α-Tocopheryl Succinate Inhibits Osteoclast Formation by Suppressing Receptor Activator of Nuclear Factor-kappaB Ligand (RANKL) Expression and Bone Resorption

Role of vitamins beyond vitamin D3 in bone health and osteoporosis (Review)

The objective of the present review was to summarize the molecular mechanisms associated with the effects of the vitamins A, C, E and K, and group B vitamins on bone and their potential roles in the development of osteoporosis. Epidemiological findings have demonstrated an association between vitamin deficiency and a higher risk of developing osteoporosis; vitamins are positively related to bone health upon their intake at the physiological range. Excessive vitamin intake can also adversely affect bone formation, as clearly demonstrated for vitamin A. Vitamins E (tocopherols and tocotrienols), K2 (menaquinones 4 and 7) and C have also been shown to promote osteoblast development through bone morphogenetic protein (BMP)/Smad and Wnt/β‑catenin signaling, as well as the TGFβ/Smad pathway (α‑tocopherol). Vitamin A metabolite (all‑trans retinoic acid) exerts both inhibitory and stimulatory effects on BMP‑ and Wnt/β‑catenin‑mediated osteogenesis at the nanomolar and micromolar range, respectively. Certain vitamins significantly reduce receptor activator of nuclear factor kappa‑B ligand (RANKL) production and RANKL/RANK signaling, while increasing the level of osteoprotegerin (OPG), thus reducing the RANKL/OPG ratio and exerting anti‑osteoclastogenic effects. Ascorbic acid can both promote and inhibit RANKL signaling, being essential for osteoclastogenesis. Vitamin K2 has also been shown to prevent vascular calcification by activating matrix Gla protein through its carboxylation. Therefore, the maintenance of a physiological intake of vitamins should be considered as a nutritional strategy for the prevention of osteoporosis.

Multifunctional periodontal membrane for treatment and regeneration purposes

Periodontitis is a chronic inflammatory disease that causes gum tissue degeneration and alveolar bone and tooth loss. The aim of this study is to develop a multifunctional matrix for the treatment of periodontitis and enhancement of regeneration of the periodontal tissue. The matrix was prepared from vitamin E containing hydrogel made of alginate and gelatin, and doxycycline HCl containing methoxy poly(ethylene glycol)-block-polycaprolactone micelles. Methoxy poly(ethylene glycol)-block-polycaprolactone was synthesized with ring-opening polymerization technique and characterized by proton nuclear magnetic resonance (1H NMR), Fourier-transform infrared spectroscopy, differential scanning calorimetry, and gel permeation chromatography. Micelles were characterized by measuring zeta potential, hydrodynamic diameter, drug encapsulation efficiency, drug loading capacity, and in vitro drug-release kinetics. Micelles were obtained with an average size of 164 nm and drug loading amount of 5.8%. The activity of doxycycline HCl–loaded micelles and vitamin E containing hydrogels was determined against Escherichia coli ( E. coli) and Staphylococcus aureus ( S. aureus) with disk diffusion method. Bio-efficacy of micelle-loaded alginate–gelatin hydrogels were tested in vitro using L929 fibroblasts and dental pulp stem cells. Doxycycline HCl–loaded micelles and vitamin E containing hydrogels showed a sustained release and exhibited inhibition zone against E. coli and S. aureus. Hydrogels with vitamin E and doxycycline HCl–loaded micelles promoted osteogenic differentiation of dental pulp stem cells. Results suggest that alginate–gelatin hydrogels containing doxycycline HCl–loaded micelles and vitamin E can be good candidates for the treatment of periodontitis and tissue regeneration.

Do Dietary Supplements and Nutraceuticals Have Effects on Dental Implant Osseointegration? A Scoping Review

Several factors affect dental implant osseointegration, including surgical issues, bone quality and quantity, and host-related factors, such as patients' nutritional status. Many micronutrients might play a key role in dental implant osseointegration by influencing some alveolar bone parameters, such as healing of the alveolus after tooth extraction. This scoping review aims to summarize the role of dietary supplements in optimizing osseointegration after implant insertion surgery. A technical expert panel (TEP) of 11 medical specialists with expertise in oral surgery, bone metabolism, nutrition, and orthopedic surgery performed the review following the PRISMA-ScR (Preferred Reporting Items for Systematic Reviews and Meta-Analyses Extension for Scoping Reviews) model. The TEP identified micronutrients from the "European Union (EU) Register of nutrition and health claims made on foods" that have a relationship with bone and tooth health, and planned a PubMed search, selecting micronutrients previously identified as MeSH (Medical Subject Headings) terms and adding to each of them the words "dental implants" and "osseointegration". The TEP identified 19 studies concerning vitamin D, magnesium, resveratrol, vitamin C, a mixture of calcium, magnesium, zinc, and vitamin D, and synthetic bone mineral. However, several micronutrients are non-authorized by the "EU Register on nutrition and health claims" for improving bone and/or tooth health. Our scoping review suggests a limited role of nutraceuticals in promoting osseointegration of dental implants, although, in some cases, such as for vitamin D deficiency, there is a clear link among their deficit, reduced osseointegration, and early implant failure, thus requiring an adequate supplementation.

