Proteolytic activity of Porphyromonas gingivalis attenuates MCP-1 mRNA expression in LPS-stimulated THP-1 cells.

Bacteria can modulate cytokine production of host cells. In this study, we examined effects of Porphyromonas gingivalis, an important periodontal pathogen, on the cytokine production in lipopolysaccharide (LPS)-stimulated THP-1 macrophagic cells. A wide range of doses of P. gingivalis increased the tumor necrosis factor-α (TNF-α) production. However, monocyte chemoattractant protein-1 (MCP-1) production was substantially suppressed by high doses of P. gingivalis and this effect was demonstrated at the mRNA level. Challenges with a congenic protease mutant strain did not significantly attenuate the MCP-1 mRNA expression and addition of leupeptin, a protease inhibitor, to the cultures largely prevented the inhibition of MCP-1 expression by P. gingivalis. Transwell experiments showed that direct contact of P. gingivalis with THP-1 cells was not required for the MCP-1 inhibition. Furthermore, blockade of internalization of P. gingivalis into THP-1 cells had no effect on the MCP-1 inhibition by P. gingivalis. Finally, degradation of MCP-1 mRNA in LPS-stimulated THP-1 cells was accelerated in the presence of P. gingivalis. These results suggest that the proteolytic activity of P. gingivalis attenuate MCP-1 mRNA expression by promoting the decay of MCP-1 mRNA in LPS-stimulated THP-1 cells.

A bacterial RTX toxin causes programmed necrotic cell death through calcium-mediated mitochondrial dysfunction.

Vibrio vulnificus, a halophilic estuarine bacterium causing fatal septicemia and necrotic wound infection, is highly cytotoxic to eukaryotic cells. We have reported that RtxA1 toxin kills host cells only after they come into contact with bacteria and plays an essential role in the pathogenesis of V. vulnificus. This study was performed to elucidate the mechanism by which the RtxA1 toxin mediates the death of HeLa cells. By using confocal microscopy and immunoblot analysis, we show that the 501-kDa RtxA1 toxin is processed into 2 fragments after its secretion into host cells. The largerN-terminal fragment (RtxA1-N; approximately 370 kDa) remained at the host cell membrane, whereas the smaller C-terminal fragment (RtxA1-C; approximately 130 kDa) was internalized into the host cell cytoplasm. RtxA1-N is believed to polymerize and form pores at the host cell membrane and to induce an increase in necrotic volume related to calcium. The RtxA1 toxin caused an increase in the intracellular Ca(2+) concentration and the subsequent activation of JNK. The cell death mechanism occurred via calcium-dependent mitochondrial pathways, which caused calcium sequestration in the mitochondria, accompanied by irreversible mitochondrial membrane dysfunction and adenosine triphosphate depletion, and was later accompanied by the disruption of the integrity of the plasma membrane.

Induction of TNF-α by Filifactor alocis in THP-1 macrophagic cells.

OBJECTIVES: Filifactor alocis is an emerging periodontal pathogen, and macrophage-produced tumor necrosis factor-α (TNF-α) plays important roles in periodontal pathogenesis. In this study, we investigated F. alocis-stimulated TNF-α production in THP-1 macrophagic cells. DESIGN: Phorbol 12-myristate 13-acetate-differentiated THP-1 macrophagic cells were challenged with F. alocis ATCC 35896 for various durations. TNF-α mRNA expression and protein secretion were determined using RT-PCR and ELISA, respectively. Activation of protein kinases and transcription factor proteins was evaluated by Western blot analysis. RESULTS: Live F. alocis stimulated THP-1 cells to produce TNF-α in a dose-dependent manner. However, glutaraldehyde-killed or heat-killed F. alocis showed no effectiveness for TNF-α induction. In contrast, both live and killed Porphyromonas gingivalis robustly increased TNF-α expression. Furthermore, F. alocis was unable to stimulate TNF-α expression in Toll-like receptor 2 (TLR2) knockout THP-1 cells. F. alocis activated all three mitogen-activated protein kinases: extracellular signal-regulated kinase (ERK), p38, and c-Jun N-terminal kinase (JNK). Pharmacological inhibition of ERK and JNK, but not p38, significantly reduced F. alocis-induced TNF-α production. Finally, increased levels of phospho-c-Jun were detected in F. alocis-stimulated THP-1 cells. CONCLUSIONS: These results suggest that F. alocis induces TNF-α production in THP-1 macrophagic cells primarily by activating the TLR2, JNK, and c-Jun pathways.

