Induction of c-fos and c-jun protooncogenes expression by formaldehyde-releasing and epoxy resin-based root-canal sealers in human osteoblastic cells

Genotoxicity of root canal sealers: a literature review

OBJECTIVES

Root canal sealers are widely used worldwide in endodontics to prevent reinfection and growth of surviving microorganisms. Considering the strong correlation between genetic damage and carcinogenesis, evaluation of genotoxicity induced by endodontic sealers is recommended for elucidating the true health risks to patients and professionals. The purpose of this article was to provide a comprehensive review of studies involving genotoxicity analysis of endodontic sealers and the used methodologies.

MATERIALS AND METHODS

A literature search was made in PubMed using the following combination of words "genotoxicity," "mutagenicity," "endodontic sealers," and "root canal sealers." A total of 39 articles with genotoxicity studies were selected for the present study.

RESULTS

Sealers have been ranked in decreasing order of their genotoxicity as: ZOE sealers > GIC sealers > S sealers > ER sealers > MR sealers > Novel sealers > CH sealers > CS sealers.

CONCLUSIONS

All published data showed some evidence of genotoxicity for most of the commercial root canal sealers; however, contradictory results were found, mainly for AH Plus, the most studied sealer.

CLINICAL RELEVANCE

The information provided would direct the endodontists to use the less genotoxic materials in endodontic treatment in a way to reduce DNA damage promoting oral healthcare.

Cytotoxicity, genotoxicity and antibacterial effectiveness of a bioceramic endodontic sealer

AIM

To compare the characteristics of bioceramic endodontic sealer Endosequence BC sealer with those of AH Plus sealer.

METHODOLOGY

Cytotoxicity and genotoxicity were analysed on human gingival fibroblasts submitted to cell culture medium conditioned by sealers using the MTT reduction assay and micronucleus formation test (MNT), respectively. Cells grown on fresh medium served as controls. Cell viabilities were measured at 1, 3, 5 and 7 days. The antibacterial activity was analysed on an Enterococcus faecalis strain (ATCC 29212) using both on agar diffusion test (ADT) and a direct contact test (DCT). The inhibition zones in ADT were measured after 48 h and the colony-forming units counting in the DCT after 1, 24, 72 and 168 h. Data were compared by anova and Tukey's test and MNT by Fisher's exact test (P < 0.05).

RESULTS

Cultures submitted to Endosequence BC sealer had a significantly higher number of viable cells (P < 0.01) and less micronucleus formation (P < 0.05) than AH Plus sealer. Endosequence BC sealer exhibited significantly smaller inhibition zones (6.00 ± 0.03 mm) than AH Plus sealer (10.31 ± 0.21 mm) (P < 0.05). Moreover, Endosequence BC sealer had significantly smaller antibacterial activity than AH Plus sealer up to 1 h of direct contact (P < 0.05). On other exposure times, both materials had similar antibacterial effectiveness (P > 0.05).

CONCLUSIONS

Bioceramic-based sealer had less cytotoxicity and genotoxicity and similar antibacterial effect against E. faecalis in comparison with AH Plus sealer.

A comparative evaluation of cytotoxicity of root canal sealers: an in vitro study

OBJECTIVES

The objective of this in vitro study was to evaluate and compare the cytotoxicity of four different root canal sealers i.e. Apexit Plus (Ivoclar Vivadent), Endomethasone N (Septodont), AH-26 (Dentsply) and Pulpdent Root Canal Sealer (Pulpdent), on a mouse fibroblast cell line (L929).

MATERIALS AND METHODS

Thirty two discs for each sealer (5 mm in diameter and 2 mm in height) were fabricated in Teflon mould. The sealer extraction was made in cell culture medium (Dulbecco's Modified Eagle's Medium, DMEM) using the ratio 1.25 cm(2)/mL between the surface of the sealer samples and the volume of medium in a shaker incubator. Extraction of each sealer was obtained at 24 hr, 7th day, 14th day, and one month of interval. These extracts were incubated with L929 cell line and 3-(4,5-dimethylthiazol-2yl)-2,5-diphenyltetrazolium bromide (MTT) assay was done. Two-way ANOVA for interaction effects between sealer and time and Post-hoc multiple comparison using Tukey's test across all the 16 different groups were used for statistical analysis.