The Molecular Mechanism of Vitamin E as a Bone-Protecting Agent: A Review on Current Evidence

Bone remodelling is a tightly-coordinated and lifelong process of replacing old damaged bone with newly-synthesized healthy bone. In the bone remodelling cycle, bone resorption is coupled with bone formation to maintain the bone volume and microarchitecture. This process is a result of communication between bone cells (osteoclasts, osteoblasts, and osteocytes) with paracrine and endocrine regulators, such as cytokines, reactive oxygen species, growth factors, and hormones. The essential signalling pathways responsible for osteoclastic bone resorption and osteoblastic bone formation include the receptor activator of nuclear factor kappa-B (RANK)/receptor activator of nuclear factor kappa-B ligand (RANKL)/osteoprotegerin (OPG), Wnt/β-catenin, and oxidative stress signalling. The imbalance between bone formation and degradation, in favour of resorption, leads to the occurrence of osteoporosis. Intriguingly, vitamin E has been extensively reported for its anti-osteoporotic properties using various male and female animal models. Thus, understanding the underlying cellular and molecular mechanisms contributing to the skeletal action of vitamin E is vital to promote its use as a potential bone-protecting agent. This review aims to summarize the current evidence elucidating the molecular actions of vitamin E in regulating the bone remodelling cycle.

Effect of Runx2 silencing on autophagy and RANKL expression in osteoblasts

OBJECTIVE

This study aimed to investigate the effect of Runx2 silencing on autophagy and RANKL expression in mouse osteoblasts, and provide an experimental basis to assess obstacles in dental eruption.

METHODS

In accordance with previously reported methods, LVpFU-GW-016PSC60109-1 virus was used to transfect mouse osteoblasts (MOI = 40). Target gene expression was assessed via cytometer, and the effect of silencing Runx2 was assessed via a two-step quantitative real-time polymerase chain reaction (qRT-PCR)-based method. Western blotting was performed to assess LC3, Beclin-1 and RANKL expression.

RESULTS

As confirmed via qRT-PCR analysis, Runx2 was efficiently silenced in the experimental group (>90% efficiency). Western blotting revealed that LC3 and RANKL proteins were significantly down -regulated in the experimental group (group KD), their expression levels being particularly lower than those in the control group (group NC). However, Beclin-1 protein expression was not significantly different from that of the control.

CONCLUSION

Upon Runx2 silencing, autophagy-related proteins and RANKL were repressed in osteoblasts, thereby potentially causing the tooth eruption disorder.

α-Tocopheryl Succinate Inhibits Osteolytic Bone Metastasis of Breast Cancer by Suppressing Migration of Cancer Cells and Receptor Activator of Nuclear Factor-κB Ligand Expression of Osteoblasts

Background

Breast cancer is one of the most common cancers affecting women and has a high incidence of bone metastasis, causing osteolytic lesions. The elevated expression of receptor activator of nuclear factor-κB ligand (RANKL) in cancer activates osteoclasts, leading to bone destruction. We previously reported that α-tocopheryl succinate (αTP-suc) inhibited interleukin-1-induced RANKL expression in osteoblasts. Here, we examined the effect of αTP-suc on osteolytic bone metastasis in breast cancer.

Methods

To examine the effect of αTP-suc on the metastatic capacity of breast cancer, MDA-MB-231-FL cells were injected into the left cardiac ventricle of BALB/c nude mice along with intraperitoneal injection of αTP-suc. The mice were then analyzed by bioluminescence imaging. To investigate the effect of αTP-suc on osteolysis, 4T1 cells were directly injected into the femur of BALB/c mice along with intraperitoneal injection of αTP-suc. Microcomputed tomography analysis and histomorphometric analysis of the femora were performed.

Results

αTP-suc inhibited cell migration and cell growth of 4T1 cells. In line with these results, bone metastasis of MDA-MB-231-FL cells was reduced in mice injected with αTP-suc. In addition, αTP-suc decreased osteoclastogenesis by inhibiting 4T1-induced RANKL expression in osteoblasts. Consistent with these results, 4T1-induced bone destruction was ameliorated by αTP-suc, with in vivo analysis showing reduced tumor burden and osteoclast numbers.

