Melatonin + Melatonin administered orally. In the latter two groups, the animals drank water dosed with melatonin ad libitum (10 mg/100 mL). After 30 days, the animals were sacrificed, and 5 ml of blood, the kidneys, and the liver were extracted in order to evaluate oxidative stress using thiobarbituric acid reactive substances testing (TBARS). Fragments of the maxilla containing the study molars were prepared for histological evaluation. The degree of pulp inflammation and pulp necrosis, the presence of reparative dentin and dentin bridging the pulp chamber, the presence and regularity of the odontoblastic layer, and the presence of pulp fibrosis were evaluated. No significant differences were found between the four study groups for any of the studied histological variables. The oral administration of melatonin did not modify the local effects of MTA or melatonin on dental pulp, or reduce basal-level oxidative stress. The effect of melatonin on pulp is similar to that of MTA and may be used as an agent for direct pulp capping.

Melatonin: an anti-tumor agent for osteosarcoma

Osteosarcoma is the most common bone tumors which consisted of malignant mesenchymal cells generating osteoid and immature bone. It has been showed that osteosarcoma is common in children and adolescents and shows high mortality rate. A variety of therapeutic approaches (i.e., resection surgery, combined with chemotherapy and radiotherapy) have been used as conventional treatments in patients with osteosarcoma. Despite several attempts to improve therapeutic response, the rate of survival for osteosarcoma has not changed during the past 3 decades. Therefore, the discovery and developing new effective therapeutic platforms are required. Along to the established anti-cancer agents, some physiological regulators such melatonin, have been emerged as new anti-cancer agents. Melatonin is an indolamine hormone which is secreted from the pineal glands during the night and acts as physiological regulator. Given that melatonin shows a wide spectrum anti-tumor impacts. Besides different biologic activities of melatonin (e.g., immunomodulation and antioxidant properties), melatonin has a crucial role in the formation of bones, and its deficiency could be directly related to bone cancers. Several in vitro and in vivo experiments evaluated the effects of melatonin on osteosarcoma and other types of bone cancer. Taken together, the results of these studies indicated that melatonin could be introduced as new therapeutic candidate or as adjuvant in combination with other anti-tumor agents in the treatment of osteosarcoma. Herein, we summarized the anti-tumor effects of melatonin for osteosarcoma cancer as well as its mechanism of action.

Melatonin prevents bone destruction in mice with retinoic acid-induced osteoporosis

BACKGROUND

The protective effect of melatonin against bone metabolism imbalance in osteoporosis (OP) induced by drugs such as retinoic acid (RA) is unclear. The aim of this study was to explore the role of melatonin in bone destruction based on a mouse model.

METHODS

RA-induced OP model mice were established. To assess the effect of melatonin on these mice, micro-CT was used to characterize the trabecular structure of normal mice and those treated with RA (model), RA + low-dose melatonin (Mlt-L), RA + high-dose melatonin (Mlt-H), and RA + alendronate sodium (positive control). The shape of the trabecular bone, the length and diameter of the femoral head and the height and diameter of vertebra(L1) of each group were also measured and the number of osteoclasts was determined by Tartrate-resistant acid phosphatase (TRACP) staining. Meanwhile, the expression of alkaline phosphatase (ALP) was evaluated by immunohistochemistry assays. The differences between groups in terms of liver and kidney oxidation-related indexes and serum and urinary indicators related to bone metabolism were also analyzed. Furthermore, qRT-PCR and western blotting were used to evaluate the effect of melatonin on osteogenic and osteoclastic differentiation in MC3T3-E1 and RAW264.7 cells, respectively.

RESULTS

RA induction led to a decrease in the amount and density of trabecular bone, a decrease in the length and diameter of the femur and height, diameter of the vertebra (L1), a decrease in bone mass and density and the expression of ALP, and an increase in the number of osteoclasts. Melatonin treatment alleviated these effects induced by RA, increasing the amount of trabecular bone in OP mice, improving the microstructure of the femur and vertebra(L1) and increasing bone mass bone density and the expression of ALP, as well as decreasing the number of osteoclasts. Additionally, blood and urinary bone metabolism-related indicators showed that melatonin promoted bone formation and inhibited bone resorption. Determination of oxidant and antioxidant biomarkers in the livers and kidneys of the mice revealed that melatonin promoted the antioxidant level and suppressed the level of oxidant molecules in these organs. In vitro, RA promoted osteoclasts and inhibit osteogenesis by increasing oxidative stress levels in the RAW264.7 and MC3T3-E1 cells, but melatonin reversed this effect. Melatonin may, therefore, play a role in the ERK/SMAD and NF-κB pathways.

CONCLUSIONS

Melatonin can alleviate bone loss in RA-induced OP model mice, repair the trabecular microstructure, and promote bone formation. These effects may be related to reducing oxidation levels in vivo and vitro through the ERK/SMAD and NF-κB pathways.