A built-in adjuvant-engineered mucosal vaccine against dysbiotic periodontal diseases.

Periodontitis is associated with a dysbiotic shift in the oral microbiome. Vaccine approaches to prevent microbial shifts from healthy to diseased state in oral biofilms would provide a fundamental therapeutic strategy against periodontitis. Since dental plaque formation is a polymicrobial and multilayered process, vaccines targeting single bacterial species would have limited efficacy in clinical applications. In this study, we developed a divalent mucosal vaccine consisting of a mixture of FlaB-tFomA and Hgp44-FlaB fusion proteins targeting virulence factors of inflammophilic bacteria Fusobacterium nucleatum and Porphyromonas gingivalis, respectively. Introduction of peptide linkers between FlaB and antigen improved the stability and immunogenicity of engineered vaccine antigens. The intranasal immunization of divalent vaccine induced protective immune responses inhibiting alveolar bone loss elicited by F. nucleatum and P. gingivalis infection. The built-in flagellin adjuvant fused to protective antigens enhanced antigen-specific antibody responses and class switch recombination. The divalent vaccine antisera recognized natural forms of surface antigens and reacted with diverse clinical isolates of Fusobacterium subspecies and P. gingivalis. The antisera inhibited F. nucleatum-mediated biofilm formation, co-aggregation of P. gingivalis and Treponema denticola, and P. gingivalis-host cell interactions. Taken together, the built-in adjuvant-engineered mucosal vaccine provides a technological platform for multivalent periodontitis vaccines targeting dysbiotic microbiome.

Antibacterial activity of pyrrolidine dithiocarbamate.

Pyrrolidine dithiocarbamate (PDTC), an antioxidant with a metal-chelating activity, has been used widely to inhibit the expression of inflammatory genes in vitro and in vivo. This study investigated whether PDTC has an antimicrobial activity against various bacteria. The antibacterial activity of PDTC and other compounds was evaluated in vitro by the broth microdilution method against Porphyromonas gingivalis, Actinobacillus actinomycetemcomitans, Staphylococcus aureus, and Escherichia coli. Bacterial growth was inhibited by PDTC, where a wide range of sensitivity was demonstrated among the tested bacteria. The antibacterial activity of PDTC was reduced by the addition of copper chloride; in contrast, it was enhanced considerably by zinc chloride. Two different zinc chelators, Ca-saturated EDTA (Ca-EDTA) and N,N,N',N'-tetrakis (2-pyridylmethyl) ethylenediamine, blocked the antibacterial activity of PDTC, whereas Zn-EDTA failed to reduce the activity of PDTC. These results demonstrate for the first time that PDTC possesses an antibacterial activity, for which zinc is required, and suggest that PDTC, possessing a dual anti-inflammatory and antibacterial activity, may be considered for topical use for inflammatory diseases of bacterial origin.

Inhibitory effect of methyl gallate and gallic acid on oral bacteria.

This study examined the ability of methyl gallate (MG) and gallic acid (GA), the main compounds of gallo-tannins in Galla Rhois, to inhibit the proliferation of oral bacterial and the in vitro formation of Streptococcus mutans biofilms. The antimicrobial activities of these compounds were evaluated in vitro using the broth microdilution method and a beaker-wire test. Both MG and GA had inhibitory effects on the growth of cariogenic (MIC<8 mg/ml) and periodontopathic bacteria (MIC=1 mg/ml). Moreover, these compounds significantly inhibited the in vitro formation of S. mutans biofilms (MG, 1 mg/ml; GA, 4 mg/ml; P<0.05). MG was more effective in inhibiting bacterial growth and the formation of S. mutans biofilm than GA. In conclusion, MG and GA can inhibit the growth of oral pathogens and S. mutans biofilm formation, and may be used to prevent the formation of oral biofilms.

Effect of Leuconostoc spp. on the formation of Streptococcus mutans biofilm.

