Interaction between LPS and a dental resin monomer on cell viability in mouse macrophages

An in vitro coculture approach to study the interplay between dental pulp cells and Streptococcus mutans

AIM

To develop a new coculture system that allows exposure of dental pulp cells (DPCs) to Streptococcus mutans and dentine matrix proteins (eDMP) to study cellular interactions in dentine caries.

METHODOLOGY

Dental pulp cells and S. mutans were cocultured with or without eDMP for 72 h. Cell proliferation and viability were assessed by cell counting and MTT assays, while bacterial growth and viability were determined by CFU and LIVE/DEAD staining. Glucose catabolism and lactate excretion were measured photometrically as metabolic indicators. To evaluate the inflammatory response, the release of cytokines and growth factors (IL-6, IL-8, TGF-β1, VEGF) was determined by ELISA. Non-parametric statistical analyses were performed to compare all groups and time points (Mann-Whitney U test or Kruskal-Wallis test; α = .05).

RESULTS

While eDMP and especially S. mutans reduced the number and viability of DPCs (p ≤ .0462), neither DPCs nor eDMP affected the growth and viability of S. mutans during coculture (p > .0546). The growth of S. mutans followed a common curve, but the death phase was not reached within 72 h. S. mutans consumed medium glucose in only 30 h, whereas in the absence of S. mutans, cells were able to catabolize glucose throughout 72 h, resulting in the corresponding amount of l-lactate. No change in medium pH was observed. S. mutans induced IL-6 production in DPCs (p ≤ .0011), whereas eDMP had no discernible effect (p > .7509). No significant changes in IL-8 were observed (p > .198). TGF-β1, available from eDMP supplementation, was reduced by DPCs over time. VEGF, on the other hand, was increased in all groups during coculture.

CONCLUSIONS

The results show that the coculture of DPCs and S. mutans is possible without functional impairment. The bacterially induced stimulation of proinflammatory and regenerative cytokines provides a basis for future investigations and the elucidation of molecular biological relationships in pulp defence against caries.

Influence of HEMA on LPS- and LTA-stimulated IL-6 release from human dental pulp cells

OBJECTIVE

Dental pulp cells interact with immunogenic components such as LPS (lipopolysaccharide) or LTA (lipoteichoic acid) released from microorganisms in carious lesions. In the present investigation, the formation of the pro-inflammatory cytokines TNFα and IL-6 in LPS- or LTA-stimulated cells from the dental pulp interface and pulp fibroblasts was analyzed in the presence of the resin monomer 2-hydroxyethyl methacrylate (HEMA) under varying cellular redox conditions.

METHOD

Human pulp fibroblasts (HPC) or cells from the dental pulp interface expressing an odontoblast phenotype (hOD-1) were exposed to LTA, LPS or HEMA for 1 h or 24 h. Redox homeostasis was modified by the prooxidant BSO (L-buthionine sulfoximine) or the antioxidant NAC (N-acetyl cysteine). Formation of TNFα or IL-6 was analyzed by ELISA, and cell survival was determined by a crystal violet assay. Statistical analyses were performed using the Mann-Whitney-U-test.

RESULTS

Secretion of TNFα was not detected in LPS- or LTA-stimulated HPC or hOD-1, and IL-6 was not found after a short exposure (1 h). After a 24 h exposure, LPS induced a 3-fold increase in IL-6 formation in HPC, while LTA stimulated IL-6 release about 20-fold. Likewise, LTA was more effective than LPS in hOD-1 stimulating IL-6 levels about 50-fold. HEMA inhibited the LPS- and LTA-induced IL-6 release, and this effect was enhanced by BSO but counteracted by NAC in both cell types. IL-6 release was independent of cell survival rates.

CONCLUSIONS

The protective immune response in odontoblasts and pulp fibroblasts is impaired by monomers such as HEMA through the disturbance of the redox homeostasis.

