The mechanisms of cytotoxicity of urethane dimethacrylate to Chinese hamster ovary cells

A Pilot Study on Monomer and Bisphenol A (BPA) Release from UDMA-Based and Conventional Indirect Veneering Composites

This study aimed to investigate the release of common monomers from conventional (Dialog Vario, Enamel Plus HFO) and UDMA-based indirect veneering composites (VITA VM LC, GC Gradia). Ten cylindrical samples of each material were prepared (n = 40), immersed in HPLC grade water, and incubated for 24 h in an incubation shaker at 37 °C and 112 rpm. Extraction was performed following ISO 10993-12 and monomers were detected and quantified by HPLC-MS/MS. In all the samples, urethane dimethacrylate (UDMA) and bisphenol A (BPA) were quantifiable. Compared to water blanks, BPA levels were only elevated in the eluates from conventional composites. In all other samples, concentrations were in the range of extraneous BPA and were therefore clinically irrelevant. Low concentrations of Bisphenol A-glycidyl methacrylate (BisGMA) were found in one BPA-free composite and in both conventional materials. Statistical analyses showed that BPA-free materials released significantly less BisGMA and no BPA, while UDMA elution was comparable to elution from conventional materials. All measured concentrations were below reported effective cytotoxic concentrations. Considering these results, the substitution of BPA-derivatives with UDMA might be beneficial since BPA-associated adverse effects are ruled out. Further studies should be enrolled to test the biocompatibility of UDMA on cells of the oral environment.

A comparative in vitro study on monomer release from bisphenol A-free and conventional temporary crown and bridge materials

This study aimed to investigate the release of common monomers from two conventional and two bisphenol A (BPA)-free temporary crown and bridge materials. Cylindrical samples of all materials were prepared (N = 90; five samples for each material and cycle of analysis). All samples were immersed in high-performance liquid chromatography (HPLC)-grade water and incubated for 1 h, 12 h, 24 h, and 7 days in an incubation shaker at 37°C and 112 rpm. Extraction was performed in accordance with ISO 10993-12. Eluted monomers were detected and quantified by HPLC coupled with ultraviolet-visible spectroscopy and mass spectrometry (HPLC-UV/Vis-MS). Analysis of BPA was performed by HPLC coupled with ultraviolet-visible spectroscopy (HPLC-UV/Vis) and positive results were verified by HPLC-tandem mass spectrometry (HPLC-MS/MS). Neither bisphenol A-glycidyl methacrylate (Bis-GMA) nor BPA was quantifiable in any of the crown and bridge samples investigated in the present study. However, all samples contained triethylene glycol dimethacrylate (TEGDMA) and/or urethane dimethacrylate (UDMA) after 24 h of incubation. Statistical analysis showed that significantly more UDMA was released from the BPA-free materials than from the conventional materials. All concentrations of UDMA measured were below the effective cytotoxic concentrations previously reported. However, for a few materials, especially BPA-free temporary crown and bridge materials, the levels of UDMA were above previously reported potentially harmful concentrations for local cells. As BPA-free materials were introduced as being more biocompatible than materials containing BPA, substitution of Bis-GMA with UDMA should be further investigated.

Effect of post-polymerization with autoclaving treatment on monomer elution and mechanical properties of 3D-printing acrylic resin for splint fabrication

OBJECTIVES

To evaluate the effect of post-treatment autoclaving on monomer elution and mechanical properties of three-dimensionally (3D) printed resin for splint fabrication.

METHODS

Photopolymer resin specimens (Dental LT Clear) were 3D-printed and processed according to the manufacturer's instructions. The specimens were randomly divided to different post-treatment protocols: water storage, autoclaving at different temperatures (121 °C or 132 °C), times (4 or 30 min) and no treatment as a control. The elution of UDMA, HEMA, and EGDMA monomers was determined using high-performance liquid chromatography (HPLC) by immersing the specimens in 75% ethanol for 72 h. The flexural modulus, surface microhardness and linear dimensional changes were measured. The monomer elution and flexural modulus were statistically analyzed using Welch's ANOVA followed by Dunnett's T3 tests, while the surface microhardness and dimensional changes were analyzed using one-way ANOVA followed by Bonferroni tests (α = 0.05).

RESULTS

The overall monomer elution concentrations were significantly highest for the control group and lowest for specimens treated in an autoclave at 132 °C for 4 min. The flexural modulus was not significantly different between all groups. The surface microhardness was significantly higher for all autoclaved groups than the control and water storage groups. The linear expansion was significantly higher after post-treatment autoclaving in contrast to water storage.

SIGNIFICANCE/CONCLUSIONS

Post-polymerization autoclave treatment of the 3D-printed resin reduced monomer elution and improved surface microhardness without deteriorating the flexural modulus. Post-treatment with an autoclave at 132 °C for 4 min can be recommended for 3D-printed resin for splint fabrication.

