Melatonin restores the osteoporosis-impaired osteogenic potential of bone marrow mesenchymal stem cells by preserving SIRT1-mediated intracellular antioxidant properties

Melatonin Inhibits Osteoclastogenesis and Osteolytic Bone Metastasis: Implications for Osteoporosis

Osteoblasts and osteoclasts are major cellular components in the bone microenvironment and they play a key role in the bone turnover cycle. Many risk factors interfere with this cycle and contribute to bone-wasting diseases that progressively destroy bone and markedly reduce quality of life. Melatonin (N-acetyl-5-methoxy-tryptamine) has demonstrated intriguing therapeutic potential in the bone microenvironment, with reported effects that include the regulation of bone metabolism, acceleration of osteoblastogenesis, inhibition of osteoclastogenesis and the induction of apoptosis in mature osteoclasts, as well as the suppression of osteolytic bone metastasis. This review aims to shed light on molecular and clinical evidence that points to possibilities of melatonin for the treatment of both osteoporosis and osteolytic bone metastasis. It appears that the therapeutic qualities of melatonin supplementation may enable existing antiresorptive osteoporotic drugs to treat osteolytic metastasis.

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.

Melatonin as a Trigger of Therapeutic Bone Regenerating Capacity in Biomaterials

Bone defects are usually treated with bone grafting. Several synthetic biomaterials have emerged to replace autologous and allogeneic bone grafts, but there are still shortcomings in bone regeneration. Melatonin has demonstrated a beneficial effect on bone metabolism with the potential to treat fractures, bone defects, and osteoporosis. The hormone promoted osteogenesis, inhibited osteoclastogenesis, stimulated angiogenesis, and reduced peri-implantitis around the graft. Recently, a growing number of studies showed beneficial effects of melatonin to treat bone defects. However, cellular and molecular mechanisms involved in bone healing are still poorly understood. In this review, we recapitulate the potential mechanisms of melatonin, providing a new horizon to the clinical treatment of bone defects.

Ginkgolide B monotherapy reverses osteoporosis by regulating oxidative stress-mediated bone homeostasis

Osteoporosis is characterized by reductions in bone mass, which could be attributed to the dysregulation of bone homeostasis, such as the loss of balance between bone-resorbing osteoclasts and bone-forming osteoblasts. Elevated levels of oxidative stress increase bone resorption by promoting osteoclastogenesis and inhibiting the osteogenesis. Ginkgolide B (GB), a small natural molecule from Ginkgo biloba, has been reported to possess pharmacological activities by regulating reactive oxygen species (ROS) in aging-related degenerative diseases. Herein, we assessed the therapeutic effects of GB on the bone phenotypes of mice with osteoporosis induced by (I) aging, (II) ovariectomy, and (III) glucocorticoids. In all three animal models, oral gavage of GB significantly improved bone mass consistent with the increase in the OPG-to-RANKL ratio. In the in vitro experiments, GB promoted osteogenesis in aged mesenchymal stem cells (MSCs) and repressed osteoclastogenesis in aged macrophages by reducing ROS. The serum protein profile in GB-treated aged mice revealed moderate rejuvenating effects; signaling pathways associated with ROS were also regulated. The anabolic and anti-catabolic effects of GB were illustrated by the reduction in ROS. Our results indicate that GB is effective in treating osteoporosis. The use of GB in patients with osteoporosis is worthy of further clinical investigation.

Kartogenin prevents cartilage degradation and alleviates osteoarthritis progression in mice via the miR-146a/NRF2 axis

