Nitric oxide-mediated cytotoxic effect induced by zoledronic acid treatment on human gingival fibroblasts

H2O2 gel bleaching induces cytotoxicity and pain conduction in dental pulp stem cells via intracellular reactive oxygen species on enamel/dentin disc

Background

Bleaching is widely accepted for improving the appearance of discolored teeth; however, patient compliance is affected by bleaching-related complications, especially bleaching sensitivity. This study aimed to investigate the role of reactive oxygen species (ROS) in cytotoxicity and pain conduction activated by experimental tooth bleaching.

Methods

Dental pulp stem cells with or without N-acetyl-L-cysteine (NAC), an ROS scavenger, were cultured on the dentin side of the enamel/dentin disc. Subsequently, 15% (90 min) and 40% (30 min) bleaching gels were painted on the enamel surface. Cell viability, intracellular ROS, Ca²⁺, adenosine triphosphate (ATP), and extracellular ATP levels were evaluated using the Cell Counting Kit-8 assay, 2’,7’-dichlorodihydrofluorescein diacetate, CellROX, fura-3AM fluorescence assay, and ATP measurement kit. The rat incisor model was used to evaluate in vivo effects after 0, 1, 3, 7, and 30 days of bleaching. Changes in gene and protein expression of interleukin 6 (IL-6), tumor necrosis factor-alpha (TNFα), transient receptor potential ankyrin 1 (TRPA1), and Pannexin1 (PANX1) in dental pulp stem cells and pulp tissue were detected through RT-PCR, western blotting, and immunofluorescence.

Results

The bleaching gel suppressed dental pulp stem cell viability and extracellular ATP levels and increased intracellular ROS, Ca²⁺, and intracellular ATP levels. The mRNA and protein expression of IL-6, TNFα, TRPA1, and PANX1 were up-regulated in vitro and in vivo. Furthermore, the 40% gel had a stronger effect than the 15% gel, and NAC ameliorated the gel effects.

Conclusions

Our findings suggest that bleaching gels induce cytotoxicity and pain conduction in dental pulp stem cells via intracellular ROS, which may provide a potential therapeutic target for alleviating tooth bleaching nociception.

Dose-Dependent Effects of Zoledronic Acid on Human Periodontal Ligament Stem Cells: An In Vitro Pilot Study

Bisphosphonates (BPs) are widely used to treat several metabolic and oncological diseases affecting the skeletal system. Despite BPs’ well-known therapeutic potential, they also displayed important side effects, among which is BPs-related osteonecrosis of the jaw, by targeting osteoclast activities, osteoblast, and osteocyte behavior. The aim of this study is to evaluate the biological effects of zoledronic acid (ZOL) in an in vitro model of periodontal ligament stem cells (PDLSCs) by using an experimental setting that resembles the in vivo conditions. PDLSCs were treated with different concentrations of ZOL ranging from 0.1 to 5 μM. The effects of ZOL exposure were evaluated on cell viability via 3-[4,5-Dimethylthiaoly]-2,5-diphenyltetrazolium bromide (MTT), cell cycle analysis, apoptosis detection, and immunofluorescence. Quantitative real-time polymerase chain reaction (PCR), colorimetric detection of alkaline phosphatase activity, and Alizarin Red S staining were performed to investigate the osteogenic potential of PDLSCs exposed to ZOL. MTT analysis showed that the viability of PDLSCs exposed to ZOL concentration ≥1.5 μM for 3 and 6 days was significantly lower (P < 0.001) than that of untreated cells. The percentage of apoptotic cells was significantly higher in PDLSCs exposed for 4 days to ZOL at 2 μM (P < 0.01) and 5 μM (P < 0.001) when compared to the control. Moreover, ZOL treatment (3 days) accounted for alterations in cell cycle distribution, with an increase in the proportion of cells in G0/G1 phase and a reduction in the proportion of cells in S phase. Chronic exposure (longer than 7 days) of PDLSCs to ZOL accounted for the downregulation of ALP, RUNX2, and COL1 genes at all tested concentrations, which fit well with the reduced alkaline phosphatase activity reported after 7 and 14 days of treatment. Reduced Col1 deposition in the extracellular matrix was reported after 14 days of treatment. Increased calcium deposits were observed in treated cells when compared to the control cultures. In conclusion, chronic exposure to 1 μM ZOL induced significant reduction of osteogenic differentiation, while ZOL concentrations ≥1.5 μM are required to impair PDLSCs viability and induce apoptosis.