Insoluble glucans synthesized by Streptococcus mutans enhance the pathogenicity of oral biofilm by promoting the adherence and accumulation of cariogenic bacteria on the surface of the tooth. The objective of this study was to investigate the effect of Leuconostoc spp. on the in vitro formation of S. mutans biofilm. Three strains, Leuconostoc gelidum ATCC 49366, Leuconostoc mesenteroides ssp. cremoris ATCC 19254 and Leuconostoc mesenteroides ssp. mesenteroides ATCC 8293, were used in this study. They exhibited profound inhibitory effects on the formation of S. mutans biofilm and on the proliferation of S. mutans. The water-soluble polymers produced from sucrose were most strongly produced by L. gelidum, followed by L. mesenteroides ssp. cremoris and L. mesenteroides ssp. mesenteroides. The mean wet weights of the artificial biofilm of S. mutans were also significantly reduced as a result of the addition of the water-soluble polymers obtained from Leuconostoc cultures. According to the results of thin-layer chromatographic analysis, the hydrolysates of the water-soluble polymers produced by Leuconostoc were identical to those of dextran T-2000, forming predominately alpha-(1-6) glucose linkages. These results indicate that dextran-producing Leuconostoc strains are able to inhibit the formation of S. mutans biofilm in vitro.

Mucosal immunization with a flagellin-adjuvanted Hgp44 vaccine enhances protective immune responses in a murine Porphyromonas gingivalis infection model.

Chronic periodontitis is caused by interactions between the oral polymicrobial community and host factors. Periodontal diseases are associated with dysbiotic shift in oral microbiota. Vaccination against periodontopathic bacteria could be a fundamental therapeutic to modulate polymicrobial biofilms. Because oral cavity is the site of periodontopathic bacterial colonization, mucosal vaccines should provide better protection than vaccines administered systemically. We previously reported that bacterial flagellin is an excellent mucosal adjuvant. In this study, we investigated whether mucosal immunization with a flagellin-adjuvanted polypeptide vaccine induces protective immune responses using a Porphyromonas gingivalis infection model. We used the Hgp44 domain polypeptide of Arg-gingipain A (RgpA) as a mucosal antigen. Intranasal (IN) immunization induced a significantly higher Hgp44-specific IgG titer in the serum of mice than sublingual (SL) administration. The co-administration of flagellin potentiated serum IgG responses for both the IN and SL vaccinations. On the other hand, the anti-Hgp44-specific IgA titer in the saliva was comparable between IN and SL vaccinations, suggesting SL administration as more compliant vaccination route for periodontal vaccines. The co-administration of flagellin significantly potentiated the secretory IgA response in saliva also. Furthermore, mice administered a mixture of Hgp44 and flagellin via the IN and SL routes exhibited significant reductions in alveolar bone loss induced by live P. gingivalis infections. An intranasally administered Hgp44-flagellin fusion protein induced a comparable level of Hgp44-specific antibody responses to the mixture of Hgp44 and flagellin. Overall, a flagellin-adjuvanted Hgp44 antigen would serve an important component for a multivalent mucosal vaccine against polymicrobial periodontitis.

Enhancement of cytokine-mediated NF-kappaB activation by phosphatidylinositol 3-kinase inhibitors in monocytic cells.

Nuclear factor-kappaB (NF-kappaB) is a transcription factor that plays crucial roles in inflammation and immunity. Understanding the positive and negative regulation of NF-kappaB activity is therefore of fundamental importance. A few previous studies reported that inhibition of the phosphatidylinositol 3-kinase (PI3K)-Akt pathway enhances lipopolysaccharide (LPS)-induced activation of NF-kappaB. However, many aspects of the PI3K negative regulation of NF-kappaB activation remain to be clarified. The present study was conducted to shed light on cell-type specificity, stimulus specificity, and upstream mechanisms of the enhanced NF-kappaB activation by PI3K inhibitors. Gel shift assays showed that LY294002 (LY29) potently increased interleukin (IL)-1-induced NF-kappaB DNA binding in human monocytic THP-1 cells. Moreover, another PI3K inhibitor 3-methyladenine also strongly enhanced IL-1-induced NF-kappaB DNA binding, while LY303511, an inactive analogue of LY29, did not increase the NF-kappaB DNA binding. Compared with LY29, wortmannin (WM) effected only a marginal enhancement of NF-kappaB DNA binding. LY29 treatment also augmented tumor necrosis factor (TNF)-mediated NF-kappaB DNA binding. Furthermore, LY29, but not WM, increased cyclooxygenase (COX)-2 mRNA expression by IL-1 or TNF in THP-1 cells. Likewise, prostaglandin E2 production by IL-1 was increased by LY29, but not by WM. Western blot analysis demonstrated that IkappaB kinase (IKK) activation as well as IkappaB-alpha degradation and NF-kappaB nuclear translocation was elevated by LY29 and WM. Among the tested cell lines (HL-60, ECV304, Hep-2, and Molt-4), only HL-60, a promyelocytic cell line, showed enhanced NF-kappaB DNA binding by LY29. These results suggest that pharmacological inhibition of PI3K enhances the NF-kappaB-activating pathways by IL-1 through augmentation of IKK activation in myeloid/monocytic cells and the NF-kappaB enhancement is more robustly achieved by LY29 than by WM.