Osteoarthritis (OA) is a common articular degenerative disease characterized by loss of cartilage matrix and subchondral bone sclerosis. Kartogenin (KGN) has been reported to improve chondrogenic differentiation of mesenchymal stem cells. However, the therapeutic effect of KGN on OA-induced cartilage degeneration was still unclear. This study aimed to explore the protective effects and underlying mechanisms of KGN on articular cartilage degradation using mice with post-traumatic OA. To mimic the in vivo arthritic environment, in vitro cultured chondrocytes were exposed to interleukin-1β (IL-1β). We found that KGN barely affected the cell proliferation of chondrocytes; however, KGN significantly enhanced the synthesis of cartilage matrix components such as type II collagen and aggrecan in a dose-dependent manner. Meanwhile, KGN markedly suppressed the expression of matrix degradation enzymes such as MMP13 and ADAMTS5. In vivo experiments showed that intra-articular administration of KGN ameliorated cartilage degeneration and inhibited subchondral bone sclerosis in an experimental OA mouse model. Molecular biology experiments revealed that KGN modulated intracellular reactive oxygen species in IL-1β-stimulated chondrocytes by up-regulating nuclear factor erythroid 2-related factor 2 (NRF2), while barely affecting its mRNA expression. Microarray analysis further revealed that IL-1β significantly up-regulated miR-146a that played a critical role in regulating the protein levels of NRF2. KGN treatment showed a strong inhibitory effect on the expression of miR-146a in IL-1β-stimulated chondrocytes. Over-expression of miR-146a abolished the anti-arthritic effects of KGN not only by down-regulating the protein levels of NRF2 but also by up-regulating the expression of matrix degradation enzymes. Our findings demonstrate, for the first time, that KGN exerts anti-arthritic effects via activation of the miR-146a-NRF2 axis and KGN is a promising heterocyclic molecule to prevent OA-induced cartilage degeneration.

Melatonin in Cancer Treatment: Current Knowledge and Future Opportunities

Melatonin is a pleotropic molecule with numerous biological activities. Epidemiological and experimental studies have documented that melatonin could inhibit different types of cancer in vitro and in vivo. Results showed the involvement of melatonin in different anticancer mechanisms including apoptosis induction, cell proliferation inhibition, reduction in tumor growth and metastases, reduction in the side effects associated with chemotherapy and radiotherapy, decreasing drug resistance in cancer therapy, and augmentation of the therapeutic effects of conventional anticancer therapies. Clinical trials revealed that melatonin is an effective adjuvant drug to all conventional therapies. This review summarized melatonin biosynthesis, availability from natural sources, metabolism, bioavailability, anticancer mechanisms of melatonin, its use in clinical trials, and pharmaceutical formulation. Studies discussed in this review will provide a solid foundation for researchers and physicians to design and develop new therapies to treat and prevent cancer using melatonin.

Melatonin Prevents Non-image-Forming Visual System Alterations Induced by Experimental Glaucoma in Rats

Glaucoma is a blindness-causing disease that involves selective damage to retinal ganglion cells (RGCs) and their axons. A subset of RGCs expressing the photopigment melanopsin regulates non-image-forming visual system functions, such as pupillary light reflex and circadian rhythms. We analyzed the effect of melatonin on the non-image-forming visual system alterations induced by experimental glaucoma. For this purpose, male Wistar rats were weekly injected with vehicle or chondroitin sulfate into the eye anterior chamber. The non-image-forming visual system was analyzed in terms of (1) melanopsin-expressing RGC number, (2) anterograde transport from the retina to the olivary pretectal nucleus and the suprachiasmatic nuclei, (3) blue- and white light-induced pupillary light reflex, (4) light-induced c-Fos expression in the suprachiasmatic nuclei, (5) daily rhythm of locomotor activity, and (6) mitochondria in melanopsin-expressing RGC cells. Melatonin prevented the effect of experimental glaucoma on melanopsin-expressing RGC number, blue- and white light-induced pupil constriction, retina-olivary pretectal nucleus, and retina- suprachiasmatic nuclei communication, light-induced c-Fos expression in the suprachiasmatic nuclei, and alterations in the locomotor activity daily rhythm. In addition, melatonin prevented the effect of glaucoma on melanopsin-expressing RGC mitochondrial alterations. These results support that melatonin protected the non-image-forming visual system against glaucoma, probably through a mitochondrial protective mechanism.