Parathyroid hormone-related protein inhibits nitrogen-containing bisphosphonate-induced apoptosis of human periodontal ligament fibroblasts by activating MKP1 phosphatase

Massive production of reactive oxygen species (ROS) in human periodontal ligament fibroblasts (HPdLFs) by nitrogen-containing bisphosphonates (BPs) is the main factor causing BP-related osteonecrosis of the jaw. Further, oxidative stress and apoptosis of fibroblasts induced by ROS are closely associated with the activation of MAPK. Parathyroid hormone-related protein (PTHrP) can block the activity of MAPK by regulating the levels of MAPK phosphatase 1 (MKP1). Therefore, it is speculated that PTHrP can inhibit the apoptosis of HPdLFs caused by nitrogen-containing BP via regulating the expression levels of MKP1. Herein, alendronate sodium salt trihydrate (nitrogen-containing BP, FOS) and HPdLFs were co-cultured for 24 h, 48 h, and 72 h, and the levels of ROS and apoptosis were determined, respectively. After 48 h co-culture, FOS significantly increased the levels of ROS and apoptosis, and high phosphorylation levels of p38, ERK1/2 and p66^Shc were found in this study. However, the inhibitors of p38 and ERK1/2 significantly reduced the apoptosis of HPdLFs. Interestingly, PTHrP pre-treatment significantly reduced the phosphorylation levels of p38, ERK1/2, and p66^Shc. More importantly, MKP1 inhibitor sanguinarine inhibited the dephosphorylation levels of p38, ERK1/2, and p66^Shc caused by PTHrP. Altogether, PTHrP can inhibit nitrogen-containing BP-induced apoptosis of HPdLFs by activating MKP1 phosphatase.

Influence of bisphosphonates on oral implantology: Sodium alendronate and zoledronic acid enhance the synthesis and activity of matrix metalloproteinases by gingival fibroblasts seeded on titanium

OBJECTIVE

This study aimed to assess the influence of the bisphosphonates zoledronic acid and sodium alendronate on MMP-2 and MMP-9 synthesis and activity by gingival fibroblasts seeded onto titanium substrate.

DESIGN

Titanium discs were placed in 24-well cell culture plates and gingival fibroblasts were seeded (1 × 10⁵ cells/discs) on them using Dulbecco's Modified Eagle's Medium (DMEM) + 10 % fetal bovine serum (FBS) for 24 h. After this period, a fresh serum-free DMEM containing zoledronic acid or sodium alendronate at 0.5 μM, 1 μM or 5 μM was applied on the cells for an additional of 24 h. Serum-free DMEM and tumor necrosis factor alpha (TNF-α) were used as negative and positive controls, respectively. MMP-2 and MMP-9 synthesis and activity were determined by ELISA (Enzyme-Linked Immunosorbent Assay) and conventional/in situ zymography. Quantitative data were analyzed by one-way ANOVA and Tukey's tests (α = 0.05). The in situ zymography data were qualitatively described.

RESULTS

Despite both bisphosphonates increased the MMPs synthesis, this effect was significant higher in zoledronic acid groups. MMPs activity resembled by gelatinolytic activity was also enhanced by sodium alendronate and zoledronic acid in a similar pattern.

CONCLUSIONS

Zoledronic acid and sodium alendronate increased in a dose-dependent manner MMP-2 and MMP-9 synthesis by gingival fibroblasts seeded on titanium. MMP-2 activity was up-regulated by zoledronic acid treatment.