The effect of exogenous melatonin on reducing scoliotic curvature and improving bone quality in melatonin-deficient C57BL/6J mice

It is well-documented that melatonin deficiency has been linked to the etiopathogenesis of adolescent idiopathic scoliosis. In this study, we intended to apply melatonin in melatonin-deficient mice to ascertain whether melatonin could reduce the incidence/severity of scoliosis, and investigate the role of melatonin on bone mineral density in scoliosis. A total of 80 mice were divided into 4 groups: 20 quadrupedal mice and 20 bipedal mice served as controls; 20 quadrupedal and 20 bipedal mice received oral melatonin (8 mg/kg BW) daily. After 5th, 10th, 15th and 20th weeks of treatment, radiographs and in vivo micro-CT were used to determine the incidence of scoliosis and bone qualities, respectively. Upon sacrifice, the levels of melatonin were measured in each group. At 20th week, the occurrence of scoliosis was 80%, 30%, 22% and 5% in bipedal, quadrupedal, bipedal + melatonin and quadrupedal + melatonin group, respectively. The trabecular bone quality of the vertebral body was significantly ameliorated in the melatonin-treated bipedal models. Likewise, the number of osteoclasts was significantly less in those treated with melatonin. Our results indicated that melatonin deficiency may be crucial for scoliotic development, and restoration of melatonin levels can prevent scoliotic development with the improvement in bone density.

Relationship between melatonin and bone resorption rhythms in premenopausal women

Although evidence exists for a daily rhythm in bone metabolism, the contribution of factors such as melatonin levels, the light-dark cycle, and the sleep-wake cycle is difficult to differentiate given their highly correlated time courses. To examine these influences on bone resorption, we collected 48-h sequential urine samples under both ambulatory (8-h sleep:16-h wake) and constant routine (CR) (constant wake, posture, nutrition and dim light) conditions from 20 healthy premenopausal women. Urinary 6-sulphatoxymelatonin (aMT6s; ng/h) and the bone resorption marker amino-terminal cross-linked collagen I telopeptide (NTx; bone collagen equivalents nM/h) were assayed and fit by cosinor models to determine significant 24-h rhythms and acrophase. Most participants had significant 24-h aMT6s rhythms during both ambulatory and CR conditions (95 and 85%, respectively), but fewer had significant 24-h NTx rhythms (70 and 70%, respectively). Among individuals with significant rhythms, mean (± SD) aMT6s acrophase times were 3:57 ± 1:50 and 3:43 ± 1:25 h under ambulatory and CR conditions, respectively, and 23:44 ± 5:55 and 3:06 ± 5:15 h, respectively, for NTx. Mean 24-h levels of both aMT6s and NTx were significantly higher during CR compared with ambulatory conditions (p < 0.0001 and p = 0.03, respectively). Menstrual phase (follicular versus luteal) had no impact on aMT6s or NTx timing or 24-h levels. This study confirms an endogenous circadian rhythm in NTx with a night-time peak when measured under CR conditions, but also confirms that environmental factors such as the sleep-wake or light-dark cycles, posture or meal timing affects overall concentrations and peak timing under ambulatory conditions, the significance of which remains unclear.

Can Melatonin Improve the Osteopenia of Perimenopausal and Postmenopausal Women? A Meta-Analysis

OBJECTIVE

To assess the effectiveness and safety of melatonin for perimenopausal and postmenopausal women with osteopenia.

METHODS

In this meta-analysis, data from randomized controlled trials were obtained to assess the effects of melatonin versus placebo or western medicine in perimenopausal and postmenopausal women with osteopenia. The study's registration number is CRD42018086238. The primary outcomes included bone mineral density (BMD) and T-score.

RESULT

From 551 articles retrieved, three trials involving 121 patients were included. Due to the high-to-substantial heterogeneity (BMD: I²=96.9%, P=0.000; T-score: I²=74.9%, and P=0.019), the statistical analysis of BMD and T-score was abandoned. A systematic review was undergone for the two outcomes. Compared with the control group, melatonin may increase osteocalcin (WMD 4.97; 95% CI 3.14, 6.79; P < 0.00001).

CONCLUSION

Based on current evidence, melatonin might be used as a safe nutritional supplement to improve bone density in perimenopausal and postmenopausal women, but its efficacy needs to be further affirmed.

The multiple protective roles and molecular mechanisms of melatonin and its precursor N-acetylserotonin in targeting brain injury and liver damage and in maintaining bone health

Melatonin is a neurohormone associated with sleep and wakefulness and is mainly produced by the pineal gland. Numerous physiological functions of melatonin have been demonstrated including anti-inflammation, suppressing neoplastic growth, circadian and endocrine rhythm regulation, and its potent antioxidant activity as well as its role in regeneration of various tissues including the nervous system, liver, bone, kidney, bladder, skin, and muscle, among others. In this review, we summarize the recent advances related to the multiple protective roles of melatonin receptor agonists, melatonin and N-acetylserotonin (NAS), in brain injury, liver damage, and bone health. Brain injury, including traumatic brain injury, ischemic stroke, intracerebral hemorrhage, subarachnoid hemorrhage, and newborn perinatal hypoxia-ischemia encephalopathy, is a major cause of mortality and disability. Liver disease causes serious public health problems and various factors including alcohol, chemical pollutants, and drugs induce hepatic damage. Osteoporosis is the most common bone disease in humans. Due in part to an aging population, both the cost of care of fracture patients and the annual fracture rate have increased steadily. Despite the discrepancy in the pathophysiological processes of these disorders, time frames and severity, they may share several common molecular mechanisms. Oxidative stress is considered to be a critical factor in these pathogeneses. We update the current state of knowledge related to the molecular processes, mainly including anti-oxidative stress, anti-apoptosis, autophagy dysfunction, and anti-inflammation as well as other properties of melatonin and NAS. Particularly, the abilities of melatonin and NAS to directly scavenge oxygen-centered radicals and toxic reactive oxygen species, and indirectly act through antioxidant enzymes are disscussed. In this review, we summarize the similarities and differences in the protection provided by melatonin and/or NAS in brain, liver and bone damage. We analyze the involvement of melatonin receptor 1A (MT1), melatonin receptor 1B (MT2), and melatonin receptor 1C (MT3) in the protection of melatonin and/or NAS. Additionally, we evaluate their potential clinical applications. The multiple mechanisms of action and multiple organ-targeted properties of melatonin and NAS may contribute to development of promising therapies for clinical trials.