Resveratrol-enhanced SIRT1-mediated osteogenesis in porous endplates attenuates low back pain and anxiety behaviors

Low back pain (LBP) is a major clinical problem that lacks effective treatments. The sensory innervation in porous vertebral endplates and anxiety contributes to spinal hyperalgesia. We hypothesized that SIRT1 activator resveratrol alleviates LBP and anxiety via promotion of osteogenesis in the porous endplates. The hyperalgesia and anxiety-related behaviors; sensory innervation, inflammation and porosity of endplates; and osteogenic/osteoclastic factors expression were measured following resveratrol treatment after lumbar spine instability (LSI) surgery. To explore whether resveratrol promotes endplates osteogenesis and thus alleviates LBP through activation of SIRT1 in the osteoprogenitor cells of endplates, SIRT1OSX-/- mice were employed. Additionally, the levels of inflammation markers, phosphorylation of cAMP response element-binding protein (pCREB), and brain-derived neurotrophic factor (BDNF) in hippocampus were evaluated. After 4 or 8 weeks LSI surgery, the mice suffered from hyperalgesia and anxiety, which were efficiently attenuated by resveratrol at 8 weeks. Resveratrol treatment-enhanced osteogenesis and decreased endplates porosities accompanied with the reduction of TNFα, IL-1β, and COX2 levels and CGRP+ nerve fibers innervation in porous endplates. Resveratrol-mediated endplates osteogenesis, decreased endplates porosities, and analgesic and antianxiety effects were abrogated in SIRT1OSX-/- mice. Furthermore, resveratrol relieved inflammation and increased pCREB and BDNF expression in the hippocampus after 8 weeks, which alleviate anxiety-related behaviors. This study provides that resveratrol-mediated porous endplates osteogenesis via the activation of SIRT1 markedly blocked sensory innervation and inflammation in endplates, therefore, alleviating LSI surgery-induced LBP and hippocampus-related anxiety.

Role of histone deacetylases in bone development and skeletal disorders

Bone cells must constantly respond to hormonal and mechanical cues to change gene expression programs. Of the myriad of epigenomic mechanisms used by cells to dynamically alter cell type-specific gene expression, histone acetylation and deacetylation has received intense focus over the past two decades. Histone deacetylases (HDACs) represent a large family of proteins with a conserved deacetylase domain first described to deacetylate lysine residues on histone tails. It is now appreciated that multiple classes of HDACs exist, some of which are clearly misnamed in that acetylated lysine residues on histone tails is not the major function of their deacetylase domain. Here, we will review the roles of proteins bearing deacetylase domains in bone cells, focusing on current genetic evidence for each individual HDAC gene. While class I HDACs are nuclear proteins whose primary role is to deacetylate histones, class IIa and class III HDACs serve other important cellular functions. Detailed knowledge of the roles of individual HDACs in bone development and remodeling will set the stage for future efforts to specifically target individual HDAC family members in the treatment of skeletal diseases such as osteoporosis.

Effects of melatonin on protecting against lung injury (Review)

Melatonin (MT; N-acetyl-5-methoxy-tryptamine), which has multiple effects and roles, is secreted from the pineal gland at night according to the daily rhythm. In addition to circadian regulation, MT has anti-inflammatory, antioxidant and anticancer functions. Recent studies postulated that MT serves a critical role in apoptosis, anti-ischemic reperfusion injury and anti-proliferative effects on various cells. The current review reported on the underlying mechanism behind the protective effect of MT on lung diseases, such as acute lung injury, acute respiratory distress syndrome, chronic obstructive pulmonary disease, lung ischemia-reperfusion injury, sepsis-induced lung injury and ventilator-induced lung injury. MT is considered an adjuvant with therapeutic drugs for preventing inflammation and is responsible for regulating patient sleep cycles in the intensive care unit. The current review described the anti-inflammatory and antioxidant efficiency of MT with a focus on the molecular mechanisms of action in various lung injuries.

