Application of HEMA on intact mouse skin - effects on the immune system

The effects of the dental methacrylates TEGDMA, Bis-GMA, and UDMA on neutrophils in vitro

Objectives

The prevalent usage of methacrylates in modern dentistry demands good knowledge of their biological impacts. While there have been several studies demonstrating the effects of different methacrylic monomers on mononuclear white blood cells, very little is known about the effects caused by these monomers on neutrophilic granulocytes. The objective of this study was to add novel knowledge about how neutrophils are affected by exposure to triethylene glycol dimethacrylate (TEGDMA), urethane dimethacrylate (UDMA), and bisphenol A glycol dimethacrylate (Bis‐GMA) alone or in combinations.

Materials and Methods

Isolated neutrophils were cultured in the presence or absence of methacrylates. The IL‐8 release was measured using a DuoSet ELISA development kit. Apoptosis and necrosis were analyzed using flow cytometry. The formation of neutrophil extracellular traps (NETs) was investigated using Sytox green DNA staining combined with microscopically examination of released DNA and myeloperoxidase (MPO).

Results

The release of IL‐8 was significantly increased after exposure to TEGDMA, Bis‐GMA, UDMA, or TEGDMA in combination with Bis‐GMA or UDMA compared to the unstimulated controls. Exposure to TEGDMA, UDMA, and Bis‐GMA for 24 hr separately or in combination did not affect apoptosis or necrosis of the exposed neutrophils. NET structures were formed by neutrophils after exposure to the different combinations of the methacrylates.

Conclusion

The combination of TEGDMA and Bis‐GMA had a synergistic proinflammatory effect on neutrophils by increasing the release of IL‐8 and the formation of NET structures. The changes in the normal functions of neutrophils caused by methacrylate exposure may lead to altered inflammatory response and relate to previously reported adverse immune reactions caused by these substances.

Effects of HEMA on Nrf2-related gene expression using a newly developed 3D co-culture model of the oral mucosa

OBJECTIVE

2-Hydroxyethyl methacrylate (HEMA) is a component of many resin-modified materials and elutes from dental restorations into the oral cavity. Objective of our investigation was to determine the impact of HEMA on oral keratinocytes (OKF6/TERT2) and gingival fibroblasts (HGFs) in a newly established 3D co-culture model (3D-CCM) and to analyze the permeability of OKF6/TERT2 cells for HEMA.

METHODS

Well-characterized 3D-CCMs, consisting of confluent OKF6/TERT2 cells on cell culture inserts above HGF-containing collagen gels, were treated supra-epithelial with HEMA. Mass spectrometry was used to measure the supra- and sub-epithelial distribution of HEMA after 24 h. The impact of HEMA on nuclear factor erythroid 2-related factor 2 (Nrf2) target genes was measured by qRT-PCR and western blot analysis.

RESULTS

Mass spectrometry showed that HEMA was evenly distributed above and below the keratinocyte layer after 24 h. Analyzed target genes of Nrf2 were induced in both cell types on the mRNA-level but less pronounced in HGFs. On the protein-level, both cell types showed similar effects: At 5 mM HEMA, heme oxygenase-1 was induced 5.1-fold in OKF6/TERT2 cells and 4.1-fold in HGFs. NAD(P)H quinone dehydrogenase-1 was approximately induced 1.85-fold in both cell types.

SIGNIFICANCE

Our 3D-CCM is suitable to analyze the biocompatibility of dental materials due to an improved simulation of the oral mucosa compared to monolayer cultures. Our results indicate that HEMA is able to penetrate a dense layer of keratinocytes and to activate the cellular oxidative defense response. This may be due to the activation of the Nrf2-pathway in both cell types.

Sublingual administration of 2-hydroxyethyl methacrylate enhances antibody responses to co-administered ovalbumin and Streptococcus mutans

OBJECTIVE

The oral mucosa of patients undergoing dental procedures is often exposed to residual monomers leaking from incompletely cured acrylic resins. We investigated whether 2-hydroxyethyl methacrylate (HEMA) monomers applied to the sublingual mucosa in mice modulate the antibody responses towards co-administered ovalbumin (OVA) or live oral bacteria.

MATERIAL AND METHODS

OVA, live mouse oral commensal Lactobacillus murinus or live human oral commensal Streptococcus mutans were administered sublingually with or without HEMA to BALB/c mice on four weekly occasions. One week after the last administration, the experiment was terminated and serum antibody levels were analyzed using ELISA.

RESULTS

Significantly increased IgG and IgE anti-OVA antibody activity was found in the sera from mice immunized with OVA together with HEMA, as compared to mice immunized with OVA alone. Likewise, S. mutans together with HEMA induced an IgG anti-S. mutans antibody response that was significantly higher than the antibody response detected after application of S. mutans alone. No IgG anti-L. murinus antibody response was detected in mice immunized with L. murinus together with HEMA, as compared to the background activity.