The Toxicity of Universal Dental Adhesives: An In Vitro Study

There is no consensus in the literature regarding the potential toxicity of universal dental adhesives (UDA). Being used in close proximity to the pulp, their biocompatibility should be an important factor in dental research. The aim of the present study was to evaluate the biocompatibility of UDA in an in vitro model. The study was performed using a monocyte/macrophage peripheral blood SC cell line (ATCC CRL-9855) on four specific UDA, namely: All-Bond Universal (Bisco); CLEARFIL Universal Bond Quick (Kuraray); G-Premio BOND (GC); Single Bond Universal (3M ESPE). The cytotoxicity of the investigated UDA was measured using the XTT colorimetric assay. The genotoxicity of the analyzed compounds was evaluated using an alkaline version of the comet assay. Furthermore, flow cytometry (FC) apoptosis detection was performed using the FITC Annexin V Apoptosis Detection Kit I. FC cell-cycle arrest assessment was performed using propidium iodide staining. The study observed significant differences in the toxicity of the UDA that were tested, as G-Premio BOND showed significant in vitro toxicity in all of the tests performed, while All-Bond Universal, CLEARFIL Universal Bond Quick and Single Bond Universal did not present any significant toxic effects toward SC cell line. The in vitro toxicity of UDA should be taken into consideration prior to in vivo and clinical studies. The flow cytometry could improve the accuracy of dental materials research and should be incorporated into the standardization criteria.

Cytotoxicity and estrogenicity in simulated dental wastewater after grinding of resin-based materials

OBJECTIVE

This study evaluated the cytotoxic and estrogenic effects of dust and eluates released into simulated wastewater after grinding of dental resin-based materials.

METHODS

Four materials were used: ceram.x® universal, Filtek™ Supreme XTE, Lava™ Ultimate and Core-X™ flow. From each composite material, samples (5 × 2 mm, n = 50) were prepared according to the manufacturers' instructions. Lava™ Ultimate was used as blocks. All samples were ground to dust with a diamond bur (106 μm) and suspended in distilled water at 60 mg/mL. After storage for 72 h, the suspensions were separated into a soluble (eluate) and a particulate (dust) fraction. Eluates and dusts were evaluated for inhibition of Vibrio fischeri bioluminescence and cytotoxicity on human A549 lung cells (WST-1-Assay). The estrogenic activity was assessed by YES-Assay using Saccharomyces cerevisiae. Additionally, dental monomers (BisGMA, BisEMA, UDMA, TEGDMA, HEMA) and Bisphenol A were investigated.

RESULTS

All eluates showed inhibition of V. fischeri bioluminescence at concentrations above 1.1 mg/mL (p < 0.05). The activity of the eluates of ceram.x® universal and Filtek™ Supreme XTE was significantly higher than Lava™ Ultimate and Core-X™ flow (p < 0.05). In the WST-1-Assay, all materials induced cytotoxic effects at concentrations of 0.1 mg/mL (p < 0.05), while no significant differences were detected among them. The tested materials revealed no estrogenic activity. All dental monomers and Bisphenol A showed concentration dependent cytotoxic effects (p < 0.05), whereas only Bisphenol A induced an estrogenic effect (p < 0.01).

SIGNIFICANCE

Dust and eluates of resin-based dental materials released into wastewater exert bactericidal and cytotoxic effects in vitro. However, they reveal no estrogenic effect.

Cytotoxicity evaluation of eluates from universal adhesives by real-time cell analysis

The aim of this study was to evaluate the cytotoxicity of universal adhesives on L929 mouse fibroblast cell line by using a real-time cell analysis. In order to obtain extract, six different cured dental adhesives were immersed in Dulbecco's Modified Eagle's Medium (DMEM) at 37°C for 24 h. A real-time cell analysis system was used to assess cytotoxicity of the dental adhesives. After seeding 25,000 cells/300 μL/well cell suspensions into the wells of an e-plate, fibroblasts were exposed to extracts of tested adhesives at varying dilutions (1:1, 1:2, and 1:10) and observed at every 30 min intervals for 72 h. Three-way ANOVA one factor repeated measures were used to analyze the results (α=0.05). All tested adhesives induced cell viability loss, cell morphology alteration, and cell death depending on extract concentration and time. Cell viability of L929 cells to between 44 and 10% for 1:1 diluted extracts, at 72 h, when compared to the negative control.

The influence of a liner on deep bulk-fill restorations: Randomized clinical trial

OBJECTIVE

The aim of this study was to evaluate the influence of a liner on the clinical performance of deep posterior restorations performed with bulk-fill composite.