Cytotoxicity of printed resin-based splint materials

OBJECTIVES

Printed splints may be an alternative as a treatment of functional disorders in addition to physical, manual and physiological therapeutics. The objective is to investigate whether different 3D printed splint materials, which are fabricated with different fabrication orientation and post-processing (washing and post polymerisation) exhibit different in vitro cytotoxicity.

MATERIAL AND METHODS

600 discs (n = 25 per group, 5mmx1mm) were printed (P30+ DLP-printer, Straumann, CH; 100 µm layer) from splint materials (M1: Luxaprint OrthoPlus, DMG, G; M2: V-Print Splint, Voco, G). Printing was performed under 90° (A1), 45° (A2) or 0° (A3) alignment to the building platform. Specimens were either automatically washed (W1) (Straumann P Wash, Straumann, CH) or manually cleaned (W2) (Voco Pre-/Main-Clean protocol, Voco, G), and post polymerization was performed (P1: Cure, Straumann, CH; P2: Otoflash N171, Ernst Hinrichs Dental, G). RAW264.7 mouse macrophages were exposed to extracts of the specimens and cytotoxicity was determined as cell survival using a crystal violet assay. Optical density values obtained from exposed cell cultures were normalized to untreated controls (100%), summarized as means and statistically analyzed (ANOVA, α=0.05).

RESULTS

Cell survival varied between 9.1+/-1.3% (alignment A2/post cure P2/material M2/wash system W2) and 58.5+/-5.9% (alignment A1/post cure P1/material M1/wash system W1). Univariate analysis of variance revealed significant differences between mean values for post cure (p = 0.000), wash system (p = 0.002) and materials (p = 0.000), but not for the alignment (p = 0.406). With standardised washing and adapted post cure, both tested materials provided lowest cytotoxicity even in all three printing alignments.

CONCLUSIONS

The selection of the material as well as the post-processing (post-polymerization, washing procedure) show influence on the in vitro cytotoxicity. Alignment during manufacturing does not affect toxicity.

CLINICAL RELEVANCE

Materials, washing and post-polymerization should be matched to reduce cytotoxic effects during additive manufacturing.

Three-dimensional tissue engineering-based Dentin/Pulp tissue analogue as advanced biocompatibility evaluation tool of dental restorative materials

OBJECTIVE

Two-dimensional (2D) in vitro models have been extensively utilized for cytotoxicity assessment of dental materials, but with certain limitations in terms of direct in vitro-in vivo extrapolation (IVIVE). Three-dimensional (3D) models seem more appropriate, recapitulating the structure of human tissues. This study established a 3D dentin/pulp analogue, as advanced cytotoxicity assessment tool of dental restorative materials (DentCytoTool).

METHODS

DentCytoTool comprised two compartments: the upper, representing the dentin component, with a layer of odontoblast-like cells expanded on microporous membrane of a cell culture insert and covered by a treated dentin matrix; and the lower, representing a pulp analogue, incorporating HUVEC/SCAP co-cultures into collagen I/fibrin hydrogels. Representative resinous monomers (HEMA: 1-8mM; TEGDMA: 0.5-5mM) and bacterial components (LPS: 1μg/ml) were applied into the construct. Cytotoxicity was assessed by MTT and LDH assays, live/dead staining and real-time PCR for odontogenesis- and angiogenesis-related markers.

RESULTS

DentCytoTool supported cell viability and promoted capillary-like network formation inside the pulp analogue. LPS induced expression of odontogenesis-related markers (RUNX2, ALP, DSPP) without compromising viability of the odontoblast-like cells, while co-treatment with LPS and resin monomers induced cytotoxic effects (live/dead staining, MTT and LDH assays) in cells of both upper and lower compartments and reduced expression angiogenesis-related markers (VEGF, VEGFR2, ANGPT-1, Tie-2, PECAM-1) in a concentration- and time- dependent manner. LPS treatment aggravated TEGDMA-induced and -in certain concentrations (2-4mM)- HEMA-induced cytotoxicity.

