Synergistic effects of H2O2 with components of dental restorative materials on gluconeogenesis in rat kidney tubules

Effect of bleaching agent extracts on murine macrophages

OBJECTIVES

The aim of this study was to evaluate the cytotoxicity and the influence of bleaching agents on immunologically cell surface antigens of murine macrophages in vitro.

MATERIALS AND METHODS

RAW 264.7 cells were exposed to bleaching gel extracts (40% hydrogen peroxide or 20% carbamide peroxide) and different H₂O₂ concentrations after 1 and 24-h exposure periods and 1-h exposure and 23-h recovery. Tests were performed with and without N-acetyl cysteine (NAC) and buthionine sulfoximine (BSO). Cell viability was determined by MTT assay. The expression of surface markers CD14, CD40, and CD54 with and without LPS stimulation was detected by flow cytometry, while the production of TNF-α was measured by ELISA. Statistical analysis was performed using the Mann-Whitney U test (α = 0.05).

RESULTS

Extracts of bleaching agents were cytotoxic for cells after a 1-h exposure; cells could not recover after 24 h. This effect can be mitigated by the antioxidant NAC and increased by BSO, an inhibitor of glutathione (GSH) synthesis. LPS stimulated expression of all surface markers and TNF-α production. Exposure to bleaching agent extracts and H₂O₂ leads to a reduction of TNF-α, CD14, and CD40 expression, while the expression of CD54 was upregulated at non-cytotoxic concentrations. Whereas NAC reduced this effect, it was increased in the presence of BSO.

CONCLUSIONS

Extracts of bleaching agents were irreversibly cytotoxic to macrophages after a 1-h exposure. Only the expression of CD54 was upregulated. The reactions are mediated by the non-enzymatic antioxidant GSH.

CLINICAL RELEVANCE

The addition of an antioxidant can downregulate unfavorable effects of dental bleaching.

NAC ameliorates dental composite-induced DNA double-strand breaks and chromatin condensation

Released (co)monomers from dental composite components can induce DNA damage of which DNA double-strand breaks (DSBs) threaten genome integrity. Here, we tested whether the administration of the antioxidant N-acetylcysteine (NAC) is able to reduce the dental composite-induced DSBs in primary human gingiva fibroblasts. The dental composites Bis-GMA (bisphenol-A-glycerolate dimethacrylate), GMA (glycidyl methacrylate), HEMA (2-hydroxyethyl methacrylate) and TEGDMA (triethyleneglycol dimethacrylate) were found to induce co-localizing microscopic nuclear foci numbers of the DSB markers γ-H2AX and 53BP1 per cell in the order: GMA>Bis-GMA>TEGDMA>HEMA. Supplementation of (co)monomer-containing culture medium with NAC led to a significant reduction of resin-induced DSBs as well as to an amelioration of dental monomer-induced nuclear chromatin condensation in gingival fibroblasts. Thus, antioxidant treatment can reduce radical-induced chromatin and DNA damage and open avenues to mitigate genotoxic effects of dental composite compounds.

Real-time xCELLigence impedance analysis of the cytotoxicity of dental composite components on human gingival fibroblasts

OBJECTIVES

Aim of this study was by continuous monitoring to assay the proliferative capacity of human gingival fibroblasts (HGFs), to investigate cytotoxicity of the most common monomers/comonomers in dental resin composites: bisphenol-A-glycidylmethacrylate (BisGMA), hydroxyethylenemethacrylate (HEMA), triethyleneglycoldimethacrylate (TEGDMA), and urethanedimethacrylate (UDMA) in HGFs during 24h exposure using the xCELLigence system.

METHODS

xCELLigence cell index (CI) impedance measurements were performed according to the instructions of the supplier. HGFs were resuspended in medium and subsequently adjusted to 400,000, 200,000, 100,000, and 50,000 cells/mL. After seeding 100 microL of the cell suspensions into the wells of the E-plate 96, HGFs were monitored every 15 min for a period of up to 18 h by the xCELLigence system.

RESULTS

Half maximum effect concentrations (EC(50)) were determined based on the dose-response curves derived by xCELLigence measurements. Following real-time analysis, significantly increased EC(50) values of HGFs exposed for 24h to the following substances were obtained: HEMA(a), TEGDMA(b), UDMA(c). The EC(50) values (mean [mmol/L]+/-S.E.M.; n=5) were: HEMA 11.20+/-0.3, TEGDMA(a) 3.61+/-0.2, UDMA(a,b) 0.20+/-0.1, and BisGMA(a,b,c) 0.08+/-0.1. These results are similar to the EC(50) values previously observed with the XTT end-point assay.

SIGNIFICANCE

Our data suggests that the xCELLigence live cell analysis system offers dynamic live cell monitoring and combines high data acquisition rates with ease of handling. Therefore, the xCELLigence system can be used as a rapid monitoring tool for cellular viability and be applied in toxicity testing of xenobiotics using in vitro cell cultures.

