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

Melatonin intervention to prevent nanomaterial exposure-induced damages: A systematic review and meta-analysis of in vitro and in vivo studies

Given its antioxidant, anti-inflammatory, and antiapoptotic properties, melatonin (MEL), a health-caring food to improve sleep disorders, is hypothesized to protect against nanomaterial exposure-induced toxicity. However, the conclusion derived from different studies seemed inconsistent. A meta-analysis of all available preclinical studies was performed to examine the effects of MEL on nanomaterial-induced damages. Eighteen relevant studies were retrieved through searching five electronic databases up to December 2023. The meta-analysis showed that relative to control, MEL treatment significantly increased cell viability (standardized mean difference [SMD = 1.27]) and alleviated liver function (lowered AST [SMD = -3.89] and ALT [SMD = -5.89]), bone formation (enhanced BV/TV [SMD = 4.13] and lessened eroded bone surface [SMD = -5.40]), and brain nerve (inhibition of AChE activity [SMD = -3.60]) damages in animals. The protective mechanisms of MEL against damages caused by nanomaterial exposure were associated with its antiapoptotic (decreased Bax/Bcl-2 ratio [SMD = -4.50] and caspase-3 levels [dose <100 μM: SMD = -3.66]), antioxidant (decreased MDA [in vitro: SMD = -2.84; in vivo: SMD = -4.27]), and anti-inflammatory (downregulated TNF-α [in vitro: SMD = -5.41; in vivo: SMD = -3.21] and IL-6 [in vitro: SMD = -5.90; in vivo: SMD = -2.81]) capabilities. In conclusion, our study suggests that MEL should be supplemented to prevent damages in populations exposed to nanomaterials.

Melatonin via MTNR1B regulates METTL3 to protect ileum cell differentiation

Intestinal stem cells rapidly differentiate into various epithelial cells, playing a crucial role in maintaining intestinal homeostasis. Melatonin, a known endogenous molecule with anti-inflammatory and antioxidant properties, has its potential efficacy in ileum stem cells differentiation not fully understood to date. This study indicates that melatonin suppresses ileum inflammation and maintains normal differentiation of ileum stem cells through MTNR1B. Subsequent outcomes following treatment with MTNR1B inhibitors further substantiate these findings. Additionally, overexpression of METTL3 protein appears to be a potential instigator for promoting ileum inflammation and disruptions in cell differentiation. Treatment with the METTL3 inhibitor SAH significantly inhibits ileum inflammation and Wnt/β-catenin activity, thereby sustaining normal cellular differentiation functions. In summary, this study showed that melatonin may improve ileum inflammation and maintain cell differentiation functions by inhibiting abnormal METTL3 expression via MTNR1B.

The Role and Therapeutic Potential of Melatonin in Degenerative Fundus Diseases: Diabetes Retinopathy and Age-Related Macular Degeneration

Degenerative fundus disease encompasses a spectrum of ocular diseases, including diabetic retinopathy (DR) and age-related macular degeneration (AMD), which are major contributors to visual impairment and blindness worldwide. The development and implementation of effective strategies for managing and preventing the onset and progression of these diseases are crucial for preserving patients' visual acuity. Melatonin, a neurohormone primarily produced by the pineal gland, exhibits properties such as circadian rhythm modulation, antioxidant activity, anti-inflammatory effects, and neuroprotection within the ocular environment. Furthermore, melatonin has been shown to suppress neovascularization and reduce vascular leakage, both of which are critical in the pathogenesis of degenerative fundus lesions. Consequently, melatonin emerges as a promising therapeutic candidate for degenerative ocular diseases. This review provides a comprehensive overview of melatonin synthesis, its localization within ocular tissues, and its mechanisms of action, particularly in regulating melatonin production, thereby underscoring its potential as a therapeutic agent for degenerative fundus diseases.

Crosstalk Between the Neuroendocrine System and Bone Homeostasis

The homeostasis of bone microenvironment is the foundation of bone health and comprises 2 concerted events: bone formation by osteoblasts and bone resorption by osteoclasts. In the early 21st century, leptin, an adipocytes-derived hormone, was found to affect bone homeostasis through hypothalamic relay and the sympathetic nervous system, involving neurotransmitters like serotonin and norepinephrine. This discovery has provided a new perspective regarding the synergistic effects of endocrine and nervous systems on skeletal homeostasis. Since then, more studies have been conducted, gradually uncovering the complex neuroendocrine regulation underlying bone homeostasis. Intriguingly, bone is also considered as an endocrine organ that can produce regulatory factors that in turn exert effects on neuroendocrine activities. After decades of exploration into bone regulation mechanisms, separate bioactive factors have been extensively investigated, whereas few studies have systematically shown a global view of bone homeostasis regulation. Therefore, we summarized the previously studied regulatory patterns from the nervous system and endocrine system to bone. This review will provide readers with a panoramic view of the intimate relationship between the neuroendocrine system and bone, compensating for the current understanding of the regulation patterns of bone homeostasis, and probably developing new therapeutic strategies for its related disorders.

Titanium particles in peri-implantitis: distribution, pathogenesis and prospects

Peri-implantitis is one of the most important biological complications in the field of oral implantology. Identifying the causative factors of peri-implant inflammation and osteolysis is crucial for the disease's prevention and treatment. The underlying risk factors and detailed pathogenesis of peri-implantitis remain to be elucidated. Titanium-based implants as the most widely used implant inevitably release titanium particles into the surrounding tissue. Notably, the concentration of titanium particles increases significantly at peri-implantitis sites, suggesting titanium particles as a potential risk factor for the condition. Previous studies have indicated that titanium particles can induce peripheral osteolysis and foster the development of aseptic osteoarthritis in orthopedic joint replacement. However, it remains unconfirmed whether this phenomenon also triggers inflammation and bone resorption in peri-implant tissues. This review summarizes the distribution of titanium particles around the implant, the potential roles in peri-implantitis and the prevalent prevention strategies, which expects to provide new directions for the study of the pathogenesis and treatment of peri-implantitis.

Selenomethionine against titanium particle-induced osteolysis by regulating the ROS-dependent NLRP3 inflammasome activation via the β-catenin signaling pathway

Wear debris-induced osteolysis, especially titanium (Ti) particles-induced osteolysis, is the most common cause of arthroplasty failure with no effective therapy. Previous studies have suggested that inflammation and impaired osteogenesis are associated with Ti particles -induced osteolysis. Selenium (Se) is an essential trace element in the human body, which forms selenomethionine (Se-Met) in nature, and selenoproteins has strong anti-inflammatory and antioxidant stress effects. In this study, the effects of Se-Met on Ti particles-induced osteolysis were observed and the potential mechanism was explored. We found that exogenous Se-Met relieved osteolysis induced by Ti particles in two animal models and MC3T3-E1 cells. We found that the addition of Se-Met effectively inhibited Ti particle-induced inflammation by regulating reactive oxygen species-dependent (ROS-dependent) NOD-like receptor protein 3 (NLRP3) inflammasome activation. These therapeutic effects were abrogated in MC3T3-E1 cells that had received a β-catenin antagonist, suggesting that Se-Met alleviates inflammatory osteolysis via the β-catenin signaling pathway. Collectively, these findings indicated that Se-Met may serve as a potential therapeutic agent for treating Ti particle-induced osteolysis.