Choosing the Right Partner for Medication Related Osteonecrosis of the Jaw: What Central European Dentists Know

Medication-related osteonecrosis of the jaw (MRONJ) is a side effect of antiresorptive drugs. In this online survey, the awareness and knowledge of dentists regarding MRONJ was evaluated, and potential implications for oncologists are discussed. Questionnaires were emailed to dentists from Germany, Austria, Switzerland, and South Tyrol to evaluate disease-related knowledge and management. In addition to the overall score, a separate score was calculated for knowledge (maximum score: 15 points) and management (maximum score: 6 points) questions, and 1197 valid replies with completed questionnaires were received. The mean overall score was 10.45 ± 3.97 points, the mean knowledge score was 7.68 ± 3.05 points, and the mean management score was 2.76 ± 1.77 points. Factors influencing the outcome of the overall score were age, specialization, continuous professional education, and the number of dental screening exams in patients before antiresorptive therapy. Due to the considerable lack of knowledge regarding MRONJ among dentists, MRONJ patients and subjects at risk should be guided towards specialists for dental screening, treatment, and follow-up. This is important from an oncologic point of view to avoid any delay for treatment start of antiresorptives, and to reveal a potentially emerging osteonecrosis at an early stage, thus, avoiding the need for interruption or even cancellation of antiresorptive therapy.

The Case of Medication-Related Osteonecrosis of the Jaw Addressed from a Pathogenic Point of View. Innovative Therapeutic Strategies: Focus on the Most Recent Discoveries on Oral Mesenchymal Stem Cell-Derived Exosomes

Bisphosphonates-related osteonecrosis of the jaw (BRONJ) was firstly reported by Marx in 2003. Since 2014, the term medication-related osteonecrosis of the jaw (MRONJ) is recommended by the American Association of Oral and Maxillofacial Surgeons (AAOMS). Development of MRONJ has been associated to the assumption of bisphosphonates but many MRONJ-promoting factors have been identified. A strong involvement of immunity components has been suggested. Therapeutic intervention includes surgical and non-surgical treatments, as well as regenerative medicine procedures for the replacement of the lost tissues. The literature confirms that the combination of mesenchymal stem cells (MSCs), biomaterials and local biomolecules can support the regeneration/repair of different structures. In this review, we report the major open topics in the pathogenesis of MRONJ. Then, we introduce the oral tissues recognized as sources of MSCs, summing up in functional terms what is known about the exosomes release in physiological and pathological conditions.

Enhanced VEGF/VEGF-R and RUNX2 Expression in Human Periodontal Ligament Stem Cells Cultured on Sandblasted/Etched Titanium Disk

Bone formation, in skeletal development or in osseointegration processes, is the result of interaction between angiogenesis and osteogenesis. To establish osseointegration, cells must attach to the implant in a direct way without any deposition of soft tissue. Structural design and surface topography of dental implants enhance the cell attachment and can affect the biological response. The aim of the study was to evaluate the cytocompatibility, osteogenic and angiogenic markers involved in bone differentiation of human periodontal ligament stem cells (hPDLSCs) on different titanium disks surfaces. The hPDLSCs were cultured on pure titanium surfaces modified with two different procedures, sandblasted (Control—CTRL) and sandblasted/etched (Test—TEST) as experimental titanium surfaces. After 1 and 8 weeks of culture VEGF, VEGF-R, and RUNX2 expression was evaluated under confocal laser scanning microscopy. To confirm the obtained data, RT-PCR and WB analyses were performed in order to evaluate the best implant surface performance. TEST surfaces compared to CTRL titanium surfaces enhanced cell adhesion and increased VEGF and RUNX2 expression. Moreover, titanium TEST surfaces showed a different topographic morphology that promoted cell adhesion, proliferation, and osteogenic/angiogenic commitment. To conclude, TEST surfaces performed more efficiently than CTRL surfaces; furthermore, TEST surface results showed them to be more biocompatible, better tolerated, and appropriate for allowing hPDLSC growth and proliferation. This fact could also lead to more rapid bone–titanium integration.