METHODS

30 subjects received two restorations on deep preparations in posterior teeth, without pulpal exposure, after selective carious-tissue removal in one-stage. The internal walls reached the inner quarter of dentin, but with a radiographically detectable zone of firm dentin remaining. The pulpal protection using a layer of glass ionomer composite liner (Ionoseal, Voco) was applied in just one preparation. The adhesive system Futurabond U (Voco) was applied in all preparations, which were restored with the bulk-fill pure Ormocer nanohybrid composite (Admira Fusion Xtra - Voco), in up to 4 mm thick increments. All restorations were evaluated using the FDI criteria after 7 days, 6, 12 and 24 months postoperatively.

RESULTS

After 24-months, 25 patients attended the recall and 50 restorations were evaluated. The Fisher's statistical analysis (5%) showed no difference between the techniques for the esthetic, functional and biological properties. No postoperative sensitivity was reported for both groups.

CONCLUSION

The application of a liner did not influence the clinical performance of deep restorations with bulk-fill Ormocer composite.

CLINICAL RELEVANCE

The application of a liner with a GIC-based material did not have a significant effect on the clinical performance of bulk-fill restorations and seems to be unnecessary for the material tested.

Toxic Effects of Urethane Dimethacrylate on Macrophages Through Caspase Activation, Mitochondrial Dysfunction, and Reactive Oxygen Species Generation

Urethane dimethacrylate (UDMA) is a dimethacrylate-based resin monomer that can react with other related monomers and inorganic particles, causing hydrophobic polymerization through cross-linking upon light activation. UDMA polymers are commonly used for the reconstruction and reinforcement of teeth and bones. UDMA can become unbound and be released from light-cured polymer resins. Thus far, no evidence exists on the toxic effects of UDMA and its related working mechanisms for macrophages. Therefore, in the present study, we investigated the cytotoxicity, mode of cell death, DNA damage, caspase activities, mitochondrial dysfunction, and reactive oxygen species (ROS) generation in RAW264.7 macrophages treated with UDMA using the lactate dehydrogenase (LDH) assay kit, Annexin V-FITC and PI assays, micronucleus formation and comet assay, caspase fluorometric assay, JC-1 assay, and 2ʹ,7ʹ-dichlorofluorescin diacetate (DCFH-DA) assay, respectively. Our results show that UDMA induced cytotoxicity; apoptosis and necrosis; genotoxicity, which is also called DNA damage; increased caspase-3, -8, and -9 activities; mitochondrial dysfunction; and intracellular ROS generation in a concentration-dependent manner in RAW264.7 macrophages. Thus, based on the observed inhibited concentration parallel trends, we concluded that UDMA induces toxic effects in macrophages. Furthermore, UDMA-induced intracellular ROS generation, cytotoxicity, and DNA damage were reduced by N-acetyl-L-cysteine.

Cytotoxicity and genotoxicity of DMABEE, a co-photoinitiator of resin polymerization, on CHO-K1 cells: Role of redox and carboxylesterase

The 4-dimethylaminobenzoic acid ethyl ester (DMABEE) is an important co-initiator for resin polymerization in dental resinous materials. As a radical forming chemical with high lipophilicity, the genotoxicity and cytotoxicity of DMABEE deserve prudent investigation. In this study, we found that DMABEE reduced the viability and proliferation of Chinese hamster ovary (CHO-K1) cells in a dose-dependent manner, and altered cell morphology at higher concentrations. G0/G1 cell cycle arrest was induced by DMABEE at 0.25-0.75 mM, and cell proportion of sub-G0/G1 phase was significantly elevated at 1 mM while cell apoptosis was observed. Genotoxic effect was noted when cells were treated by 0.1 mM DMABEE, as revealed by increase of micronucleus formation. Reactive oxygen species overproduction was observed as cells treated with 0.75 and 1 mM, while elevation of intracellular glutathione was noticeable since 0.1 mM. Contrary to our expectation, pretreatment by N-acetyl-l-cysteine enhanced the toxicity of DMABEE on CHO-K1 cells. Catalase mildly reduced the toxic effect and carboxylesterase showed obvious ability to reverse the toxicity of DMABEE. These findings highlight the mechanism of DMABEE toxicity and provide clues for safety improvement of its application in clinical dental treatment.

