Biological effects of melatonin on osteoblast/osteoclast cocultures, bone, and quality of life: Implications of a role for MT2 melatonin receptors, MEK1/2, and MEK5 in melatonin-mediated osteoblastogenesis

Bone and Extracellular Signal-Related Kinase 5 (ERK5)

Bones are vital for anchoring muscles, tendons, and ligaments, serving as a fundamental element of the human skeletal structure. However, our understanding of bone development mechanisms and the maintenance of bone homeostasis is still limited. Extracellular signal-related kinase 5 (ERK5), a recently identified member of the mitogen-activated protein kinase (MAPK) family, plays a critical role in the pathogenesis and progression of various diseases, especially neoplasms. Recent studies have highlighted ERK5's significant role in both bone development and bone-associated pathologies. This review offers a detailed examination of the latest research on ERK5 in different tissues and diseases, with a particular focus on its implications for bone health. It also examines therapeutic strategies and future research avenues targeting ERK5.

Biodegradable Zn-5Dy Alloy with Enhanced Osteo/Angio-Genic Activity and Osteointegration Effect via Regulation of SIRT4-Dependent Mitochondrial Function

Zinc (Zn)-dysprosium (Dy) binary alloys are promising biodegradable bone fracture fixation implants owing to their attractive biodegradability and mechanical properties. However, their clinical application is a challenge for bone fracture healing, due to the lack of Zn-Dy alloys with tailored proper bio-mechanical and osteointegration properties for bone regeneration. A Zn-5Dy alloy with high strength and ductility and a degradation rate aligned with the bone remodeling cycle is developed. Here, mechanical stability is further confirmed, proving that Zn-5Dy alloy can resist aging in the degradation process, thus meeting the mechanical requirements of fracture fixation. In vitro cellular experiments reveal that the Zn-5Dy alloy enhances osteogenesis and angiogenesis by elevating SIRT4-mediated mitochondrial function. In vivo Micro-CT, SEM-EDS, and immunohistochemistry analyses further indicate good biosafety, suitable biodegradation rate, and great osteointegration of Zn-5Dy alloy during bone healing, which also depends on the upregulation of SIRT4-mediated mitochondrial events. Overall, the study is the first to report a Zn-5Dy alloy that exerts remarkable osteointegration properties and has a strong potential to promote bone healing. Furthermore, the results highlight the importance of mitochondrial modulation and shall guide the future development of mitochondria-targeting materials in enhancing bone fracture healing.

Gut microbially produced tryptophan metabolite melatonin ameliorates osteoporosis via modulating SCFA and TMAO metabolism

Osteoporosis (OP) is a severe global health issue that has significant implications for productivity and human lifespan. Gut microbiota dysbiosis has been demonstrated to be closely associated with OP progression. Melatonin (MLT) is an important endogenous hormone that modulates bone metabolism, maintains bone homeostasis, and improves OP progression. Multiple studies indicated that MLT participates in the regulation of intestinal microbiota and gut barrier function. However, the promising effects of gut microbiota-derived MLT in OP remain unclear. Here, we found that OP resulted in intestinal tryptophan disorder and decreased the production of gut microbiota-derived MLT, while administration with MLT could mitigate OP-related clinical symptoms and reverse gut microbiota dysbiosis, including the diversity of intestinal microbiota, the relative abundance of many probiotics such as Allobaculum and Parasutterella, and metabolic function of intestinal flora such as amino acid metabolism, nucleotide metabolism, and energy metabolism. Notably, MLT significantly increased the production of short-chain fatty acids and decreased trimethylamine N-oxide-related metabolites. Importantly, MLT could modulate the dynamic balance of M1/M2 macrophages, reduce the serum levels of pro-inflammatory cytokines, and restore gut-barrier function. Taken together, our results highlighted the important roles of gut microbially derived MLT in OP progression via the "gut-bone" axis associated with SCFA metabolism, which may provide novel insight into the development of MLT as a promising drug for treating OP.

Melatonin protects TEGDMA-induced preodontoblast mitochondrial apoptosis via the JNK/MAPK signaling pathway

Resin monomer-induced dental pulp injury presents a pathology related to mitochondrial dysfunction. Melatonin has been regarded as a strong mitochondrial protective bioactive compound from the pineal gland. However, it remains unknown whether melatonin can prevent dental pulp from resin monomer-induced injury. The aim of this study is to investigate the effects of melatonin on apoptosis of mouse preodontoblast cells (mDPC6T) induced by triethylene glycol dimethacrylate (TEGDMA), a major component in dental resin, and to determine whether the JNK/MAPK signaling pathway mediates the protective effect of melatonin. A well-established TEGDMA-induced mDPC6T apoptosis model is adopted to investigate the preventive function of melatonin by detecting cell viability, apoptosis rate, expressions of apoptosis-related proteins, mitochondrial ROS (mtROS) production, mitochondrial membrane potential (MMP) and adenosine triphosphate (ATP) level. Inhibitors of MAPKs are used to explore which pathway is involved in TEGDMA-induced apoptosis. Finally, the role of the JNK/MAPK pathway is verified using JNK agonists and antagonists. Our results show that melatonin attenuates TEGDMA-induced mDPC6T apoptosis by reducing mtROS production and rescuing MMP and ATP levels. Furthermore, mitochondrial dysfunction and apoptosis are alleviated only by the JNK/MAPK inhibitor SP600125 but not by other MAPK inhibitors. Additionally, melatonin downregulates the expression of phosphorylated JNK and counteractes the activating effects of anisomycin on the JNK/MAPK pathway, mimicking the effects of SP600125. Our findings demonstrate that melatonin protects mDPC6T cells against TEGDMA-induced apoptosis partly through JNK/MAPK and the maintenance of mitochondrial function, offering a novel therapeutic strategy for the prevention of resin monomer-induced dental pulp injury.

Ingenious Synergy of a Pathology-Specific Biomimetic Multifunctional Nanoplatform for Targeted Therapy in Rheumatoid Arthritis

Based on the pathological characteristics of rheumatoid arthritis, including the overproduction of reactive oxygen species (ROS), inflammatory responses, and osteoclast differentiation, a biomimetic multifunctional nanomedicine (M-M@I) is designed. Iguratimod (IGU) is loaded, which inhibits inflammatory responses and osteoclast differentiation, into mesoporous polydopamine (MPDA), which scavenges ROS. Subsequently, the nanoparticles are coated with a cell membrane of macrophages to achieve actively targeted delivery of the nanoparticles to inflamed joints. It is shown that the M-M@I nanoparticles are taken up well by lipopolysaccharide-induced RAW 264.7 macrophages or bone marrow-derived macrophages (BMDMs). In vitro, the M-M@I nanoparticles effectively scavenge ROS, downregulate genes related to inflammation promotion and osteoclast differentiation, and reduce the proinflammatory cytokines and osteoclast-related enzymes. They also reduce the polarization of macrophages to a pro-inflammatory M1 phenotype and inhibit differentiation into osteoclasts. In mice with collagen-induced arthritis, the M-M@I nanoparticles accumulate at arthritic sites and circulate longer, significantly mitigating arthritis symptoms and bone destruction. These results suggest that the pathology-specific biomimetic multifunctional nanoparticles are effective against rheumatoid arthritis, and they validate the approach of developing multifunctional therapies that target various pathological processes simultaneously.

Knockdown of NEAT1 prevents post-stroke lipid droplet agglomeration in microglia by regulating autophagy

BACKGROUND

Lipid droplets (LD), lipid-storing organelles containing neutral lipids like glycerolipids and cholesterol, are increasingly accepted as hallmarks of inflammation. The nuclear paraspeckle assembly transcript 1 (NEAT1), a long non-coding RNA with over 200 nucleotides, exerts an indispensable impact on regulating both LD agglomeration and autophagy in multiple neurological disorders. However, knowledge as to how NEAT1 modulates the formation of LD and associated signaling pathways is limited.

METHODS

In this study, primary microglia were isolated from newborn mice and exposed to oxygen-glucose-deprivation/reoxygenation (OGD/R). To further explore NEAT1-dependent mechanisms, an antisense oligonucleotide (ASO) was adopted to silence NEAT1 under in vitro conditions. Studying NEAT1-dependent interactions with regard to autophagy and LD agglomeration under hypoxic conditions, the inhibitor and activator of autophagy 3-methyladenine (3-MA) and rapamycin (RAPA) were used, respectively. In a preclinical stroke model, mice received intraventricular injections of ASO NEAT1 or control vectors in order to yield NEAT1 knockdown. Analysis of readout parameters included qRT-PCR, immunofluorescence, western blot assays, and behavioral tests.

RESULTS

Microglia exposed to OGD/R displayed a temporal pattern of NEAT1 expression, peaking at four hours of hypoxia followed by six hours of reoxygenation. After effectively silencing NEAT1, LD formation and autophagy-related proteins were significantly repressed in hypoxic microglia. Stimulating autophagy in ASO NEAT1 microglia under OGD/R conditions by means of RAPA reversed the downregulation of LD agglomeration and perilipin 2 (PLIN2) expression. On the contrary, application of 3-MA promoted repression of both LD agglomeration and expression of the LD-associated protein PLIN2. Under in vivo conditions, NEAT1 was significantly increased in mice at 24 h post-stroke. Knockdown of NEAT1 significantly alleviated LD agglomeration and inhibited autophagy, resulting in improved cerebral perfusion, reduced brain injury and increased neurological recovery.

CONCLUSION

NEAT1 is a key player of LD agglomeration and autophagy stimulation, and NEAT1 knockdown provides a promising therapeutic value against stroke.