SIGNIFICANCE

DentCytoTool represents a promising tissue-engineering-based cytotoxicity assessment tool, providing more insight into the mechanistic aspects of interactions of dental materials to the dentin/pulp complex.

Evaluation of biofilm formation on novel copper-catalyzed azide-alkyne cycloaddition (CuAAC)-based resins for dental restoratives

OBJECTIVE

For the past several decades, the resins used in dental restorations have been plagued with numerous problems, including their implication in biofilm formation and secondary caries. The need for alternative resins is critical, and evaluation of biofilm formation on these resins is essential. The aim of this study was to evaluate in vitro biofilm formation on the surface of novel copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC)-based resins and composites.

METHODS

CuAAC-based resins/composites made from varying azide monomers and different copper concentrations were compared with BisGMA-TEGDMA resins/composites that served as the control. Biofilms were formed using a mono-species model containing a luciferase-expressing strain of Streptococcus mutans. Luciferase activity was measured and the number of viable bacteria was enumerated on biofilms associated with each resin and composite.

RESULTS

A significant reduction (p<0.05) in luciferase activity, and the number of viable bacteria recovered from biofilms on CuAAC-based resins and composites was observed in comparison to biofilms associated with the BisGMA-TEGDMA controls.

SIGNIFICANCE

CuAAC-based resins do still allow for the formation of biofilms; however, the statistically significant reduction of growth that was associated with the CuAAC resin may enhance the longevity of restorations that incorporate CuAAC-based materials.

Dose- and time-dependent effects of triethylene glycol dimethacrylate on the proteome of human THP-1 monocytes

Triethylene glycol dimethacrylate (TEGDMA) is commonly used in polymer resin-based dental materials. This study investigated the molecular mechanisms of TEGDMA toxicity by identifying its time- and dose-dependent effects on the proteome of human THP-1 monocytes. The effects of different concentrations (0.07-5 mM) and exposure times (0-72 h) of TEGDMA on cell viability, proliferation, and morphology were determined using a real-time viability assay, automated cell counting, and electron microscopy, and laid the fundament for choice of exposure scenarios in the proteomic experiments. Solvents were not used, as TEGDMA is soluble in cell culture medium (determined by photon correlation spectroscopy). Cells were metabolically labeled [using the stable isotope labeled amino acids in cell culture (SILAC) strategy], and exposed to 0, 0.3 or 2.5 mM TEGDMA for 6 or 16 h before liquid chromatography-tandem mass spectrometry (LC-MS/MS) analyses. Regulated proteins were analyzed in the STRING database. Cells exposed to 0.3 mM TEGDMA showed increased viability and time-dependent upregulation of proteins associated with stress/oxidative stress, autophagy, and cytoprotective functions. Cells exposed to 2.5 mM TEGDMA showed diminished viability and a protein expression profile associated with oxidative stress, DNA damage, mitochondrial dysfunction, and cell cycle inhibition. Altered expression of immune genes was observed in both groups. The study provides novel knowledge about TEGDMA toxicity at the proteomic level. Of note, even low doses of TEGDMA induced a substantial cellular response.

Functions of transcription factors NF-κB and Nrf2 in the inhibition of LPS-stimulated cytokine release by the resin monomer HEMA

OBJECTIVE

Resin monomers like 2-hydroxyethyl methacrylate (HEMA) interfere with effects induced by stressors such as lipopolysaccharide (LPS) released from cariogenic microorganisms. In this study, mechanisms underlying monomer-induced inhibition of the LPS-stimulated secretion of inflammatory cytokines from immunocompetent cells were investigated.

METHODS

Secretion of pro-inflammatory cytokines TNF-α, IL-6 and the anti-inflammatory IL-10 from RAW264.7 mouse macrophages exposed to LPS and HEMA (0-6-8mM) was determined by ELISA. The formation of reactive oxygen (ROS) and nitrogen species (RNS) was determined by flow cytometry (FACS) after staining of cells with specific fluorescent dyes. Cell viability was analyzed by FACS, and protein expression was detected by Western blotting.