Stoichiometry and Kinetics of Sequential Dimethacrylate Enzymolysis

The increasing use of methacrylate-based materials in tissue engineering and dental restorations demands detailed evaluation of enzymolysis of these materials due to toxicity, durability, and biocompatibility concerns. The objective of this study is to develop tools for assessing and ranking the enzymolysis kinetics of dimethacrylate (DMA) compounds. Triethyleneglycol DMA and diurethane DMA are employed as model DMAs for kinetic studies of 2-step enzymolysis by 2 esterases, pseudocholine esterase and cholesterol esterase. In addition, the intermediate hydrolysis products, mono-methacrylates (mono-MAs), are prepared via esterases. The kinetics of DMA enzymolysis are evaluated per the concentrations of DMA. The enzymolysis products are quantified by high-performance liquid chromatography. Additionally, stoichiometric analysis and a Berkeley Madonna model are employed to compare the efficacy of esterases in DMA enzymolysis. The chemical structure of mono-MAs is verified by proton and heteronuclear single quantum coherence (2D 1H-13C) nuclear magnetic resonance spectroscopy and mass spectrometry. In evaluating the ratio of sequential and simultaneous degradations of DMA and mono-MA, the stoichiometric analysis draws the same conclusions without using [mono-MA] as the experimental observation using [mono-MA]. The majority of the 4 esterase-DMA combinations undergo the sequential enzyme-catalyzed hydrolysis, from DMA to mono-MA to diol. However, cholesterol esterase is more effective than pseudocholine esterase in maintaining sequential degradation until >90% of DMA is decomposed. Both enzymolysis steps are first-order reactions. The mono-MAs are more hydrolysis resistant than DMAs. Moreover, esterase efficacy and selectivity on DMA enzymolysis are presented. The stoichiometric analysis provides valuable tools in assessing DMA enzymolysis when mono-MA is difficult to be obtained. The resistance of mono-MAs to enzymolysis suggests a need for thorough toxicity evaluations of these intermediate compounds. It also advocates the alternative approaches in designing and developing durable and biocompatible materials.

Synergistic effect of functionalized poly(l-lactide) with surface-modified MgO and chitin whiskers on osteogenesis in vivo and in vitro

Favorable cytocompatibility and osteogenesis potential are critical for the development of a bone repair material. In this study, two types of surface-modified whiskers, grafted magnesia and chitin (g-MgO and g-CHN) whiskers, were synthesized and introduced into a poly(l-lactide) (PLLA) matrix singly or together to prepare PLLA/g-MgO/g-CHN composite films and bone nails via injection molding. On the account of the synergetic contribution of g-MgO and g-CHN whiskers, the enhanced cell adhesion, spreading, proliferation of mouse embryo osteoblast precursor (MC3T3-E1) cells, as well as the alteration of cell-cycle and inhibition of cell apoptosis, were observed on PLLA/g-MgO/g-CHN film as compared to pure PLLA, PLLA/g-MgO and PLLA/g-CHN films. More importantly, the highest level of the secretion of ALP and the formation of calcium deposition, accompanied with expression of osteogenesis genes (ALP, Runx-2, COL I, OCN) in vitro were obtained for the PLLA/g-MgO/g-CHN film among all of the material groups. Additionally, the PLLA and PLLA composite bone nails were implanted in rabbits' femurs and new bone formation was detected on PLLA/g-MgO/g-CHN group after 16 weeks of implantation by 3D reconstruction of micro-CT and histological analyses. Besides, the bending strength of defected bone repaired by PLLA/g-MgO/g-CHN bone nail was high to 48 MPa, which was far stronger than other bone nail groups. Overall, this study demonstrated the addition of g-MgO and g-CHN whiskers together in PLLA matrix played a synergistic promoting role in cell affinity and osteogenic differentiation, and the developed PLLA/g-MgO/g-CHN composites hold great potential in fields of bone repair.

Effects of triethylene glycol dimethacrylate (TEGDMA) on the odontoclastic differentiation ability of human dental pulp cells

OBJECTIVES

The primary purpose of this study was to examine the effects of triethylene glycol dimethacrylate (TEGDMA) on odontoclastic differentiation in the dental pulp tissue.

MATERIAL AND METHODS

The effects of different TEGDMA dosages on the odontoclastic differentiation capability of dental pulp cells were analyzed in vitro using the following methodologies: i) flow cytometry and tartrate-resistant acid phosphatase (TRAP) staining; ii) apoptotic effects using Annexin V staining; iii) mRNA expression of osteoprotegerin (OPG) and receptor activator of nuclear factor (NF)-kB ligand (RANKL) genes by quantitative Real-time PCR (qRT-PCR); and iv) OPG and RANKL protein expression by enzyme-linked immunosorbent assay (ELISA).

RESULTS

TEGDMA caused relatively less odontoclastic differentiation in comparison with the control group; however, odontoclastic differentiation augmented with increasing doses of TEGDMA (p<0.05). The mRNA and protein expression of OPG was lower in TEGDMA treated pulp cells than in the control group (p<0.05). While the mRNA expression of RANKL remained unchanged compared to the control group (p>0.05), its protein expression was higher than the control group (p<0.05). In addition, TEGDMA increased the apoptosis of dental pulp cells dose dependently.

CONCLUSIONS

TEGDMA reduced the odontoclastic differentiation ability of human dental pulp cells. However, odontoclastic differentiation ratios increased proportionally with the increasing dose of TEGDMA.