SOST gene suppression stimulates osteocyte Wnt/β-catenin signaling to prevent bone resorption and attenuates particle-induced osteolysis

The most common cause for prosthetic revision surgery is wear particle-induced periprosthetic osteolysis, which leads to aseptic loosening of the prosthesis. Both SOST gene and its synthetic protein, sclerostin, are hallmarks of osteocytes. According to our previous findings, blocking SOST induces bone formation and protects against bone loss and deformation caused by titanium (Ti) particles by activating the Wnt/β-catenin cascade. Although SOST has been shown to influence osteoblasts, its ability to control wear-particle-induced osteolysis via targeting osteoclasts remains unclear. Mice were subjected to development of a cranial osteolysis model. Micro CT, HE staining, and TRAP staining were performed to evaluate bone loss in the mouse model. Bone marrow-derived monocyte-macrophages (BMMs) made from the C57BL/6 mice were exposed to the medium of MLO-Y4 (co-cultured with Ti particles) to transform them into osteoclasts. Bioinformatics methods were used to predict and validate the interaction among SOST, Wnt/β-catenin, RANKL/OPG, TNF-α, and IL-6. Local bone density and bone volume improved after SOST inhibition, both the number of lysis pores and the rate of skull erosion decreased. Histological research showed that β-catenin and OPG expression were markedly increased after SOST inhibition, whereas TRAP and RANKL levels were markedly decreased. In-vitro, Ti particle treatment elevated the expression of sclerostin, suppressed the expression of β-catenin, and increased the RANKL/OPG ratio in the MLO-Y4 cell line. TNF-α and IL-6 also elevated after treatment with Ti particles. The expression levels of NFATc1, CTSK, and TRAP in osteoclasts were significantly increased, and the number of positive cells for TRAP staining was increased. Additionally, the volume of bone resorption increased at the same time. In contrast, when SOST expression was inhibited in the MLO-Y4 cell line, these effects produced by Ti particles were reversed. All the results strongly show that SOST inhibition triggered the osteocyte Wnt/β-catenin signaling cascade and prevented wear particle-induced osteoclastogenesis, which might reduce periprosthetic osteolysis. KEY MESSAGES: SOST is a molecular regulator in maintaining bone homeostasis. SOST plays in regulating bone homeostasis through the Wnt/β-catenin signaling pathway. SOST gene suppression stimulates osteocyte Wnt/β-catenin signaling to prevent bone resorption and attenuates particle-induced osteolysis.

Copper modified cobalt-chromium particles for attenuating wear particle induced-inflammation and osteoclastogenesis

The nature of aseptic prosthetic loosening mainly relates to the wear particles that induce inflammation and subsequent osteoclastogenesis. The ideal approach to impede wear particle-induced osteolysis should minimize inflammation and osteoclastogenesis. In this work, Co29Cr9W3Cu particles were used as a research model for the first time to explore the response of Co29Cr9W3Cu particles to inflammatory response and osteoclast activation in vitro and in vivo by using Co29Cr9W particles as the control group. In vitro studies showed that the Co29Cr9W3Cu particles could promote the generation of M2-phenotype macrophages and increase the expression level of anti-inflammatory factor IL-10, while inhibiting the formation of M1-phenotype macrophages and down-regulating the expression of inflammatory factors TNF-α, IL-6 and IL-1β; More importantly, the Co29Cr9W3Cu particles reduced the expression of NF-κB and downstream osteoclast related-specific transcription marker genes, such as TRAP, NFATc1, and Cath-K; In vivo results indicated that the Co29Cr9W3Cu particles exposed to murine calvarial contributed to decreasing the amount of osteoclast and osteolysis area. These findings collectively demonstrated that Cu-bearing cobalt-chromium alloy may potentially delay the development of aseptic prosthetic loosening induced by wear particles, which is expected to provide evidence of Co29Cr9W3Cu alloy as an alternative material of joint implants with anti-wear associated osteolysis.

Melatonin promotes the restoration of bone defects via enhancement of miR-335-5p combined with inhibition of TNFα/NF-κB signaling

Accelerating the repair of a bone defect is crucial clinically due to the increased prevalence of trauma, tumor, and infections in bone. Studies have found that excess acute and chronic inflammation attenuate osteogenic differentiation of BMSCs (bone marrow mesenchymal stem cells). Moreover, TNF-α and NF-κB could inhibit osteoblasts differentiation of BMSCs and promote osteoclastogenesis via multiple mechanisms, such as increasing osteoclast precursor cells and acting synergistically with cell cytokines. However, melatonin could inhibit the expression of TNFα/NF-κB and promote bone formation by activating the Wnt/β-catenin signaling pathway. However, there has been no evidence regarding the effect of melatonin on TNFα/NF-κB-inhibited osteoblastogenesis and bone formation. This study aimed to investigate the role of melatonin on TNFα/NF-κB-inhibited osteoblastogenesis and bone formation. Micro-CT, high-throughput screening, overexpression, and other methods were used, and we found that the number of osteoblasts was elevated with melatonin treatment. Additionally, TNFα/NF-κB signaling was inhibited, while miR-335-5p expression increased markedly following treatment with melatonin. Furthermore, miR-335-5p negatively regulated TNFα/NF-κB signaling, while miR-335-5p inhibitor ameliorated the effects of melatonin on TNFα/NF-κB. In conclusion, melatonin facilitates osteogenesis in bone defect healing by enhancing miR-335-5p expression and inhibiting the TNFα/NF-κB pathway.

Circular RNA CircSLC8A1 contributes to osteogenic differentiation in hBMSCs via CircSLC8A1/miR-144-3p/RUNX1 in periprosthetic osteolysis

Circular RNAs (circRNAs) are often found in eukaryocyte and have a role in the pathogenesis of a variety of human disorders. Our related research has shown the differential expression of circRNAs in periprosthetic osteolysis (PPOL). However, the involvement of circRNAs in the exact process is yet unknown. CircSLC8A1 expression was evaluated in clinical samples and human bone marrow mesenchymal stem cells (hBMSCs) in this investigation using quantitative real-time PCR. In vitro and in vivo studies were conducted to explicate its functional role and pathway. We demonstrated CircSLC8A1 is involved in PPOL using gain- and loss-of-function methods. The association of CircSLC8A1 and miR-144-3p, along with miR-144-3p and RUNX1, was predicted using bioinformatics. RNA pull-down and luciferase assays confirmed it. The impact of CircSLC8A1 in the PPOL-mouse model was also investigated using adeno-associated virus. CircSLC8A1 was found to be downregulated in PPOL patients' periprosthetic tissues. Overexpression of CircSLC8A1 promoted osteogenic differentiation (OD) and inhibited apoptosis of hBMSCs in vitro. The osteogenic markers of RUNX1, osteopontin (OPN) and osteocalcin (OCN) were significantly upregulated in hBMSCs after miR-144-3p inhibitor was transferred. Mechanistic analysis demonstrated that CircSLC8A1 directly bound to miR-144-3p and participated in PPOL through the miR-144-3p/RUNX1 pathway in hBMSCs. Micro-CT and quantitative analysis showed that CircSLC8A1 markedly inhibited PPOL, and osteogenic markers (RUNX1, OPN and OCN) were significantly increased (P<0.05) in the mice model. Our findings prove that CircSLC8A1 exerted a regulatory role in promoting osteogenic differentiation in hBMSCs, and CircSLC8A1/miR-144-3p/RUNX1 pathway may provide a potential target for prevention of PPOL.

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.

The role of melatonin in bone regeneration: A review of involved signaling pathways

Increasing bone resorption followed by decreasing bone mineralization are hallmarks of bone degeneration, which mostly occurs in the elderly population and post-menopausal women. The use of mesenchymal stem cells (MSCs) has raised many promises in the field of bone regeneration due to their high osteoblastic differentiation capacity and easy availability from abundant sources. A variety of compounds, including growth factors, cytokines, and other internal factors, have been combined with MSCs to increase their osteoblastic differentiation capacity. One of these factors is melatonin, whose possible regulatory role in bone metabolism and formation has recently been suggested by many studies. Melatonin also is a potential signaling molecule and can affect many of the signaling pathways involved in MSCs osteoblastic differentiation, such as activation of PI3K/AKT, BMP/Smad, MAPK, NFkB, Nrf2/HO-1, Wnt, SIRT/SOD, PERK/ATF4. Furthermore, melatonin in combination with other components such as strontium, vitamin D3, and vitamin K2 has a synergistic effect on bone microstructure and improves bone mineral density (BMD). In this review article, we aim to summarize the regulatory mechanisms of melatonin in osteoblastic differentiation of MSCs and underling involved signaling pathways as well as the clinical potential of using melatonin in bone degenerative disorders.