In vitro and in vivo studies on the toxicity of dental resin components: a review

In vitro and in vivo studies have clearly identified that some components of restorative composite resins, adhesives, and resin-modified glass ionomer cements are toxic. The mechanisms of cytotoxicity are related firstly to the short-term release of free monomers occurring during the monomer-polymer conversion. Secondly, long-term release of leachable substances is generated by erosion and degradation over time. In addition, ion release and proliferation of bacteria located at the interface between the restorative material and dental tissues are also implicated in the tissue response. Molecular mechanisms involve glutathione depletion and reactive oxygen species (ROS) production as key factors leading to pulp or gingival cell apoptosis. Experimental animal approaches substantiate the occurrence of allergic reactions. There is a large gap between the results published by research laboratories and clinical reports.

Toxicity potentiation by H2O2 with components of dental restorative materials on human oral cells

Toxicity potentiation of two monomers [bisphenol-A-glycidyldimethacrylate (BisGMA) and urethanedimethacrylate (UDMA)] as well as two comonomers [triethyleneglycoldimethacrylate (TEGDMA) and 2-hydroxyethylmethacrylate (HEMA)], each in combination with H(2)O(2), was investigated on the viability on human gingival fibroblasts (HGF) and human pulpal fibroblasts (HPF). The applied concentration of H(2)O(2) was 0.06 or 0.1 mmol/l, respectively, corresponding to the EC(0) of H(2)O(2) in HGF or HPF. The cell viability was assessed by the XTT test. From this test the half maximum effect concentrations (EC(50)) were calculated from fitted sigmoidale curves. EC(50) values were (HGF; mmol/l; mean +/- s.e.m.; n = 5): HEMA 11.9 +/- 0.9, TEGDMA 3.7 +/- 0.3, H(2)O(2) 0.36 +/- 0.04, UDMA 0.27 +/- 0.08, and BisGMA 0.11 +/- 0.03. No significant (P < 0.05) differences in the EC(50) values were observed when HGF was exposed to substances, as compared to HPF. No significant decrease of the EC(50) values was found when HGF or HPF, respectively, was exposed to HEMA or BisGMA in addition with H(2)O(2) up to the concentration of 0.1 mmol/l, as compared to those EC(50) values of each compound without H(2)O(2) addition. A significant decrease of the TEGDMA EC(50) value from 3.7 to 2.1 or 0.4 mmol/l, respectively, was found when cells were exposed to TEGDMA in combination with H(2)O(2) (0.06 or 0.1 mmol/l), as compared to that TEGDMA EC(50) value without H(2)O(2) addition. A significant decrease of the UDMA EC(50) value from 0.27 to 0.11 or 0.08 mmol/l, respectively, was found when HGF or HPF was exposed to UDMA in combination with H(2)O(2) (0.06 or 0.1 mmol/l), as compared to that UDMA EC(50) value without H(2)O(2) addition. The addition of H(2)O(2) (0.06 or 0.1 mmol/l) resulted in a toxicity potentiation of TEGDMA and UDMA, but not of HEMA and BisGMA, on HGF or HPF.

Effects of combinations of ROS scavengers on oxidative DNA damage caused by visible-light-activated camphorquinone/N,N-dimethyl-p-toluidine

The objective of this investigation was to analyze whether various combinations of the ROS scavengers glutathione (GSH), N-acetyl-cysteine (NAC), and vitamins C and E decrease DNA damage due to visible-light-irradiated (VL-irradiated) camphorquinone/N,N-dimethyl-p-toluidine (CQ/DMT) compared with individual vitamin C or E. PhiX-174 RF plasmid DNA was used to determine single and double strand breaks as parameters of DNA damage. Individual ROS scavengers and combinations of the antioxidants were added to plasmid DNA treated with VL-irradiated CQ/DMT/Cu (II). After incubation, DNA was loaded into a 1% agarose gel. Following electrophoresis, gels stained with 0.5 microg/mL ethidium bromide were photographed under ultraviolet illumination and analyzed with NIH ImageJ software. Results were evaluated between groups for statistical significance using Student's paired t-test (p < 0.05). Glutathione significantly reduced oxidative DNA damage at all test concentrations when combined with vitamin C or vitamin E. The concentration of damaged DNA observed in the presence of combinations of GSH with vitamin C or vitamin E was significantly lower compared with all other combinations of antioxidants investigated in our study (p < 0.05). In contrast to GSH, NAC was not able to compensate the pro-oxidative effects of vitamin C and vitamin E. Only at a concentration of 2 mM, NAC combined with vitamin C efficiently prevented CQ/DMT/Cu (II)-associated DNA damage. Our data indicate that solely the combinations of GSH with vitamin C or vitamin E significantly reduce the severity of oxidative DNA damage caused by CQ/DMT, whereas NAC may even increase the pro-oxidant activity of vitamin C and vitamin E.

Additive effects of TEGDMA and hydrogenperoxide on the cellular glutathione content of human gingival fibroblasts

OBJECTIVES

Only few data are available about cytotoxic effects of leachable dental resin compounds in combination with hydrogen peroxide (H(2)O(2)) segregated from dental bleaching agents. Therefore, the purpose of this study was to evaluate the effects of various concentrations of triethylene-glycol dimethacrylate (TEGDMA) and H(2)O(2) on intracellular glutathione levels (GSH) and viability of human gingival fibroblasts (HGF) that are primary target cells of cytotoxic actions of these substances.