The Role of Vitamin D in the Pathogenesis of Adolescent Idiopathic Scoliosis

Several theories have been proposed to explain the etiology of adolescent idiopathic scoliosis (AIS) until present. However, limited data are available regarding the impact of vitamin D insufficiency or deficiency on scoliosis. Previous studies have shown that vitamin D deficiency and insufficiency are prevalent in adolescents, including AIS patients. A series of studies conducted in Hong Kong have shown that as many as 30% of these patients have osteopenia. The 25-hydroxyvitamin D3 level has been found to positively correlate with bone mineral density (BMD) in healthy adolescents and negatively with Cobb angle in AIS patients; therefore, vitamin D deficiency is believed to play a role in AIS pathogenesis. This study attempts to review the relevant literature on AIS etiology to examine the association of vitamin D and various current theories. Our review suggested that vitamin D deficiency is associated with several current etiological theories of AIS. We postulate that vitamin D deficiency and/or insufficiency affects AIS development by its effect on the regulation of fibrosis, postural control, and BMD. Subclinical deficiency of vitamin K2, a fat-soluble vitamin, is also prevalent in adolescents; therefore, it is possible that the high prevalence of vitamin D deficiency is related to decreased fat intake. Further studies are required to elucidate the possible role of vitamin D in the pathogenesis and clinical management of AIS.

Combined Fluid Shear Stress and Melatonin Enhances the ERK/Akt/mTOR Signal in Cilia-Less MC3T3-E1 Preosteoblast Cells

We investigated whether combined fluid shear stress (FSS) and melatonin stimulated signal transduction in cilia-less MC3T3-E1 preosteoblast cells. MC3T3-E1 cells were treated with chloral hydrate or nocodazole, and mechanotransduction sensor primary cilia were removed. p-extracellular signal–regulated kinase (ERK) and p-Akt with/without melatonin increased with nocodazole treatment and decreased with chloral hydrate treatment, whereas p-ERK and p-Akt in FSS with/without melatonin increased in cilia-less groups compared to cilia groups. Furthermore, p-mammalian target of rapamycin (mTOR) with FSS-plus melatonin increased in cilia-less groups compared to only melatonin treatments in cilia groups. Expressions of Bcl-2, Cu/Zn-superoxide dismutase (SOD), and catalase proteins were higher in FSS with/without melatonin with cilia-less groups than only melatonin treatments in cilia groups. Bax protein expression was high in FSS-plus melatonin with chloral hydrate treatment. In chloral hydrate treatment with/without FSS, expressions of Cu/Zn-SOD, Mn-SOD, and catalase proteins were high compared to only-melatonin treatments. In nocodazole treatment, Mn-SOD protein expression without FSS was high, and catalase protein level with FSS was low, compared to only melatonin treatments. These data show that the combination with FSS and melatonin enhances ERK/Akt/mTOR signal in cilia-less MC3T3-E1, and the enhanced signaling in cilia-less MC3T3-E1 osteoblast cells may activate the anabolic effect for the preservation of cell structure and function.

Melatonin: A Molecule for Reducing Breast Cancer Risk

The objective of this article is to review the basis supporting the usefulness of melatonin as an adjuvant therapy for breast cancer (BC) prevention in several groups of individuals at high risk for this disease. Melatonin, as a result of its antiestrogenic and antioxidant properties, as well as its ability to improve the efficacy and reduce the side effects of conventional antiestrogens, could safely be associated with the antiestrogenic drugs presently in use. In individuals at risk of BC due to night shift work, the light-induced inhibition of melatonin secretion, with the consequent loss of its antiestrogenic effects, would be countered by administering this neurohormone. BC risk from exposure to metalloestrogens, such as cadmium, could be treated with melatonin supplements to individuals at risk of BC due to exposure to this xenoestrogen. The BC risk related to obesity may be reduced by melatonin which decrease body fat mass, inhibits the enhanced aromatase expression in obese women, increases adiponectin secretion, counteracts the oncogenic effects of elevated concentrations of leptin; and decreases blood glucose levels and insulin resistance. Despite compelling experimental evidence of melatonin's oncostatic actions being susceptible to lowering BC risk, there is still a paucity of clinical trials focused on this subject.

Etiological Theories of Adolescent Idiopathic Scoliosis: Past and Present

Adolescent idiopathic scoliosis is one of the most common spinal deformities, yet its cause is unknown. Various theories look to biomechanical, neuromuscular, genetic, and environmental origins, yet our understanding of scoliosis etiology is still limited. Determining the cause of a disease is crucial to developing the most effective treatment. Associations made with scoliosis do not necessarily point to causality, and it is difficult to determine whether said associations are primary (playing a role in development) or secondary (develop as a result of scoliosis). Scoliosis is a complex condition with highly variable expression, even among family members, and likely has many causes. These causes could be similar among homogenous groups of AIS patients, or they could be individual. Here, we review the most prevalent theories of scoliosis etiology and recent trends in research.