Involvement of NF-κB/NLRP3 axis in the progression of aseptic loosening of total joint arthroplasties: a review of molecular mechanisms

Particulate wear debris can trigger pro-inflammatory bone resorption and result in aseptic loosening. This complication remains major postoperative discomforts and complications for patients who underwent total joint arthroplasty. Recent studies have indicated that wear debris-induced aseptic loosening is associated with the overproduction of pro-inflammatory cytokines. The activation of osteoclasts as a result of inflammatory responses is associated with osteolysis. Moreover, stimulation of inflammatory signaling pathways such as the NF-κB/NLRP3 axis results in the production of pro-inflammatory cytokines. In this review, we first summarized the potential inflammatory mechanisms of wear particle-induced peri-implant osteolysis. Then, the therapeutic approaches, e.g., biological inhibitors, herbal products, and stem cells or their derivatives, with the ability to suppress the inflammatory responses, mainly NF-κB/NLRP3 signaling pathways, were discussed. Based on the results, activation of macrophages following inflammatory stimuli, overproduction of pro-inflammatory cytokines, and subsequent differentiation of osteoclasts in the presence of wear particles lead to bone resorption. The activation of NF-κB/NLRP3 signaling pathways within the macrophages stimulates the production of pro-inflammatory cytokines, e.g., IL-1β, IL-6, and TNF-α. According to in vitro and in vivo studies, novel therapeutics significantly promoted osteogenesis, suppressed osteoclastogenesis, and diminished particle-mediated bone resorption. Conclusively, these findings offer that suppressing pro-inflammatory cytokines by regulating both NF-κB and NLRP3 inflammasome represents a novel approach to attenuate wear-particle-related osteolytic diseases.

Modification of implant surfaces to stimulate mesenchymal cell activation

BACKGROUND

The process of osteointegration, as key point has the activation of mesenchymal cells at implant-bone interspace, their differentiation into osteoblasts and connection between the implant surface and the surrounding bone.

MAIN TEXT

Implant surfaces composed by biocompatible, organism-friendly materials require changes in content and surface morphology; changes that may further stimulate mesenchymal cell activation. The way the implant surfaces are affected with advantages and disadvantages, that typically bring each methodology, is also the purpose of this study. The study is of review type, based on finding articles about implant surface modification, with the aim of promoting the mesenchymal cell activation, utilizing keyword combination.

CONCLUSIONS

Implant success beyond the human element of the practicioner and the protocol element of implant treatment, also relies on the application of the right type of implant, at the right implant site, in accordance with oral and individual health status of the patient. Implant success does not depend on type of "coating" material of the implants. Based at this physiological process, the success or implant failure is not a process depending on the type of selected implant, because types of synthetic or natural materials that promote osteointegration are relatively in large number.

Activation of dopamine receptor D1 promotes osteogenic differentiation and reduces glucocorticoid-induced bone loss by upregulating the ERK1/2 signaling pathway

Background

The inhibition of osteogenic differentiation is a major factor in glucocorticoid-induced bone loss, but there is currently no effective treatment. Dopamine, a major neurotransmitter, transmits signals via five different seven-transmembrane G protein-coupled receptors termed D1 to D5. Although the relevance of the neuroendocrine system in bone metabolism has emerged, the precise effects of dopamine receptor signaling on osteoblastogenesis remain unknown.

Methods

In vitro, western blotting and immunofluorescence staining were used to observe the expression of dopamine receptors in MC3T3-E1 and BMSCs cells treated with dexamethasone (Dex). In addition, Alizarin red S (ARS) and alkaline phosphatase (ALP) staining and western blotting were used to evaluate the effect of D1R activation on osteogenic differentiation in Dex-induced MC3T3-E1 cells via the ERK1/2 signaling pathway. In vivo, micro-CT and hematoxylin and eosin (H&E), toluidine blue and immunohistochemical staining were used to determine the effect of D1R activation on Dex-induced bone loss.

Results

We demonstrated that the trend in D1R but not D2-5R was consistent with that of osteogenic markers in the presence of Dex. We also demonstrated that the activation of D1R promoted Dex-induced osteogenic differentiation by activating the ERK1/2 pathway in vitro. We further demonstrated that a D1R agonist could reduce Dex-induced bone loss, while pretreatment with a D1R inhibitor blocked the effect of a D1R agonist in vivo.

Conclusions

Activation of D1R promotes osteogenic differentiation and reduces Dex-induced bone loss by activating the ERK1/2 pathway. Hence, D1R could serve as a potential therapeutic target for glucocorticoid-induced osteoporosis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s10020-022-00453-0.

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 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.

Bioactive coatings with anti-osteoclast therapeutic agents for bone implants: Enhanced compliance and prolonged implant life

The use of therapeutic agents that inhibit bone resorption is crucial to prolong implant life, delay revision surgery, and reduce the burden on the healthcare system. These therapeutic agents include bisphosphonates, various nucleic acids, statins, proteins, and protein complexes. Their use in systemic treatment has several drawbacks, such as side effects and insufficient efficacy in terms of concentration, which can be eliminated by local treatment. This review focuses on the incorporation of osteoclast inhibitors (antiresorptive agents) into bioactive coatings for bone implants. The ability of bioactive coatings as systems for local delivery of antiresorptive agents to achieve optimal loading of the bioactive coating and its release is described in detail. Various parameters such as the suitable concentrations, release times, and the effects of the antiresorptive agents on nearby cells or bone tissue are discussed. However, further research is needed to support the optimization of the implant, as this will enable subsequent personalized design of the coating in terms of the design and selection of the coating material, the choice of an antiresorptive agent and its amount in the coating. In addition, therapeutic agents that have not yet been incorporated into bioactive coatings but appear promising are also mentioned. From this work, it can be concluded that therapeutic agents contribute to the biocompatibility of the bioactive coating by enhancing its beneficial properties.

Melatonin pretreatment alleviates the long-term synaptic toxicity and dysmyelination induced by neonatal Sevoflurane exposure via MT1 receptor-mediated Wnt signaling modulation

Sevoflurane (Sev) is one of the most widely used pediatric anesthetics. The major concern of neonatal repeated application of Sev is its potential long-term impairment of cognition and learning/memory, for which there still lacks effective treatment. At the cellular level, Sev exerts toxic effects in multiple aspects, making it difficult for effective interference. Melatonin is a pineal hormone regulated by and feedbacks to biological rhythm at physiological condition. Recent studies have revealed significant neuroprotective effects of exogenous melatonin or its agonists under various pathological conditions. Whether melatonin could prevent the long-term toxicity of Sev remains elusive. Here, we report that neonatal repeated Sev exposure up-regulated MT1 receptor in hippocampal neurons and oligodendrocytes. Pretreatment with melatonin significantly alleviated Sev-induced synaptic deficiency, dysmyelination, and long-term learning impairment. Both MT1-shRNA and MT1 knockout effectively blocked the protective effects of melatonin on synaptic development, myelination, and behavior performance. Interestingly, long-lasting suppression of Wnt signaling, instead of cAMP/PKA signaling, was observed in hippocampal neurons and oligodendrocytes after neonatal Sev exposure. Pharmacologically activating Wnt signaling rescued both the long-term synaptic deficits and dysmyelination induced by Sev. Further analysis showed that MT1 receptor co-expressed well with β-catenin and Axin2 and bound to β-catenin by its C-terminal. Melatonin pretreatment effectively rescued Sev-induced Wnt suppression. Wnt signaling inhibitor XAV939 significantly compromised the protective effects of melatonin. Taken together, our data demonstrated a beneficial effect of melatonin pretreatment on the long-term synaptic impairment and dysmyelination induced by neonatal Sev exposure, and a novel MT1 receptor-mediated interaction between melatonin and canonical Wnt signaling, indicating that melatonin may be clinically applied for improving the safety of pediatric Sev anesthesia.

Therapeutic Effects of Melatonin on Ocular Diseases: Knowledge Map and Perspective

Melatonin plays a critical role in the pathophysiological process including circadian rhythm, apoptosis, and oxidative stress. It can be synthesized in ocular tissues, and its receptors are also found in the eye, triggering more investigations concentrated on the role of melatonin in the eye. In the past decades, the protective and therapeutic potentials of melatonin for ocular diseases have been widely revealed in animal models. Herein, we construct a knowledge map of melatonin in treating ocular diseases through bibliometric analysis and review its current understanding and clinical evidence. The overall field could be divided into twelve topics through keywords co-occurrence analysis, in which the glaucoma, myopia, and retinal diseases were of greatest research interests according to the keywords burst detection. The existing clinical trials of melatonin in ocular diseases mainly focused on the glaucoma, and more research should be promoted, especially for various diseases and drug administration. We also discuss its bioavailability and further research topics including developing melatonin sensors for personalized medication, acting as stem cell therapy assistant drug, and consuming food-derived melatonin for facilitating its clinical transformation.