VEGF/VEGF-R/RUNX2 Upregulation in Human Periodontal Ligament Stem Cells Seeded on Dual Acid Etched Titanium Disk

In restorative dentistry, the main implants characteristic is the ability to promote the osseointegration process as the result of interaction between angiogenesis and osteogenesis events. On the other hand, implants cytocompatibility remains a necessary feature for the success of surgery. The purpose of the current study was to investigate the interaction between human periodontal stem cells and two different types of titanium surfaces, to verify their cytocompatibility and cell adhesion ability, and to detect osteogenic and angiogenic markers, trough cell viability assay (MTT), Confocal Laser Scanning Microscopy (CLSM), scanning electron microscopy (SEM), and gene expression (RT-PCR). The titanium surfaces, machined (CTRL) and dual acid etched (TEST), tested in culture with human periodontal ligament stem cells (hPDLSCs), were previously treated in two different ways, in order to evaluate the effects of CTRL and TEST and define the best implant surface. Furthermore, the average surface roughness (Ra) of both titanium surfaces, CTRL and TEST, has been assessed through atomic force microscopy (AFM). The vascular endothelial growth factor (VEGF) and Runt-related transcription factor 2 (RUNX2) expressions have been analyzed by RT-PCR, WB analysis, and confocal laser scanning microscopy. Data evidenced that the different morphology and topography of the TEST disk increased cell growth, cell adhesion, improved osteogenic and angiogenic events, as well osseointegration process. For this reason, the TEST surface was more biocompatible than the CTRL disk surface.

Bisphosphonate-induced reactive oxygen species inhibit proliferation and migration of oral fibroblasts: A pathogenesis of bisphosphonate-related osteonecrosis of the jaw

BACKGROUND

The onset mechanism for bisphosphonate-related osteonecrosis of the jaw (BRONJ) has been reported, with a focus on bone remodeling, biofilm formation, and epithelial cell proliferation and migration. However, the involvement of stromal cells, especially fibroblasts, in the oral cavity is unclear. Therefore, this study was focused on how bisphosphonates (BPs) affect orthotopic periodontal ligament fibroblasts from the viewpoint of oxidative stress compared with ectopically obtained fibroblasts.

METHODS

Normal human periodontal ligament fibroblasts (HPdLFs) and normal human dermal fibroblasts (NHDFs) were used to gain insight into the functional differences in sensitivity and reactions to BPs. Cell growth assay, measurement of reactive oxygen species (ROS) and nitric oxide (NO) production, and wound-healing assay in vitro were performed. Maxillary first molars were extracted in C57BL/6 mice and either BP, N-acetyl-cysteine (NAC), and BP or saline were administered.

RESULTS

BP-induced IC₅₀ values were significantly lower in HPdLFs (30.6 µM) than in NHDFs (109.7 µM). BP resulted in an increase in ROS, but not NO generation in HPdLFs. BPs also inhibited proliferation and migration of HPdLFs but not NHDFs, while the addition of a ROS inhibitor, NAC, reversed those inhibitions. A BRONJ mouse model in which BP was administered and then the tooth was extracted, impaired wound healing of the socket was observed. When NAC was administered before tooth extraction, wound healing was significantly improved.

CONCLUSION

These results suggest that BP causes fibroblasts obtained from the oral cavity but not from skin to generate ROS and that the subsequent ROS-mediated inhibition of fibroblast growth and migration definitely delays wound healing, thereby contributing to BRONJ pathogenesis.