RESULTS

Apexit Plus root canal sealer was significantly less toxic than other sealers (p < 0.05) and showed higher cellular growth than control. Endomethasone N showed mild cytotoxicity. AH-26 showed severe toxicity which became mild after one month while Pulpdent Root Canal Sealer showed severe to moderate toxicity.

CONCLUSIONS

Apexit Plus was relatively biocompatible sealer as compared to other three sealers which were cytotoxic at their initial stages, however, they became biocompatible with time.

Inhibitory effects of bioactive leads isolated from Pseudomonas aeruginosa PS3 and Pseudomonas fluorescens PS7 on MAP kinases and down regulation of pro inflammatory cytokines (TNF-α, IL-1β) and mediators (NO, iNOS and COX)

Pure lead molecules, showing anti-inflammatory effect were isolated from the marine Pseudomonas aeruginosa PS3 (GenBank Accession No. EF488968) and Pseudomonas fluorescens PS7 (GenBank Accession No. EF488969) using solvent extraction procedures, subsequent column fractionation, followed by bio activity based screening. The structures of the lead molecules (3S, 8aS)-3-isobutylhexahydropyrrolo[1,2-a]pyrazine-1,4-dione (Compound 1) and (8aS)-3-(4-hydroxybenyl) hexahydropyrrolo[1,2-a]pyrazine-1,4-dione (Compound 2) obtained from P. aeruginosa PS3 and P. fluorescens PS7 respectively were established employing spectral analysis. Compounds 1 and 2 at their IC(50) values of 84 and 53μM concentrations respectively down regulated expression of tumor necrosis factor-α (TNF-α) and interleukin 1-β (IL-1β) in peripheral blood mononuclear cells (PBMCs) and inducible nitric oxide synthase (iNOS) gene in RAW 264.7 cells. Immunoblot analysis revealed the inhibitory effect of pure compounds on phosphorylation of all the three mitogen activated protein kinases (MAPK) such as ERK, JNK and p38 MAPK. The results of the present investigation revealed that the pure compounds are anti-inflammatory in nature.

Bioactive materials in endodontics

Endodontic treatment in dentistry is a delicate procedure and many treatment attempts fail. Despite constant development of new root canal filling techniques, the clinician is confronted with both a complex root canal system and the use of filling materials that are harmful for periapical tissues. This paper evaluates reported studies on biomaterials used in endodontics, including calcium hydroxide, mineral trioxide aggregate, calcium phosphate ceramics and calcium phosphate cements. Special emphasis is made on promising new biomaterials, such as injectable bone substitute and injectable calcium phosphate cements. These materials, which combine biocompatibility, bioactivity and rheological properties, could be good alternatives in endodontics as root canal fillers. They could also be used as drug-delivery vehicles (e.g., for antibiotics and growth factors) or as scaffolds in pulp tissue engineering.

Mechanisms of root canal sealers cytotoxicity on osteoblastic cell line MC3T3-E1

OBJECTIVE

The cytotoxic mechanisms of root canal sealers (Sealapex, AH26, and N2 Universal) were studied in vitro with MC3T3-E1 osteoblastic cells.

STUDY DESIGN

MC3T3-E1 cells were cotreated with root canal sealers and antioxidants, and concentrations of intracellular glutathione (GSH) and reactive oxygen species (ROS) were measured. DNA fragmentation was observed after treatment with the sealers.

RESULTS

N-Acetylcysteine (NAC) prevented N2 Universal- and AH26-induced cytotoxicities. However, ascorbic acid and Trolox did not affect the cytotoxicity of the sealers. N2 Universal and AH26 significantly decreased the GSH pool within a 3-hour treatment period. Unlike GSH levels, the ROS levels were not altered by the sealers. Cytotoxicity of Sealapex was not affected by NAC, and there were no changes of GSH/glutathione disulfide levels in cells treated with Sealapex.

CONCLUSION

Cytotoxicities of N2 Universal and AH26 are caused by an intracellular GSH depletion without a burst of ROS. Sealapex may cause cytotoxicity in a way different from N2 Universal and AH26.