Melatonin prevents peri‑implantitis via suppression of TLR4/NF-κB

Peri‑implantitis, which is characterized by peri‑implant mucositis and alveolar bone resorption, significantly shortens the service life of dental implants. Melatonin is well-known for its anti-inflammatory and osteoprotective activities. Nevertheless, the effects and mechanisms of melatonin to prevent peri‑implantitis remain unknown. In this study, the lipopolysaccharide-induced peri‑implantitis model was established after the titanium implants were osseointegrated, and the rats received daily administrations of melatonin. The gingival fibroblasts and osteoclasts/osteoblasts were also co-cultured to simulate the inflammatory environment in vitro. We found that prophylactic administration of melatonin decreased proinflammatory cytokine levels and osteoclast numbers, attenuated alveolar bone resorption, and reduced the incidence of peri‑implantitis in vivo. Furthermore, melatonin suppressed osteoclastic formation and function in the inflammatory co-culture environment, while melatonin promoted osteoblastic differentiation and function in the in vitro model. Mechanistically, melatonin reduced TLR4 protein levels, and inhibited activation of NF-κB to downregulate the levels of TNF, IL-1β, and IL-6. These data showed that melatonin was a potent agent to prevent peri‑implantitis through inhibiting TLR4/NF-κB signaling. Our findings provide a novel strategy to prevent peri‑implantitis, and expand the applications of melatonin. STATEMENT OF SIGNIFICANCE: Dental implants have become the first choice for restoring partial and full edentulism, but its service life is seriously affected by peri‑implantitis. Exploration of novel and effective approaches to prevent peri‑implantitis is an important and urgent need. In the present study, we have reported for the first time that prophylactic administration of melatonin delayed the occurrence and reduced the incidence of peri‑implantitis by decreasing proinflammatory cytokine levels, inhibiting osteoclastogenesis, and promoting osteogenesis. The study is expected to have an important significance on the prevention of peri‑implantitis.

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.

Effect of Oxidative Stress on Bone Remodeling in Periprosthetic Osteolysis

The success of implant performance and arthroplasty is based on several factors, including oxidative stress-induced osteolysis. Oxidative stress is a key factor of the inflammatory response. Implant biomaterials can release wear particles which may elicit adverse reactions in patients, such as local inflammatory response leading to tissue damage, which eventually results in loosening of the implant. Wear debris undergo phagocytosis by macrophages, inducing a low-grade chronic inflammation and reactive oxygen species (ROS) production. In addition, ROS can also be directly produced by prosthetic biomaterial oxidation. Overall, ROS amplify the inflammatory response and stimulate both RANKL-induced osteoclastogenesis and osteoblast apoptosis, resulting in bone resorption, leading to periprosthetic osteolysis. Therefore, a growing understanding of the mechanism of oxidative stress-induced periprosthetic osteolysis and anti-oxidant strategies of implant design as well as the addition of anti-oxidant agents will help to improve implants’ performances and therapeutic approaches.

The lncRNA H19/miR-541-3p/Wnt/β-catenin axis plays a vital role in melatonin-mediated osteogenic differentiation of bone marrow mesenchymal stem cells

Implant dentures become the first choice for denture restoration in patients with tooth loss. However, oral implants often fail in osteoporosis (OP) patients. Melatonin (MT) induces osteogenic differentiation of bone mesenchymal stem cells (BMSCs), suggesting its therapeutic potential in OP treatment. Long non-coding RNA H19 induces osteogenic differentiation of BMSCs, while its regulatory mechanism in MT-involved osteogenic and adipogenic differentiation of BMSCs remains elusive. Ovariectomized (OVX) rat was used to construct an OP model, and bone quality was assessed. Meanwhile, the expression of H19, miR-541-3p, MT and adiponectin (APN) was examined by quantitative reverse transcription-PCR (qRT-PCR) or ELISA. The adipogenic and osteogenic differentiation of BMSCs were determined by oil red O staining and alizarin red S staining, respectively. The targeting relationships between H19, miR-541-3p and APN mRNA were predicted by bioinformatics and confirmed by RNA immunoprecipitation and dual-luciferase reporter assay. The results showed that MT, H19 and APN were down-regulated, while miR-541-3p was up-regulated in the OVX rat model. At the cellular level, MT reduced adipogenic differentiation, heightened osteogenic differentiation of BMSCs, and activated Wnt/β-catenin pathway, which were reversed by the MT2 selective inhibitor 4-P-PDOT. Overexpressing H19 facilitated the osteogenic differentiation and inhibited the adipogenic differentiation of BMSCs mediated by MT, while H19 knockdown or overexpressing miR-541-3p had the opposite effect. Moreover, H19 functioned as a competitive endogenous RNA and sponged miR-541-3p, and miR-541-3p targeted APN. Overall, MT modulates the osteogenic and adipogenic differentiation of BMSCs by mediating H19/miR-541-3p/APN axis, providing a new reference for the targeted therapy of OP.

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.

Effects of the Local Bone Renin-Angiotensin System on Titanium-Particle-Induced Periprosthetic Osteolysis

Wear particles may induce osteoclast formation and osteoblast inhibition that lead to periprosthetic osteolysis (PPOL) and subsequent aseptic loosening, which is the primary reason for total joint arthroplasty failure. Local bone renin-angiotensin system (RAS) has been found to participate in the pathogenic process of various bone-related diseases via promoting bone resorption and inhibiting bone formation. However, it remains unclear whether and how local bone RAS participates in wear-particle-induced PPOL. In this study, we investigated the potential role of RAS in titanium (Ti) particle-induced osteolysis in vivo and osteoclast and osteoblast differentiation in vitro. We found that the expressions of AT1R, AT2R and ACE in the interface membrane from patients with PPOL and in calvarial tissues from a murine model of Ti-particle-induced osteolysis were up-regulated, but the increase of ACE in the calvarial tissues was abrogated by perindopril. Moreover, perindopril mitigated the Ti-particle-induced osteolysis in the murine model by suppressing bone resorption and increasing bone formation. We also observed in RAW264.7 macrophages that Ang II promoted but perindopril suppressed Ti-particle-induced osteoclastogenesis, osteoclast-mediated bone resorption and expression of osteoclast-related genes. Meanwhile, Ang II enhanced but perindopril repressed Ti-particle-induced suppression of osteogenic differentiation and expression of osteoblast-specific genes in mouse bone marrow mesenchymal stem cells (BMSCs). In addition, local bone RAS promoted Ti-particle-induced osteolysis by increasing bone resorption and decreasing bone formation through modulating the RANKL/RANK and Wnt/β-catenin pathways. Taken together, we suggest that inhibition of RAS may be a potential approach to the treatment of wear-particle-induced PPOL.

Melatonin alleviates titanium nanoparticles induced osteolysis via activation of butyrate/GPR109A signaling pathway

BACKGROUND

Inflammatory osteolysis after total joint replacement (TJR) may cause implant failure, periprosthetic fractures, and be a severe threat to global public health. Our previous studies demonstrated that melatonin had a therapeutic effect on wear-particles induced osteolysis. Gut microbiota is closely related to bone homeostasis, and has been proven to be affected by melatonin. However, whether melatonin could play its anti-osteolysis effects through reprogramming gut microbiota remains elusive.

RESULTS

Here, we demonstrated that melatonin could alleviate Ti-particles induced osteolysis, while this therapeutic effect was blocked by antibiotic cocktail treatment. Interestingly, transplantation of fecal microbiota from mice treated with melatonin reappeared the same beneficial effect. Analysis of the 16S rRNA revealed that melatonin could reverse dysbacteriosis triggered by osteolysis, and elevate the relative abundance of some short chain fatty acid (SCFA) producing bacteria. Moreover, butyrate was enriched by exogenous melatonin administration, while acetate and propionate did not show an evident difference. This was consistent with the results of the metagenomic approach (PICRUSt2) analysis, which revealed a general increase in the synthetic enzymes of butyrate. More importantly, direct supplementation of butyrate could also recapitulate the anti-osteolysis effect of melatonin. Further analysis identified that butyrate alleviated osteolysis via activating its receptor GPR109A, and thus to suppress the activation of NLRP3 inflammasome triggered by Ti-particles.