SIRT1, a promising regulator of bone homeostasis

Sirtuin 1 (SIRT1), a nicotinamide adenine dinucleotide-dependent deacetylase, epigenetically regulates various cell metabolisms, including inflammation, tumorigenesis, and bone metabolism. Many clinical studies have found the potential of SIRT1 in predicting and treating bone-related disorders, such as osteoporosis and osteonecrosis, suggesting that SIRT1 might be a regulator of bone homeostasis. In order to identify the mechanisms that underlie the pivotal role of SIRT1 in bone homeostasis, many studies revealed that SIRT1 could maintain the balance between bone formation and absorption via regulating the ratio of osteoblasts to osteoclasts. SIRT1 controls the differentiation of mesenchymal stem cells (MSCs) and bone marrow-derived macrophages, increasing osteogenesis and reducing osteoclastogenesis. Besides, SIRT1 can enhance bone-forming cells' viability, including MSCs and osteoblasts under adverse conditions by resisting senescence, suppressing apoptosis, and promoting autophagy in favor of osteogenesis. Furthermore, the effect on bone vasculature homeostasis enables SIRT1 to become a valuable strategy for ischemic osteonecrosis and senile osteoporosis. The review systemically discusses SIRT1 pathways and the critical role in bone homeostasis and assesses whether SIRT1 is a potential target for manipulation and therapy, to lay a solid foundation for further researches in the future.

Melatonin alleviates d-galactose-decreased hyaluronic acid production in synovial membrane cells via Sirt1 signalling

Hyaluronic acid (HA) exerts a critical role in the lubricating and buffering properties of synovial fluid in joints. The production of HA is regulated by growth factors, hormones, inflammatory cytokines and mechanical load. The reduction of HA contributes to the progression of osteoarthritis. Herein, we found that d-galactose (d-gal) induced the senescence of rabbit synovial membrane cells, accompanied by decreased HA production. The mRNA level of HA synthase 2 (HAS2) was downregulated by d-gal, as analysed by real-time polymerase chain reaction. Melatonin, an endocrine hormone, can regulate the homeostasis of bone and cartilage. We found that melatonin treatment attenuated d-gal-induced cell senescence and decreased the expression of p21, p16 and pp65 proteins. Melatonin could reverse HA production and maintain HAS2 expression. Furthermore, we revealed that Sirt1 signalling was required for melatonin effects. Sirt1 inhibitor could counteract melatonin-mediated HA production and HAS2 expression. Additionally, Sirt1 overexpression directly antagonized d-gal-induced cell aging and HA downregulation. Taken together, our results suggest that melatonin-Sirt1 signal has a protective effect on synovial membrane cells, enhancing HA synthesis and interrupting cell senescence.

The association of circulating kynurenine, a tryptophan metabolite, with frailty in older adults

Despite the accumulating evidence from in vitro and animal experiments supporting the role of kynurenine (a tryptophan metabolite) in a number of degenerative age-related changes, the relationship between kynurenine and frailty in older adults is not well understood. We collected blood samples from 73 participants who underwent a comprehensive geriatric assessment, measuring kynurenine levels using liquid chromatography-tandem mass spectrometry. We assessed the phenotypic frailty and the deficit accumulation frailty index using widely validated approaches proposed by Fried et al. and Rockwood et al., respectively. After adjusting for sex, age, and body mass index, the frail participants presented 52.9% and 34.3% higher serum kynurenine levels than those with robustness and prefrailty, respectively (P = 0.005 and 0.014, respectively). Serum kynurenine levels were positively associated with the frailty index, time to complete 5 chair stands, and patient health questionnaire-2 score and inversely associated with grip strength and gait speed (P = 0.042 to <0.001). Furthermore, the odds ratio per increase in serum kynurenine level for phenotypic frailty was approximately 2.62 (95% confidence interval = 1.22-5.65, P = 0.014). These data provide clinical evidence that circulating kynurenine might be a potential biomarker for assessing the risk of frailty in humans.

Osteogenic differentiation potential of human bone marrow-derived mesenchymal stem cells enhanced by bacoside-A