Induction of heme oxygenase-1 expression by root canal sealers in human gingival fibroblasts is augmented by oxidative stress

Heme oxygenase-1 (HO-1) is known as a stress-inducible protein and functions as an antioxidant enzyme. It has been shown that HO-1 is induced rapidly by a variety of chemical and physical stimuli. However, little is known about the induction of cellular signaling events after cell exposure to root canal sealers. The aim of this study was to investigate the effects of zinc oxide-eugenol-based root canal sealer N2 and epoxy resin-based root canal sealer Topseal on the expression of HO-1 protein in cultured human gingival fibroblasts (HGFs). The results showed that both N2 and Topseal were cytotoxic to HGFs in a concentration-dependent manner (p < 0.05). The exposure of quiescent HGFs to N2 and Topseal resulted in the induction of HO-1 protein expression in a time-dependent manner (p < 0.05). Furthermore, to determine whether oxidative stress could modulate HO-1 expression in HGFs by root canal sealers, HGFs were pretreated with glutathione (GSH) synthesis precursor 2-oxothiazolidine-4-carboxylic acid (OTZ) and GSH synthesis inhibitor buthionine sulfoximine (BSO) for 24 h. The pretreatment with OTZ decreased the N2-induced HO-1 protein level by approximately 32% (p < 0.05). However, BSO enhanced the N2-induced HO-1 protein level by up to twofold (p < 0.05). Similar results were found by Topseal. The pretreatment with OTZ decreased the Topseal-induced HO-1 protein level by approximately 12% (p < 0.05). However, BSO enhanced the Topseal-induced HO-1 protein level by up to 1.7-fold (p < 0.05). Taken together, HO-1 expression might be one signal transduction pathway linked to the induction of stress-inducible protein by root canal sealers. In addition, the activation of HO-1 is augmented by oxidative stress. Factors that induce GSH synthesis may appear useful in preventing oxidative damage mediated by root canal sealers.

Induction of Interleukin-6 and Interleukin-8 Gene Expression by Root Canal Sealers in Human Osteoblastic Cells

Histological investigations have demonstrated that root canal sealers can induce mild to severe inflammatory alternations. However, there is little information on the precise mechanisms about root canal sealers-induced inflammatory reaction. Dysregulated cytokine productions at local disease sites have been considered to be major contributors to the development of inflammatory diseases. Interleukin (IL)-6 and IL-8 released have been reported to play an important role in the pathogenesis of inflammation. The aim of this study was to investigate the effects of root canal sealers N2 (zinc-oxide eugenol based) and AH Plus (epoxy resin based) on the expression of IL-6 and IL-8 mRNA gene in human osteoblastic cell line U2OS cells. The levels of mRNAs were measured by the semi-quantitative reverse-transcriptase polymerase chain reaction analysis. The exposure of quiescent U2OS cells to N2 and AH Plus resulted in the induction of IL-6 and IL-8 mRNA gene expression (p < 0.05). The intensity of IL-8 mRNA gene was found to be significant higher than IL-6 mRNA gene (p < 0.05). Taken together, the activation of IL-6 and IL-8 mRNA gene expression may be one of the pathogenesis of zinc oxide-eugenol based and epoxy resin based root canal sealers-induced periapical inflammation.

Inhibition of MAP kinases by crude extract and pure compound isolated from Commiphora mukul leads to down regulation of TNF-alpha, IL-1beta and IL-2

The anti-inflammatory effect of the medicinal plant, Commiphora mukul gum was studied in peripheral blood mononuclear cells (PBMC). Bioassay-guided fractionation using conventional solvent extraction procedures, subsequent column fractionation, followed by monitoring specific activity in PBMC led to the isolation of a lead compound. Both crude ethyl acetate extract and the lead compound, thus isolated, showed inhibitory effect on proliferative response of PBMC in mitogenic lymphocyte proliferation and MLR assays. Further studies on inflammatory mediators such as IFN-gamma, IL-12, TNF-alpha, IL-1beta and NO showed down regulation, whereas no inhibition was observed in the case of anti-inflammatory cytokine IL-10. Immunoblot analysis revealed the inhibitory effect of crude ethyl acetate extract on phosphorylation of all the three mitogen activated protein kinases (MAPK) such as ERK, JNK and p38 MAPK. In contrast treatment with pure compound showed no inhibitory effect on ERK. c-fos and c-jun mRNA levels were also reduced in PMA stimulated cells on treatment with crude extract and pure compound. This reduction in c-fos and c-jun levels, when taken together with inhibition of MAPK activation, provides a possible mechanism by which both crude ethyl acetate extract and purified compound isolated from C. mukul exert its action.