THE ELEVATION OF OSTEOBLAST ACTIVITY IN RAT BONE MARROW MESENCHYMAL STEM CELLS IN OSTEOGENIC MEDIUM EXPOSED WITH MELATONIN IN PHYSIOLOGICAL DOSES

The objective of this study was to analyze the elevation of osteoblast activity in bone marrow mesenchymal stem cells (BM-MSCs) in osteogenic medium by physiological doses of melatonin administration by measuring alkaline phosphatase (ALP) and osteocalcin level.This studyused BM-MSCs from Rattusnorvegiccus femur bone. Rat BM-MSCs were cultured in a-Mem medium, differentiated in osteogenic medium, and administrated melatonin up to 21 days. This study was divided into 4 groups, K0 (control group), K1 (administrated of 25 nM melatonin), K2 (administrated of 50 nM melatonin), and K3 (administrated of 100 nM melatonin). Rat BM-MSCs were characterized CD 45- and CD 105+ marker using imunocytochemistry analysis and stained with Alizarin red after 15 days treatment. ALP and osteocalcin level were measured using ELISA Kit in days 21st.There weren’t differences ofALP level beetwen groups and there are differences ofosteocalcin level between control groups (K0) withK1, K2, dan K3, and beetwen K1 and K2. The conclusion of this study was that there were an elevation of osteoblast activity in rat BM-MSCs in osteogenic medium by physiological doses of melatonin administration characterized by the elevation of osteocalcin level.

Melatonin promotes osteoblast differentiation by regulating Osterix protein stability and expression

Although the biological role of melatonin in osteogenic differentiation has been suggested, the mechanism of osteoblast differentiation remains unclear. Thus, the present study investigated the underlying molecular mechanisms based on osteoblast-specific transcription factors. We found that melatonin enhanced BMP-4-induced osteogenic differentiation and increased the expression of osteogenic markers, especially Osterix, which is an essential transcription factor for the differentiation of preosteoblasts into mature osteoblasts in the late stage of osteoblast differentiation. Melatonin treatment increased the expression of Osterix during osteoblast differentiation and stabilized its expression by the inhibition of ubiquitin-proteasome-mediated degradation of Osterix, leading to up-regulated Osterix transcriptional activity on the osteogenic promoter and promoting alkaline phosphatase activity and bone mineralization. Furthermore, treatment with protein kinase A (PKA) inhibitor H89 and protein kinase C (PKC) inhibitor Go6976 blocked the melatonin-induced transcriptional activity and phosphorylation of Osterix, indicating that melatonin regulates Osterix expression via the PKA and PKC signaling pathways. Overall, these findings suggest that melatonin directly regulates the late stage of osteoblast differentiation by enhancing Osterix expression; this provides further evidence of melatonin as a potent agent for treating osteoporosis.

Melatonin attenuates titanium particle-induced osteolysis via activation of Wnt/β-catenin signaling pathway

Wear debris-induced inhibition of bone regeneration and extensive bone resorption were common features in peri-prosthetic osteolysis (PPO). Here, we investigated the effect of melatonin on titanium particle-stimulated osteolysis in a murine calvariae model and mouse-mesenchymal-stem cells (mMSCs) culture system. Melatonin inhibited titanium particle-induced osteolysis and increased bone formation at osteolytic sites, confirmed by radiological and histomorphometric data. Furthermore, osteoclast numbers decreased dramatically in the low- and high-melatonin administration mice, as respectively, compared with the untreated animals. Melatonin alleviated titanium particle-induced depression of osteoblastic differentiation and mineralization in mMSCs. Mechanistically, melatonin was found to reduce the degradation of β-catenin, levels of which were decreased in presence of titanium particles both in vivo and in vitro. To further ensure whether the protective effect of melatonin was mediated by the Wnt/β-catenin signaling pathway, ICG-001, a selective β-catenin inhibitor, was added to the melatonin-treated groups and was found to attenuate the effect of melatonin on mMSC mineralization. We also demonstrated that melatonin modulated the balance between receptor activator of nuclear factor kappa-B ligand and osteoprotegerin via activation of Wnt/β-catenin signaling pathway. These findings strongly suggest that melatonin represents a promising candidate in the treatment of PPO.

STATEMENT OF SIGNIFICANCE

Peri-prosthetic osteolysis, initiated by wear debris-induced inhibition of bone regeneration and extensive bone resorption, is the leading cause for implant failure and reason for revision surgery. In the current study, we demonstrated for the first time that melatonin can induce bone regeneration and reduce bone resorption at osteolytic sites caused by titanium-particle stimulation. These effects might be mediated by activating Wnt/β-catenin signaling pathway and enhancing osteogenic differentiation. Meanwhile, the ability of melatonin to modulate the balance between receptor activator of nuclear factor kappa-B ligand and osteoprotegerin mediated by Wnt/β-catenin signaling pathway, thereby suppressing osteoclastogenesis, may be implicated in the protective effects of melatonin on titanium-particle-induced bone resorption. These results suggested that melatonin can be considered as a promising therapeutic agent for the prevention and treatment of peri-prosthetic osteolysis.