Effect of isobutyl methacrylate and methacrylic acid eluted from chairside denture hard reliners on enzymatic cellular antioxidants: An in vitro study in human primary buccal mucosal fibroblasts

AIM

This study was conducted with the objective to evaluate the cytotoxicity of monomers isobutyl methacrylate (IBMA) and methacrylic acid (MA) in human buccal mucosal fibroblast primary cell culture and to study their effect on cellular enzymatic antioxidants-glutathione peroxidase (GPx), superoxide dismutase (SOD), and catalase (CAT).

MATERIALS AND METHODS

The tissue for fibroblast cell culture was harvested from oral buccal mucosa of a healthy donor. Fibroblast cells were plated at a density of 1 × 10⁴ cells per well in 96-well tissue culture plates. Cells were exposed to various concentrations of IBMA and MA. The cell viability and various enzyme activities were evaluated 24 h after exposure to the above treatments. All tests were done in triplicate. Cell viability was assessed by trypan blue dye exclusion assay and all enzyme activities were done using assay kits from Cayman Chemicals, Ann Arbor, USA.

RESULTS

At all concentrations tested a statistically significant decrease in viability was observed in IBMA- and MA-treated cells. Around 42% cells were viable at the highest test concentration of IBMA (80 μmol/L) and only 20% cells were viable at the highest dose (144 μmol/L) of MA exposure (P < 0.05). Dose-dependent decrease in the GPx and SOD activities was observed in cells treated with IBMA and MA (P < 0.05). CAT activity was not detectable in the controls. However, a fall in CAT activity was detected in cells exposed to IBMA and MA at all concentrations tested (P < 0.05).

CONCLUSION

IBMA and MA leaching out from the chairside denture hard reliners are cytotoxic on human buccal fibroblast primary cell cultures. This could be due to the oxidative stress caused by the generation of reactive oxygen species which is evidenced by the fall in activities of antioxidant enzymes (GPx, SOD, and CAT) and cytotoxicity.

Polydopamine-Templated Hydroxyapatite Reinforced Polycaprolactone Composite Nanofibers with Enhanced Cytocompatibility and Osteogenesis for Bone Tissue Engineering

Nanohydroxyapatite (HA) synthesized by biomimetic strategy is a promising nanomaterial as bone substitute due to its physicochemical features similar to those of natural nanocrystal in bone tissue. Inspired by mussel adhesive chemistry, a novel nano-HA was synthesized in our work by employing polydopamine (pDA) as template under weak alkaline condition. Subsequently, the as-prepared pDA-templated HA (tHA) was introduced into polycaprolactone (PCL) matrix via coelectrospinning, and a bioactive tHA/PCL composite nanofiber scaffold was developed targeted at bone regeneration application. Our research showed that tHA reinforced PCL composite nanofibers exhibited favorable cytocompatibility at given concentration of tHA (0-10 w.t%). Compared to pure PCL and traditional nano-HA enriched PCL (HA/PCL) composite nanofibers, enhanced cell adhesion, spreading and proliferation of human mesenchymal stem cells (hMSCs) were observed on tHA/PCL composite nanofibers on account of the contribution of pDA present in tHA. More importantly, tHA nanoparticles exposed on the surface of composite nanofibers could further promote osteogenesis of hMSCs in vitro even in the absence of osteogenesis soluble inducing factors when compared to traditional HA/PCL scaffolds, which was supported by in vivo test as well according to the histological analysis. Overall, our study demonstrated that the developed tHA/PCL composite nanofibers with enhanced cytocompatibility and osteogenic capacity hold great potential as scaffolds for bone tissue engineering.

N-acetyl cysteine protects human oral keratinocytes from Bis-GMA-induced apoptosis and cell cycle arrest by inhibiting reactive oxygen species-mediated mitochondrial dysfunction and the PI3K/Akt pathway

Bisphenol-A-glycidyl methacrylate (Bis-GMA) released from dental resin materials causes various toxic effects on gingival epithelium. Thus the underlying mechanisms of its cytotoxicity should be elucidated for safety use. One potential cause of cell damage is the generation of reactive oxygen species (ROS) beyond the capacity of a balanced redox regulation. In this study, we found that exposure of human oral keratinocytes (HOKs) to Bis-GMA caused apoptosis and G1/S cell cycle arrest in parallel with an increased ROS level. Moreover, Bis-GMA induced a depletion of mitochondrial membrane potential, an increase in the Bax/Bcl-2 ratio, an activation of caspase-3 and altered expressions of cell cycle-related proteins (p21, PCNA, cyclinD1). Furthermore, the co-treatment of the ROS scavenger N-acetyl cysteine (NAC) obviously attenuated Bis-GMA-induced toxicity. Here we also evaluated the effects of Bis-GMA on the ROS-related PI3k/Akt pathway. We found that Bis-GMA inhibited the phosphorylation of Akt, whereas the amount of phosphorylated Akt was reverted to the control level in the presence of NAC. Our findings suggested that the toxic effects of Bis-GMA were related to ROS production and the antioxidant NAC effectively reduced Bis-GMA-mediated cytotoxicity.