Melatonin as a chronobiotic/cytoprotective agent in bone. Doses involved

Because the chronobiotic and cytoprotective molecule melatonin diminishes with age, its involvement in postmenopausal and senescence pathology has been considered since long. One relevant melatonin target site in aging individuals is bone where melatonin chronobiotic effects mediated by MT1 and MT2 receptors are demonstrable. Precursors of bone cells located in bone marrow are exposed to high quantities of melatonin and the possibility arises that melatonin acts a cytoprotective compound via an autacoid effect. Proteins that are incorporated into the bone matrix, like procollagen type I c-peptide, augment after melatonin exposure. Melatonin augments osteoprotegerin, an osteoblastic protein that inhibits the differentiation of osteoclasts. Osteoclasts are target cells for melatonin as they degrade bone partly by generating free radicals. Osteoclast activity and bone resorption are impaired via the free radical scavenger properties of melatonin. The administration of melatonin in chronobiotic doses (less than 10 mg daily) is commonly used in clinical studies on melatonin effect on bone. However, human equivalent doses allometrically derived from animal studies are in the 1-1.5 mg/kg/day range for a 75 kg human adult, a dose rarely used clinically. In view of the absence of toxicity of melatonin in phase 1 pharmacological studies with doses up to 100 mg in normal volunteers, further investigation is needed to determine whether high melatonin doses have higher therapeutic efficacy in preventing bone loss.

Cucumber seed polypeptides regulate RANKL-induced osteoclastogenesis through OPG/RANKL/RANK and NF-κB

Postmenopausal osteoporosis (PMOP) is a common disease that endangers the health of elderly women. Cucumber seeds have shown excellent therapeutic effects on PMOP, but the mechanism of cucumber seed peptide (CSP) remains unclear. The expression levels of NF-κB and osteoclast-related genes were detected by RT-qPCR. The levels of apoptosis-related proteins were detected by Western blotting. Nuclear translocation of NF-κB p65 and osteoclast formation were detected by immunofluorescence and tartrate-resistant acid phosphatase (TRAP) staining, respectively. ELISA was used to detect the expression levels of OPG, M-CSF, and RANKL. Hematoxylin-eosin (H&E) and TRAP staining were used to observe the effects of CSP on bone formation. In RAW264.7 cells, CSP (0.4 mg/L, 4 mg/L, and 40 mg/L) effectively inhibited the expression of osteoclast-related genes (Cathepsin-K, MT1-MMP, MMP-9, and TRAP). TRAP-positive multinucleated giant cells gradually decreased. Furthermore, NF-κB pathway activation downstream of RANK was inhibited. In bone marrow stromal cells (BMSCs), the expression levels of M-CSF and RANKL gradually decreased, and OPG gradually increased with increasing CSP concentrations. Treatment of RAW264.7 cells with pyrrolidine dithiocarbamate (PDTC, an inhibitor of NF-κB) prevented the formation of osteoclasts. Treatment with different concentrations of CSP effectively decreased the levels of RANKL and M-CSF in rat serum and increased the expression of OPG in the oophorectomy (OVX) rat model. Furthermore, different concentrations of CSP could ameliorate the loss of bone structure and inhibit the formation of osteoclasts in rats. CSP inhibits osteoclastogenesis by regulating the OPG/RANKL/RANK pathway and inhibiting the NF-kB pathway.

Influence of Melatonin Treatment on Emotion, Sleep, and Life Quality in Perimenopausal Women: A Clinical Study

Method

100 healthy perimenopausal women were recruited and randomly assigned to two groups, with 50 subjects in each group. In the control group, placebo was administrated daily for 3 cycles (4 weeks of treatment for 1 cycle and drug withdrawals for 1 week). The study group received 3 mg oral melatonin treatment daily in the same period of time. All subjects completed the study. We compared the uterine volume, endometrial thickness, LH (luteinizing hormone), FSH (follicle generating hormone), E2 (estradiol), and melatonin levels during daytime between the two groups before and after the study. Moreover, perimenopause syndrome, sleep, mood, and QoL were analyzed at the baseline and 3 cycles by the questionnaires of the Kupperman index, the Pittsburgh sleep quality index (PSQI), the Hamilton anxiety scale (HAMA), and the Hamilton depression scale (HAMD), as well as menopausal QoL (MENQOL), respectively. Any adverse reactions experienced by the subjects were also compared in the study. Finally, 91 participants (92%) completed the whole study, 47 and 44 in the study and control groups, respectively, and their data were considered in subsequent analyses.

Results

After therapy, the two groups were similar in the uterine volume and endometrial thickness. In contrast to the control group, the study group showed notably decreased LH and FSH levels. No notable difference was discovered in E2 and melatonin levels between the two groups in the study. Moreover, the study group exhibited a significantly lower score in the Kupperman index, PSQI, HAMA, HAMD, and MENQOL scale than the control group. Moreover, the two groups had no notable difference in adverse reactions.

Conclusion

Melatonin was a useful treatment to relieve climacteric symptoms and improve sleep, mood, and life quality in perimenopausal women without obvious adverse reactions.

Melatonin and bone-related diseases: an updated mechanistic overview of current evidence and future prospects

PURPOSE

Bone diseases account for an enormous cost burden on health systems. Bone disorders are considered as age-dependent diseases. The aging of world population has encouraged scientists to further explore the most effective preventive modalities and therapeutic strategies to overcome and reduce the high cost of bone disorders. Herein, we review the current evidence of melatonin's therapeutic effects on bone-related diseases.

METHODS

This review summarized evidences from in vitro, in vivo, and clinical studies regarding the effects of melatonin on bone-related diseases, with a focus on the molecular mechanisms. Electronically, Scopus and MEDLINE®/PubMed databases were searched for articles published on melatonin and bone-related diseases from inception to June 2023.

RESULTS

The findings demonstrated that melatonin has beneficial effect in bone- and cartilage-related disorders such as osteoporosis, bone fracture healing, osteoarthritis, and rheumatoid arthritis, in addition to the control of sleep and circadian rhythms.

CONCLUSION

A number of animal and clinical studies have indicated that various biological effects of melatonin may suggest this molecule as an effective therapeutic agent for controlling, diminishing, or suppressing bone-related disorders. Therefore, further clinical studies are required to clarify whether melatonin can be effective in patients with bone-related diseases.

Zoledronate Promotes Peri-Implant Osteogenesis in Diabetic Osteoporosis by the AMPK Pathway

Together with diabetic osteoporosis (DOP), diabetes patients experience poor peri-implant osteogenesis following implantation for dentition defects. Zoledronate (ZOL) is widely used to treat osteoporosis clinically. To evaluate the mechanism of ZOL for the treatment of DOP, experiments with DOP rats and high glucose-grown MC3T3-E1 cells were used. The DOP rats treated with ZOL and/or ZOL implants underwent a 4-week implant-healing interval, and then microcomputed tomography, biomechanical testing, and immunohistochemical staining were performed to elucidate the mechanism. In addition, MC3T3-E1 cells were maintained in an osteogenic medium with or without ZOL to confirm the mechanism. The cell migration, cellular actin content, and osteogenic differentiation were evaluated by a cell activity assay, a cell migration assay, as well as alkaline phosphatase, alizarin red S, and immunofluorescence staining. The mRNA and protein expression of adenosine monophosphate-activated protein kinase (AMPK), phosphorylated AMPK (p-AMPK), osteoprotegerin (OPG), receptor activator of nuclear factor kappa B ligand (RANKL), bone morphogenetic protein 2 (BMP2), and collagen type I (Col-I) were detected using real-time quantitative PCRs and western blot assays, respectively. In the DOP rats, ZOL markedly improved osteogenesis, enhanced bone strength and increased the expression of AMPK, p-AMPK, and Col-I in peri-implant bones. The in vitro findings showed that ZOL reversed the high glucose-induced inhibition of osteogenesis via the AMPK signaling pathway. In conclusion, the ability of ZOL to promote osteogenesis in DOP by targeting AMPK signaling suggests that therapy with ZOL, particularly simultaneous local and systemic administration, may be a unique approach for future implant repair in diabetes patients.

Absence of melatonin during development impairs craniofacial and dental onset in rats

OBJECTIVE

Herein, we evaluated pinealectomy-induced melatonin absence to determine its effects on craniofacial and dental development in the offspring.

DESIGN

Female Wistar rats in three groups, i.e., intact pregnant rats, pinealectomized pregnant rats (PINX), and pinealectomized pregnant rats subjected to oral melatonin replacement therapy, were crossed 30 days after surgery. The heads of 7-day-old pups were harvested for cephalometric and histological analyses, and maxillae and incisors were collected for mRNA expression analysis.

RESULTS

The PINX pups exhibited a reduction in neurocranial and facial parameters such as a decrease in alveolar bone area, incisor size and proliferation, and an increase in odontoblasts and the dentin layer. Based on incisor mRNA expression analysis, we found that Dmp1 expression was upregulated, whereas Col1a1 expression was downregulated. Maxillary mRNA expression revealed that Rankl expression was upregulated, whereas that of Opn and Osx was downregulated.

CONCLUSION

Our results demonstrated that the absence of maternal melatonin during early life could affect dental and maxillary development in offspring, as well as delay odontogenesis and osteogenesis in maxillary tissues.

CLINICAL RELEVANCE

Our findings suggest that disruptions or a lack of melatonin during pregnancy may cause changes in craniofacial and dental development, at least in animal experiments; however, in humans, these feedings are still poorly understood, and thus careful evaluations of melatonin levels in humans need to be investigated in craniofacial alterations.

Exogenous melatonin ameliorates steroid-induced osteonecrosis of the femoral head by modulating ferroptosis through GDF15-mediated signaling

BACKGROUND

Ferroptosis is an iron-related form of programmed cell death. Accumulating evidence has identified the pathogenic role of ferroptosis in multiple orthopedic disorders. However, the relationship between ferroptosis and SONFH is still unclear. In addition, despite being a common disease in orthopedics, there is still no effective treatment for SONFH. Therefore, clarifying the pathogenic mechanism of SONFH and investigating pharmacologic inhibitors from approved clinical drugs for SONFH is an effective strategy for clinical translation. Melatonin (MT), an endocrine hormone that has become a popular dietary supplement because of its excellent antioxidation, was supplemented from an external source to treat glucocorticoid-induced damage in this study.