Melatonin, bone regulation and the ubiquitin-proteasome connection: A review

Recently, investigators have shown that ubiquitin-proteasome-mediated protein degradation is critical in regulating the balance between bone formation and bone resorption. The major signal transduction pathways regulating bone formation are the RANK/NF-κB pathway and the Wnt/β-catenin pathway. These signal transduction pathways regulate the activity of mature osteoblasts and osteoclasts. In addition, the Wnt/β-catenin pathway is one of the major signaling pathways in the differentiation of osteoblasts. The ubiquitin ligases that are reported to be of major significance in regulating these pathways are the ubiquitin SCF(B-TrCP) ligase (which regulates activation of NF-κB via degradation of IkBα in osteoclasts, and regulates bone transcription factors via degradation of β-catenin), the Keap-Cul3-Rbx1 ligase (which regulates degradation of IkB kinase, Nrf2, and the antiapoptotic factor Bcl-2), and Smurf1. Also of significance in regulating osteoclastogenesis is the deubiquitinase, CYLD (cylindramatosis protein), which facilitates the separation of NF-κB from IkBα. The degradation of CYLD is also under the regulation of SCF(B-TrCP). Proteasome inhibitors influence the activity of mature osteoblasts and osteoclasts, but also modulate the differentiation of precursor cells into osteoblasts. Preclinical studies show that melatonin also influences bone metabolism by stimulating bone growth and inhibiting osteoclast activity. These actions of melatonin could be interpreted as being mediated by the ubiquitin ligases SCF(B-TrCP) and Keap-Cul3-Rbx, or as an inhibitory effect on proteasomes. Clinical trials of the use of melatonin in the treatment of bone disease, including multiple myeloma, using both continuous and intermittent modes of administration, are warranted.

[THE EFFECT OF EXOGENOUS MELATONIN ON BONE REMODELING]

It was investigated in spring 28-day experiment the administration of pharmacological doses (5 mg/kg) of melatonin to 3-month male rats with high and low levels of energy metabolismat remodeling of bone tissue. It was shown the decrease in activity of osteoblast and increase of osteoclast activity regardless of energy metabolism intensity, increase in concentration of glycosaminoglycans and free amino acids. This indicates the inhibition of physiological bone remodeling and helps to maintain the integrity of the organic matrix and the inorganic component of the fixation of the connective tissue - hydroxyapatite crystals.

Effect of Melatonin on the Extracellular-Regulated Kinase Signal Pathway Activation and Human Osteoblastic Cell Line hFOB 1.19 Proliferation

It has been shown that melatonin may affect bone metabolism. However, it is controversial whether melatonin could promote osteoblast proliferation, and the precise molecular mechanism of melatonin on osteoblast proliferation is still obscure. In this study, the results of the CCK-8 assay showed that melatonin significantly promoted human osteoblastic cell line hFOB 1.19 cell proliferation at 1, 2.5, 5, 10, 25, 50 and 100 µM concentrations for 24 h, but there were no significant differences among the groups. Western blot demonstrated that 10 µM melatonin significantly promoted ERK1/2 phosphorylation. Furthermore, we also detected the phosphorylation of c-Raf, MEK1/2, p90RSK and MSK1, and all of them increased with 10 µM melatonin. U0126 (a selective inhibitor of MEK that disrupts downstream activation of ERK1/2) downregulated the phosphorylation of ERK1/2, p90RSK and MSK1. U0126 also attenuated the proliferation of osteoblasts stimulated by melatonin. In conclusion, this study for the first time indicates that melatonin (10 nM–100 µM) promotes the proliferation of a human osteoblastic cell line hFOB 1.19 through activation of c-Raf, MEK1/2, ERK1/2, p90RSK and MSK1.

Melatonin promotes osteoblast differentiation and mineralization of MC3T3-E1 cells under hypoxic conditions through activation of PKD/p38 pathways

Osteoblastic differentiation and bone-forming capacity are known to be suppressed under hypoxic conditions. Melatonin has been shown to influence cell differentiation. A number of in vitro and in vivo studies have suggested that melatonin also has an anabolic effect on bone, by promoting osteoblastic differentiation. However, the precise mechanisms and the signaling pathways involved in this process, particularly under hypoxic conditions, are unknown. This study investigated whether melatonin could promote osteoblastic differentiation and mineralization of preosteoblastic MC3T3-E1 cells under hypoxic conditions. Additionally, we examined the molecular signaling pathways by which melatonin mediates this process. We found that melatonin is capable of promoting differentiation and mineralization of MC3T3-E1 cells cultured under hypoxic conditions. Melatonin upregulated ALP activity and mRNA levels of Alp, Osx, Col1, and Ocn in a time- and concentration-dependent manner. Alizarin red S staining showed that the mineralized matrix in hypoxic MC3T3-E1 cells formed in a manner that was dependent on melatonin concentration. Moreover, melatonin stimulated phosphorylation of p38 Mapk and Prkd1 in these MC3T3-E1 cells. We concluded that melatonin promotes osteoblastic differentiation of MC3T3-E1 cells under hypoxic conditions via the p38 Mapk and Prkd1 signaling pathways.

Urinary levels of melatonin and risk of postmenopausal breast cancer: women's health initiative observational cohort

BACKGROUND

Results from prospective studies on the association between urinary levels of melatonin and risk of postmenopausal breast cancer have been mixed. Several although not all studies have found lower urinary levels of melatonin in women who developed breast cancer compared with cancer-free women.

METHODS

We examined the association between urinary levels of melatonin and breast cancer risk in postmenopausal women in a case-control study nested in the Women's Health Initiative Observational Cohort. Levels of 6-sulfatoxymelatonin were measured in first morning voids from 258 women who later developed breast cancer and from 515 matched controls. Multivariable conditional logistic regression was used to calculate ORs and 95% confidence intervals (CI).