A Novel Role of Ascorbic Acid in Anti-Inflammatory Pathway and ROS Generation in HEMA Treated Dental Pulp Stem Cells

Resin (co)monomers issued from restorative dental materials are able to distribute in the dental pulp or the gingiva, to get to the saliva and to the flowing blood. Many authors have recently shown that methacrylate-based resins, in particular 2-hydroxyethylmethacrylate (HEMA), are responsible of inflammatory and autophagic processes in human dental pulp stem cells (hDPSCs) while ascorbic acid (AS), an antioxidant molecule, can assume a protective role in cell homeostasis. The purpose of the current work was to study if 50 µg/mL AS can affect the inflammatory status induced by 2 mM HEMA in hDPSCs, a tissue–specific cell population. Cell proliferation, cytokine release, morphological arrangement and reactive oxygen species (ROS) formation were determined respectively by MTT, ELISA, morphological analysis and dichlorofluorescein assay. The hDPSCs exposed to HEMA let to an increment of ROS formation and in the expression of high levels of inflammatory mediators such as nuclear factor-κB (NFkB), inflammatory cytokines such as interleukin IL6, IL8, interferon (IFN)ɣ and monocyte chemoattractant protein (MCP)1. Moreover, HEMA induced the up-regulation of pospho-extracellular signal–regulated kinases (pERK)/ERK signaling pathway associated to the nuclear translocation. AS treatment significantly down-regulated the levels of pro-inflammatory mediators. Then, the natural product AS reduced the detrimental result promoted by methacrylates in clinical dentistry, in fact restore cell proliferation, reduce the pro-inflammatory cytokine, downregulate ROS production and of NFkB/pERK/ERK signaling path. In synthesis, AS, could improve the quality of dental care and play a strategic role as innovative endodontic compound easy to use and with reasonable cost.

Gingival fibroblasts and medication-related osteonecrosis of the jaw: Results by real-time and wound healing in vitro assays

OBJECTIVE

This study investigated the effects of bisphosphonates and denosumab on human gingival fibroblasts (HGFs) that could influence inflammation, wound healing, and angiogenesis in medication-related osteonecrosis of the jaw (MRONJ).

METHODS

A real-time in vitro assay was performed on HGFs with and without the addition of bacterial lipopolysaccharide and a mononuclear cell co-culture to observe the effects of zoledronate, ibandronate, alendronate, clodronate, denosumab, and combinations of zoledronate and denosumab at varied concentrations. A wound healing assay was performed, and gene and protein expression was analyzed for inflammatory, angiogenic, and osteoclastogenic cytokines and mediators including interleukin (IL)-1β, IL-6, tumor necrosis factor alpha (TNFα), IL-8, vascular endothelial growth factor (VEGF), RANKL, and osteoprotegerin.

RESULTS

Higher concentrations of antiresorptives resulted in impaired wound healing and HGF death, which also occurred without mechanical damage. These effects were increased with bacterial lipopolysaccharide and mononuclear cells. Increased levels of IL-1β, TNFα, IL-8, VEGF, osteoprotegerin, and decreased levels of IL-6 were observed.

CONCLUSIONS

Antiresorptive exposure was associated with HGF death and delayed wound healing, which could be attributed to an elevated inflammatory response and immune dysfunction contributing to MRONJ development. There was no evidence of anti-angiogenic effects. Our experiments present the first results of denosumab with HGFs.

Antimicrobial activity of NO-releasing compounds against periodontal pathogens

This study describes the successful synthesis of nitric oxide (NO)-releasing compounds with biodegradable and injectable properties and demonstrates that the kinetics of NO release vary according to the type of NO donor. The antimicrobial activity of NO-releasing compounds against three common periodontal pathogens, i.e., Aggregatibacter actinomycetemcomitans, Porphyromonas gingivalis, and Actinomyces israelii, was investigated using a susceptibility assay. Human gingival fibroblasts were treated with NO-releasing compounds at the minimum concentrations required for bacterial growth and cytotoxicity was evaluated using the MTT cell proliferation assay. Our results suggest that NO-releasing compounds can be used topically to treat both gram-negative and gram-positive periodontal pathogens. Comparison of the antimicrobial activity and cytotoxicity assay results between the NO-releasing compounds revealed that an NO donor comprising a macromolecule without surface charge, a lower instantaneous NO concentration, and an adequate supply of NO were associated with a strong bactericidal effect and low cytotoxicity. NO-releasing compounds with these properties may be suitable for treatment of periodontitis.