Synthesis and properties of temperature-sensitive and chemically crosslinkable poly(ether-urethane) hydrogel

The PEU-MA solutions can gelate at physiological temperature, and be further crosslinked by UV light.

Composite-induced toxicity in human gingival and pulp fibroblast cells

OBJECTIVE

The most important requirement for a material to be used in medical applications is its biocompatibility. Dental composite materials come into direct contact with oral tissues, especially gingival and pulpal cells. This study was performed to evaluate possible DNA damage in cells of human origin exposed to dental composites in vitro using a cytogenetic assay.

MATERIALS AND METHODS

Two composite resins (Vertise Flow, Kalore) were tested on human gingival and pulp fibroblasts using the acridine orange/ethidium bromide viability staining and alkaline comet assay. Cultures were treated with polymerized composites in two different concentrations (20 mg/ml, 40 mg/ml) for 14 days. Chi-square and Kruskall-Wallis non-parametric test were used for the statistical analysis (p < 0.05).

RESULTS

Significant cytotoxicity was observed for 40 mg/ml of Vertise Flow in both cultures, while Kalore (40 mg/ml) showed cytotoxic effect only on human pulp fibroblasts. A significant level of DNA damage was detected for both materials and concentrations, in both cell cultures.

CONCLUSION

If the two cell cultures are compared, the pulp cells were more sensitive to the cyto/genotoxic effects of dental composites. Based on the results, one can conclude that the use of tested materials may cause cellular damage in gingival and pulp fibroblasts in vitro.

Effects of dental methacrylates on oxygen consumption and redox status of human pulp cells

Several studies have already demonstrated that the incomplete polymerization of resin-based dental materials causes the release of monomers which might affect cell metabolism. The aim of this study was to investigate the effects of triethylene glycol dimethacrylate, 1,4-butanediol dimethacrylate, urethane dimethacrylate, and 2-hydroxyethyl methacrylate on (1) cellular energy metabolism, evaluating oxygen consumption rate, glucose consumption, glucose 6-phosphate dehydrogenase activity, and lactate production, and (2) cellular redox status, through the evaluation of glutathione concentration and of the activities of enzymes regulating glutathione metabolism. Methods. Human pulp cells were used and oxygen consumption was measured by means of a Clark electrode. Moreover, reactive oxygen species production was quantified. Enzymatic activity and glucose and lactate concentrations were determined through a specific kit. Results. Triethylene glycol dimethacrylate, 1,4-butanediol dimethacrylate, and 2-hydroxyethyl methacrylate induced a decrease in oxygen consumption rate, an enhancement of glucose consumption, and lactate production, whilst glucose 6-phosphate dehydrogenase and glutathione reductase activity were not significantly modified. Moreover, the monomers induced an increase of reactive oxygen species production with a consequent increase of superoxide dismutase and catalase enzymatic activities. A depletion of both reduced and total glutathione was also observed. Conclusion. The obtained results indicate that dental monomers might alter energy metabolism and glutathione redox balance in human pulp cells.

Urethane dimethacrylate induces cytotoxicity and regulates cyclooxygenase-2, hemeoxygenase and carboxylesterase expression in human dental pulp cells

The toxic effect of urethane dimethacrylate (UDMA), a major dental resin monomer, on human dental pulp is not fully clear. In this study, we investigated the influence of UDMA on the cytotoxicity, cell cycle distribution, apoptosis and related gene expression of dental pulp cells. The role of reactive oxygen species, hemeoxygenase-1 (HO-1) and carboxylesterase (CES) in UDMA cytotoxicity, was evaluated. UDMA induced morphological changes of pulp cells and decreased cell viability by 29-49% at concentrations of 0.1-0.35 mM. UDMA induced G0/G1, G2/M cell cycle arrest and apoptosis. The expression of cdc2, cyclinB1 and cdc25C was inhibited by UDMA. Moreover, UDMA stimulated COX-2, HO-1 and CES2 mRNA expression of pulp cells. The cytotoxicity of UDMA was attenuated by N-acetyl-l-cysteine, catalase and esterase, but was enhanced by Zn-protoporphyrin (HO-1 inhibitor), BNPP (CES inhibitor) and loperamide (CES2 inhibitor). Exposure of UDMA may potentially induce the inflammation and toxicity of dental pulp. These findings are important for understanding the clinical response of human pulp to resin monomers after operative restoration and pulp capping, and also provide clues for improvement of dental materials.