CONCLUSIONS

Taken together, our results suggested that the benefits of melatonin mainly depend on the ability of modulating gut microbiota and regulating butyrate production.

Carnosol suppresses RANKL-induced osteoclastogenesis and attenuates titanium particles-induced osteolysis

Osteolysis is a common medical condition characterized by excessive activity of osteoclasts and bone resorption, leading to severe poor quality of life. It is essential to identify the medications that can effectively suppress the excessive differentiation and function of osteoclasts to prevent and reduce the osteolytic conditions. It has been reported that Carnosol (Car), isolated from rosemary and salvia, has anti-inflammatory, antioxidative, and anticancer effects, but its activity on osteolysis has not been determined. In this study, we found that Car has a strong inhibitory effect on the receptor activator of nuclear factor-κB ligand (RANKL)-induced osteoclast differentiation dose-dependently without any observable cytotoxicity. Moreover, Car can inhibit the RANKL-induced osteoclastogenesis and resorptive function via suppressing NFATc1, which is a result of affecting MAPK, NF-κB and Ca2+ signaling pathways. Moreover, the particle-induced osteolysis mouse model confirmed that Car could be effective for the treatment of bone loss in vivo. Taken together, by suppressing the formation and function of RANKL-induced osteoclast, Car, may be a therapeutic supplementary in the prevention or the treatment of osteolysis.

Inhibitory effect of acetyl-11-keto-β-boswellic acid on titanium particle-induced bone loss by abrogating osteoclast formation and downregulating the ERK signaling pathway

Wear debris-induced osteoclast accumulation around implants plays a crucial role during the progression of periprosthetic osteolysis (PPO). We have confirmed that acetyl-11-keto-β-boswellic acid (AKBA) promotes bone formation and protects against particle-induced bone destruction in vivo. However, the effect of AKBA on titanium-induced bone resorption is unknown. In this study, we detected the inhibitory effect of AKBA on titanium-induced bone erosion in vivo and used RAW264.7 cells and bone marrow macrophages (BMMs) to investigate the effect and underlying mechanism of AKBA on the differentiation and resorptive function of osteoclasts. Our findings revealed that AKBA inhibited particle-induced bone loss and osteoclast formation in vivo. Furthermore, AKBA exerted inhibitory effects on RANKL-induced osteoclastogenesis, osteoclastic ring-dependent resorption and the expression of osteoclast marker genes via the ERK signaling pathway in vitro. Our data further established the protective effect of AKBA on titanium particle-induced bone erosion from a new perspective of bone erosion prevention, strongly confirming that AKBA is an appropriate agent for protection against PPO.

Local Cellular Responses to Metallic and Ceramic Nanoparticles from Orthopedic Joint Arthroplasty Implants

Over the last decades, joint arthroplasty has become a successful treatment for joint disease. Nowadays, with a growing demand and increasingly younger and active patients accepting these approaches, orthopedic surgeons are seeking implants with improved mechanical behavior and longer life span. However, aseptic loosening as a result of wear debris from implants is considered to be the main cause of long-term implant failure. Previous studies have neatly illustrated the role of micrometric wear particles in the pathological mechanisms underlying aseptic loosening. Recent osteoimmunologic insights into aseptic loosening highlight the important and heretofore underrepresented contribution of nanometric orthopedic wear particles. The present review updates the characteristics of metallic and ceramic nanoparticles generated after prosthesis implantation and summarizes the current understanding of their hazardous effects on peri-prosthetic cells.

5-Aza-2-deoxycytidine inhibits osteolysis induced by titanium particles by regulating RANKL/OPG ratio

Periprosthetic osteolysis (PIO) caused by wear particles is the main cause of implant failure, which is regulated by nuclear factor κ B receptor activator ligand (RANKL)/osteoprotegerin (OPG) system. At present, there is a lack of effective drugs to prevent or treat PIO. Previous studies have confirmed that DNA methylation is closely related to postmenopausal osteoporosis and can affect the expression of OPG and RANKL. However, the relationship between DNA methylation and PIO is not clear. In this study, we investigated the inhibitory effect of 5-Aza-2-deoxycytidine (AzadC) on osteolysis induced by titanium particles in a mouse model. This inhibition mechanism is achieved by changing the ratio of RANKL/OPG in the osteolysis model. In conclusion, there is a relationship between DNA methylation and PIO. AzadC has a certain inhibitory effect on osteolysis induced by titanium particles. Regulating DNA methylation may be a new way to treat PIO. Our findings lay a foundation for epigenetic understanding and intervention of osteolysis.

A possible use of melatonin in the dental field: Protein adsorption and in vitro cell response on coated titanium

Melatonin (MLT) is widely known for regulating the circadian cycles and has been studied for its role in bone regeneration and inflammation. Its application as a coating for dental implants can condition the local microenvironment, affecting protein deposition on its surface and the cellular and tissue response. Using sol-gel coatings as a release vehicle for MLT, the aim of this work was to assess the potential of this molecule in improving the osseointegration and inflammatory responses of a titanium substrate. The materials obtained were physicochemically characterized (scanning electron microscopy, contact angle, roughness, Fourier-transform infrared spectroscopy, nuclear magnetic resonance, Si release, MLT liberation, and degradation) and studied in vitro with MC3T3-E1 osteoblastic cells and RAW264.7 macrophage cells. Although MLT application led to an increased gene expression of RUNX2 and BMP2 in 10MTL, it did not improve ALP activity. On the other hand, MLT-enriched sol-gel materials presented potential effects in the adsorption of proteins related to inflammation, coagulation and angiogenesis pathways depending on the dosage used. Using LC-MS/MS, protein adsorption patterns were studied after incubation with human serum. Proteins related to the complement systems (CO7, IC1, CO5, CO8A, and CO9) were less adsorbed in materials with MLT; on the other hand, proteins with functions in the coagulation and angiogenesis pathways, such as A2GL and PLMN, showed a significant adsorption pattern.

The Effects of Biomaterial Implant Wear Debris on Osteoblasts

Aseptic loosening subsequent to periprosthetic osteolysis is the leading cause for the revision of arthroplasty failure. The biological response of macrophages to wear debris has been well established, however, the equilibrium of bone remodeling is not only dictated by osteoclastic bone resorption but also by osteoblast-mediated bone formation. Increasing evidence shows that wear debris significantly impair osteoblastic physiology and subsequent bone formation. In the present review, we update the current state of knowledge regarding the effect of biomaterial implant wear debris on osteoblasts. The interaction of osteoblasts with osteoclasts and macrophages under wear debris challenge, and potential treatment options targeting osteoblasts are also presented.

MiR-106b inhibition suppresses inflammatory bone destruction of wear debris-induced periprosthetic osteolysis in rats

Aseptic loosening caused by periprosthetic osteolysis (PPO) is the main reason for the primary artificial joint replacement. Inhibition of inflammatory osteolysis has become the main target of drug therapy for prosthesis loosening. MiR‐106b is a newly discovered miRNA that plays an important role in tumour biology, inflammation and the regulation of bone mass. In this study, we analysed the in vivo effect of miR‐106b on wear debris‐induced PPO. A rat implant loosening model was established. The rats were then administrated a lentivirus‐mediated miR‐106b inhibitor, miR‐106b mimics or an equivalent volume of PBS by tail vein injection. The expression levels of miR‐106b were analysed by real‐time PCR. Morphological changes in the distal femurs were assessed via micro‐CT and histopathological analysis, and cytokine expression levels were examined via immunohistochemical staining and ELISA. The results showed that treatment with the miR‐106b inhibitor markedly suppressed the expression of miR‐106b in distal femur and alleviated titanium particle‐induced osteolysis and bone loss. Moreover, the miR‐106b inhibitor decreased TRAP‐positive cell numbers and suppressed osteoclast formation, in addition to promoting the activity of osteoblasts and increasing bone formation. MiR‐106b inhibition also significantly regulated macrophage polarization and decreased the inflammatory response as compared to the control group. Furthermore, miR‐106b inhibition blocked the activation of the PTEN/PI3K/AKT and NF‐κB signalling pathways. Our findings indicated that miR‐106b inhibition suppresses wear particles‐induced osteolysis and bone destruction and thus may serve as a potential therapy for PPO and aseptic loosening.