METHODS

Methylprednisolone, a commonly used glucocorticoid in the clinic, was selected to simulate glucocorticoid-induced injury in the current study. Ferroptosis was observed through the detection of ferroptosis-associated genes, lipid peroxidation and mitochondrial function. Bioinformatics analysis was performed to explore the mechanism of SONFH. In addition, a melatonin receptor antagonist and shGDF15 were applied to block the therapeutic effect of MT to further confirm the mechanism. Finally, cell experiments and the SONFH rat model were used to detect the therapeutic effects of MT.

RESULTS

MT alleviated bone loss in SONFH rats by maintaining BMSC activity through suppression of ferroptosis. The results are further verified by the melatonin MT2 receptor antagonist that can block the therapeutic effects of MT. In addition, bioinformatic analysis and subsequent experiments confirmed that growth differentiation factor 15 (GDF15), a stress response cytokine, was downregulated in the process of SONFH. On the contrary, MT treatment increased the expression of GDF15 in bone marrow mesenchymal stem cells. Lastly, rescue experiments performed with shGDF15 confirmed that GDF15 plays a key role in the therapeutic effects of melatonin.

CONCLUSIONS

We proposed that MT attenuated SONFH by inhibiting ferroptosis through the regulation of GDF15, and supplementation with exogenous MT might be a promising method for the treatment of SONFH.

The association of melatonin use and hip fracture: a matched cohort study

By using propensity-score matched cohorts, we compared the risk of incident hip fracture between melatonin initiators and hypnotic benzodiazepines initiators. The initiation of melatonin was not associated with an increased risk of hip fracture.

INTRODUCTION

Melatonin is hypothesized to suppress bone loss, but a previous study reported an increased risk of hip fracture among melatonin users compared with non-users, which was however susceptible to confounding by indication. This study aimed to compare the risk of hip fracture between melatonin initiators and initiators of its active comparators, i.e., hypnotic benzodiazepines.

METHODS

Among individuals aged 40 years or older without a history of hip fracture or cancer in the IQVIA Medical Research Database (IMRD) in the UK (2000-2018), a propensity score-matched cohort study was conducted to examine the association of melatonin initiation vs. hypnotic benzodiazepines initiation with the risk of hip fracture.

RESULTS

After propensity score matching, 9,038 patients were included (4,519 melatonin initiators and 4,519 hypnotic benzodiazepines initiators). During the entire follow-up, 41 cases of hip fracture occurred in the melatonin cohort, and 51 cases occurred in the hypnotic benzodiazepines cohort. The absolute rate difference in hip fracture between melatonin initiators and hypnotic benzodiazepines initiators was -0.8 (95% CI: -1.9 to 0.3) per 1000 person-years and the multivariable-adjusted hazard ratio (HR) of hip fracture for melatonin initiators was 0.78 (95% CI: 0.51 to 1.17).

CONCLUSION

In this population-based cohort study, the risk of hip fracture among melatonin initiators was not higher, if not lower, than that among hypnotic benzodiazepines initiators.

Daytime administration of melatonin has better protective effects on bone loss in ovariectomized rats

OBJECTIVE

To explore the difference in the protective effects of intraperitoneal injection of exogenous melatonin of daytime or nighttime on bone loss in ovariectomized (OVX) rats.

METHODS

After bilateral ovariectomy and sham surgery, 40 rats were randomly divided into four groups: sham operation group (Sham), ovariectomy (OVX), and daytime melatonin injection group (OVX + DMLT, 9:00, 30 mg/kg/d) and nighttime injection of melatonin (OVX + NMLT, 22:00, 30 mg/kg/d). After 12 weeks of treatment, the rats were sacrificed. The distal femur, blood and femoral marrow cavity contents were saved. The rest of the samples were tested by Micro-CT, histology, biomechanics and molecular biology. Blood was used for bone metabolism marker measurements. CCK-8, ROS, and Cell apoptosis are performed using MC3E3-T1 cells.

RESULTS

Compared with treatment at night, the bone mass of the OVX rats was significantly increased after the daytime administration. All microscopic parameters of trabecular bone increased, only Tb.Sp decreased. Histologically, the bone microarchitecture of the OVX + DMLT was also more dense than the bone microarchitecture of the OVX + LMLT. In the biomechanical experiment, the femur samples of the day treatment group were able to withstand greater loads and deformation. In molecular biology experiments, bone formation-related molecules increased, while bone resorption-related molecules decreased. After treatment with melatonin administration at night, the expression of MT-1β was significantly decreased. In cell experiments, the MC3E3-T1 cells treated with low-dose MLT had higher cell viability and greater efficiency in inhibiting ROS production than the MC3E3-T1 cells treated with high-dose MLT, which in turn more effectively inhibited apoptosis.

CONCLUSION

Daytime administration of melatonin acquires better protective effects on bone loss than night in OVX rats.

Hormone-Related and Drug-Induced Osteoporosis: A Cellular and Molecular Overview

Osteoporosis resulting from an imbalance of bone turnover between resorption and formation is a critical health issue worldwide. Estrogen deficiency following a nature aging process is the leading cause of hormone-related osteoporosis for postmenopausal women, while glucocorticoid-induced osteoporosis remains the most common in drug-induced osteoporosis. Other medications and medical conditions related to secondary osteoporosis include proton pump inhibitors, hypogonadism, selective serotonin receptor inhibitors, chemotherapies, and medroxyprogesterone acetate. This review is a summary of the cellular and molecular mechanisms of bone turnover, the pathophysiology of osteoporosis, and their treatment. Nuclear factor-κβ ligand (RANKL) appears to be the critical uncoupling factor that enhances osteoclastogenesis. In contrast, osteoprotegerin (OPG) is a RANKL antagonist secreted by osteoblast lineage cells. Estrogen promotes apoptosis of osteoclasts and inhibits osteoclastogenesis by stimulating the production of OPG and reducing osteoclast differentiation after suppression of IL-1 and TNF, and subsequent M-CSF, RANKL, and IL-6 release. It can also activate the Wnt signaling pathway to increase osteogenesis, and upregulate BMP signaling to promote mesenchymal stem cell differentiation from pre-osteoblasts to osteoblasts rather than adipocytes. Estrogen deficiency leads to the uncoupling of bone resorption and formation; therefore, resulting in greater bone loss. Excessive glucocorticoids increase PPAR-2 production, upregulate the expression of Dickkopf-1 (DKK1) in osteoblasts, and inhibit the Wnt signaling pathway, thus decreasing osteoblast differentiation. They promote osteoclast survival by enhancing RANKL expression and inhibiting OPG expression. Appropriate estrogen supplement and avoiding excessive glucocorticoid use are deemed the primary treatment for hormone-related and glucocorticoid-induced osteoporosis. Additionally, current pharmacological treatment includes bisphosphonates, teriparatide (PTH), and RANKL inhibitors (such as denosumab). However, many detailed cellular and molecular mechanisms underlying osteoporosis seem complicated and unexplored and warrant further investigation.

Peiminine regulates bone-fat balance by canonical Wnt/β-catenin pathway in an ovariectomized rat model

Peiminine is a major biologically active component of Fritillaria thunbergii Miq that exhibits good anticancer, antiinflammatory, and anti-osteoclast effects. However, its effects on osteoporosis (OP) remain unknown. This study aimed to explore whether Peiminine was able to regulate osteogenesis and adipogenesis in ovariectomized (OVX) rat. The effects on the differentiation of bone marrow stem cells (BMSCs), function of Wnt/β-catenin pathway, ALP activity, calcium nodule deposition, as well as adipocyte formation in vitro by Peiminine at different concentrations, were detected. The curative effects of Peiminine on the ovariectomy-induced osteoporosis model by micro-CT and bone histomorphology assays were analyzed. The promotion of osteogenic differentiation and inhibition of adipogenic differentiation by Peiminine (5-40 μg/mL) was detected and the optimum concentration was 20 μg/mL. Mechanistically, Peiminine regulated the fate of BMSCs in vitro, and activated Wnt/β-catenin signaling pathway by restraining phosphorylation of β-catenin and promoting the nuclear translocation of β-catenin. Moreover, Peiminine prevented ovariectomy-induced osteoporosis by alleviating trabecular bone loss and inhibiting adipose formation. Our data suggested that Peiminine could attenuate ovariectomy-induced osteoporosis by alleviating trabecular bone loss and inhibiting adipose formation. These encouraging discoveries could lay the foundation for Peiminine to be a promising preventive treatment strategy for skeletal diseases, such as osteoporosis.

The effects of resveratrol and melatonin on biochemical and molecular parameters in diabetic old female rat hearts

The roles of melatonin and resveratrol-enhanced activation of SIRT1 (silent information regulator 1), GLUT4 (glucose transporter type 4), and PGC-1α (peroxisome proliferator-activated receptor gamma coactivator 1-alpha) in mediating the protective effects on the heart in aged female rats with streptozotocin-induced diabetes were investigated. 16-month-old 48 Wistar female rats were separated into 8 groups with equal numbers. Group 1: Control, Group 2: Resveratrol Control, Group 3: Melatonin Control, Group 4: Resveratrol and Melatonin Control, Group 5: Diabetes, Group 6: Diabetes Resveratrol, Group 7: Diabetes Melatonin, Group 8: Diabetes Resveratrol and Melatonin. A single dose of 40 mg/kg intraperitoneal streptozotocin was injected into the rats of Groups 5, 6, 7, and 8 to induce experimental diabetes. Blood glucose levels were measured from the tail veins of the animals six days after the injections, using a diagnostic glucose kit. Rats with a blood glucose levels ≥300 mg/dl were considered diabetic. 5 mg/kg/day of resveratrol (intraperitoneal) and melatonin (subcutaneous) were administered for four weeks. At the end of the applications, SIRT1, GLUT4, PGC-1α gene expression as well as MDA and GSH levels in the heart tissues were determined by the PCR method from heart tissue samples taken under general anesthesia. The findings of our study show that suppressed antioxidant activity and decreased GLUT4, SIRT1, and PGC-1α gene expression in heart tissue can be reversed by the combination of resveratrol, melatonin, and resveratrol + melatonin in a diabetic aged female rat model. Resveratrol and melatonin supplementation may have a protective effect on cardiac functions in the diabetic aged female rat model.