RESULTS

Fully adjusted risk estimates of breast cancer, relative to the lowest quartile level of creatinine-adjusted melatonin, were 1.07 (95% CI, 0.67-1.71), 1.26 (95% CI, 0.79-2.01), and 1.25 (95% CI, 0.78-2.02) for women in the second, third, and highest quartile (Ptrend = 0.27). Comparable results for cases diagnosed less than four years after urinary collection and matched controls were 1.0, 1.25 (95% CI, 0.51-3.06), 1.85 (95% CI, 0.75-4.57), and 1.94 (95% CI, 0.75-5.03; Ptrend = 0.11). Melatonin levels and breast cancer were not associated in cases diagnosed four or more years after urinary collection and matched controls (Ptrend = 0.89).

CONCLUSIONS

We found no evidence that higher urinary levels of melatonin are inversely associated with breast cancer risk in postmenopausal women.

IMPACT

Accumulating discrepancies in results across studies warrant further exploration.

Melatonin effects on bone: potential use for the prevention and treatment for osteopenia, osteoporosis, and periodontal disease and for use in bone-grafting procedures

An important role for melatonin in bone formation and restructuring has emerged, and studies demonstrate the multiple mechanisms for these beneficial actions. Statistical analysis shows that even with existing osteoporotic therapies, bone-related disease, and mortality are on the rise, creating a huge financial burden for societies worldwide. These findings suggest that novel alternatives need to be developed to either prevent or reverse bone loss to combat osteoporosis-related fractures. The focus of this review describes melatonin's role in bone physiology and discusses how disruption of melatonin rhythms by light exposure at night, shift work, and disease can adversely impact on bone. The signal transduction mechanisms underlying osteoblast and osteoclast differentiation and coupling with one another are discussed with a focus on how melatonin, through the regulation of RANKL and osteoprotegerin synthesis and release from osteoblasts, can induce osteoblastogenesis while inhibiting osteoclastogenesis. Also, melatonin's free-radical scavenging and antioxidant properties of this indoleamine are discussed as yet an additional mechanism by which melatonin can maintain one's bone health, especially oral health. The clinical use for melatonin in bone-grafting procedures, in reversing bone loss due to osteopenia and osteoporosis, and in managing periodontal disease is discussed.

Pinealectomy in a broiler chicken model impairs endochondral ossification and induces rapid cancellous bone loss

BACKGROUND CONTEXT

Adolescent idiopathic scoliosis (AIS) in humans is a lateral curvature of the spine often associated with osteopenia. It has recently been accepted that the development of AIS is closely associated with spinal overgrowth. Pinealectomy (PNX) in a chicken model consistently induces scoliosis with anatomic features similar to human AIS; however, the mechanism of PNX inducing scoliosis is poorly understood.

PURPOSE

This experimental study attempts to improve the understanding of the mechanisms underlying the onset of scoliosis in a PNX broiler chicken model.

METHODS

A histomorphometric study was performed to analyze longitudinal bone growth and cancellous bone remodeling before the development of scoliosis. Static and dynamic parameters in cancellous bone and chondro-osseous junction of the 7th thoracic vertebral body at 9 days after hatching were compared between PNX chickens (n=9) and control chickens with no surgery (n=5).

RESULTS

PNX resulted in a rapid and marked loss of cancellous bone volume (7.9±0.9% vs. 14.2±1.8%, mean±SD, p<.0005) and profoundly disrupted trabecular structure with increases in dynamic formative parameters, such as mineralizing surface, mineralization apposition rate, and adjusted appositional rate. In the chondro-osseous junction, activated osteoclasts phagocytized degenerating chondrocytes, leaving a minimal amount of cartilage matrix and activated osteoblasts, losing their scaffolding for bone formation, and directly covering the hypertrophic zone cells. The osteoid surface and thickness in the chondro-osseous junction were significantly increased in PNX chickens (43.1±14.2% vs. 11.6±5.7% and 4.1±0.2 μm vs. 2.9±0.4 μm). In the subjacent cartilage regions being protected from further resorption, abundant labeled cartilage remained with higher cellularity.

CONCLUSIONS

It is known that fast-growing birds have a unique paradigm of rapid bone elongation with minimal metaphyseal bone production. A bone-forming surface exists at the front of cartilage ossification in the growth plate; therefore, papillae of hypertrophic chondrocytes become included between the trabeculae of metaphyseal bone and the overall thickness of the growth plate increases considerably in addition to distal expansion. Our results indicate that the unique mechanism for rapid bone elongation in chicken is more pronounced after PNX. PNX also induces high turnover osteoporosis, which may also contribute to the development of scoliosis in the chicken.

Melatonin inhibits the proliferation of human osteosarcoma cell line MG-63

It seems established that the onset of osteosarcoma and the reduction in melatonin production run in parallel; this suggests that the decline in the cancer-inhibiting agent, melatonin, may contribute to the occurrence of osteosarcoma and that melatonin supplementation may have promise for preventing the development and progression of this condition. There is, however, no direct evidence regarding an antiproliferative effect of melatonin in osteosarcoma cells. In the current study, we examined whether melatonin inhibits the proliferation of human osteosarcoma cell line MG-63. MTT staining showed that at 4 mM-10 mM concentrations, melatonin significantly reduced the MG-63 cell proliferation in a dose-dependent and time-dependent manner. Flow cytometry documented that 4 mM melatonin significantly increased the fraction of cells in the G(0)/G(1) phase of the cell cycle, while simultaneously reducing the proportion in the S and G(2)/M phases. Western blot and real-time PCR analyses further confirmed that melatonin's inhibitory effect was possibly because of downregulation of cyclin D1 and CDK4, related to the G(1) phase, and of cyclin B1 and CDK1, related to the G(2)/M phase. There was no downregulation of cyclin E, CDK2, and cyclin A, which are related to G(1)/S transition and S phase. These findings provide evidence that melatonin may significantly inhibit human osteosarcoma cell proliferation in a dose-dependent and time-dependent manner and this inhibition involves the downregulation of cyclin D1, CDK4, cyclin B1 and CDK1.