Mechanisms of Porphyromonas gingivalis-induced monocyte chemoattractant protein-1 expression in endothelial cells.

Monocyte chemoattractant protein-1 (MCP-1) is expressed in vascular endothelial cells of inflamed gingival tissues and plays an important role in periodontal pathogenesis. Endothelial cells produce high levels of MCP-1 in response to Porphyromonas gingivalis, an important periodontal pathogen. The present study investigated the mechanisms involved in MCP-1 production by human umbilical vein endothelial cells (HUVEC) following infection with P. gingivalis. In contrast to P. gingivalis, Bacteroides forsythus only weakly stimulated MCP-1 production while Treponema denticola could not induce MCP-1 in HUVEC. The MCP-1 production was independent of endogenous interleukin (IL)-1alpha as IL-1 receptor antagonist treatment did not reduce MCP-1 production by P. gingivalis. Meanwhile, antioxidant treatment and inhibition of NAD(P)H oxidase significantly reduced MCP-1 production. Pharmacological inhibition of p38 mitogen-associated protein (MAP) kinase, c-Jun N-terminal kinase (JNK), nuclear factor-kappaB (NF-kappaB) or activator protein-1 (AP-1) also substantially attenuated P. gingivalis-induced MCP-1 expression by HUVEC. Indeed, activation of NF-kappaB and AP-1 was observed in P. gingivalis-infected HUVEC. These results suggest that MCP-1 expression is upregulated in P. gingivalis-infected endothelial cells via reactive oxygen species, p38 MAP kinase, JNK, NF-kappaB, and AP-1.

Evaluation of antibacterial activity and osteoblast-like cell viability of TiN, ZrN and (Ti1-xZrx)N coating on titanium.

PURPOSE: The aim of this study was to evaluate antibacterial activity and osteoblast-like cell viability according to the ratio of titanium nitride and zirconium nitride coating on commercially pure titanium using an arc ion plating system. MATERIALS AND METHODS: Polished titanium surfaces were used as controls. Surface topography was observed by scanning electron microscopy, and surface roughness was measured using a two-dimensional contact stylus profilometer. Antibacterial activity was evaluated against Streptococcus mutans and Porphyromonas gingivalis with the colony-forming unit assay. Cell compatibility, mRNA expression, and morphology related to human osteoblast-like cells (MG-63) on the coated specimens were determined by the XTT assay and reverse transcriptase-polymerase chain reaction. RESULTS: The number of S. mutans colonies on the TiN, ZrN and (Ti1-xZrx)N coated surface decreased significantly compared to those on the non-coated titanium surface (P<0.05). CONCLUSION: The number of P. gingivalis colonies on all surfaces showed no significant differences. TiN, ZrN and (Ti1-xZrx)N coated titanium showed antibacterial activity against S. mutans related to initial biofilm formation but not P. gingivalis associated with advanced periimplantitis, and did not influence osteoblast-like cell viability.

LY294002 inhibits monocyte chemoattractant protein-1 expression through a phosphatidylinositol 3-kinase-independent mechanism.

The effects of LY294002 (LY29) and wortmannin (WM), inhibitors of phosphatidylinositol 3-kinase (PI3K), on monocyte chemoattractant protein-1 (MCP-1) expression by human umbilical vein endothelial cells were investigated. Complete inhibition of interleukin (IL)-1beta-induced Akt phosphorylation occurred at 50 microM LY29 or 100 nM WM. At these concentrations, LY29, but not WM, significantly inhibited constitutive and IL-1beta-induced MCP-1 expression at both protein and mRNA levels. LY303511 (LY30), an inactive analogue of LY29, also inhibited MCP-1 expression. LY29 and LY30 inhibited activation of nuclear factor-kappaB (NF-kappaB). These results suggest that LY29 inhibits MCP-1 expression at least in part via suppression of NF-kappaB, independent of PI3K, and the structure of LY29 and LY30 may be a novel template for development of new anti-inflammatory drugs.