Mechanism of detoxification of the cationic antibacterial monomer 12-methacryloyloxydodecylpyridiniumbromide (MDPB) by N-acetyl cysteine

OBJECTIVES

The protective effects of N-acetyl cysteine (NAC) against cytotoxicity induced by conventional dental resin monomers have been widely documented. However, its effectiveness to detoxify cationic antibacterial monomers has not yet been elucidated. The aim of the present study was to investigate the possible protective effects of NAC against the cytotoxicity of 12-methacryloyloxydodecylpyridiniumbromide (MDPB) and explore the role of adduct formation in NAC-directed detoxification.

METHODS

The influences of NAC on the cytotoxicity of MDPB were studied in mouse osteoblast-like MC3T3-E1 cells using the MTT assay. Ultra-performance liquid chromatography (UPLC) and liquid chromatography-mass spectrometry (LC-MS) analysis were performed to investigate the possible chemical reaction between NAC and MDPB.

RESULTS

While only slight reduction in the cytotoxicity of MDPB by NAC was observed immediately after mixing with MDPB, remarkable protection against MDPB-induced cell death was detected when the mixture was tested after 24h of pre-incubation. UPLC and LC-MS analysis revealed that chemical binding of MDPB and NAC occurred under neutral conditions after 24h of pre-incubation.

SIGNIFICANCE

Our findings suggest that NAC reduces the toxicity of the cationic antibacterial monomer MDPB, and adduct formation is partially responsible for the detoxification ability of NAC against MDPB-induced cell damage.

Hace1 controls ROS generation of vertebrate Rac1-dependent NADPH oxidase complexes

The Hace1-HECT E3 ligase is a tumor suppressor that ubiquitylates the activated GTP-bound form of the Rho family GTPase Rac1, leading to Rac1 proteasomal degradation. Here we show that, in vertebrates, Hace1 targets Rac1 for degradation when Rac1 is localized to the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase holoenzyme. This event blocks de novo reactive oxygen species generation by Rac1-dependent NADPH oxidases, and thereby confers cellular protection from reactive oxygen species-induced DNA damage and cyclin D1-driven hyper-proliferation. Genetic inactivation of Hace1 in mice or zebrafish, as well as Hace1 loss in human tumor cell lines or primary murine or human tumors, leads to chronic NADPH oxidase-dependent reactive oxygen species elevation, DNA damage responses and enhanced cyclin D1 expression. Our data reveal a conserved ubiquitin-dependent molecular mechanism that controls the activity of Rac1-dependent NADPH oxidase complexes, and thus constitutes the first known example of a tumor suppressor protein that directly regulates reactive oxygen species production in vertebrates.

Butyrate induces reactive oxygen species production and affects cell cycle progression in human gingival fibroblasts

BACKGROUND AND OBJECTIVE

Short-chain fatty acids, such as butyric acid and propionic acid, are metabolic by-products generated by periodontal microflora such as Porphyromonas gingivalis, and contribute to the pathogenesis of periodontitis. However, the effects of butyrate on the biological activities of gingival fibroblasts (GFs) are not well elucidated.

MATERIAL AND METHODS

Human GFs were exposed to various concentrations of butyrate (0.5-16 mm) for 24 h. Viable cells that excluded trypan blue were counted. Cell cycle distribution of GFs was analyzed by propidium iodide-staining flow cytometry. Cellular reactive oxygen species (ROS) production was measured by flow cytometry using 2',7'-dichlorofluorescein (DCF). Total RNA and protein lysates were isolated and subjected to RT-PCR using specific primers or to western blotting using specific antibodies, respectively.

RESULTS

Butyrate inhibited the growth of GFs, as indicated by a decrease in the number of viable cells. This event was associated with an induction of G0/G1 and G2/M cell cycle arrest by butyrate (4-16 mm) in GFs. However, no marked apoptosis of GFs was noted in this experimental condition. Butyrate (> 2 mm) inhibited the expression of cdc2, cdc25C and cyclinB1 mRNAs and reduced the levels of Cdc2, Cdc25C and cyclinB1 proteins in GFs, as determined using RT-PCR and western blotting, respectively. This toxic effect of butyrate was associated with the production of ROS.

CONCLUSION

These results suggest that butyrate generated by periodontal pathogens may be involved in the pathogenesis of periodontal diseases via the induction of ROS production and the impairment of cell growth, cell cycle progression and expression of cell cycle-related genes in GFs. These events are important in the initiation and prolongation of inflammatory processes in periodontal diseases.