Prevention of the epoxy resin-based root canal sealers-induced cyclooxygenase-2 expression and cytotoxicity of human osteoblastic cells by various antioxidants

Cyclooxygenase-2 (COX-2) is an inducible enzyme believed to be responsible for prostaglandin synthesis at the site of inflammation. Recently, the activation of COX-2 expression may be one of the important pathogenesis of root canal sealers-induced periapical inflammation. However, little is known about whether chemical interaction can modulate the epoxy resin-based root canal sealers-induced cytotoxicity as well as COX-2 expression. The aim of the present study was to investigate the effects of antioxidants catalase, superoxide dismutase (SOD), and N-acetyl-L-cysteine (NAC) on AH26- and Topseal-induced COX-2 mRNA gene and cytotoxicity in human osteoblastic cell line U2OS cells. The results showed that both epoxy resin-based root canal sealers were cytotoxic to U2OS cells in a concentration-dependent manner (p<0.05). AH26 and Topseal were found to induce COX-2 mRNA gene expression in U2OS cells. The addition of glutathione (GSH) precursor NAC led to decrease the induction of COX-2 mRNA gene expression and cytotoxicity by both AH26 and Topseal (p<0.05). However, catalase and SOD lacked the ability to prevent AH26-and Topseal-induced cytotoxicity and COX-2 mRNA gene expression (p>0.05). Taken together, the activation of COX-2 mRNA gene expression may be one of the pathogenesis of epoxy resin-based root canal sealers-induced periapical inflammation. In addition, GSH depletion, but not the attack of oxygen free radicals, could be the mechanism for epoxy resin-based root canal sealers-induced cytotoxicity and COX-2 mRNA gene expression. Factors that induce GSH synthesis may appear useful in preventing cell damage mediated by epoxy resin-based root canal sealers.

Regulation of extracellular signal-regulated protein kinase signaling in human osteosarcoma cells stimulated with nicotine

BACKGROUND

Cigarette smoking is a major risk factor in the development and further progression of periodontal diseases. Currently, there is limited information on the regulation of mitogen-activated protein kinases (MAPK) expression in smoking-associated periodontal disease.

OBJECTIVES

The aim of the present study was to investigate the effects of nicotine on the expression of MAPKs in human osteosarcoma cell line U2OS cells. Furthermore, various pharmacological agents were added to search the possible regulation mechanisms on nicotine-induced MAPKs expression.

METHODS

Cytotoxicity and western blot assays were used to investigate the effects of U2OS cells exposed to nicotine. In addition, various pharmacological agents [NS-398, dexamethasome, 2-oxothiazolidine-4-carboxylic acid (OTZ), herbimycin A, and curcumin] were added to test how they modulated the effects of nicotine-induced MAPKs expression.

RESULTS

Concentrations of nicotine higher than 5 mm demonstrated cytotoxicity to U2OS cells (p<0.05). A nicotine concentration of 5 mm was found to induce extracellular signal-regulated kinase (ERK) phosphorylation in a time-dependent manner (p<0.05). In addition, amounts of ERK protein were unaffected by nicotine during the same time interval. By contrast, nicotine has no effect on either c-Jun N-terminal kinase (JNK) or p38, respectively. In addition, NS-398, dexamethasone, OTZ, herbimycin A, and curcumin were found to inhibit the nicotine-induced ERK expression (p<0.05).

CONCLUSIONS

The activation of ERK expression by nicotine suggests a potential role for nicotine in the pathogenesis of cigarette smoking-associated periodontal disease. In addition, nicotine-induced ERK expression was down-regulated by NS-398, dexamethasone, OTZ, herbimycin A, and curcumin.