Stem cell therapy is growing rapidly to treat numerous diseases including bone-associated diseases. Mesenchymal stem cells (MSCs) are most commonly preferred to treat bone diseases because it possesses high osteogenic potency. Though, to obtain maximum osteogenic efficiency of MSCs is challenging. Therefore, this study was planned to evaluate the osteogenic efficiency of human bone marrow derived mesenchymal stem cells (hBMSCs) by bacoside-A. This study was investigated the activity of alkaline phosphatase (ALP) and expressions of the genes specific to osteogenic regulation mainly runt-related transcription factor 2 (Runx2), osterix (Osx), osteocalcin (OCN) and collagen type Iα1 (Col I α1) in hBMSCs cultured under osteogenic conditions at different concentrations of bacoside-A for 14 days. The results of this study depicted significant upregulation in the activity of ALP and expressions of osteogenic regulator genes in bacoside-A treated cells when compared with control cells. Besides, expressions of glycogen synthase kinase-3β (GSK-3β) and Wnt/β-catenin were evaluated; these expressions were also significantly increased in bacoside-A treated cells when compared with control cells. This result provides a further supporting evidence of bacoside-A role on osteogenesis in hBMSCs. The present study suggest that bacoside-A will be applied to ameliorate the process of osteogenesis in hBMSCs to repair damaged bone structure during MSC-based therapy; this will be an excellent and auspicious treatment for bone-associated disorders including osteoporosis. Significance of the study Osteoporosis is a bone metabolic disorder characterized by an imbalance between the activity of osteoblastic bone formation and osteoclastic bone resorption that disrupts the bone microarchitecture. Current anti-osteoporotic drugs are inhibiting bone resorption, but they are unable to restore the bone structure due to extreme bone remodelling process and causes numerous side effects. The finding of natural bioactive compounds with osteogenic property is very essential for osteoporosis treatment. This study was reported that bacoside-A ameliorated osteogenic differentiation of hBMSCs through upregulation of osteogenic differentiation genes and Wnt/β-catenin signalling pathway. This result is indicating that bacoside-A may be useful for osteoporosis treatments.

Melatonin Rescues the Ti Particle-Impaired Osteogenic Potential of Bone Marrow Mesenchymal Stem Cells via the SIRT1/SOD2 Signaling Pathway

Wear particles released by joint implants are a major cause of osteolysis around the prosthesis by negatively affecting bone reconstruction. Bone marrow mesenchymal stem cells (BMMSCs) stimulated by wear particles showed an impaired osteogenic potential. Melatonin has been shown beneficial effects on intracellular antioxidant functions and bone formation; however, whether it could restore the osteogenic potential of BMMSCs inhibited by wear particles was unknown. This study aimed to evaluate the protective effect of melatonin on the osteogenic capacity of BMMSCs exposed to titanium (Ti) wear particles and to investigated the underlying mechanisms involving intracellular antioxidant properties. When BMMSCs were exposed to Ti particles in vitro, melatonin treatment successfully improved the matrix mineralization and expression of osteogenic markers in BMMSCs, while decreasing the levels of intracellular reactive oxygen species (ROS) and mitochondrial superoxide. The protective effect of melatonin on osteolysis was validated in a Ti particle-exposed murine calvarial model. Meanwhile, silent information regulator type 1 (SIRT1) and intracellular antioxidant enzymes were significantly up-regulated, particularly superoxide dismutase 2 (SOD2), in melatonin-treated BMMSCs. Furthermore, inhibition of SIRT1 by EX527 completely counteracted the protective effect of melatonin on Ti particle-treated BMMSCs, evidenced by the reduced expression of SOD2, increased ROS and superoxide, and decreased osteogenic differentiation. These results demonstrated that melatonin restored the osteogenic potential and improved the antioxidant properties of BMMSCs through the SIRT1 signaling pathway. Our findings suggest that melatonin is a promising candidate for treating osteolysis induced by wear particles.

Melatonin suppresses ER stress-dependent proapoptotic effects via AMPK in bone mesenchymal stem cells during mitochondrial oxidative damage

Background

Bone marrow mesenchymal stem cells (BMSCs) have been used as important cell-based tools for clinical applications. Oxidative stress-induced apoptosis causes a low survival rate after transplantation, and the underlying mechanisms remain unknown. The endoplasmic reticulum (ER) and mitochondria are vital organelles regulated by adenosine monophosphate (AMP)-activated protein kinase (AMPK), especially during oxidative stress injury. Melatonin exerts an antioxidant effect by scavenging free radicals. Here, we aimed to explore whether cytoprotective melatonin relieves ER stress-mediated mitochondrial dysfunction through AMPK in BMSCs after oxidative stress injury.