Genetic and pharmacological activation of Hedgehog signaling inhibits osteoclastogenesis and attenuates titanium particle-induced osteolysis partly through suppressing the JNK/c-Fos-NFATc1 cascade

Rationale: Wear particle-induced periprosthetic osteolysis (PPO) is a common long-term complication of total joint arthroplasty, and represents the major cause of aseptic loosening and subsequent implant failure. Previous studies have identified the central role of osteoclast-mediated bone resorption in the pathogenesis of PPO. Thus, therapeutic approaches of inhibiting osteoclast formation and activity are considered to be of great potential to prevent and treat this osteolytic disease. Hedgehog (Hh) signaling has been shown to play an important role in promoting osteoblast differentiation and bone formation. While Hh signaling is also implicated in regulating osteoclastogenesis, whether it can directly inhibit osteoclast differentiation and bone resorption remains controversial. Moreover, its potential therapeutic effects on PPO have never been assessed. In this study, we explored the cell-autonomous role of Hh signaling in regulating osteoclastogenesis and its therapeutic potential in preventing wear particle-induced osteolysis. Methods: Hh signaling was activated in macrophages by genetically ablating Sufu in these cells using LysM-Cre or by treating them with purmorphamine (PM), a pharmacological activator of Smoothened (Smo). In vitro cell-autonomous effects of Hh pathway activation on RANKL-induced osteoclast differentiation and activity were evaluated by TRAP staining, phalloidin staining, qPCR analyses, and bone resorption assays. In vivo evaluation of its therapeutic efficacy against PPO was performed in a murine calvarial model of titanium particle-induced osteolysis by μCT and histological analyses. Mechanistic details were explored in RANKL-treated macrophages through Western blot analyses. Results: We found that Sufu deletion or PM treatment potently activated Hh signaling in macrophages, and strongly inhibited RANKL-induced TRAP+ osteoclast production, F-actin ring formation, osteoclast-specific gene expression, and osteoclast activity in vitro. Furthermore, we found that Sufu deletion or PM administration significantly attenuated titanium particle-induced osteoclast formation and bone loss in vivo. Our mechanistic study revealed that activation of Hh signaling suppressed RANKL-induced activation of JNK pathway and downregulated protein levels of two key osteoclastic transcriptional factors, c-Fos and its downstream target NFATc1. Conclusions: Both genetic and pharmacological activation of Hh signaling can cell-autonomously inhibit RANKL-induced osteoclast differentiation and activity in vitro and protect against titanium particle-induced osteolysis in vivo. Mechanistically, Hh signaling hinders osteoclastogenesis partly through suppressing the JNK/c-Fos-NFATc1 cascade. Thus, Hh signaling may serve as a promising therapeutic target for the prevention and treatment of PPO and other osteolytic diseases.

Autophagy negative-regulating Wnt signaling enhanced inflammatory osteoclastogenesis from Pre-OCs in vitro

Periodontitis thereby the alveolar bone loss induced by inflammation, is a wide-spread phenomenon around the world. It is an ongoing challenge faced by clinicians worldwide. This study aimed to identify the effects of lipopolysaccharide (LPS) on osteoclasts (OCs) differentiation in vitro and to investigate its molecular mechanism. For bone marrow derived macrophages (considered as Pro-OCs), LPS impaired their differentiation into OCs in a dose-dependent manner. In contrast, it promoted Pre-OCs (referred to receptor activator of nuclear factor-κB ligand (RANKL) pretreated Pro-OCs) and differentiated to OCs with increased maximum diameter, quantity, the covering area and the fusion index in vitro. It also facilitated OCs proliferation, bone resorption and OCs related genes expression. Furthermore, it was revealed that LPS enhanced OCs genesis from Pre-OCs via activating autophagy pathway consequently elevated the accumulation of TRAP, Cts K and NFATC1, specific genes of OCs. The members of Wnt signaling were expressed as at lower states during the LPS induced OCs formation, but they could be rescued in the presence of autophagy inhibitor. The most promising observation was the direct interaction of LC3B and Dvl2, indicating that the crosstalk between above pathways existed in OCs. Taken together, we consider that LPS activates autophagy which negatively regulates Wnt signaling via autophagic degradation of Dvl2 is significant for osteoclastogenesis from Pre-OCs in vitro. Our study sheds light on the fact that autophagy inhibitors will become a new, potentially applicable therapeutic option in the treatment of periodontal bone loss.

Structural characterization of melatonin as an inhibitor of the Wnt deacylase Notum

The hormone melatonin, secreted from the pineal gland, mediates multiple physiological effects including modulation of Wnt/β-catenin signalling. The Wnt palmitoleate lipid modification is essential for its signalling activity, while the carboxylesterase Notum can remove the lipid from Wnt and inactivate it. Notum enzyme inhibition can therefore upregulate Wnt signalling. While searching for Notum inhibitors by crystallographic fragment screening, a hit compound N-[2-(5-fluoro-1H-indol-3-yl)ethyl]acetamide that is structurally similar to melatonin came to our attention. We then soaked melatonin and its precursor N-acetylserotonin into Notum crystals and obtained high-resolution structures (≤1.5 Å) of their complexes. In each of the structures, two compound molecules bind with Notum: one at the enzyme's catalytic pocket, overlapping the space occupied by the acyl tail of the Wnt palmitoleate lipid, and the other at the edge of the pocket opposite the substrate entrance. Although the inhibitory activity of melatonin shown by in vitro enzyme assays is low (IC50 75 µmol/L), the structural information reported here provides a basis for the design of potent and brain accessible drugs for neurodegenerative diseases such as Alzheimer's disease, in which upregulation of Wnt signalling may be beneficial.

Melatonin up-regulates bone marrow mesenchymal stem cells osteogenic action but suppresses their mediated osteoclastogenesis via MT2 -inactivated NF-κB pathway

BACKGROUND AND PURPOSE

Melatonin is a neurohormone involved in bone homeostasis. Melatonin directs bone remodelling and the role of bone marrow mesenchymal stem cells (BMMSCs) in the regulating melatonin-mediated bone formation-resorption balance remains undefined.

EXPERIMENTAL APPROACH

Osteoporosis models were established and bone tissue and serum were collected to test the effects of melatonin on bone homeostasis. Melatonin receptors were knocked down, the NF-κB signalling pathway and receptor activator of NF-κB ligand (RANKL) expression were investigated. Communication between bone marrow mesenchymal stem cells and osteoclasts was detected with direct-contact or indirect-contact system.

KEY RESULTS

Bone loss and microstructure disorder in mice were reversed after melatonin treatment, as a result of anabolic and anti-resorptive effects. In vitro, a physiological (low) concentration of melatonin promoted the bone marrow mesenchymal stem cells, osteogenic lineage commitment and extracellular mineralization but had no impact on extracellular matrix synthesis. After MT knockdown, especially MT₂ , the positive effects of melatonin on osteogenesis were attenuated. The canonical NF-κB signalling pathway was the first discovered downstream signalling pathway after MT receptor activation and was found to be down-regulated by melatonin during osteogenesis. Melatonin suppressed BMMSC-mediated osteoclastogenesis by inhibiting RANKL production in BMMSCs and this effect only occurred when BMMSCs and osteoclast precursors were co-cultured in an indirect-contact manner.

CONCLUSION AND IMPLICATIONS

Our work suggests that melatonin plays a crucial role in bone balance, significantly accelerates the osteogenic differentiation of bone marrow mesenchymal stem cells by suppressing the MT₂ -dependent NF-κB signalling pathway, and down-regulates osteoclastogenesis via RANKL paracrine secretion.