Carboxylesterase expression in human dental pulp cells: role in regulation of BisGMA-induced prostanoid production and cytotoxicity

Biocompatibility of dentin bonding agents (DBA) and composite resin may affect the treatment outcome (e.g., healthy pulp, pulpal inflammation, pulp necrosis) after operative restoration. Bisphenol-glycidyl methacrylate (BisGMA) is one of the major monomers present in DBA and resin. Prior studies focused on salivary esterase for metabolism and degradation of resin monomers clinically. This study found that human dental pulp cells expressed mainly carboxylesterase-2 (CES2) and smaller amounts of CES1A1 and CES3 isoforms. Exposure to BisGMA stimulated CES isoforms expression of pulp cells, and this event was inhibited by catalase. Exogenous addition of porcine esterase prevented BisGMA- and DBA-induced cytotoxicity. Interestingly, inhibition of CES by bis(p-nitrophenyl) phosphate (BNPP) and CES2 by loperamide enhanced the cytotoxicity of BisGMA and DBA. Addition of porcine esterase or N-acetyl-l-cysteine prevented BisGMA-induced prostaglandin E(2) (PGE(2)) and PGF(2α) production. In contrast, addition of BNPP and loperamide, but not mevastatin, enhanced BisGMA-induced PGE(2) and PGF(2α) production in dental pulp cells. These results suggest that BisGMA may induce the cytotoxicity and prostanoid production of pulp cells, leading to pulpal inflammation or necrosis via reactive oxygen species production. Expression of CES, especially CES2, in dental pulp cells can be an adaptive response to protect dental pulp against BisGMA-induced cytotoxicity and prostanoid release. Resin monomers are the main toxic components in DBA, and the ester group is crucial for monomer toxicity.

The cytotoxicity of methacryloxylethyl cetyl ammonium chloride, a cationic antibacterial monomer, is related to oxidative stress and the intrinsic mitochondrial apoptotic pathway

Antibacterial monomers incorporated in dentin bonding systems may have toxic effects on the pulp. Thus, the cytotoxicity of antibacterial monomers and its underlying mechanisms must be elucidated to improve the safety of antibacterial monomer application. The influence of an antibacterial monomer, methacryloxylethyl cetyl ammonium chloride (DMAE-CB), on the vitality of L929 mouse fibroblasts was tested using MTT assay. Cell cycle progression was studied using flow cytometry. Production of intracellular reactive oxygen species (ROS) after DMAE-CB treatment was measured using 2,7-dichlorodihydrofluorescein diacetate staining and flow cytometry analysis. Loss of mitochondrial membrane potential, disturbance of Bcl-2 and Bax expression, as well as release of cytochrome C were also measured using flow cytometry analysis or Western blot to explore the possible involvement of the mitochondrial-related apoptotic pathway. DMAE-CB elicited cell death in a dose-dependent manner and more than 50% of cells were killed after treatment with 30 µM of the monomer. Both necrosis and apoptosis were observed. DMAE-CB also induced G1- and G2-phase arrest. Increased levels of intracellular ROS were observed after 1 h and this overproduction was further enhanced by 6-h treatment with the monomer. DMAE-CB may cause apoptosis by disturbing the expression of Bcl-2 and Bax, reducing the mitochondrial potential and inducing release of cytochrome C. Taken together, these findings suggest that the toxicity of the antibacterial monomer DMAE-CB is associated with ROS production, mitochondrial dysfunction, cell cycle disturbance, and cell apoptosis/necrosis.

The role of reactive oxygen species and hemeoxygenase-1 expression in the cytotoxicity, cell cycle alteration and apoptosis of dental pulp cells induced by BisGMA

Biocompatibility of dentin bonding agents (DBAs) and resin composite is important to preserve the pulp vitality after operative restoration. Bisphenol-glycidyl-methacrylate (BisGMA) is one common monomer adding into DBAs and resin. In this study, we found that exposure of human dental pulp cells to BisGMA (>0.1 mM) led to cytotoxicity, G2/M cell cycle arrest and apoptosis as analyzed by propidium iodide (PI) and PI/annexin V dual fluorescent flow cytometry. These events were associated with a decline of cdc2, cdc25C and cyclinB1 expression at both mRNA and protein levels. BisGMA also induced the expression of hemeoxygenase-1 (HO-1), an oxidative stress responsive gene, in pulp cells. Catalase could prevent the BisGMA-induced alteration of cell cycle-related genes (cdc2, cdc25C, cyclinB1) and HO-1 expression in dental pulp cells. Interestingly, Zn-protoporphyrin (2.5-5 microM), a HO inhibitor, enhanced the BisGMA-induced reactive oxygen species (ROS) production and cytotoxicity. These results suggest that exposure to higher concentrations of BisGMA may stimulate ROS production, cell cycle arrest, apoptosis and cell death. Inducing the expression of HO-1 in dental pulp cells by BisGMA is mediated by ROS production and important to protect dental pulp against the toxicity by monomers present in composite resin and DBAs.