METHODS

HGF were grown in 96-well plates for 24h, treated with various concentrations of TEGDMA (0.5-5.0mM) for 24h and subsequently for 90min with 0.2mM H(2)O(2) or culture medium (control). The relative intracellular GSH concentration was determined using a fluorescence assay with monobromobimane. Readings were normalized to cell numbers, which were determined by a propidium iodide assay. Data were statistically analyzed by t-test and ANOVA with Tukey's post test. A significance level of p<0.05 was used.

RESULTS

Exposure to TEGDMA reduced the viability of HGF at concentrations > or =1.0mM. TEGDMA induced a decrease of the GSH pool in a concentration-dependent manner (p<0.05). The depletion of GSH was correlated with a reduction of viability (p<0.05) and the total cell number. Furthermore, a significant decrease of the intracellular GSH content was found when cells were exposed to TEGDMA in combination with H(2)O(2), compared to experiments without H(2)O(2).

SIGNIFICANCE

We conclude from our findings that TEGDMA and H(2)O(2) have additive adverse effects on GSH metabolism and cell viability.

In vitro embryotoxicity assessment with dental restorative materials

OBJECTIVES

Resin (co)monomers may be released from restorative dental materials and can diffuse into the tooth pulp or the gingiva, and can reach the saliva and the circulating blood. Genotoxic potential of some dental composite components has been clearly documented. The genotoxic effects of xenobiotics can represent a possible step in tumor initiation and/or embryotoxicity/teratogenesis. A modified fluorescent mouse embryonic stem cell test (R.E.Tox) was used to test the embryotoxic potential of following dental restorative materials: Bisphenol A glycidylmethacrylate (BisGMA), urethanedimethacrylate (UDMA), hydroxyethylmethacrylate (HEMA), and triethyleneglycoldimethacrylate (TEGDMA), as well as some of their metabolic intermediates 2,3-epoxy-2-methyl-propionicacid-methylester (EMPME), methacrylic acid (MA), and 2,3-epoxy-2-methylpropionic acid (EMPA).

METHODS

Mouse embryonic stem (ES) cells stably transfected with a vector containing the gene for the green fluorescent protein under control of the cardiac alpha-myosin heavy chain promoter were differentiated in the presence of various concentrations of the test compounds for 12 days. Fluorescence was measured using the TECAN Safire and values were expressed as percent of control values. To distinguish between cytotoxic and embryotoxic effects, all compounds were tested in a standard MTT assay.

RESULTS

HEMA, TEGDMA and EMPME did not influence the differentiation process of ES cells towards cardiac myocytes. No cytotoxic effects were observed at any of the concentration levels tested. Exposure to BisGMA resulted in a 50% decrease in cell survival and a very strong inhibition of cell differentiation at 10(-5)M (p<0.01). Embryotoxic effects were also present at 10(-6) and 10(-7)M (p<0.05). EMPA induced a decrease in ES cell differentiation at 10(-5)M (p<0.01) without cytotoxic effects. No embryotoxic effects were induced at lower concentrations. Exposure to UDMA resulted in a slight decrease of cell differentiation at 10(-5)M (p<0.05). Exposure of cells to MA resulted in an increase of cardiac differentiation up to 150% (p<0.05) at 10(-5)M without cytotoxic effects.

CONCLUSIONS

BisGMA induced a significant high embryotoxic/teratogenic effect over a large range of concentration. Therefore attention should be focused on this dental monomer, which should be investigated further by in vivo experiments.

ROS formation and glutathione levels in human oral fibroblasts exposed to TEGDMA and camphorquinone

Glutathione (GSH) is important for the self-protection of cells against oxidative stress and toxic xenobiotics, whereas reactive oxygen species (ROS) at elevated concentrations may cause detrimental alterations of cell membranes, DNA, and other cellular structures. The present investigation addressed the effects of triethylene-glycoldimethacrylate (TEGDMA) and camphorquinone (CQ) on glutathione metabolism and the formation of ROS in oral cells. Primary human pulp fibroblasts were exposed to various concentrations of TEGDMA and CQ (0.1-5 mM). Subsequently, GSH concentration and ROS formation were analyzed with the use of the monobromobimane assay (GSH) and 2',7'-dichlorofluorescein diacetate (DCFH-DA) (ROS). The endogenous ROS hydrogen peroxide (H2O2) was used as a positive control (0.02-2 mM). TEGDMA significantly decreased GSH at concentrations between 0.5 and 5 mM (p<0.05), but did not elevate ROS levels. Contrary, CQ increased ROS formation at concentrations>or=1 mM, but had only a moderate effect on GSH at the highest test concentration. Hydrogen peroxide increased ROS and simultaneously decreased GSH at concentrations of >or=0.2 mM. These data show that the investigated substances may cause cell damage due to various mechanisms, GSH decrease and/or ROS increase. As a consequence, TEGDMA and CQ released into an aqueous environment from resinous materials might interact, thus generating significant cytotoxic effects even at low concentrations.