Epimedii Folium and Ligustri Lucidi Fructus Promote Osteoblastogenesis and Inhibit Osteoclastogenesis against Osteoporosis via Acting on Osteoblast-Osteoclast Communication

Osteoblast (OB) and osteoclast (OC) play important roles in bone formation and bone resorption, which can communicate with each other through cytokine paracrine. Previous studies have confirmed that Epimedii Folium (EF) and Ligustri Lucidi Fructus (LLF) used alone or in combination can treat osteoporosis (OP) through regulating bone remodeling, but the effects of EF and LLF on osteoblastogenesis, osteoclastogenesis, and OB-OC communication are unclear. In this study, we investigated the direct and indirect effects of EF and LLF on OBs and OCs via monoculture and coculture (transwell) models of OBs and OCs. We found that the combination of EF and LLF (EF&LLF) could promote osteoblastogenesis and inhibit osteoclastogenesis directly and indirectly. In order to study the mechanisms of EF&LLF on indirectly regulating osteoblastogenesis and osteoclastogenesis, we detected the expression of cytokines by which OBs and OCs could communicate with each other. We found that EF&LLF could downregulate the expression of RANKL and M-CSF and the protein ratio of RANKL/OPG of OBs and Atp6v0d2 expression of OCs and upregulate the expression of OPG and TGF-β1 of OBs and the expression of TGF-β1, BMP-2, and IGF-1 of OCs, indicating that EF&LLF could regulate cytokine expressions of OBs/OCs to affect OB-OC communication. In addition, EF&LLF had a better effect on regulating cytokines of OBs and OCs than EF or LLF in single use. This study suggested that EF&LLF exhibited the effects of promoting osteoblastogenesis and inhibiting osteoclastogenesis via acting on OB-OC communication and provided some scientific evidences for EF&LLF against OP.

Andrographis paniculata ameliorates estrogen deficiency-related osteoporosis by directing bone marrow mesenchymal stem cell fate

Background

Although Andrographis paniculata (AP) exhibits various biological functions such as anticancer, anti-inflammatory, antimalarial, antimicrobial, antioxidant, cardioprotective and immunomodulatory, its role in estrogen deficiency-related osteoporosis remains unclear.

Methods

Ovariectomy (OVX)-induced estrogen deficiency-related osteoporotic mouse models and sham mouse models were established using 8-week-old female C57BL/6J mice. Micro-computed tomography (µCT) scanning was performed to assess the skeletal phenotype. The differentiation potential of bone marrow mesenchymal stem cells (BMSCs) from the OVX and sham groups was assessed by osteogenic or adipogenic induction medium in vitro. To verify the effects of AP, alizarin red S (ARS) staining, alkaline phosphatase (ALP) staining and oil red O (ORO) staining, reverse transcription assay and quantitative real-time polymerase chain reaction were applied to detect the lineage differentiation ability of BMSCs.

Results

µCT scanning showed that AP treatment attenuated the osteoporotic phenotype in OVX-induced estrogen deficiency-related osteoporotic mice. The results of ARS staining, ALP staining, ORO staining and quantitative real-time polymerase chain reaction indicated that BMSCs from OVX-induced osteoporotic mice displayed a significant reduction in osteogenic differentiation and an increase in adipogenic differentiation, which could be reversed by AP treatment.

Conclusions

Our findings suggested that AP regulated the differentiation potential of BMSCs and ameliorated the development of estrogen deficiency-related osteoporosis, which might be an effective therapeutic method for estrogen deficiency-related osteoporosis.

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.

Melatonin suppresses bone marrow adiposity in ovariectomized rats by rescuing the imbalance between osteogenesis and adipogenesis through SIRT1 activation

INTRODUCTION

Accelerated imbalance between bone formation and bone resorption is associated with bone loss in postmenopausal osteoporosis. Studies have shown that this loss is accompanied by an increase in bone marrow adiposity. Melatonin was shown to improve impaired bone formation capacity of bone marrow-derived mesenchymal stem cells from ovariectomized rats (OVX-BMMSCs).

OBJECTIVES

To investigate whether the anti-osteoporosis effect of melatonin involves regulation of the equilibrium between osteogenic and adipogenic differentiation of osteoporotic BMMSCs.

METHODS

To induce osteoporosis, female Sprague-Dawley rats received ovariectomy (OVX). Primary BMMSCs were isolated from tibiae and femurs of OVX and sham-op rats and were induced towards osteogenic or adipogenic differentiation. Matrix mineralization was determined by Alizarin Red S (ARS) and lipid formation was evaluated by Oil Red O. OVX rats were injected with melatonin through the tail vein. Bone microarchitecture was determined using micro computed tomography and marrow adiposity were examined by histology staining.

RESULTS

OVX-BMMSCs exhibited a compromised osteogenic potential and an enhanced lineage differentiation towards adipocytes. In vitro melatonin improved osteogenic differentiation of OVX-BMMSCs and promoted matrix mineralization by enhancing the expression of transcription factor RUNX2 in a dose-dependent manner. Moreover, melatonin significantly inhibited lipid formation and suppressed OVX-BMMSCs adipogenesis by down-regulating peroxisome proliferator-activated receptor γ (PPARγ). Intravenous injection of melatonin prevented bone mass reduction and bone architecture destruction in ovariectomized rats. Importantly, there was a significant inhibition of adipose tissue formation in the bone marrow. Mechanistic investigations revealed that SIRT1 was involved in melatonin-mediated determination of stem cell fate. Inhibition of SIRT1 abolished the protective effects of melatonin on bone formation by inducing BMMSCs towards adipocyte differentiation.

CONCLUSIONS

Melatonin reversed the differentiation switch of OVX-BMMSCs from osteogenesis to adipogenesis by activating the SIRT1 signaling pathway. Restoration of stem cell lineage commitment by melatonin prevented marrow adipose tissue over-accumulation and protected from bone loss in postmenopausal osteoporosis.

THE TRANSLATIONAL POTENTIAL OF THIS ARTICLE

Determination of stem cell fate towards osteoblasts or adipocytes plays a pivotal role in regulating bone metabolism. This study demonstrates the protective effect of melatonin on bone mass in estrogen-deficient rats by suppressing adipose tissue accumulation in the bone marrow. Melatonin may serve as a promising candidate for the treatment of osteoporosis in clinics.

The role of melatonin in the development of postmenopausal osteoporosis

Melatonin is an important endogenous hormone that modulates homeostasis in the microenvironment. Recent studies have indicated that serum melatonin levels are closely associated with the occurrence and development of osteoporosis in postmenopausal women. Exogenous melatonin could also improve bone mass and increase skeletal strength. To determine the underlying mechanisms of melatonin in the prevention and treatment of postmenopausal osteoporosis, we performed this review to analyze the role of melatonin in bone metabolism according to its physiological functions. Serum melatonin is related to bone mass, the measurement of which is a potential method for the diagnosis of osteoporosis. Melatonin has a direct effect on bone remodeling by promoting osteogenesis and suppressing osteoclastogenesis. Melatonin also regulates the biological rhythm of bone tissue, which benefits its osteogenic effect. Additionally, melatonin participates in the modulation of the bone microenvironment. Melatonin attenuates the damage induced by oxidative stress and inflammation on osteoblasts and prevents osteolysis from reactive oxygen species and inflammatory factors. As an alternative drug for osteoporosis, melatonin can improve the gut ecology, remodel microbiota composition, regulate substance absorption and maintain metabolic balance, all of which are beneficial to the health of bone structure. In conclusion, our review systematically demonstrates the effects of melatonin on bone metabolism. Based on the evidence in this review, melatonin will play a more important role in the diagnosis, prevention and treatment of postmenopausal osteoporosis.

Disrupted Sleep Architecture Is Associated With Incident Bone Loss in Indian Postmenopausal Women: A Prospective Study

Inadequate sleep has been shown to be detrimental to several body systems, including the bone. We proposed to study the impact of insomnia on bone health in Indian postmenopausal women. In a 2-year prospective study, ambulant community-dwelling postmenopausal women aged >50 years were recruited through simple random sampling. Sleep duration was recorded based on self-reported sleep duration and sleep quality using the Women's Health Initiative Insomnia Rating Scale (WHIIRS). Anthropometry, bone biochemistry including bone turnover markers (C-terminal telopeptide of type 1 collagen [CTX], N-terminal telopeptide of type 1 pro-collagen [P1NP]), bone mineral density (BMD), and trabecular bone score (TBS) were assessed at baseline and at the end of 2 years. Among 190 postmenopausal women with mean (SD) age of 58.2 (6.9) years, 65/190 (34.2%) had insomnia (WHIIRS ≥ 9) and 20/190 (10.5%) developed osteoporosis at any site on follow-up. The percentage decline over 2 years in BMD in women with insomnia was significantly (p < 0.001) higher at femoral neck (2.9 [1.6] versus 1.2 [1.2]%) and lumbar spine (4.5 [2.0] versus 1.6 [1.1]%). The decrement in TBS was also significantly higher (p < 0.001) in women with suboptimal sleep (1.5 [2.1] versus 0.5 [1.0] %) when compared with those with adequate sleep. The increment in CTX (46.4 [32.2] versus 18.9 [26.4]) and decrement in P1NP (35.4 [9.1] versus 16.7 [18.9]), respectively, were also greater (p < 0.001) in women with insomnia compared with those without. On multivariate analysis, insomnia was the sole factor that was predictive (adjusted odds ratio [OR] = 9.3; 95% confidence interval [CI] 2.9-29.6; p < 0.001) of incident osteoporosis. In conclusion, poor sleep quality was associated with incident osteoporosis in Indian postmenopausal women. Optimal sleep may help to retard ongoing bone loss that results from sleep deprivation and requires further research. © 2022 American Society for Bone and Mineral Research (ASBMR).