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.

Melatonin effects on hard tissues: bone and tooth

Melatonin is an endogenous hormone rhythmically produced in the pineal gland under the control of the suprachiasmatic nucleus (SCN) and the light/dark cycle. This indole plays an important role in many physiological processes including circadian entrainment, blood pressure regulation, seasonal reproduction, ovarian physiology, immune function, etc. Recently, the investigation and applications of melatonin in the hard tissues bone and tooth have received great attention. Melatonin has been investigated relative to bone remolding, osteoporosis, osseointegration of dental implants and dentine formation. In the present review, we discuss the large body of published evidence and review data of melatonin effects on hard tissues, specifically, bone and tooth.

Fluid shear stress and melatonin in combination activate anabolic proteins in MC3T3-E1 osteoblast cells

In this study, we investigated whether fluid shear stress and melatonin in combination stimulate the anabolic proteins through the phosphorylation of extracellular signal-regulated kinase (p-ERK) in MC3T3-E1 osteoblast cells. First, we researched why fluid shear stress and melatonin in combination influence cell survival. Fluid shear stress (1 hr) and melatonin (1 mM) in combination reduced autophagic marker LC3-II compared with fluid shear stress (1 hr) and/or melatonin (0.1 mM). Under the same conditions for fluid shear stress, markers of cell survival signaling pathway p-ERK, phosphorylation of serine-threonine protein kinase (p-Akt), phosphorylation of mammalian target of rapamycin (p-mTOR), and p85-S6K were investigated. p-Akt, p-mTOR (Ser 2481) expressions increased with the addition of 1 mM melatonin prior to 0.1 mM melatonin treatment. However, p-S6K expression did not change significantly. Next, mitochondria activity including Bcl-2, Bax, catalase, and Mn-superoxide dismutase (Mn-SOD) were studied. Expressions of Bcl-2, Bax, and catalase proteins were low under fluid shear stress plus 1 mM melatonin compared with only fluid shear stress alone, whereas Mn-SOD expression was high compared with conditions of no fluid shear stress. Finally, the anabolic proteins of bone, osteoprotegerin, type I collagen (collagen I), and bone sialoprotein II (BSP II) were checked. These proteins increased with combined fluid shear stress (1, 4 hr) and melatonin (0.1, 1 mM). Together, these results suggest that fluid shear stress and melatonin in combination may increase the expression of anabolic proteins through the p-ERK in MC3T3-E1 osteoblast cells. Therefore, fluid shear stress in combination with melatonin may promote the anabolic response of osteoblasts.

Melatonin Suppresses the Expression of 45S Preribosomal RNA and Upstream Binding Factor and Enhances the Antitumor Activity of Puromycin in MDA-MB-231 Breast Cancer Cells

Since the dysregulation of ribosome biogenesis is closely associated with tumor progression, in the current study, the critical role of ribosome biogenesis related signaling was investigated in melatonin and/or puromycin induced apoptosis in MDA-MB-231 breast cancer cells. Despite its weak cytotoxicity, melatonin from 3 mM attenuated the expression of 45S pre-ribosomal RNA (pre-rRNA), UBF as a nucleolar transcription factor, and fibrillarin at mRNA level and consistently downregulated nucleolar proteins such as UBF and fibrillarin at protein level in MDA-MB-231 cells. Furthermore, immunofluorescence assay revealed that UBF was also degraded by melatonin in MDA-MB-231 cells. In contrast, melatonin attenuated the expression of survival genes such as Bcl-xL, Mcl-1, cyclinD1, and cyclin E, suppressed the phosphorylation of AKT, mTOR, and STAT3, and cleaved PARP and activated caspase 3 only at a high concentration of 12 mM. However, combined treatment of melatonin (3 mM) and puromycin (1 μM) synergistically inhibited viability, attenuated the expression of 45S pre-rRNA and UBF, and consistently downregulated UBF, XPO1 and IPO7, procaspase 3, and Bcl-xL in MDA-MB 231 cells. Overall, these findings suggest that melatonin can be a cancer preventive agent by combination with puromycin via the inhibition of 45S pre-rRNA and UBF in MDA-MB 231 breast cancer cells.

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.