Induction of monocyte chemoattractant protein-1 by Porphyromonas gingivalis in human endothelial cells.

The association between periodontal and cardiovascular diseases could be mediated by direct interaction of periodontal pathogens with cardiac tissue. In order to explore this possibility, the effect of the periodontal pathogen Porphyromonas gingivalis on monocyte chemoattractant protein-1 (MCP-1) production by endothelial cells was investigated. When incubated with live P. gingivalis 381, MCP-1 production by human umbilical vein endothelial cells (HUVEC) was potently increased. Compared to the type strain 381, non-adhesive/invasive strains (W50 and DPG3) did not increase MCP-1 production, which was also demonstrated at the mRNA level. Killed P. gingivalis 381 was much less effective than live bacteria for MCP-1 induction. Treatment of HUVEC with cytochalasin D, an inhibitor of endocytosis, prevented MCP-1 mRNA up-regulation by P. gingivalis 381, suggesting that internalization of P. gingivalis is necessary for MCP-1 induction. In conclusion, the secretion of high levels of MCP-1 resulting from interactions of P. gingivalis with endothelial cells could enhance atherosclerosis progression by contributing to the recruitment of monocytes.

Interactions of Porphyromonas gingivalis with host cells: implications for cardiovascular diseases.

BACKGROUND: Recent epidemiological studies have suggested a contribution of periodontitis in atherosclerotic diseases. Two mechanisms have been proposed to explain such a connection involving general inflammatory responses and/or specific effects of periodontal bacteria on host tissues. METHODS: The role of the periodontopathogen Porphyromonas gingivalis as a potential contributor to atherosclerosis has been investigated in model systems using human umbilical vein endothelial cells (HUVEC) and murine J774 macrophage cell cultures. RESULTS: P. gingivalis 381 was demonstrated to induce foam cell formation in J774 macrophage cell cultures in the presence of low-density lipoproteins. The active bacterial component involved in this process appears to be lipopolysaccharide. This effect was not limited to these organisms as several other Gram-positive and Gram-negative oral bacteria exhibited the same property. In addition, in a more specific manner, P. gingivalis induced monocyte chemoattractant protein-1 secretion in HUVEC cultures. CONCLUSIONS: The fimbriae of strain 381 are important, but are not required, for this inductive effect. Taken together, these results suggest a potential role for P. gingivalis in several steps involved in atherosclerotic lesion formation.

Ketoprofen inhibits expression of inflammatory mediators in human dental pulp cells.

INTRODUCTION: Conventional root canal treatment is the treatment of choice for the irreversible pulpitis caused by bacterial infection. More recently, vital pulp therapy has been proposed as an alternative for management of inflamed dental pulp. Ketoprofen is an anti-inflammatory agent commonly used as a component of mouth rinse for oral lesions. Here, we examined the effect and mechanisms of action of ketoprofen on the expression of inflammatory mediators induced by the lipopolysaccharide (LPS) in dental pulp cells. METHODS: Human dental pulp cells were exposed to LPS or LPS + ketoprofen, and reverse-transcription polymerase chain reaction was used to detect interleukin-1ß and tumor necrosis factor α. The effect of these treatments on mitogen-activated protein kinase pathways was assessed by Western blots for extracellular signal-regulated kinase and c-Jun N-terminal kinase. RESULTS: LPS induced interleukin-1ß and tumor necrosis factor α in dental pulp cells. Ketoprofen effectively inhibited interleukin-1ß and tumor necrosis factor α production in LPS-stimulated dental pulp cells. Notably, ketoprofen inhibited phosphorylation of extracellular signal-regulated kinase and c-Jun N-terminal kinase. CONCLUSIONS: Ketoprofen inhibited expression inflammatory mediators in dental pulp cells stimulated with LPS. The inhibitory effect of ketoprofen on inflammatory cytokines is associated with inhibition of the mitogen-activated protein kinase pathway.

Potentiation of bacterial killing activity of zinc chloride by pyrrolidine dithiocarbamate.

