Antioxidant defense and apoptotic effectors in ascorbic acid and β-glycerophosphate-induced osteoblastic differentiation

Leveraging selective knockdown of Sost gene by polyethyleneimine-siRNA-chitosan reduced gold nanoparticles to promote osteogenesis in MC3T3-E1 & MEF cells

Aim: Osteoporosis is a systemic skeletal disorder characterized by reduced osteoblast differentiation, predominantly by overexpression of the Sost gene. A layer-by-layer approach enabled encapsulation of Sost siRNA to enhance the short half-life and poor transfection capacity of siRNA. Materials & methods: Polyethyleneimine and siRNA on chitosan-coated gold nanoparticles (PEI/siRNA/Cs-AuNPs) were engineered using chitosan-reduced gold nanoparticles. They were characterized by dynamic light scattering, scanning electron microscopy, transmission electron microscopy, Fourier transform infrared and gel-mobility assays. Detailed in vitro experiments, gene silencing and western blots were performed. Results: A total of 80% knockdown of the target sclerostin protein was observed by PEI/siRNA/Cs-AuNPs, q-PCR showed threefold downregulation of the Sost gene. Osteogenic markers RunX2 and Alp were significantly upregulated. Conclusion: We report a safe, biocompatible nanotherapeutic strategy to enhance siRNA protection and subsequent silencing to augment bone formation.

Dose-response effect of Montelukast on post-extraction dental socket repair and skeletal phenotype of mice

Bone metabolism and repair are directly regulated by arachidonic acid metabolites. At present, we analyzed the dose-response effects of a selective cysteinyl leukotriene receptor type-1 antagonist during bone repair after tooth extraction and on non-injured skeleton. Sixty-three 129 Sv/Ev male mice composed the groups: C-Control (saline solution); MTK2-2 mg/Kg of Montelukast (MTK) and MTK4-4 mg/Kg of MTK, daily administered by mouth throughout all experimental periods set at 7, 14, and 21 days post-operative. Dental sockets were analyzed by computed microtomography (microCT), histopathology, and immunohistochemistry. Femurs, L5 vertebra and organs were also removed for observation. Blood was collected for plasma bone and liver markers. Histopathology and microCT analysis revealed early socket repair of MTK2 and MTK4 animals, with significant increased BV/TV at days 14 and 21 compared to C. Higher plasma calcium was detected at days 7 and 21 in MTK4 in comparison to C, while phosphate was significantly increased in MTK2 in the same periods in comparison to C and MTK4. No significant differences were found regarding plasma ALP and TRAP, neither for local TRAP and Runx2 immunolabeling at the healing sockets. Organs did not present histological abnormalities. Increased AST levels have been detected in distinct groups and periods. In general, femur phenotype was improved in MTK treated animals. Collectively, MTK promoted early bone formation after tooth extraction and increased bone quality of femurs and vertebra in a time-dose-dependent manner, and should be considered as an alternative therapy when improved post-extraction socket repair or skeleton preservation is required.

Isolation, Identification, and Characterization of Bioactive Peptides in Human Bone Cells from Tortoiseshell and Deer Antler Gelatin

Tortoiseshell and deer antler gelatin has been used to treat bone diseases in Chinese society. A pepsin-digested gelatin peptide with osteoblast-proliferation-stimulating properties was identified via LC-MS/MS. The resulting pentapeptide, TSKYR, was presumably subjected to further degradation into TSKY, TSK, and YR fragments in the small intestine. The above four peptides were chemically synthesized. Treatment of tripeptide TSK can lead to a significant 30- and 50-fold increase in the mineralized nodule area and density in osteoblast cells and a 47.5% increase in the number of chondrocyte cells. The calcium content in tortoiseshell was relatively higher than in human soft tissue. The synergistic effects of calcium ions and the peptides were observed for changes in osteoblast proliferation and differentiation. Moreover, these peptides can enhance the expression of RUNX2, OCN, FGFR2, and FRFR3 genes in osteoblasts, and aggrecan and collagen type II in chondrocyte (patent pending).