Conclusions

Our findings suggest that αTP-suc may be efficiently utilized to prevent and treat osteolytic bone metastasis of breast cancer with dual effects.

Mechanism of NF-κB signaling pathway and autophagy in the regulation of osteoblast differentiation

OBJECTIVE

The objective of the present work was to investigate a possible mechanism of NF-κB signaling pathway and autophagy in the regulation of osteoblast differentiation, and provide experimental basis for the study of tooth eruption disorder.

METHODS

Mouse osteoblast-like (MC3T3-E1) cells were inoculated with a cell density of 70%. According to the grouping experimental design, Western blot and monodansylcadaverine (MDC) detection were conducted after dosing for 24 h. The cells were divided into the following five groups: blank control group; 6.25 µg/mL SN50 group; 12.5 µg/mL SN50 group; 25 µg/mL SN50 group and 50 µg/mL SN50 group.

RESULTS

Western blot analysis revealed that the expression of LC3 protein was present in the blank control group; 6.25 µg/mL SN50 group; 12.5 µg/mL SN50 group and 50 µg/mL SN50 group, with no significant differences among these groups. However, the expression of LC3 protein was significantly lower in the 25 µg/mL SN50 group. MDC detection showed that, in the blank control group; 6.25 µg/mL SN50 group; 12.5 µg/mL SN50 group and 50 µg/mL SN50 group, there was obvious green fluorescence in the cytoplasm of the osteoblasts. However, in the 25 µg/mL SN50 group, it was found that there were significantly fewer green fluorescent particles.

CONCLUSION

The osteoblast itself had a strong function of autophagy. The appropriate concentration of SN50 in blocking the NF-κB pathway of the osteoblast was associated with the obvious inhibition of autophagy. However, the relationship between NF-κB signaling pathway and autophagy in the process of tooth eruption requires further study.

Succinate and its G-protein-coupled receptor stimulates osteoclastogenesis

The mechanism underlying bone impairment in patients with diabetes mellitus, a metabolic disorder characterized by chronic hyperglycaemia and dysregulation in metabolism, is unclear. Here we show the difference in the metabolomics of bone marrow stromal cells (BMSCs) derived from hyperglycaemic (type 2 diabetes mellitus, T2D) and normoglycaemic mice. One hundred and forty-two metabolites are substantially regulated in BMSCs from T2D mice, with the tricarboxylic acid (TCA) cycle being one of the primary metabolic pathways impaired by hyperglycaemia. Importantly, succinate, an intermediate metabolite in the TCA cycle, is increased by 24-fold in BMSCs from T2D mice. Succinate functions as an extracellular ligand through binding to its specific receptor on osteoclastic lineage cells and stimulates osteoclastogenesis in vitro and in vivo. Strategies targeting the receptor activation inhibit osteoclastogenesis. This study reveals a metabolite-mediated mechanism of osteoclastogenesis modulation that contributes to bone dysregulation in metabolic disorders.

Bone loss is common in patients with diabetes, but the underlying molecular and cellular mechanisms are unclear. Here the authors show high succinate levels in mice with type 2 diabetes and that succinate can signal through succinate receptor 1 on osteoclasts to induce bone resorption.

Osteoactivin inhibition of osteoclastogenesis is mediated through CD44-ERK signaling

Osteoactivin is a heavily glycosylated protein shown to have a role in bone remodeling. Previous studies from our lab have shown that mutation in Osteoactivin enhances osteoclast differentiation but inhibits their function. To date, a classical receptor and a signaling pathway for Osteoactivin-mediated osteoclast inhibition has not yet been characterized. In this study, we examined the role of Osteoactivin treatment on osteoclastogenesis using bone marrow-derived osteoclast progenitor cells and identify a signaling pathway relating to Osteoactivin function. We reveal that recombinant Osteoactivin treatment inhibited osteoclast differentiation in a dose-dependent manner shown by qPCR, TRAP staining, activity and count. Using several approaches, we show that Osteoactivin binds CD44 in osteoclasts. Furthermore, recombinant Osteoactivin treatment inhibited ERK phosphorylation in a CD44-dependent manner. Finally, we examined the role of Osteoactivin on receptor activator of nuclear factor-κ B ligand (RANKL)-induced osteolysis in vivo. Our data indicate that recombinant Osteoactivin inhibits RANKL-induced osteolysis in vivo and this effect is CD44-dependent. Overall, our data indicate that Osteoactivin is a negative regulator of osteoclastogenesis in vitro and in vivo and that this process is regulated through CD44 and ERK activation.