Induction of cyclooxygenase-2 mRNA and protein expression by epoxy resin and zinc oxide-eugenol based root canal sealers in human osteoblastic cells

An ideal root canal sealer should be nonirritating to the surrounding tissues. Unfortunately, all histological investigation demonstrated that all types of root canal sealer can induce mild to severe inflammatory alternations. However, there is little information on the precise mechanisms about root canal sealers-induced inflammatory reaction. Cyclooxygenase-2 (COX-2) is an inducible enzyme believed to be responsible for prostaglandin synthesis at site of inflammation. The aim of the present study was to investigate the effects of epoxy resin (AH26) and zinc oxide-eugenol based (Endomethansone and N2) root canal sealers on the expression of COX-2 mRNA gene and protein in cultured human osteoblastic cells. Investigations of the time dependence of COX-2 mRNA expression in root canal sealer-treated human osteoblastic cells revealed a rapid accumulation of the transcript, a significant signal first detectable within 2h and diminished to control level after 24h. In addition, all root canal sealers also induced COX-2 protein expression in human osteoblastic cells. Furthermore, to elucidate whether induction of COX-2 is associated with cytotoxicity, NS-398 (a selective COX-2 inhibitor), was added to test its protective effects. NS-398 at non-cytotoxic dose is not able to prevent root canal sealers-induced cytotoxicity. Taken together, the activation of COX-2 expression may be one of the pathogenesis of root canal sealers-induced periapical inflammation. In addition, root canal sealers-induced cytotoxicity is not directly via the induction of COX-2 expression.

Effect of black-pigmented bacteria on the plasminogen-plasmin system in human pulp and osteoblastic cells

OBJECTIVE

To date, there have been relatively few studies addressing the presence and expression of the plasminogen-plasmin system at the site of bacterial infection. The aim of the present study was to investigate the effect of black-pigmented bacteria on the expression of the plasminogen-plasmin system in human pulp and osteoblastic cells.

STUDY DESIGN

The supernatants of Porphyromonas endodontalis, Porphyromonas gingivalis, and Prevotella intermedia were used to evaluate tissue-type plasminogen activator (t-PA) and type 1 plasminogen activator inhibitor (PAI-1) gene expression in human pulp and osteoblastic cells. The levels of mRNA were quantitatively measured by using reverse transcription-polymerase chain reaction.

RESULTS

In this study, black-pigmented bacteria induced not only t-PA but also PAI-1 gene expression in human pulp and osteoblastic cells. In addition, the ratio of t-PA to PAI-1 was higher in human pulp and osteoblastic cells stimulated by black-pigmented bacteria than in untreated cell cultures (P <.05).

CONCLUSIONS

A fine balance exists in the expression of components of the plasminogen-plasmin system, whereby tissue homeostasis is maintained. Black-pigmented bacteria activate the activator-inhibitor system in human pulp and osteoblastic cells through unbalance regulation of t-PA and PAI-1, which might result in an uncontrolled degradation of pulpal and periapical tissues.

Dentin bonding agents induce c-fos and c-jun protooncogenes expression in human gingival fibroblasts

An important requirement for a dentin bonding agent is biologic compatibility; the bonding agent usually remains in close contact with living dental tissues over a long period of time. Information on the genotoxicity/mutagenicity and cacinogenicity potentials of dentin bonding agents is rare. It has been shown that c-fos and c-jun are induced rapidly by a variety of chemical and physical stimuli. Little is known about the induction of cellular signaling events and specific gene expression after cell exposure to dentin bonding agents. Therefore, we used primary human gingival fibroblasts to examine the effect of six dentin bonding agents on the expression of c-fos and c-jun protooncogenes to evaluate the genotoxicity/mutagenicity and cacinogenicity potential of the dentin bonding agents. The levels of mRNA were measured by the quantitative RT-PCR analysis. c-fos and c-jun mRNA expression in dentin bonding agents-treated cells revealed a rapid accumulation of the transcript, a significant signal first was detectable after 1h of exposure. Persistent induction of c-jun and c-fos protooncogenes by dentine bonding agents may distribute systemically to cause some unexpected adverse effects on human beings. It would be necessary to identify the severely toxic compounds and replace these substances by better biocompatible components. Otherwise, leaching of those genotoxicity/mutagenicity and cacinogenicity components must be minimized or prevented.