Bu-Gu-Sheng-Sui decoction promotes osteogenesis via activating the ERK/Smad signaling pathways

Osteoporosis is a systemic metabolic skeletal disease, which becomes a common public health problem that seriously endangers people’s health. Bu-Gu-Sheng-Sui decoction (BGSSD) is a safe and effective Chinese medicine formulation for the treatment of osteoporosis. Numerous studies have indicated that it played a significant role in bone anabolism. However, the underlying mechanism remains unclear. Herein, we selected senescence-accelerated mice prone 6 (SAMP6) and MC3T3-E1 cells to study the effects of BGSSD on osteogenesis and then investigated the potential mechanism of BGSSD. Our research found that BGSSD protected the bone mass in SAMP6, increased the expression of osteogenic specific factor Runx2, and improved bone trabecular structure. In vitro, BGSSD accelerated the proliferation and differentiation of MC3T3-E1 cells, which was characterized by stimulating the activity of Alkaline phosphatase (ALP) and raising the expression of Runx2. Moreover, BGSSD could effectively boost the expression levels of ERK and Smad in SAMP6 and MC3T3-E1. Therefore, we speculate that BGSSD may promote bone formation through ERK/Smad pathways. Collectively, our results highlight the importance of BGSSD as a compound in promoting osteogenic differentiation and osteogenesis, demonstrating that BGSSD may become a latent drug to prevent and treat osteoporosis.

Silent Mating Type Information Regulation 2 Homolog (SIRT1) Influences Osteogenic Proliferation and Differentiation of MC3T3-E1 Cells via Regulation of miR-132-3p

Background

The essence of osteoporosis is mainly the imbalance of bone formation and absorption. Previous studies indicated that SIRT1 is closely related to bone metabolism and bone mass as a regulator of bone mass. The literature reports that microRNAs are significant regulators of osteoblast proliferation and differentiation.

Material/Methods

In this study, SIRT1 protein and mRNA levels were examined by Western blot and RT-PCR. Osteogenic proliferation was examined by CCK8 assay and osteogenic markers, including ALP, OCN, and RUNX2, were examined by ELISA. The target of miR-132-3p was identified by luciferase reporter assay.

Results

LPS downregulated the SIRT1 protein level and β-glycerophosphate upregulated the SIRT1 protein level. The results demonstrated that SIRT1 overexpression promoted the proliferation and differentiation in MC3T3-E1 cells, and SIRT1 interference had the opposite effect. Luciferase reporter assay revealed that miR-132-3p inhibited the reporter gene activity of SIRT1. LPS upregulated the mRNA level of miR-132-3p, and β-glycerophosphate downregulated the mRNA level of miR-132-3p.

Conclusions

miR-132-3p is a pivotal regulator in osteogenic proliferation and differentiation by targeting SIRT1.

Effects of strength training and raloxifene on femoral neck metabolism and microarchitecture of aging female Wistar rats

The aim of this study was to prevent female osteoporosis using strength training (ST), raloxifene (Ral) or a combination of ST plus Ral during the natural female aging process, specifically in the periestropause period. For a total of 120 days, aging female Wistar rats at 18-21 months of age performed ST on a ladder three times per week, and Ral was administered daily by gavage (1 mg/kg/day). Bone microarchitecture, areal bone mineral density, bone strength of the femoral neck, immunohistochemistry, osteoclast and osteoblast surface were assessed. We found that the treatments modulate the bone remodeling cycle in different ways. Both ST and Ral treatment resulted in improved bone microarchitecture in the femoral neck of rats in late periestropause. However, only ST improved cortical microarchitecture and bone strength in the femoral neck. Thus, we suggest that performing ST during the late period of periestropause is a valid intervention to prevent age-associated osteoporosis in females.

Smad4 controls bone homeostasis through regulation of osteoblast/osteocyte viability

Regulation of osteoblast and osteocyte viability is essential for bone homeostasis. Smad4, a major transducer of bone morphogenetic protein and transforming growth factor-β signaling pathways, regulates apoptosis in various cell types through a mitochondrial pathway. However, it remains poorly understood whether Smad4 is necessary for the regulation of osteoblast and osteocyte viability. In this study, we analyzed Smad4Δ(Os) mice, in which Smad4 was subjected to tissue-specific disruption under the control of the 2.3-kb Col1a1 promoter, to understand the functional significance of Smad4 in regulating osteoblast/osteocyte viability during bone formation and remodeling. Smad4Δ(Os) mice showed a significant increase in osteoblast number and osteocyte density in the trabecular and cortical regions of the femur, whereas osteoclast activity was significantly decreased. The proliferation of osteoblasts/osteocytes did not alter, as shown by measuring 5'-bromo-2'deoxyuridine incorporation. By contrast, the percentage of TUNEL-positive cells decreased, together with a decrease in the Bax/Bcl-2 ratio and in the proteolytic cleavage of caspase 3, in Smad4Δ(Os) mice. Apoptosis in isolated calvaria cells from Smad4Δ(Os) mice decreased after differentiation, which was consistent with the results of the TUNEL assay and western blotting in Smad4Δ(Os) mice. Conversely, osteoblast cells overexpressing Smad4 showed increased apoptosis. In an apoptosis induction model of Smad4Δ(Os) mice, osteoblasts/osteocytes were more resistant to apoptosis than were control cells, and, consequently, bone remodeling was attenuated. These findings indicate that Smad4 has a significant role in regulating osteoblast/osteocyte viability and therefore controls bone homeostasis.