Fabrication of bioactive 3D printed porous titanium implants with Sr ion-incorporated zeolite coatings for bone ingrowth

Functionalization of porous titanium alloy implants with bioactive coatings to improve bone regeneration performance is hotly pursued in recent decade. Here we demonstrate a facile strategy to design bioactive 3D printed porous titanium implants with strontium (Sr) ion incorporated zeolite coatings (SZCs). The SZCs can be uniformly fabricated on the 3D porous scaffolds using an in situ hydrothermal crystal growth method to improve their osteogenesis and osteointegration capacity. In vitro experiments of SZCs on a TC4 disk show that Sr ions can slowly release in the simulated body fluid by means of ion-exchange, thus can drastically improve apatite forming ability, biocompatibility, corrosion resistance, and alkaline phosphatase (ALP) activity. In vivo evaluation on a rabbit model with 3D printed titanium implants shows that the SZCs could significantly induce new bone formation both in and around the porous implants within four weeks. This work may open up a new method for the development of bioactive customized porous implants by functionalization with zeolite coatings for orthopedic applications.

Bisphosfonate matrix metalloproteinase inhibitors for the treatment of periodontitis: An in vitro study

Periodontitis is an inflammatory disease caused by anaerobic bacteria, including Porphyromonas gingivalis. Lipopolysaccharide (LPS)‑stimulated persistent inflammation is responsible for an increase in matrix metalloproteinase (MMP) expression, resulting in periodontal tissue destruction. The aim of the present study was to investigate synthesized bisphosphonic MMP inhibitors, in an in vitro model consisting of human gingival fibroblasts exposed to LPS, and to compare the biological responses to those induced by zoledronate (ZA), a commercial bisphosphonate. MTT and lactate dehydrogenase (LDH) assays were used to measure cell viability and cytotoxicity, respectively. ELISA was performed to evaluate prostaglandin E2 (PGE2), interleukin (IL)6 and collagen secretion, while western blotting was used to analyze MMP expression. No effect on viability and low cytotoxicity were observed following treatment with bisphosphonate compounds. In the present study, treatment with compound 1 did not increase the release of PGE2 and IL6. Increased levels of collagen I secretion were reported when compound 3 and ZA were administered. An increase of MMP8 was observed following ZA treatment, while a decrease of MMP9 and MMP14 following treatment with compounds 1, 2 and ZA were reported. The performance of compound 1 was optimal in terms of cell viability. Compound 1 also did not induce inflammation, and had the ability to counteract LPS‑induced increases in MMP expression. These data suggested that compound 1 was the most suitable treatment to progress to an in vivo animal study, with the aim to confirm its use for the treatment of periodontitis.

Mechanical loading increases pro-inflammatory effects of nitrogen-containing bisphosphonate in human periodontal fibroblasts

OBJECTIVES

There is increasing evidence that inflammation and biomechanical loading can influence the effects of bisphosphonates (BP). The aim of this study was to investigate the influence of tensile strain application combined with IL-1ß and clodronate or zoledronate on human periodontal ligament fibroblasts (HPdLF) in vitro.

MATERIALS AND METHODS

HPdLF were cultured with 10 nM IL-1ß and 5 μM clodronate or zoledronate for 48 h. Cells were applied to cyclic tensile strain (CTS; 3% elongation) for 12 h in vitro. Cell number was analyzed directly after CTS by MTT assay. Gene expression of receptor activator of cyclooxygenase-2 (COX-2) was investigated using real-time PCR. MMP-8, TIMP-1, and PGE2 were measured by ELISA. Statistics were performed with SPSS (ANOVA, p < 0.05).