The role of circadian rhythm in osteoporosis; a review

Osteoporosis is characterized by a high incidence rate, with significant effects on people’s lives. The underlying mechanisms are complex, with no treatments for the condition. Recent studies have indicated that melatonin can be used to treat osteoporosis by promoting osteoblast proliferation and differentiation, and inhibiting osteoclast differentiation. Specifically, in vivo mechanisms are initiated by stabilizing biological rhythms in bone tissue. In healthy organisms, these biological rhythms are present in bone tissue, and are characterized by bone formation during the day, and bone resorption at night. When this rhythm is disrupted, osteoporosis occurs. Thus, taking appropriate medication at different times of the day could produce different effects on osteoporosis rhythms. In this review, we characterized these processes, and provided treatments and management strategies for individuals with osteoporosis.

Effect of melatonin on quality of life and symptoms in patients with cancer: a systematic review and meta-analysis of randomised controlled trials

OBJECTIVE

This study systematically reviewed the effect of melatonin (MLT) on quality of life (QoL) and symptoms among patients with cancer.

DESIGN

Systematic review and meta-analysis.

DATA SOURCES

Cochrane Library, PubMed, Embase, Web of Science, Medline, CINAHL, Scopus, ClinicalTrials.gov, China Biology Medicine (CBM), ProQuest and Open Grey were searched from inception to November 2021.

ELIGIBILITY CRITERIA

We included randomised controlled trials (RCTs) assessing the effects of MLT on QoL, sleep quality, fatigue, depression, pain, stomatitis rate and stomatitis severity in adult patients with cancer, without language restrictions. Studies that reported the effects of MLT along with other interventions and had incomplete or absent outcome data were excluded.

DATA EXTRACTION AND SYNTHESIS

Two independent reviewers extracted data, and another two reviewers assessed the risk of bias. The risk of bias for each eligible study was assessed using the Cochrane assessment tool. The mean difference or standard mean difference (SMD) with 95% CIs was used in the computation of continuous variables to synthesise data. The relative risk was used for dichotomous outcomes. Heterogeneity was assessed and quantified (I² statistic).

RESULTS

A total of 19 qualified studies that included 2101 patients with cancer (MLT: 1078, control: 1023) were included in the meta-analysis. The results indicated that MLT had no significant effect on QoL (SMD=-0.01, 95% CI (-0.14 to 0.11), p=0.83), sleep quality (SMD=-0.18, 95% CI (-0.62 to 0.26), p=0.42), fatigue (SMD=-0.34, 95% CI (-0.73 to 0.06), p=0.10), pain (SMD=-0.34, 95% CI (-0.7 to 0.02), p=0.06) or stomatitis severity (RR=0.78, 95% CI (0.47 to 1.30), p=0.35). MLT reduced stomatitis rate among patients with cancer (RR=0.47, 95% CI (0.26 to 0.88), p=0.02), except those with head and neck cancer (RR=1.09, 95% CI (0.92 to 1.29), p=0.35). MLT eased depression in patients who received administration for more than 14 days (SMD=-0.14, 95% CI (-0.27 to -0.01), p=0.03) and those who underwent surgery (SMD=-0.17, 95% CI (-0.32 to -0.03), p=0.02).

CONCLUSION

The findings showed that MLT did not improve the QoL, sleep quality, fatigue, pain or stomatitis severity among patients with cancer. It had a limited effect on decreasing the stomatitis rate and easing depression. Different treatments, durations and cancer types were the main sources of heterogeneity. Further large-scale RCTs are urgently needed. In addition, the effects of different combinations of MLT dosage and duration, administration types and joint measures are worthy of further study.

PROSPERO REGISTRATION NUMBER

CRD42021292855.

The role of MEK1/2 and MEK5 in melatonin-mediated actions on osteoblastogenesis, osteoclastogenesis, bone microarchitecture, biomechanics, and bone formation

Melatonin, the primary hormone involved in circadian entrainment, plays a significant role in bone physiology. This study aimed to assess the role of MEK1/2 and MEK5 in melatonin-mediated actions in mouse and human mesenchymal stem cells (MSCs) and on bone using small-molecule inhibitors and CRISPR/Cas9 knockout approaches. Consistent with in vitro studies performed in mMSCs and hMSCs, nightly (25 mg/kg, i.p., 45 days) injections with PD184352 (MEK1/2 inhibitor) or Bix02189 (MEK5 inhibitor) or SC-1-151 (MEK1/2/5 inhibitor) demonstrated that MEK1/2 and MEK5 were the primary drivers underlying melatonin's actions on bone density, microarchitecture (i.e., trabecular number, separation, and connectivity density), and bone mechanical properties (i.e., ultimate stress) through increases in osteogenic (RUNX2, BMP-2, FRA-1, OPG) expression and decreases in PPARγ. Furthermore, CRISPR/Cas9 knockout of MEK1 or MEK5 in mMSCs seeded on PLGA scaffolds and placed into critical-size calvarial defects in Balb(c) mice (male and female) revealed that treatment with melatonin (15 mg/L; p.o., nightly, 90 days) mediates sex-specific actions of MEK1 and MEK5 in new bone formation. This study is the first to demonstrate a role for MEK1/2 and MEK5 in modulating melatonin-mediated actions on bone formation in vivo and in a sex-specific manner.

Melatonin protects gingival mesenchymal stem cells and promotes differentiation into osteoblasts

Melatonin (MEL) has antioxidant properties and participates in osteogenic differentiation. In periodontitis, in which increased oxidative stress and bone resorption are involved, mesenchymal stem cells derived from the gingiva (GMSCs) combined with MEL could be relevant for osteogenic regeneration. In this study, we studied the antioxidant and differentiating effect of MEL on an in vitro system of GMSCs. Primary culture of GMSCs from Wistar rats was developed to evaluate differentiation into osteoblasts with an appropriate medium with or without MEL. Marker genes of mesenchymal stem cells by real time-polymerase chain reaction, clonogenic capacity, and cell migration after wound assay were used to characterize GMSCs as mesenchymal stem cells. Alkaline phosphatase activity and the alizarin red technique were used to evaluate osteogenic activity and differentiation. MEL increased alkaline phosphatase activity and alizarin red values, promoting osteogenic differentiation. Besides this, MEL protected GMSCs in a model of cellular damage related to oxidative stress, returning viability to baseline. MEL was more effective in promoting and protecting GMSCs by the production of osteogenic cells when oxidative stress is present. This evidence supports the use of MEL as a novel bone-regenerative therapy in periodontal diseases.

Melatonin inhibits osteoclastogenesis via RANKL/OPG suppression mediated by Rev-Erbα in osteoblasts

Diabetic osteoporosis is secondary osteoporosis and a serious complication of diabetes with a high incidence rate and poor prognosis. The specific mechanism of diabetic osteoporosis is unclear, and prevention and treatment options are limited. Recently, melatonin has been found to prevent and treat diabetic osteoporosis. Herein, we investigated the mechanism whereby melatonin inhibits osteoclastogenesis and identified a new target for osteoporosis treatment. We established an in vitro osteoblast–osteoclast co‐culture system as a diabetic osteoporosis model. Osteoclastogenesis was determined using tartrate‐resistant acid phosphatase staining and cathepsin K expression. Real‐time PCR was used to ascertain expression of microRNA mir‐882, targeting Rev‐Erbα. Western blotting was performed to detect the expression of Rev‐Erbα, receptor activator of NF‐kB ligand (RANKL), and osteoprotegerin (OPG), and ELISA was utilized to analyse the secreted form of RANKL. High glucose promoted osteoclastogenesis and elevated the RANKL/OPG ratio in osteoblasts, while melatonin reversed these effects. High glucose inhibited Rev‐Erbα expression, while melatonin promoted its expression. Conversely, high glucose promoted mir‐882 expression, while melatonin inhibited it. We infer that melatonin inhibits RANKL expression in osteoblasts via the mir‐882/Rev‐Erbα axis, thus inhibiting osteoclastogenesis. Our findings provide insights into diabetic osteoporosis and identify a new therapeutic target for osteoporosis.

Assessment of the Therapeutic Potential of Melatonin for the Treatment of Osteoporosis Through a Narrative Review of Its Signaling and Preclinical and Clinical Studies

Melatonin is a bioamine produced primarily in the pineal gland, although peripheral sites, including the gut, may also be its minor source. Melatonin regulates various functions, including circadian rhythm, reproduction, temperature regulation, immune system, cardiovascular system, energy metabolism, and bone metabolism. Studies on cultured bone cells, preclinical disease models of bone loss, and clinical trials suggest favorable modulation of bone metabolism by melatonin. This narrative review gives a comprehensive account of the current understanding of melatonin at the cell/molecular to the systems levels. Melatonin predominantly acts through its cognate receptors, of which melatonin receptor 2 (MT2R) is expressed in mesenchymal stem cells (MSCs), osteoblasts (bone-forming), and osteoclasts (bone-resorbing). Melatonin favors the osteoblastic fate of MSCs, stimulates osteoblast survival and differentiation, and inhibits osteoclastogenic differentiation of hematopoietic stem cells. Produced from osteoblastic cells, osteoprotegerin (OPG) and receptor activator of nuclear factor kappa B ligand (RANKL) critically regulate osteoclastogenesis and melatonin by suppressing the osteoclastogenic RANKL, and upregulating the anti-osteoclastogenic OPG exerts a strong anti-resorptive effect. Although the anti-inflammatory role of melatonin favors osteogenic function and antagonizes the osteoclastogenic function with the participation of SIRT signaling, various miRNAs also mediate the effects of the hormone on bone cells. In rodent models of osteoporosis, melatonin has been unequivocally shown to have an anti-osteoporotic effect. Several clinical trials indicate the bone mass conserving effect of melatonin in aging/postmenopausal osteoporosis. This review aims to determine the possibility of melatonin as a novel class of anti-osteoporosis therapy through the critical assessment of the available literature.