Zinc has antimicrobial activity and zinc salts including zinc chloride (ZnCl(2)) have been used for the control of oral malodor. In this study, we hypothesized that pyrrolidine dithiocarbamate (PDTC), a zinc ionophore, may enhance antimicrobial efficacy of ZnCl(2). The bactericidal effectiveness of ZnCl(2) alone (0.5-8 mM) or in combination with PDTC (1 or 10 microM) was evaluated by in vitro short (1 h) time-killing assays against Fusobacterium nucleatum and Porphyromonas gingivalis. Only a slight viability decrease was observed with ZnCl(2) or PDTC alone after 1-h incubation. By contrast, combination of ZnCl(2) and PDTC could achieve a more than 100-fold viability reduction compared with ZnCl(2) or PDTC alone in F. nucleatum and P. gingivalis. Therefore, PDTC greatly enhanced the bactericidal activity of ZnCl(2) against the oral malodor-producing bacteria. These results suggest that use of PDTC may be useful for enhancing bactericidal activity of antimalodor regimens of zinc salts.

COMP-Ang1, a chimeric form of Angiopoietin 1, enhances BMP2-induced osteoblast differentiation and bone formation.

INTRODUCTION: Angiogenesis is closely associated with bone formation, especially endochondral ossification. Angiopoietin 1 (Ang1) is a specific growth factor functioning to generate a stable and matured vasculature through the Tie2 receptor/PI3K/AKT pathway. Recently cartilage oligomeric matrix protein (COMP)-Ang1, an Ang1 variant which is more potent than native Ang1 in phosphorylating Tie2 receptor and AKT, was developed. This study was designed to examine the effects of angiogenic COMP-Ang1 on BMP2-induced osteoblast differentiation and bone formation. METHODS: Expression of endogenous Ang-1 and its binding receptor Tie 2 mRNA was examined in osteoblast-like cells and primary mouse calvarial cells by RT-PCR analysis, and was also monitored during osteoblast differentiation induced by BMP-2 and/or ascorbic acid and beta-glycerophosphate. Effects of COMP-Ang-1 on osteoblast differentiation and mineralization were evaluated by alkaline phosphatase (ALP) activity and osteocalcin (OC) production, and Alizarin red stain. For a molecular mechanism, Western blot and OG2 and 6xOSE promoter assays were done. For in vivo evaluation, adenoviral (Ad) vectors containing COMP-Ang-1 or BMP-2 gene were administered into thigh muscle of mice, and after 2 weeks bone formation was analyzed by micro-computed tomography and histology. Angiogenic event of COMP-Ang1 was confirmed by immunofluorescence analysis with anti-CD31 antibody. RESULTS: Expression of Tie2 receptor was significantly increased in the course of osteoblast differentiation. Treatment or overexpression of COMP-Ang1 enhanced BMP2-induced ALP activity, OC production, and mineral deposition in a dose-dependent manner. In addition, COMP-Ang1 synergistically increased OG2 and 6xOSE promoter activities of BMP2, and sustained p38, Smad and AKT phosphorylation of BMP2. Notably, in vivo intramuscular injection of COMP-Ang1 dose-dependently enhanced BMP2-induced ectopic bone formation with increases in CD31 reactivity. CONCLUSIONS: These results suggest that COMP-Ang1 synergistically enhanced osteoblast differentiation and bone formation through potentiating BMP2 signaling pathways and angiogenesis. Combination of BMP2 and COMP-Ang1 should be clinically useful for therapeutic application to fracture and destructive bone diseases.

Chemical composition, radiopacity, and biocompatibility of Portland cement with bismuth oxide.

OBJECTIVE: This study compared the chemical constitution, radiopacity, and biocompatibility of Portland cement containing bismuth oxide (experimental cement) with those of Portland cement and mineral trioxide aggregate (MTA). STUDY DESIGN: The chemical constitution of materials was determined by scanning electron microscopy and energy-dispersive X-ray analysis. The radiopacity of the materials was determined using the ISO/6876 method. The biocompatibility of the materials was tested by MTT assay and tissue reaction. RESULTS: The constitution of all materials was similar. However, the Portland cement and experimental cement were more irregular and had a larger particle size than MTA. The radiopacity of the experimental cement was similar to MTA. The MTT assay revealed MTA to have slightly higher cell viability than the other materials. However, there were no statistically significant differences between the materials, with the exception of MTA at 24 h. There was no significant difference in the tissue reaction between the experimental groups. CONCLUSIONS: These results suggest that the experimental cement may be used as a substitute for MTA.