RESULTS

Zoledronate reduced the cell number of HPdLF (60.3 vs. 100%), which was significant when combined with IL-1ß. Combined with 3% CTS, this effect was voided and cell number increased over the level of the control cells. IL-1ß led to a 10-fold increase of COX-2 gene expression. Combined with CTS and zoledronate, this increase was enhanced to a gene expression 70-fold that of control cells with related PGE2 synthesis. Clodronate neither reduce the cell number nor enhanced the COX-2 gene expression. CTS increased MMP-8 protein synthesis. Combined with BP, this increase was voided. TIMP-1 protein synthesis was increased at all conditions under CTS.

CONCLUSIONS

Mechanical loading might activate cell metabolism and abolish BP- and inflammation-induced reduction of viability. Combination of mechanical loading, inflammation, and nitrogen-containing bisphosphonates can cause pro-inflammatory effects.

CLINICAL RELEVANCE

Periodontal inflammation should be treated initially before BP intake to prevent decreased cell viability of the periodontium and increased inflammation, which might be enhanced by the addition of mastication forces.

Reactive oxygen species are required for zoledronic acid-induced apoptosis in osteoclast precursors and mature osteoclast-like cells

Inhibiting osteoclasts and osteoclast precursors to reduce bone resorption is an important strategy to treat osteoclast-related diseases, such as osteoporosis, inflammatory bone loss, and malignant bone metastasis. However, the mechanism by which apoptosis is induced in the osteoclasts and their precursors are not completely understood. Here, we used nitrogen-containing bisphosphonate zoledronic acid (ZA) to induce cell apoptosis in human and murine osteoclast precursors and mature osteoclast-like cells. Caspase-3-mediated cell apoptosis occurred following the ZA (100 μM) treatment. Reactive oxygen species (ROS) were also generated in a time-dependent manner. Following knock-down of the p47^phox expression, which is required for ROS activation, or co-treatment with the ROS inhibitor, N-acetyl-L-cysteine, ZA-induced apoptosis was significantly suppressed in both osteoclast precursors and mature osteoclast-like cells. The ROS-activated mitogen-activated protein kinases pathways did not trigger cell apoptosis. However, a ROS-regulated Mcl-1 decrease simultaneously with glycogen synthase kinase (GSK)-3β promoted cell apoptosis. These findings show that ZA induces apoptosis in osteoclast precursors and mature osteoclast-like cells by triggering ROS- and GSK-3β-mediated Mcl-1 down-regulation.

Combined Use of Zoledronic Acid Augments Ursolic Acid-Induced Apoptosis in Human Osteosarcoma Cells through Enhanced Oxidative Stress and Autophagy

Ursolic acid (UA), a naturally occurring pentacyclic triterpene acid found in many medicinal herbs and edible plants, triggers apoptosis in several tumor cell lines but not in human bone cancer cells. Most recently, we have demonstrated that UA exposure reduces the viability of human osteosarcoma MG-63 cells through enhanced oxidative stress and apoptosis. Interestingly, an inhibitor of osteoclast-mediated bone resorption, zoledronic acid (ZOL), also a third-generation nitrogen-containing bisphosphonate, is effective in the treatment of bone metastases in patients with various solid tumors. In this present study, we found that UA combined with ZOL to significantly suppress cell viability, colony formation, and induce apoptosis in two lines of human osteosarcoma cells. The pre-treatment of the antioxidant had reversed the oxidative stress and cell viability inhibition in the combined treatment, indicating that oxidative stress is important in the combined anti-tumor effects. Moreover, we demonstrated that ZOL combined with UA significantly induced autophagy and co-administration of autophagy inhibitor reduces the growth inhibitory effect of combined treatment. Collectively, these data shed light on the pathways involved in the combined effects of ZOL and UA that might serve as a potential therapy against osteosarcoma.