Activation of canonical Wnt/β-catenin signaling inhibits H2O2-induced decreases in proliferation and differentiation of human periodontal ligament fibroblasts

Human periodontal ligament fibroblasts (hPLFs) are exposed to oxidative stress during periodontal inflammation and dental treatments. It is hypothesized that hydrogen peroxide (H2O2)-mediated oxidative stress decreases survival and osteogenic differentiation of hPLFs, whereas these decreases are prevented by activation of the Wnt pathway. However, there has been a lack of reports that define the exact roles of canonical Wnt/β-catenin signaling in H2O2-exposed hPLFs. Treatment with H2O2 reduced viability and proliferation in hPLFs in a dose- and time-dependent manner and led to mitochondria-mediated apoptosis. Pretreatment with lithium chloride (LiCl) or Wnt1 inhibited the oxidative damage that occurred in H2O2-exposed hPLFs. However, knockout of β-catenin or treatment with DKK1 facilitated the H2O2-induced decreases in viability, mitochondrial membrane potential, and Bcl-2 induction. Osteoblastic differentiation of hPLFs was also inhibited by combined treatment with 100 μM H2O2, as evidenced by the decreases in alkaline phosphatase (ALP) activity and mineralization. H2O2-mediated inhibition of osteoblast differentiation in hPLFs was significantly attenuated in the presence of 500 ng/ml Wnt1 or 20 mM LiCl. In particular, H2O2 stimulated the expression of nuclear factor (erythroid-derived 2)-like 2 (Nrf2) at protein and mRNA levels in hPLFs, whereas the induction was almost completely suppressed in the presence of Wnt1 or LiCl. Furthermore, siRNA-mediated silencing of Nrf2 blocked H2O2-induced decreases in ALP activity and mineralization of hPLFs with the concomitant restoration of runt-related transcription factor 2 and osteocalcin mRNA expression and ALP activity. Collectively, these results suggest that activation of the Wnt/β-catenin pathway improves proliferation and mineralization in H2O2-exposed hPLFs by downregulating Nrf2.

Stimulators of mineralization limit the invasive phenotype of human osteosarcoma cells by a mechanism involving impaired invadopodia formation

BACKGROUND

Osteosarcoma (OS) is a highly aggressive bone cancer affecting children and young adults. Growing evidence connects the invasive potential of OS cells with their ability to form invadopodia (structures specialized in extracellular matrix proteolysis).

RESULTS

In this study, we tested the hypothesis that commonly used in vitro stimulators of mineralization limit the invadopodia formation in OS cells. Here we examined the invasive potential of human osteoblast-like cells (Saos-2) and osteolytic-like (143B) OS cells treated with the stimulators of mineralization (ascorbic acid and B-glycerophosphate) and observed a significant difference in response of the tested cells to the treatment. In contrast to 143B cells, osteoblast-like cells developed a mineralization phenotype that was accompanied by a decreased proliferation rate, prolongation of the cell cycle progression and apoptosis. On the other hand, stimulators of mineralization limited osteolytic-like OS cell invasiveness into collagen matrix. We are the first to evidence the ability of 143B cells to degrade extracellular matrix to be driven by invadopodia. Herein, we show that this ability of osteolytic-like cells in vitro is limited by stimulators of mineralization.

CONCLUSIONS

Our study demonstrates that mineralization competency determines the invasive potential of cancer cells. A better understanding of the molecular mechanisms by which stimulators of mineralization regulate and execute invadopodia formation would reveal novel clinical targets for treating osteosarcoma.

Oxidative actions of hydrogen peroxide in human gingival and oral periosteal fibroblasts: responses to glutathione and nicotine, relevant to healing in a redox environment

Background

This study aims to validate pro-oxidant actions of nicotine (N), using hydrogen peroxide (H₂O₂) and the antioxidant glutathione (G) in an in vitro model of human gingival fibroblasts (HGF) and human oral periosteal fibroblasts (HPF); radiolabelled androgens are used as biomarkers of redox status. Oxidative stress is an important mediator of inflammatory repair. The androgen metabolite 5α-dihydrotestosterone (DHT) is an effective biomarker of oxidative stress and healing.

Methods

6 Cell-lines of HGF and HPF established in confluent monolayer culture were incubated in Eagle's MEM using 14C-testosterone and 14C-4-androstendione as substrate; in conjunction with effective concentrations of N, G and H₂O₂ established at N250, G3 μg/ml and 3%H₂O₂ w/w, 0.5 μl/ml. Combinations of H₂O₂G and H₂O₂GN were used in order to compare the oxidative effects of N/H₂O₂ and their responses to glutathione. At 24 h, the medium was solvent extracted, evaporated to dryness and subjected to TLC in a benzene/acetone solvent system 4:1 v/v for the separation of metabolites. The separated metabolites were quantified using a radioisotope scanner.