Abnormal Skeletal Growth in Adolescent Idiopathic Scoliosis Is Associated with Abnormal Quantitative Expression of Melatonin Receptor, MT2

The defect of the melatonin signaling pathway has been proposed to be one of the key etiopathogenic factors in adolescent idiopathic scoliosis (AIS). A previous report showed that melatonin receptor, MT2, was undetectable in some AIS girls. The present study aimed to investigate whether the abnormal MT2 expression in AIS is quantitative or qualitative. Cultured osteoblasts were obtained from 41 AIS girls and nine normal controls. Semi-quantification of protein expression by Western blot and mRNA expression by TaqMan real-time PCR for both MT1 and MT2 were performed. Anthropometric parameters were also compared and correlated with the protein expression and mRNA expression of the receptors. The results showed significantly lower protein and mRNA expression of MT2 in AIS girls compared with that in normal controls (p = 0.02 and p = 0.019, respectively). No differences were found in the expression of MT1. When dichotomizing the AIS girls according to their MT2 expression, the group with low expression was found to have a significantly longer arm span (p = 0.036). The results of this study showed for the first time a quantitative change of MT2 in AIS that was also correlated with abnormal arm span as part of abnormal systemic skeletal growth.

Effects on bone by the light/dark cycle and chronic treatment with melatonin and/or hormone replacement therapy in intact female mice

In this study, the effects of the light/dark cycle, hormone replacement therapy (HRT), and nocturnal melatonin supplementation on osteogenic markers and serum melatonin levels were examined in a blind mouse model (MMTV-Neu transgenic mice). Melatonin levels in this mouse strain (FVB/N) with retinal degeneration (rd-/-) fluctuate in a diurnal manner, suggesting that these mice, although blind, still perceive light. Real-time RT-PCR analyses demonstrated that Runx2, Bmp2, Bmp6, Bglap, and Per2 mRNA levels coincide with melatonin levels. The effect of chronic HRT (0.5 mg 17β-estradiol + 50 mg progesterone in 1800 kcal of diet) alone and in combination with melatonin (15 mg/L drinking water) on bone quality and density was also assessed by histomorphometry and microcomputed tomography, respectively. Bone density was significantly increased (P < 0.05) after 1 yr of treatment with the individual therapies, HRT (22% increase) and nocturnal melatonin (20% increase) compared to control. Hormone replacement therapy alone also increased surface bone, decreased trabecular space, and decreased the number of osteoclasts without affecting osteoblast numbers compared to the control group (P < 0.05). Chronic HRT + melatonin therapy did not significantly increase bone density, even though this combination significantly increased Bglap mRNA levels. These data suggest that the endogenous melatonin rhythm modulates markers important to bone physiology. Hormone replacement therapy with or without nocturnal melatonin in cycling mice produces unique effects on bone markers and bone density. The effects of these therapies alone and combined may improve bone health in women in perimenopause and with low nocturnal melatonin levels from too little sleep, too much light, or age.

Prevention of ERK activation involves melatonin-induced G(1) and G(2) /M phase arrest in the human osteoblastic cell line hFOB 1.19

Melatonin regulates mitogen-activated protein kinase (MAPK) and Akt signaling pathways. The MAPK family mainly includes extracellular signal-regulated kinase (ERK), p38, and c-Jun N-terminal kinase (JNK). Our previous study documented that melatonin delays osteoblast proliferation; however, the mechanism of action of melatonin remains unclear. Here, we demonstrate that melatonin significantly inhibited phosphorylation of ERK but not p38, JNK, or Akt in a human osteoblastic cell line 1.19 (hFOB), as measured by western blot. The expression of ERK, p38, JNK, and Akt was not altered. PD98059 (a selective inhibitor of MEK that disrupts downstream activation of ERK) and melatonin alone, and especially in combination, significantly induced an antiproliferative effect, G(1) and G(2) /M phase arrest of the cell cycle, and downregulation of the expression at both the protein and mRNA levels of cyclin D1 and CDK4, related to the G(1) phase, and of cyclin B1 and CDK1, related to the G(2) /M phase, as measured by the 3-(4,5-dimethyl-thiazol-2-yl)-2,5-diphenyl-tetrazolium bromide (MTT) method, flow cytometry after propidium iodide staining, and both western blot and real-time PCR, respectively. Moreover, the combination of PD98059 and melatonin synergistically and markedly augmented the action of either agent alone. Coimmunoprecipitation further confirmed that there was an interaction between phosphorylation of ERK and cyclin D1, CDK4, cyclin B1, or CDK1, which was weaken in the presence of melatonin or PD98059. These results suggest that the prevention of ERK activation is involved in melatonin-induced G(1) and G(2) /M phase arrest, and this inhibitory effect is potentially via the ERK, but not p38, JNK, or Akt, pathway.

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.

Clinical uses of melatonin in pediatrics

This study analyzes the results of clinical trials of treatments with melatonin conducted in children, mostly focused on sleep disorders of different origin. Melatonin is beneficial not only in the treatment of dyssomnias, especially delayed sleep phase syndrome, but also on sleep disorders present in children with attention-deficit hyperactivity, autism spectrum disorders, and, in general, in all sleep disturbances associated with mental, neurologic, or other medical disorders. Sedative properties of melatonin have been used in diagnostic situations requiring sedation or as a premedicant in children undergoing anesthetic procedures. Epilepsy and febrile seizures are also susceptible to treatment with melatonin, alone or associated with conventional antiepileptic drugs. Melatonin has been also used to prevent the progression in some cases of adolescent idiopathic scoliosis. In newborns, and particularly those delivered preterm, melatonin has been used to reduce oxidative stress associated with sepsis, asphyxia, respiratory distress, or surgical stress. Finally, the administration of melatonin, melatonin analogues, or melatonin precursors to the infants through the breast-feeding, or by milk formula adapted for day and night, improves their nocturnal sleep. Side effects of melatonin treatments in children have not been reported. Although the above-described results are promising, specific studies to resolve the problem of dosage, formulations, and length of treatment are necessary.