Astrocyte Dysregulation and Calcium Ion Imbalance May Link the Development of Osteoporosis and Alzheimer’s Disease

The typical symptoms of patients with Alzheimer’s disease (AD) are amyloid-β (Aβ) plaques and tau hyperphosphorylation. However, recent studies show that these symptoms are not the cause of the disease but are generated after the pathogenesis. Compared with other types of dementia, AD has the obvious features of pineal gland calcification and decreased melatonin production. The pineal gland is mainly composed of pinealocytes that release melatonin and astrocytes. Astrocytes function to maintain a balanced concentration of calcium ions, provide nerve cell nutrients, and migrate nutrients in vivo. Calcium ions are among the most important neurotransmitters. Once triggered, a calcium wave can be formed between astrocytes to activate other astrocytes to transmit information. Most calcium is stored in the skeleton. Bone tissue is composed mainly of osteocytes, osteoblasts, and osteoclasts. Of these, osteocyte is a kind of astrocyte which regulates the activity of osteoclasts and osteoblasts. The pineal gland is composed mainly of astrocytes; osteocytes are also a kind of astrocyte. Therefore, we conclude that when astrocytes are gradually disabled, calcium may be lost from the bones, prompting osteoporosis. The calcium ions then released into the blood may accumulate and cause ectopic calcification in the pineal gland, which promotes the occurrence of AD. Finally, this study used aspects of drugs and hormones (bone and calcium metabolism hormones and melatonin) to infer the hypothesis, which proposes that astrocyte dysregulation promotes the long-term imbalance of calcium ions in vivo and leads to osteoporosis and AD.

Melatonin Alleviates Venous Dysfunction in a Mouse Model of Iliac Vein Occlusion

The iliac vein can be severely stenosed and occluded due to thrombosis, tumor compression, or an anatomical abnormality. Such occlusion could result in limb swelling, venous claudication, and persistent leg ulcers. Its devastating sequelae heavily impact patients lifestyles and the social economy. Due to a lack of a stable and easy-to-operate iliac vein occlusion (IVO) model, its underlying molecular mechanism and pathophysiological process has not been completely understood. Melatonin (MLT) plays a critical role in anti-inflammation, but the potential protective effect of melatonin on venous dysfunction induced by IVO has not been revealed. In this study, a mouse model of IVO was established to study the effects of MLT on injured veins. The results of laser speckle images and Evans blue showed that MLT inhibited venous permeability in an IVO mouse model. Furthermore, MLT suppressed inflammation of surrounding tissues close to the affected vein by inhibiting the mRNA levels of TNF-α, IL-1α, and MCP-1. In addition, endothelial injury was inhibited by MLT using zonula occludens protein-1 (ZO-1) staining. Taken together, we elucidated the therapeutic effect of MLT on vascular dysfunction induced by IVO, mainly by inhibiting the TNF-α, IL-1α, and MCP-1 mRNA levels, improving endothelial function, and inhibiting vascular leakage.

Circadian rhythm modulates endochondral bone formation via MTR1/AMPKβ1/BMAL1 signaling axis

The circadian clock is a master regulator in coordinating daily oscillations of physiology and behaviors. Nevertheless, how the circadian rhythm affects endochondral ossification is poorly understood. Here we showed that endochondral bone formation exhibits circadian rhythms, manifested as fast DNA replication in the daytime, active cell mitosis, and matrix synthesis at night. Circadian rhythm disruption led to endochondral ossification deformities. The mechanistic dissection revealed that melatonin receptor 1 (MTR1) periodically activates the AMPKβ1 phosphorylation, which then orchestrates the rhythms of cell proliferation and matrix synthesis via destabilizing the clock component CRY1 and triggering BMAL1 expression. Accordingly, the AMPKβ1 agonist is capable of alleviating the abnormity of endochondral ossification caused by circadian dysrhythmias. Taken together, these findings indicated that the central circadian clock could control endochondral bone formation via the MTR1/AMPKβ1/BMAL1 signaling axis in chondrocytes. Also, our results suggested that the AMPKβ1 signaling activators are promising medications toward endochondral ossification deformities.

Influence of melatonin on systemic inflammatory status and bone histopathological modifications in female rats with surgically induced menopause

Background. Melatonin, N-acetyl-5-methoxy-tryptamine is the major secretion product of the pineal gland with important anti-inflammatory and antioxidant properties, also being an im-portant marker of bone remodelling associated with menopause. Objectives. The aim of our study was to evaluate the effect of the co-administration of melatonin and estrogen on systemic inflammatory status and bone histopathological modifications in surgically induced menopau-sal female rats. Materials and methods. The study was performed on a number of 40 female rats, Wistar breed, which underwent bilateral surgical ovariectomy. Within 14 days postoperative, hormone replacement therapy with estrogen or estrogen with melatonin was initiated, in differ-ent doses. The treatment was administered for 12 consecutive weeks. At the end of the treatment we measured the serum levels of IL-6 and TNF-α. The femoral bones were harvested after sacri-ficing the animals and the thickness of the cortical bones was measured and histologically ana-lysed. Results. Serum values of inflammatory markers were negatively correlated with melatonin ad-ministration, the differences being more important at higher doses of melatonin (for both IL-6 and TNF-α the difference between group E_2M with estrogen substitution and melatonin in double dose and control group W, without hormone replacement, was highly statistically signif-icant with p <0.0001). Bone diameters improved in the case of female rats that received hormone replacement with estrogen and higher dose of melatonin (p = 0.0004 between group E_2M, with hormone replacement and group W, control group). Conclusions. Melatonin improved inflam-matory status and bone histopathological changes in ovariectomized female rats. Keywords: melatonin, estrogen replacement therapy, inflammation, low bone density

Melatonin and the Programming of Stem Cells

Melatonin interacts with various types of stem cells, in multiple ways that comprise stimulation of proliferation, maintenance of stemness and self-renewal, protection of survival, and programming toward functionally different cell lineages. These various properties are frequently intertwined but may not be always jointly present. Melatonin typically stimulates proliferation and transition to the mature cell type. For all sufficiently studied stem or progenitor cells, melatonin’s signaling pathways leading to expression of respective morphogenetic factors are discussed. The focus of this article will be laid on the aspect of programming, particularly in pluripotent cells. This is especially but not exclusively the case in neural stem cells (NSCs) and mesenchymal stem cells (MSCs). Concerning developmental bifurcations, decisions are not exclusively made by melatonin alone. In MSCs, melatonin promotes adipogenesis in a Wnt (Wingless-Integration-1)-independent mode, but chondrogenesis and osteogenesis Wnt-dependently. Melatonin upregulates Wnt, but not in the adipogenic lineage. This decision seems to depend on microenvironment and epigenetic memory. The decision for chondrogenesis instead of osteogenesis, both being Wnt-dependent, seems to involve fibroblast growth factor receptor 3. Stem cell-specific differences in melatonin and Wnt receptors, and contributions of transcription factors and noncoding RNAs are outlined, as well as possibilities and the medical importance of re-programming for transdifferentiation.

Melatonin enhances osteoblastogenesis of senescent bone marrow stromal cells through NSD2-mediated chromatin remodelling

BACKGROUND

Aging-associated osteoporosis is frequently seen in the elderly in clinic, but efficient managements are limited because of unclear nosogenesis. The current study aims to investigate the role of melatonin on senescent bone marrow stromal cells (BMSCs) and the underlying regulating mechanism.

METHODS

Melatonin levels were tested by ELISA. Gene expression profiles were performed by RNA-sequencing, enrichment of H3K36me2 on gene promoters was analyzed by Chromatin Immunoprecipitation Sequencing (ChIP-seq), and chromatin accessibility was determined by Assay for Transposase-Accessible Chromatin with high-throughput sequencing (ATAC-seq). Osteogenesis of BMSCs in vitro was measured by Alizarin Red and Alkaline Phosphatase staining, and in vivo effects of melatonin was assessed by histological staining and micro computed tomography (micro-CT) scan. Correlation of NSD2 expression and severity of senile osteoporosis patients were analyzed by Pearson correlation.

RESULTS

Melatonin levels were decreased during aging in human bone marrow, accompanied by downregulation of the histone methyltransferase nuclear receptor binding SET domain protein 2 (NSD2) expression in the senescent BMSCs. Melatonin stimulated the expression of NSD2 through MT1/2-mediated signaling pathways, resulting in the rebalancing of H3K36me2 and H3K27me3 modifications to increase chromatin accessibility of the osteogenic genes, runt-related transcription factor 2 (RUNX2) and bone gamma-carboxyglutamate protein (BGLAP). Melatonin promoted osteogenesis of BMSCs in vitro, and alleviates osteoporosis progression in the aging mice. In clinic, severity of senile osteoporosis (SOP) was negatively correlated with melatonin level in bone marrow, as well as NSD2 expression in BMSCs. Similarly, melatonin remarkably enhanced osteogenic differentiation of BMSCs derived from SOP patients in vitro.

CONCLUSIONS

Collectively, our study dissects previously unreported mechanistic insights into the epigenetic regulating machinery of melatonin in meliorating osteogenic differentiation of senescent BMSC, and provides evidence for application of melatonin in preventing aging-associated bone loss.