Results

The mean trends of 6 cell-lines for both substrates and each cell type demonstrated that the yield of the main metabolite DHT was significantly reduced by N and H₂O₂ alone (2-fold, n=6; p<0.01). The inhibition caused by H₂O₂ was overcome by the antioxidant glutathione in the combination H₂O₂G, to values similar to those of controls (n=6; p<0.01). It is relevant that when N was added to this neutralized combination, the decrease in yields of DHT triggered by N were comparable to those induced by H₂O₂; and retaining the positive effect of G.

Conclusion

Oxidative stress mediated by H₂O₂ was overcome by glutathione and recurred when nicotine was added, suggestive of a pro- oxidant role for nicotine. Androgen biomarkers are a sensitive index of oxidative stress which affects wound healing.

•

DHT is an effective redox marker in HGF and oral periosteal fibroblasts in vitro.

•

Both nicotine and H₂O₂ reduced yields of DHT, indicative of induced oxidative stress.

•

Nicotine has oxidative effects that are comparable to those of H₂O₂ mediated by AR.

•

Effects of nicotine and H₂O₂ were reduced by glutathione in HGF and HPF cultures.

•

Redox status is relevant to androgen receptor-mediated inflammatory wound healing.

Phase composition control of calcium phosphate nanoparticles for tunable drug delivery kinetics and treatment of osteomyelitis. II. Antibacterial and osteoblastic response

Osteomyelitis has been traditionally treated by the combination of long-term antibiotic therapies and surgical removal of diseased tissue. The multifunctional material was developed in this study with the aim to improve this therapeutic approach by: (a) enabling locally delivered and sustained release of antibiotics at a tunable rate, so as to eliminate the need for repetitive administration of systemically distributed antibiotics; and (b) controllably dissolving itself, so as to promote natural remineralization of the portion of bone lost to disease. We report hereby on the effect of previously synthesized calcium phosphates (CAPs) with tunable solubilities and drug release timescales on bacterial and osteoblastic cell cultures. All CAP powders exhibited satisfying antibacterial performance against Staphylococcus aureus, the main causative agent of osteomyelitis. Still, owing to its highest drug adsorption efficiency, the most bacteriostatically effective phase was amorphous CAP with the minimal inhibitory concentration of less than 1 mg/mL. At the same time, the positive cell response and osteogenic effect of the antibiotic-loaded CAP particles was confirmed in vitro for all the sparsely soluble CAP phases. Adsorption of the antibiotic onto CAP particles reversed the deleterious effect that the pure antibiotic exerted on the osteogenic activity of the osteoblastic cells. The simultaneous osteogenic and antimicrobial performance of the material developed in this study, altogether with its ability to exhibit sustained drug release, may favor its consideration as a material base for alternative therapeutic approaches to prolonged antibiotic administration and surgical debridement typically prescribed in the treatment of osteomyelitis.

Continuously generated H2O2 stimulates the proliferation and osteoblastic differentiation of human periodontal ligament fibroblasts

Numerous studies have shown that hydrogen peroxide (H(2)O(2)) inhibits proliferation and osteoblastic differentiation in bone-like cells. Human periodontal ligament fibroblasts (PLF) are capable of differentiating into osteoblasts and are exposed to oxidative stress during periodontal inflammation. However, the cellular responses of PLF to H(2)O(2) have not been identified. In this study, we examined how H(2)O(2) affects the viability and proliferation of PLF by exposing the cells to glucose oxidase (GO) or direct addition of H(2)O(2). We also explored the effects of GO on the osteoblastic differentiation of PLF and the mechanisms involved. The viability and proliferation in PLF were increased with the addition of 10 mU/ml GO but not by volumes greater than 15 mU/ml or by H(2)O(2) itself. GO-stimulated DNA synthesis was correlated with the increase in cyclin E protein levels in the cells. Osteoblastic differentiation of PLF was also augmented by combined treatment with GO, as evidenced by the increases in alkaline phosphatase activity, mineralization, collagen synthesis, and osteocalcin content in the cells. The inductions of runt-related transcription factor 2 and osterix mRNA and proteins were further increased in PLF incubated in combination with GO compared to those in untreated cells. These results demonstrate that the continuous presence of H(2)O(2) stimulates the proliferation of PLF and augments their potential to differentiate into osteoblasts through the up-regulation of bone-specific transcription factors. Collectively, we suggest that H(2)O(2) may elicit the functions of PLF in maintaining the dimensions of the periodontal ligament and in mediating a balanced metabolism in alveolar bone.