Methods

Mouse BMSCs were isolated and exposed to H₂O₂ in the absence or presence of melatonin. Thereafter, cell damage, oxidative stress levels, mitochondrial function, AMPK activity, ER stress-related proteins, and apoptotic markers were measured. Additionally, the involvement of AMPK and ER stress in the melatonin-mediated protection of BMSCs against H₂O₂-induced injury was investigated using pharmacologic agonists and inhibitors.

Results

Melatonin improved cell survival and restored mitochondrial function. Moreover, melatonin intimately regulated the phosphorylation of AMPK and molecules associated with ER stress pathways. AMPK activation and ER stress inhibition following melatonin administration improved the mitochondrial membrane potential (MMP), reduced mitochondria-initiated oxidative damage, and ultimately suppressed apoptotic signaling pathways in BMSCs. Cotreatment with N-acetyl-l-cysteine (NAC) significantly enhanced the antioxidant effect of melatonin. Importantly, pharmacological AMPK activation/ER stress inhibition promoted melatonin-induced cytoprotection, while pharmacological AMPK inactivation/ER stress induction conferred resistance to the effect of melatonin against H₂O₂ insult.

Conclusions

Our data also reveal a new, potentially therapeutic mechanism by which melatonin protects BMSCs from oxidative stress-mediated mitochondrial apoptosis, possibly by regulating the AMPK-ER stress pathway.

Melatonin suppresses ER stress-dependent proapoptotic effects via AMPK in bone mesenchymal stem cells during mitochondrial oxidative damage

BACKGROUND

Bone marrow mesenchymal stem cells (BMSCs) have been used as important cell-based tools for clinical applications. Oxidative stress-induced apoptosis causes a low survival rate after transplantation, and the underlying mechanisms remain unknown. The endoplasmic reticulum (ER) and mitochondria are vital organelles regulated by adenosine monophosphate (AMP)-activated protein kinase (AMPK), especially during oxidative stress injury. Melatonin exerts an antioxidant effect by scavenging free radicals. Here, we aimed to explore whether cytoprotective melatonin relieves ER stress-mediated mitochondrial dysfunction through AMPK in BMSCs after oxidative stress injury.

METHODS

Mouse BMSCs were isolated and exposed to H₂O₂ in the absence or presence of melatonin. Thereafter, cell damage, oxidative stress levels, mitochondrial function, AMPK activity, ER stress-related proteins, and apoptotic markers were measured. Additionally, the involvement of AMPK and ER stress in the melatonin-mediated protection of BMSCs against H₂O₂-induced injury was investigated using pharmacologic agonists and inhibitors.

RESULTS

Melatonin improved cell survival and restored mitochondrial function. Moreover, melatonin intimately regulated the phosphorylation of AMPK and molecules associated with ER stress pathways. AMPK activation and ER stress inhibition following melatonin administration improved the mitochondrial membrane potential (MMP), reduced mitochondria-initiated oxidative damage, and ultimately suppressed apoptotic signaling pathways in BMSCs. Cotreatment with N-acetyl-L-cysteine (NAC) significantly enhanced the antioxidant effect of melatonin. Importantly, pharmacological AMPK activation/ER stress inhibition promoted melatonin-induced cytoprotection, while pharmacological AMPK inactivation/ER stress induction conferred resistance to the effect of melatonin against H₂O₂ insult.

CONCLUSIONS

Our data also reveal a new, potentially therapeutic mechanism by which melatonin protects BMSCs from oxidative stress-mediated mitochondrial apoptosis, possibly by regulating the AMPK-ER stress pathway.

Do peripheral melatonin agonists improve bone fracture healing? The effects of agomelatine and ramelteon on experimental bone fracture