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

Postmenopausal osteoporosis (OP) is one of the most common bone diseases that affects millions of aging women. Reduced osteogenesis and increased oxidative stress have been implicated in bone marrow mesenchymal stem cells (BMMSCs) derived from OP patients. Melatonin has shown positive effects on osteoblast differentiation and bone formation; however, it was unknown whether melatonin could restore OP-impaired osteogenic potential of BMMSCs and what the underlying mechanisms entailed. The objective of this study is to investigate (1) whether melatonin can restore the impaired osteogenic potential of OP BMMSCs by preserving their antioxidant functions, and if so, (2) whether intravenous administration of melatonin can prevent OP-induced bone loss in ovariectomized (OVX) rats. Ovariectomies were performed in female rats and BMMSCs were isolated from the osteoporotic rats 3 months later. In vitro treatment with melatonin successfully improved the osteogenic differentiation of OP BMMSCs, as evidenced by increased levels of matrix mineralization and osteoblast-specific genes. In melatonin-treated OP BMMSCs, intracellular oxidative stress was significantly attenuated, while levels of intracellular antioxidant enzymes were noticeably up-regulated - particularly superoxide dismutase 2 (SOD2) and glutathione peroxidase 1 (GPX1). Silent information regulator type 1 (SIRT1) was involved in the melatonin-mediated recovery of osteogenesis and antioxidant functions. Meanwhile, in vivo injections of melatonin via the tail vein successfully ameliorated the bone micro-architecture in ovariectomized rat femurs. Further experiments confirmed that BMMSCs derived from melatonin-treated OVX rats exerted well-preserved antioxidant properties and osteogenic potential. Our findings demonstrate that the administration of melatonin is a promising strategy for treating patients with postmenopausal OP by preserving the antioxidant properties and osteogenic potential of their BMMSCs.

Melatonin promotes the BMP9-induced osteogenic differentiation of mesenchymal stem cells by activating the AMPK/β-catenin signalling pathway

Background

Mesenchymal stem cells (MSCs) play a crucial role in maintaining the dynamic balance of bone metabolism. Melatonin may have a regulatory effect on bone metabolism by regulating the lineage commitment and differentiation signalling pathways of MSCs. Among the BMP families, the osteogenesis of BMP9 is considered to be one of the strongest in MSCs. Here, we explored whether melatonin and BMP9 act synergistically on MSC osteogenic differentiation.

Methods

The C3H10T1/2 osteogenic differentiation function induced by melatonin synergizes with BMP9, as detected by the expression of osteogenic markers at different periods. The result was further confirmed by foetal limb explant culture and in vivo stem cell implantation experiments. The effects of the AMPK/β-catenin pathway on the osteogenic differentiation of C3H10T1/2 cells were evaluated by Western blotting.

Results

Melatonin combined with BMP9 significantly enhanced the expression of osteogenic markers at different periods in C3H10T1/2 cells, effectively enhancing BMP9-induced bone formation in cultured foetal explants and ectopic bone formation in vivo in stem cell transplantation experiments. Melatonin increases the expression of BMP9 in C3H10T1/2 cells and induces Smad1/5/8 translocation from the cytoplasm to the nucleus. In addition, melatonin and BMP9 synergistically promote AMPK and β-catenin phosphorylation, which can be largely eliminated by AMPK siRNA pretreatment.

Conclusions

Melatonin and BMP9 in C3H10T1/2 cells synergistically promote osteogenic differentiation at least in part by activating the AMPK/β-catenin signalling pathway.

Melatonin Prevents Osteoarthritis-Induced Cartilage Degradation via Targeting MicroRNA-140

Osteoarthritis (OA) is characterized by the progressive destruction of articular cartilage, which is involved in the imbalance between extracellular matrix (ECM) synthesis and degradation. MicroRNA-140-5p (miR-140) is specifically expressed in cartilage and plays an important role in OA-induced matrix degradation. The aim of this study was to investigate (1) whether intra-articular injection of melatonin could ameliorate surgically induced OA in mice and (2) whether melatonin could regulate matrix-degrading enzymes at the posttranscriptional level by targeting miR-140. In an in vitro OA environment induced by interleukin-1 beta (IL-1β), melatonin treatment improved cell proliferation of human chondrocytes, promoted the expression of cartilage ECM proteins (e.g., type II collagen and aggrecan), and inhibited the levels of IL-1β-induced proteinases, such as matrix metalloproteinase 9 (MMP9), MMP13, ADAMTS4 (a disintegrin and metalloproteinase with thrombospondin motifs 4), and ADAMTS5. Both the microarray and polymerase chain reaction (PCR) experiments revealed that miR-140 was a melatonin-responsive microRNA and melatonin upregulated miR-140 expression, which was suppressed by IL-1β stimulation. In vivo experiments demonstrated that intra-articular injection of melatonin prevented disruptions of cartilage matrix homeostasis and successfully alleviated the progression of surgery-induced OA in mice. Transfection of miR-140 antagomir completely counteracted the antiarthritic effects of melatonin by promoting matrix destruction. Our findings demonstrate that melatonin protects the articular cartilage from OA-induced degradation by targeting miR-140, and intra-articular administration of melatonin may benefit patients suffering from OA.

Periprosthetic Osteolysis: Mechanisms, Prevention and Treatment

Clinical studies, as well as in vitro and in vivo experiments have demonstrated that byproducts from joint replacements induce an inflammatory reaction that can result in periprosthetic osteolysis (PPOL) and aseptic loosening (AL). Particle-stimulated macrophages and other cells release cytokines, chemokines, and other pro-inflammatory substances that perpetuate chronic inflammation, induce osteoclastic bone resorption and suppress bone formation. Differentiation, maturation, activation, and survival of osteoclasts at the bone-implant interface are under the control of the receptor activator of nuclear factor kappa-Β ligand (RANKL)-dependent pathways, and the transcription factors like nuclear factor κB (NF-κB) and activator protein-1 (AP-1). Mechanical factors such as prosthetic micromotion and oscillations in fluid pressures also contribute to PPOL. The treatment for progressive PPOL is only surgical. In order to mitigate ongoing loss of host bone, a number of non-operative approaches have been proposed. However, except for the use of bisphosphonates in selected cases, none are evidence based. To date, the most successful and effective approach to preventing PPOL is usage of wear-resistant bearing couples in combination with advanced implant designs, reducing the load of metallic and polymer particles. These innovations have significantly decreased the revision rate due to AL and PPOL in the last decade.

Puerarin Exerts Protective Effects on Wear Particle-Induced Inflammatory Osteolysis

Wear particle-stimulated inflammatory bone destruction and the consequent aseptic loosening remain major postoperative problems for artificial joints. Studies have indicated that puerarin promotes osteogenesis and alleviates lipopolysaccharide-induced osteoclastogenesis in vitro. However, the underlying molecular mechanism by which puerarin interacts with receptor activator of nuclear factor kappa-B ligand (RANKL)-mediated osteoclast formation in vitro and wear particle-stimulated osteolysis in vivo has not been reported. In this work, the protective effects exerted by puerarin on titanium particle-stimulated bone destruction in vivo and on RANKL-induced osteoclast activation in osteoclastic precursor cells in vitro were investigated. As expected, puerarin significantly inhibited wear particle-mediated bone resorption and proinflammatory cytokine productions in a calvarial resorption model. Additionally, puerarin inhibited RANKL-induced osteoclast activation, bone resorption ability, and F-actin ring formation in vitro as puerarin concentration increased. Furthermore, mechanistic investigation indicated that reduced RANKL-stimulated MEK/ERK/NFATc1 signaling cascades might regulate the protective effect of puerarin. Conclusively, these results indicate that puerarin, a type of polyphenol, might serve as a protective agent to prevent osteoclast-related osteolytic diseases.

Inhibition of protein phosphatase 2A attenuates titanium-particle induced suppression of bone formation

Peri-prosthetic osteolysis (PPO) often generates after total joint arthroplasty, which can bring implant failure and following revision surgery. Wear debris shed from prostheses strongly enhances bone resorption and attenuates bone formation in osteolytic process. We previously proved that suppression of protein phosphatase 2A (PP2A), a major serine-threonine phosphatase, inhibited wear-debris-induced osteoclastogenesis and alleviated local osteolysis. Whether PP2A inhibition facilitates osteoblastogenesis and bone formation in the osteolytic sites remains unclear. Here, we observed that PP2A inhibition with a selective inhibitor attenuated particle-induced bone destruction by accelerating osteoblast differentiation and promoting bone regeneration. Meanwhile, we proved inhibition of PP2A alleviated the inhibition of osteogenic differentiation by titanium particles in MC3T3-E1 cells. In addition, PP2A inhibition increased β-catenin expression and enhanced β-catenin nuclear translocation, compared with that in the vehicle group. ICG-001, a specific inhibitor of β-catenin, was further applied and was found to weaken the effect of PP2A inhibition on β-catenin expression and nuclear translocation. Therefore, we demonstrated PP2A inhibition exerts protective effects on osteogenic differentiation mainly by activating Wnt/β-catenin signaling pathway. Thus, all the results further revealed PP2A could be a promising target for treating PPO and other bone related diseases.