Melatonin Improves the Resistance of Oxidative Stress-Induced Cellular Senescence in Osteoporotic Bone Marrow Mesenchymal Stem Cells

Accumulation of senescent bone marrow-derived mesenchymal stem cells (BMMSCs) has led to an age-related bone loss. However, the role of stem cell senescence in estrogen deficiency-induced osteoporosis remains elusive. Though melatonin plays a vital role in bone metabolism regulation, the underlying mechanisms of melatonin-mediated antiosteoporosis are partially elucidated. Therefore, this study purposed to explore (1) whether estrogen deficiency causes cellular senescence of BMMSCs, and if so, (2) the potential of melatonin in preventing bone loss via senescence signaling inhibition. BMMSCs derived from ovariectomized (OVX) rats (OVX BMMSCs) showed an impaired osteogenic capacity, albeit having comparable levels of senescence biomarkers than the sham cells. When exposed to low levels of hydrogen peroxide (H₂O₂), OVX BMMSCs rapidly exhibited senescence-associated phenotypes such as the increased activity of senescence-associated β-galactosidase (SA-β-gal) and upregulation of cell cycle inhibitors. Notably, the in vitro treatment with melatonin hindered H₂O₂-induced senescence in OVX BMMSCs and restored their osteogenic capacity. Treatment with either SIRT1 inhibitor (sirtinol) or melatonin receptor antagonists (luzindole and 4-P-PDOT) eliminated melatonin protective effects, thus indicating its potential in preventing stem cell senescence via SIRT1 activation through the melatonin membrane receptors. Following in vivo intravenous administration with melatonin, it successfully protected the bone microstructure and preserved the antisenescence property of BMMSCs in OVX rats. Collectively, our findings demonstrated that melatonin protected against estrogen deficiency-related bone loss by improving the resistance of BMMSCs to cellular senescence. Therefore, melatonin-mediated antisenescence effect on stem cells provides vital information to facilitate the development of a novel and effective strategy for treating postmenopausal OP.

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.

Melatonin-Medicated Neural JNK3 Up-Regulation Promotes Ameloblastic Mineralization

Introduction: Melatonin, an endogenous neurohormone, modulates the biological circadian rhythms of vertebrates. It functions have been reported in previous stomatological studies as anti-inflammation, antioxidant, osseointegration of dental implants and stimulation to dental pulp stem cells differentiation, but its role in ameloblastic differentiation and mineralization has been rarely studied. Objective: To reveal the effects of melatonin on the mineralization of ameloblast lineage cells (ALCs), and to identify the change in gene expression and the potential mechanism based on ribonucleic acid sequencing (RNA-seq) analysis. Method: ALCs were induced in melatonin-conditioned medium. After 7-days culture, Western blot, real-time PCR, alkaline phosphatase (ALP) activity test, RNA-seq were accordingly used to detect the change in molecular level. After 1-month odontogenic induction in melatonin medium, Alizarin Red-S (ARS) staining showed the changes of mineral nodules. Differentially expressed genes (DEGs), enrichment of functions and signaling pathways analysis based on Kyoto Encyclopedia of Genes and Genomes (KEGG) and Gene Ontology (GO) database were performed. The JNK3 antagonist (JNK3 inhibitor IX, SR3576) and β-arrestin1 (Arrb1) overexpression were applied to confirm the fluctuation of melatonin-medicated JNK3 and Arrb1 expression. Results: In this study, we found out melatonin contributed to the ameloblastic mineralization, from which we can observed the elevated expression of enamel matrix protein, and increased ALP activity and mineralized nodules formation. RNA-seq analysis showed the up-regulation of neural JNK3 and down-regulation of Arrb1 in ALCs. Meanwhile, phosphorylated JNK3 deficiency (phosphorylated JNK3 inhibitor---SR3576 added to culture medium) led to mineralization delay, and Arrb1 overexpression proved Arrb1 takes bridge between melatonin receptors (MTNR) and JNK3 in MAPK signaling pathway.

Melatonin Accelerates Osteoporotic Bone Defect Repair by Promoting Osteogenesis-Angiogenesis Coupling

Previous studies have revealed that melatonin could play a role in anti-osteoporosis and promoting osteogenesis. However, the effects of melatonin treatment on osteoporotic bone defect and the mechanism underlying the effects of melatonin on angiogenesis are still unclear. Our study was aimed to investigate the potential effects of melatonin on angiogenesis and osteoporotic bone defect. Bone marrow mesenchymal stem cells (BMSCs) were isolated from the femur and tibia of rats. The BMSC osteogenic ability was assessed using alkaline phosphatase (ALP) staining, alizarin red S staining, qRT-PCR, western blot, and immunofluorescence. BMSC-mediated angiogenic potentials were determined using qRT-PCR, western blot, enzyme-linked immunosorbent assay, immunofluorescence, scratch wound assay, transwell migration assay, and tube formation assay. Ovariectomized (OVX) rats with tibia defect were used to establish an osteoporotic bone defect model and then treated with melatonin. The effects of melatonin treatment on osteoporotic bone defect in OVX rats were analyzed using micro-CT, histology, sequential fluorescent labeling, and biomechanical test. Our study showed that melatonin promoted both osteogenesis and angiogenesis in vitro. BMSCs treated with melatonin indicated higher expression levels of osteogenesis-related markers [ALP, osteocalcin (OCN), runt-related transcription factor 2, and osterix] and angiogenesis-related markers [vascular endothelial growth factor (VEGF), angiopoietin-2, and angiopoietin-4] compared to the untreated group. Significantly, melatonin was not able to facilitate human umbilical vein endothelial cell angiogenesis directly, but it possessed the ability to promote BMSC-mediated angiogenesis by upregulating the VEGF levels. In addition, we further found that melatonin treatment increased bone mineralization and formation around the tibia defect in OVX rats compared with the control group. Immunohistochemical staining indicated higher expression levels of osteogenesis-related marker (OCN) and angiogenesis-related markers (VEGF and CD31) in the melatonin-treated OVX rats. Then, it showed that melatonin treatment also increased the bone strength of tibia defect in OVX rats, with increased ultimate load and stiffness, as performed by three-point bending test. In conclusion, our study demonstrated that melatonin could promote BMSC-mediated angiogenesis and promote osteogenesis-angiogenesis coupling. We further found that melatonin could accelerate osteoporotic bone repair by promoting osteogenesis and angiogenesis in OVX rats. These findings may provide evidence for the potential application of melatonin in osteoporotic bone defect.

Mesenchymal Stem Cell and Monocyte Co-cultures

Transwell co-cultures are critical to study cell-to-cell communication through the release of factors between different cells allowing for the simultaneous assessment of treatment effects on one cell type (e.g., Cell A) and their impact on another cell type (e.g., Cell B). This allows for the simultaneous assessment of two different cell types and the factors they secrete under the same treatment conditions, which minimizes interexperimental variability, demonstrates causation rather than association, and enhances the translatability of the findings to the in vivo condition. Here we describe transwell co-cultures of human mesenchymal stem cells (MSCs) and peripheral blood monocytes or pre-osteoclasts to assess osteoblast-mediated actions on osteoclastogenesis.

The Proliferation and Stemness of Peripheral Blood-Derived Mesenchymal Stromal Cells Were Enhanced by Hypoxia

This study aimed to address the dilemma of low peripheral blood-derived mesenchymal stromal cell (PBMSC) activity and reduced phenotype in bone or cartilage tissue engineering. Rat PBMSCs (rPBMSCs) were obtained by density gradient centrifugation, and stromal cell characteristics were confirmed by flow cytometry (FCM) and multi-differentiation potential induction experiments. Cell growth curve, viability experiments, and clone formation experiments were performed by [3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium] (MTS) and cell counting, and the cell cycle was confirmed by cell FCM. The proliferation signal pathway and stemness-related proteins were detected by molecular methods including Western blot and real-time polymerase chain reaction. CD73, CD90, and CD105 were highly expressed, and CD14, CD19, CD34, CD45, and HLA-DR were barely expressed in rPBMSCs. rPBMSCs possessed the potential to differentiate into chondrocytes, adipocytes, and osteoblasts under their respective induction conditions. Cell growth curve and viability experiments were performed under hypoxic conditions: 19% O₂, 5% O₂, and 1% O₂. Specifically, 5% O₂ accelerated the proliferation and expression of the stemness of PBMSCs. Cycle experiments proved that hypoxia promoted the cell transition from the G1 phase to the S phase. Molecular experiments confirmed that 5% O₂ hypoxia significantly elevated the expressions of hypoxia-inducible factor 1α and β-catenin and simultaneously the expressions of cycle-related genes including CyclinE/CDK2 and stemness-related genes including Nanog and SOX2. The appropriate concentration of hypoxia (i.e., 5% O₂) enhanced the proliferation and stemness of rPBMSCs and increased the multidirectional differentiation potential of stromal cells. The proposed culture method could improve the viability and maintain the phenotype of rPBMSCs in cartilage or bone tissue engineering.

QiangGuYin Modulates the OPG/RANKL/RANK Pathway by Increasing Secretin Levels during Treatment of Primary Type I Osteoporosis

QiangGuYin (QGY) is a common Traditional Chinese medicine prescription for the treatment of osteoporosis. Previous clinical studies have found that QGY effectively improves bone mineral density (BMD) in postmenopausal women, but its underlying mechanism remains unclear. The osteoprotegerin (OPG)/receptor activator of nuclear factor kappa B ligand (RANKL)/receptor activator of nuclear factor kappa B (RANK) pathway is a classic pathway involved in osteoporosis. Secretin levels are a serum marker of osteoporosis, but their effect on the OPG/RANKL/RANK pathway has not been reported. Hence, we investigated the relationship between the OPG/RANKL/RANK pathway and secretin and further revealed the mechanism underlying the effect of QGY in the treatment of osteoporosis. Mice were divided into secretin knockdown, secretin overexpression, and corresponding control groups. Micro-computed tomography was used to detect BMD in different groups, and the results show that QGY significantly improved BMD in mice of the secretin knockdown group. To further verify this, the serum levels of OPG, RANKL, RANK, and secretin were measured by enzyme-linked immunosorbent assays, and femur levels of OPG, RANKL, RANK, and secretin were evaluated by real-time quantitative PCR and western blotting. The results show that the expression of OPG was inhibited and that of RANKL and RANK was increased in mice from the secretin knockdown group, whereas the expression of OPG was upregulated and that of RANKL and RANK was downregulated after QGY intervention. Therefore, QGY inhibited bone resorption by promoting the expression of secretin and modulating the OPG/RANKL/RANK pathway. In addition to the effect of QGY, we also revealed the general regulatory effect of secretin on the OPG/RANKL/RANK pathway. We conclude that QGY modulates the OPG/RANKL/RANK pathway by increasing secretin levels during treatment of primary type I osteoporosis. This work provides a theoretical basis for the clinical use of QGY in the treatment of osteoporosis.