Melatonin improves fracture healing, but the long-term use of melatonin seems impracticable in the treatment of fracture due to side effects caused by hormonal stress on chronological rhythm. Ramelteon (RAMEL) and agomelatine (AGO) are non-selective peripheral melatonin receptor (MT) agonists. This study investigated the effects on bone fracture healing of these MT agonists, which do not affect the central nervous system. The rats were divided into 6 groups, including Group 1 (SHAM): sham operated group; Group 2 (FRACTURE): femoral fracture control; Group 3 (FR + AGO30): femoral fracture + agomelatine 30 mg/kg; Group 4 (FR + AGO60): femoral fracture + agomelatine 60 mg/kg; Group 5 (FR + RAMEL3): femoral fracture + ramelteon 3 mg/kg; and Group 6 (FR + RAMEL6): femoral fracture + ramelteon 6 mg/kg. After 21 days, the rats were subjected to X-ray imaging. Bone healing was evaluated with hematoxylin-eosin (HE) staining. Messenger RNA (mRNA) expressions of bone formation markers, such as bone alkaline phosphatase (ALP), osteocalcin (OC), and osteopontin (OP), were evaluated by real-time polymerase chain reaction (RT-PCR) and with immunohistochemistry (IHC) staining. The radiographic fracture healing scores were statistically significantly higher in the FR + AGO60 group and the FR + RAMEL3 group than in the FRACTURE group. The histopathology and molecular results supported the radiographic results. It was shown that agomelatine and ramelteon increase bone fracture healing, leading to the conclusion that a preference for agomelatine, an antidepressant, and ramelteon, a sleep aid, will increase bone fracture healing in patients with fractures.

Melatonin suppresses Ti-particle-induced inflammatory osteolysis via activation of the Nrf2/Catalase signaling pathway

Aseptic loosening induced by osteolysis is recognized as a late complication of joint replacement. Osteoclasts stimulated by Titanium (Ti) nanoparticles play a critical role in periprosthetic osteolysis. Emerging evidence indicates that melatonin, a hormone primarily synthesized by the pineal gland, has been shown an inhibitory effect on osteoclast formation. However, it is unclear whether melatonin could suppress Ti-particle-induced osteoclastogenesis and what the underlying mechanisms were involved in. Herein, we aimed to investigate the effect of melatonin on osteoclast differentiation and osteolysis stimulated by Ti particles. Our results showed that the in vitro osteoclastogenesis of mouse bone marrow monocytes (BMMs) stimulated by Ti particles was suppressed by melatonin treatments in a dose-dependent manner. Further experiments revealed that melatonin up-regulated the expression of the nuclear factor erythroid 2-related factor 2 (Nrf2) and catalase (CAT) at both the mRNA and protein levels. The role of the Nrf2/CAT signaling pathway was confirmed by the fact that silencing the expression of NRF2 by small interfering RNA (siRNA) counteracted the anti-osteolysis effects of melatonin. Furthermore, in vivo intraperitoneal injection of melatonin successfully attenuated periprosthetic osteolysis induced by Ti particles in a murine calvarial model. Our findings demonstrate that melatonin is a promising therapeutic agent for treating periprosthetic osteolysis by inhibiting the Ti-particle-stimulated osteoclastogenesis via activation of the Nrf2/Catalase signaling pathway.

Melatonin protects against thoracic aortic aneurysm and dissection through SIRT1-dependent regulation of oxidative stress and vascular smooth muscle cell loss

Melatonin functions as an endogenous protective molecule in multiple vascular diseases, whereas its effects on thoracic aortic aneurysm and dissection (TAAD) and underlying mechanisms have not been reported. In this study, TAAD mouse model was successfully induced by β-aminopropionitrile fumarate (BAPN). We found that melatonin treatment remarkably prevented the deterioration of TAAD, evidenced by decreased incidence, ameliorated aneurysmal dilation and vascular stiffness, improved aortic morphology, and inhibited elastin degradation, macrophage infiltration, and matrix metalloproteinase expression. Moreover, melatonin blunted oxidative stress damage and vascular smooth muscle cell (VSMC) loss. Notably, BAPN induced a decrease in SIRT1 expression and activity of mouse aorta, whereas melatonin treatment reversed it. Further mechanistic study demonstrated that blocking SIRT1 signaling partially inhibited these beneficial effects of melatonin on TAAD. Additionally, the melatonin receptor was involved in this phenomenon. Our study is the first to report that melatonin exerts therapeutic effects against TAAD by reducing oxidative stress and VSMC loss via activation of SIRT1 signaling in a receptor-dependent manner, thus suggesting a novel therapeutic strategy for TAAD.