Aspirin inhibits osteoclast formation and wear-debris-induced bone destruction by suppressing mitogen-activated protein kinases

Excessive osteoclast recruitment and activation is the chief cause of periprosthetic osteolysis and subsequent aseptic loosening, so blocking osteolysis may be useful for protecting against osteoclastic bone resorption. We studied the effect of aspirin on titanium (Ti)-particle-induced osteolysis in vivo and in vitro using male C57BL/6J mice randomized to sham (sham surgery), Ti (Ti particles), low-dose aspirin (Ti/5 mg·kg^-1 ·d^-1 aspirin), and high-dose aspirin (Ti/30 mg·kg^-1 ·d^-1 aspirin). After 2 weeks, a three-dimensional reconstruction evaluation using micro-computed tomography and histomorphology assessment were performed on murine calvariae. Murine hematopoietic macrophages and RAW264.7 lineage cells were studied to investigate osteoclast formation and function. Aspirin attenuated Ti-particle-induced bone erosion and reduced osteoclasts. In vitro, aspirin suppressed osteoclast formation, osteoclastic-related gene expression, and osteoclastic bone erosion in a dose-dependent manner. Mechanically, aspirin reduced osteoclast formation by suppressing receptor activator of nuclear factor kappa-B ligand-induced activation of extracellular signal-related kinase, p-38 mitogen-activated protein kinase, and c-Jun N-terminal kinase. Thus, aspirin may be a promising option for preventing and curing osteoclastic bone destruction, including peri-implant osteolysis.

Elevated Systemic L-Kynurenine/L-Tryptophan Ratio and Increased IL-1 Beta and Chemokine (CX3CL1, MCP-1) Proinflammatory Mediators in Patients with Long-Term Titanium Dental Implants

Titanium is the mean biocompatible metal found in dental titanium alloys (Ti-6Al-4V). The safety of certain dental biomaterial amalgams has been questioned in patients. The levels of several systemic cytokines (interleukin (IL)-1 beta, IL-4: pg/mL) and chemokines (monocyte chemoattractant protein-1 (MCP-1), soluble fractalkine (CX3CL1: pg/mL) were determined using ELISA and compared between these study groups. The study included 30 controls without dental materials (cont), 57 patients with long-term titanium dental implants plus amalgams (A + I group) as well as 55 patients with long-term dental amalgam alone (A group). All patients (except controls) have had dental titanium implants (Ti-6Al-4V) and/or amalgams for at least 10 years (average: 15 years). We evaluated whether systemic levels of cytokines/chemokines, kyn/L-trp ratio and aromatic amino acid levels (HPLC: mM/L, Phe, L-Trp, His, Treo) could be altered in patients with long-term dental titanium and/or amalgams. These systemic markers were evaluated in 142 patients. The A + I group had higher L-Kynurenine/L-Tryptophan ratios than patients with long-term dental amalgam fillings alone (A). In addition, levels of IL-1 Beta cytokine, CX3CL1 and MCP-1 chemokines were higher in the A + I group than in the A group (A). The increased L-kyn/L-trp ratio and MCP-1 and fractalkine receptor (CX3CR1) elevations could suggest enhanced chemotactic responses by these chemokines in the A + I group.

Magnesium lithospermate B inhibits titanium particles-induced osteoclast formation by c-fos and inhibiting NFATc1 expression

Purpose: Titanium particle-induced osteolysis is one of the important causes of aseptic loosening of artificial joints. Previous studies have shown the potential of natural compounds in preventing Ti particle-induced bone resorption. In this study, we observed the effects of magnesium lithospermate B (MLB) on titanium particle-induced osteoclast activity in vitro. Materials and Methods: RAW264.7 cells were treated with titanium particles (0.1 mg/mL) in the presence or absence of MLB (200 nmol/L). We evaluated the osteoclast formation, bone pits formation and tartrate-resistant acid phosphatase 5b (Tracp5b) levels. Reverse transcription polymerase chain reaction (RT-PCR) and Western blot were used to evaluate osteoclast differentiation-related genes (TRAF6, NFATc1, and c-fos) and protein expression. Results: The number of osteoclasts, pit formation and Tracp5b levels were all the group treated with titanium particles compared to the control group (all p < 0.05). Titanium particles also promoted the expression of the TRAF6, NFATc1 and c-fos genes and protein expression. MLB significantly abolished the titanium particle-enhanced osteoclast and pits formation, and Traf6, NFATc1, and c-fos expression. Conclusions: Our data demonstrated that MLB can suppress titanium-induced osteoclast activity via inhibiting c-fos and NFATc1 expression.

Wnt4 signaling mediates protective effects of melatonin on new bone formation in an inflammatory environment

Growing evidence shows that the inhibitory effect of inflammatory cytokines on new bone formation by osteogenic precursor cells is a critical cause of net bone-density reduction. Melatonin has been proven to be a potential therapeutic candidate for osteoporosis. However, whether it is capable of antagonizing the suppressing effect of inflammatory cytokines on osteogenic precursor cells is so far elusive. In this study, using the cell culture system of human bone marrow stromal cells and MC3T3-E1 preosteoblasts, we recorded the following vital observations that provided insights of melatonin-induced bone formation: 1) melatonin induced bone formation in both normal and inflammatory conditions; 2) Wnt4 was essential for melatonin-induced bone formation in inflammatory stimulation; 3) melatonin- and Wnt4-induced bone formation occurred via activation of β-catenin and p38-JNK MAPK pathways by interaction with a distinct frizzled LDL receptor-related protein complex; 4) melatonin suppressed the inhibitory effect of NF-κB on osteogenesis in a Wnt4-dependent manner; and 5) melatonin induced Wnt4 expression through the ERK1/2-Pax2-Egr1 pathway. In summary, we showed a novel mechanism of melatonin-induced bone formation in an inflammatory environment. Melatonin-induced Wnt4 expression is essential for its osteoinductive effect and the inhibitory effect of NF-κB on bone formation. Our novel findings may provide useful information for its potential translational application.-Li, X., Li, Z., Wang, J., Li, Z., Cui, H., Dai, G., Chen, S., Zhang, M., Zheng, Z., Zhan, Z., Liu, H. Wnt4 signaling mediates protective effects of melatonin on new bone formation in an inflammatory environment.

Different effects of Wnt/β-catenin activation and parathyroid hormone on diaphyseal and metaphyseal in the early phase of femur bone healing of mice

Parathyroid hormone (PTH) and agents related to the manipulation of Wnt/β-catenin signalling are two promising anabolic anti-osteoporotic therapies that have been shown to promote the healing of bone fractures. Now, it is widely accepted that cortical bone and trabecular bone are two different compartments, and should be treated as separate compartments in pathological processes, such as fracture healing. It is currently unknown whether PTH and the activation of β-catenin signalling would demonstrate different effects on cortical bone and trabecular bone healing. In the current study, single 0.6-mm cortex holes were made in the femur metaphysis and diaphysis of mice, and then, PTH application and β-catenin activation were used to observe the promoting effect on bone healing. The effects of β-catenin and PTH signalling on fracture healing were observed by X-ray and CT at 3, 6, and 14 days after fracture, and the levels of β-catenin were detected by RT-PCR assay, and the number of specific antigen-positive cells of BRDU, OCN, RUNX2 was counted by immunohistochemical staining. While β-catenin activation and PTH were found to demonstrate similar effects on accelerating metaphyseal bone healing, activation of β-catenin showed a more striking effect than PTH on promoting diaphyseal bone healing. These findings might be helpful for selecting proper medication to accelerate fracture healing of different bone compartments.