Melatonin Promotes the Therapeutic Effect of Mesenchymal Stem Cells on Type 2 Diabetes Mellitus by Regulating TGF-β Pathway

Abundant evidence proves the therapeutic effect of adipose-derived mesenchymal stem cells (ADMSCs) in the treatment of diabetes mellitus. However, the problems have not been solved that viability of ADMSCs were inconsistent and the cells quickly undergo senescence after in vitro cell culture. In addition, the therapeutic effect of ADMSCs is still not satisfactory. In this study, melatonin (MLT) was added to canine ADMSC culture medium, and the treated cells were used to treat type 2 diabetes mellitus (T2DM). Our research reveals that adding MLT to ADMSC culture medium can promote the viability of ADMSCs. This effect depends on the binding of MLT and MLT receptors, which activates the transforming growth factor β (TGF-β) pathway and then changes the cell cycle of ADMSCs and improves the viability of ADMSCs. Since ADMSCs were found to be used to treat T2DM by anti-inflammatory and anti-endoplasmic reticulum (ER) stress capabilities, our data demonstrate that MLT augment several effects of ADMSCs in remission hyperglycemia, insulin resistance, and liver glycogen metabolism in T2DM patients. This suggest that ADMSCs and MLT-ADMSCs is safe and vabulable for pet clinic.

Sleep pattern and bone mineral density: a cross-sectional study of National Health and Nutrition Examination Survey (NHANES) 2017-2018

This research is a cross-sectional study based on the participants aged 50 years and older from National Health and Nutrition Examination Survey (NHANES) database. Poor sleep patterns were associated with lower bone mineral density (BMD) and a higher risk of osteoporosis, especially among older individuals or females.

INTRODUCTION

Accumulated evidence demonstrates that sleep duration, which is one aspect of sleep pattern, is associated with the risk of osteoporosis. However, the related studies on the association between sleep patterns and the risk of osteoporosis were limited. Therefore, this research aims to investigate the association of sleep patterns with BMD and the risk of osteoporosis among individuals aged 50 years and older.

METHODS

Participants aged ≥ 50 years from the NHANES database were included in the present study. The diagnosis of osteoporosis was based on the results of BMD testing. Moreover, all the participants were divided into different sleep pattern groups according to nocturnal sleep duration and bedtime. In addition, this study used multivariate linear regression models to evaluate the association between sleep patterns and BMD and exploited multiple logistic regression models to investigate the odds ratios (ORs) for osteoporosis.

RESULTS

Finally, 1,865 individuals (non-osteoporosis: N = 1,713; osteoporosis: N = 152) aged over 50 years old with complete data were analyzed. The results of multivariate linear regression models showed that individuals with normal sleep duration/later bedtime or long sleep duration/later bedtime had lower femoral BMD than those with normal sleep duration/usual bedtime. Moreover, subjects with long sleep duration/later bedtime had a higher risk of osteoporosis compared with those with normal sleep duration/usual bedtime. In addition, subgroup analyses revealed the association of sleep patterns with BMD and the risk of osteoporosis appeared to be more pronounced among individuals aged ≥ 65 years or females.

CONCLUSION

This study demonstrated that sleep patterns are associated with BMD and the risk of osteoporosis. Poor sleep patterns contribute to decreased bone mass and the increased risk of osteoporosis. Therefore, a healthy sleep pattern is favorable for the prevention of osteoporosis.

Melatonin in neuroskeletal biology

Osteoporosis and neurodegenerative diseases are common diseases in the aging population. Studies demonstrate the complex communication among skeletal, muscular, and nervous systems and point to the emerging roles of neuromuscular systems in bone homeostasis. The discovery that the nervous system directly regulates bone remodeling implies that osteoporosis is a neuroskeletal disease. Melatonin, a hormone secreted from the pineal gland, is a melatonin receptor 1A (MT1) and 1B (MT2) agonist and influences the function of diverse systems. Melatonin is a pharmaceutical ingredient in numerous medicines, over-the-counter medicines, nutraceuticals, and dietary supplements, which benefit disease prevention and treatment, including osteoporosis and neurodegenerative diseases. This review aims to summarize the recent advances in preventing senile, postmenopausal, and neurodegenerative osteoporosis with melatonin and provide new insights into how neuromuscular systems influence bone homeostasis. More preclinical and clinical studies in neuroskeletal biology will eventually improve the lives of people fighting osteoporosis.

Combined Effects of Low-Frequency Pulsed Electromagnetic Field and Melatonin on Ovariectomy-Induced Bone Loss in Mice

Pulsed electromagnetic field (PEMF) therapy and melatonin (MEL) supplementation are expected to be important strategies for the treatment of osteoporosis. The aim of the current study was to investigate the efficacy of PEMF therapy, MEL supplementation, a combination of PEMF therapy, and MEL supplementation (PEMF + MEL) in mice with bilateral ovariectomy (OVX)-induced osteoporosis. Forty 12-week-old female C57/BL mice were randomly assigned to five groups (n = 8/group): OVX, PEMF, MEL, PEMF + MEL, and sham-operation (sham) groups. All mice in the first four groups were subjected to OVX. The mice in the PEMF and PEMF + MEL groups were exposed to PEMF (75 Hz, 1.6 mT, 1 h/day for 12 weeks), while those in the MEL and PEMF + MEL groups were administered MEL (50 mg/kg, i.p.). Body mass, micro-computed tomography, histology, immunohistochemistry, and real-time polymerase chain reaction were performed. PEMF + MEL treatment enhanced bone volume fraction (BV/TV) 2.2-fold over OVX control (P < 0.001) and increased expression levels of collagen type I (COL1) 1.9-fold and bone morphogenetic protein 2 (BMP2) 2.5-fold. PEMF + MEL also reduced the ratio of bone surface/bone volume (BS/BV) by 40% (P < 0.05) and appeared to reduce the number of osteoclasts in the metaphysis area. Preservation of bone value and bone microarchitecture in the combined therapy group were found to be superior to those in the single treatment groups. However, there were no apparent differences between the PEMF and MEL groups. The use of a combination of PEMF therapy and MEL supplementation may be an effective method to treat osteoporosis. © 2021 Bioelectromagnetics Society.

Melatonin as a powerful antioxidant

Melatonin is a hormone that has many body functions and, for several decades, its antioxidant potential has been increasingly talked about. There is a relationship between failure in melatonin production in the pineal gland, an insufficient supply of this hormone to the body, and the occurrence of free radical etiology diseases such as neurodegenerative diseases, cardiovascular diseases, diabetes, cancer and others. Despite the development of molecular biology, numerous in vitro and in vivo studies, the exact mechanism of melatonin antioxidant activity is still unknown. Nowadays, the use of melatonin supplementation is more and more common, not only to prevent insomnia, but also to slow down the aging process and provide protection against diseases. The aim of this study is to get acquainted with current reports on melatonin, antioxidative mechanisms and their importance in diseases of free radical etiology.

Melatonin restores osteoporosis-impaired osteogenic potential of bone marrow mesenchymal stem cells and alleviates bone loss through the HGF/PTEN/Wnt/β-catenin axis

Background:

Previous studies reported that melatonin exerts its effect on mesenchymal stem cell (MSC) survival and differentiation into osteogenic and adipogenic lineage. In the current study we aimed to explore the effect of melatonin on osteoporosis and relevant mechanisms.

Methods:

Real-time qualitative polymerase chain reaction (RT-qPCR) and Western blot analysis were conducted to determine expression of HGF, PTEN, and osteoblast differentiation-related genes in ovariectomy (OVX)-induced osteoporosis mice and the isolated bone marrow MSCs (BMSCs). Pre-conditioning with melatonin (1 μmol/l, 10 μmol/l and 100 μmol/l) was carried out in OVX mice BMSCs. Bone microstructure was analyzed using micro-computed tomography and the contents of alkaline phosphatase (ALP) and tartrate-resistant acid phosphatase 5b (TRAP5b) were detected by enzyme-linked immunosorbent assay in serum. BMSC proliferation was measured by cell-counting kit (CCK)-8 assay. Alizarin red S (ARS) staining and ALP activity assay were performed to assess BMSC mineralization and calcification. The activity of the Wnt/β-catenin pathway was evaluated by dual-luciferase reporter assay.

Results:

Melatonin prevented bone loss in OVX mice. Melatonin increased ALP expression and reduced TRAP5b expression. HGF and β-catenin were downregulated, while PTEN was upregulated in the femur of OVX mice. Melatonin elevated HGF expression and then stimulated BMSC proliferation and osteogenic differentiation. Additionally, HGF diminished the expression of PTEN, resulting in activated Wnt/β-catenin pathway both in vitro and in vivo. Furthermore, melatonin was shown to ameliorate osteoporosis in OVX mice via the HGF/PTEN/Wnt/β-catenin axis.

Conclusion:

Melatonin could potentially enhance osteogenic differentiation of BMSCs and retard bone loss through the HGF/PTEN/Wnt/β-catenin axis.