RESULTS

Secretion of TNF-α, IL-6 and IL-10 from LPS-stimulated cells increased after a 24h exposure. A HEMA-induced decrease in cytokine secretion resulted from the inhibition of LPS-stimulated NF-κB activation. Nuclear translocation of NF-κB was inhibited possibly as a result of enhanced levels of hydrogen peroxide (H₂O₂) and nitric oxide (NO) in HEMA-exposed cells. Oxidative stress caused by HEMA-induced formation of H₂O₂ and LPS-stimulated peroxynitrite (ONOO) also enhanced nuclear expression of Nrf2 as the major regulator of redox homeostasis, as well as Nrf2-controlled stress protein HO-1 to inhibit NF-κB activity. HEMA inhibited the LPS-stimulated expression of NOS (nitric oxide synthase) to produce NO but counteracted the expression of Nox2, which forms superoxide anions that combine with NO to peroxynitrite.

CONCLUSIONS

Resin monomers like HEMA inhibit LPS-stimulated NF-κB activation essential for cytokine release as a crucial response of immunocompetent cells of the dental pulp to invading cariogenic pathogens.

Biological Activities and Potential Oral Applications of N-Acetylcysteine: Progress and Prospects

N-Acetylcysteine (NAC), a cysteine prodrug and glutathione (GSH) precursor, has been used for several decades in clinical therapeutic practices as a mucolytic agent and for the treatment of disorders associated with GSH deficiency. Other therapeutic activities of NAC include inhibition of inflammation/NF-κB signaling and expression of proinflammatory cytokines. N-Acetylcysteine is also a nonantibiotic compound possessing antimicrobial property and exerts anticarcinogenic and antimutagenic effects against certain types of cancer. Recently, studies describing potentially important biological and pharmacological activities of NAC have stimulated interests in using NAC-based therapeutics for oral health care. The present review focused on the biological activities of NAC and its potential oral applications. The potential side effects of NAC and formulations for drug delivery were also discussed, with the intent of advancing NAC-associated treatment modalities in oral medicine.

Astragalus polysaccharide alleviates LPS-induced inflammation injury by regulating miR-127 in H9c2 cardiomyoblasts

Astragalus polysaccharide (APS) has been widely reported to play an important role in inflammatory response. In this study, we aimed to explore the effects and underlying mechanisms of APS on lipopolysaccharide (LPS)-induced inflammation injury in H9c2 cardiomyoblasts. H9c2 cells were treated with different concentrations of APS, and cell viability was detected by the Cell Counting Kit-8 (CCK-8) assay. Then, the effect of APS on cell viability and apoptosis induced by LPS was determined by CCK-8, flow cytometry, and western blot. The expression and release of inflammatory cytokines were evaluated by quantitative real-time polymerase chain reaction (qRT-PCR), western blot, and enzyme-linked immunosorbent assay (ELISA). Furthermore, expression of miR-127 in H9c2 cells was analyzed by qRT-PCR, and knocked down by transfection with miR-127 inhibitor. Western blot was used to analyze signaling pathway molecules. APS had no effect on H9c2 cells viability. However, APS could alleviate LPS-induced inflammation injury by increasing cell viability, reducing apoptosis, and inhibiting release of inflammatory cytokines in H9c2 cells ( P < 0.05). Additionally, we found that APS increased toll-like receptor 4 (TLR4) expressions in LPS-treated H9c2 cells. Mechanistically, we found that APS exerted the protective effect by down-regulating LPS-increased expression of miR-127 ( P < 0.05), inhibiting nuclear factor kappa B (NF-κB), JNK and promoting phosphoinositide 3-kinase/protein kinase B (PI3K/AKT) signaling pathways in LPS-treated H9c2 cells. The results demonstrated that APS could protect H9c2 cells against LPS-induced inflammation injury, which might be partially due to miR-127 down-regulation and regulation of NF-κB, JNK, and PI3K/AKT signaling pathways. These findings indicated that APS might be a potential therapeutic drug for treatment of myocarditis.