CONCLUSIONS

We report that HEMA monomers have adjuvant properties when sublingually administered in combination with OVA or S. mutans.

Triethylene glycol dimethacrylate: adjuvant properties and effect on cytokine production

Objective: Leakage of monomers from dental fillings due to incomplete curing is very common. The objective of the present study was to examine the cytokine profile in cells exposed to triethyleneglycol dimethacrylate (TEGDMA) and the adjuvant properties of TEGDMA.

Materials and methods: Human peripheral blood mononuclear cells were exposed to TEGDMA (500 and 1000 μM) for 24 h in vitro. Bio-Plex Pro™ assays were used for analysis and detection of cytokines. In vivo, BALB/c mice were immunized subcutaneously in the base of the tail with TEGDMA in combination with ovalbumin (OVA).

Results: The cytokine levels of IL-8, IL-18, GRO-α and MCP-1 were significantly increased for both concentrations. IL-1β, IL-6 and TNF-α was only significantly increased in cultures exposed to 500 μM TEGDMA. The concentration of TNF-α was significantly decreased in cultures exposed to 1000 μM TEGDMA. Animals immunized with OVA co-administrated with TEGDMA had a significantly higher IgE and IgG anti-OVA antibody levels in blood than animals immunized with OVA only.

Conclusions: TEGDMA affects production of proinflammatory cytokines IL-1β, IL-6, IL-8, IL-18 and TNF-α. This inflammatogenic capacity renders TEGDMAs adjuvant properties, which may interfere with the homeostasis between the immune system and the indigenous microflora in the oral cavity.

Effects of the methacrylate/acrylate monomers HEMA, TEGDMA, DEGDA, and EMA on the immune system

Incomplete curing of dental fillings may lead to leakage of methacrylate/acrylate monomers, which may come in contact with different cells of the immune system in oral tissues. Very little is known about the different immunologic effects caused by these methacrylates/acrylates. The objective of the present study was to study if and how the methacrylate/acrylate monomers ethyl methacrylate (EMA) and diethylene glycol diacrylate (DEGDA) affect the immune system in vivo and in vitro in comparison to 2-hydroxyethyl methacrylate (HEMA) and triethylene glycol dimethacrylate (TEGDMA). Human peripheral blood mononuclear cells were exposed to the different monomers (500 and 1000 μM) for 24 hr in vitro. BioPlex Pro™ assays were used for cytokine analysis. In vivo, BALB/c mice were immunized subcutaneously at the base of the tail with HEMA, TEGDMA, EMA, or DEGDA in combination with ovalbumin (OVA) in order to study adjuvant properties of the 4 monomers. Peripheral blood mononuclear cells exposed to DEGDA had viability less than 50% of the cells. A pattern was observed where the levels of most cytokines were elevated after exposure to HEMA or TEGDMA. Since that, many cells died after DEGDA-exposure, the only observed cytokine secretion was a significantly increased production of interleukin-18. In the in vivo experiments, all mice immunized with DEGDA died after the booster injection. Mice receiving OVA in combination with HEMA, TEGDMA, or EMA developed a higher immunoglobulin G anti-OVA antibody levels compared to the group immunized with OVA alone. We could not demonstrate any significant difference in antibody levels among the mice receiving the various methacrylate/acrylate monomers. The different monomers affected the production, increase and decrease, of different cytokines in vitro but resulted also in vivo in increased antibody production and T-cell activity.

Analysis of organic components in resin-modified pulp capping materials: critical considerations

The purpose of this study was to elucidate the organic composition and eluates of three resin-based pulp-capping materials in relation to their indications and safety data sheets. Uncured samples of Theracal LC, Ultra-Blend Plus, and Calcimol LC were investigated using gas chromatography-mass spectrometry (GC-MS) and ultra-performance liquid chromatography-mass spectrometry (UPLC-MS). Identification/quantification of 7-d leachables of cured samples was performed using GC-MS for 2-hydroxyethyl methacrylate (HEMA), 2-(dimethylamino)ethyl methacrylate (DMAEMA), camphorquinone (CQ), ethylene glycol dimethacrylate (EGDMA), ethyl-4-(dimethylamino)benzoate (DMABEE), and triethylene glycol dimethacrylate (TEGDMA). A similar organic composition was found for Ultra-Blend and Calcimol; however, only Ultra-Blend is indicated for direct pulp-capping. In contrast to the other materials analysed, Theracal contained substances of high molecular weight. The safety data sheets of all materials were incomplete. We detected HEMA, CQ, and TEGDMA in eluates from Ultra-Blend and Calcimol, and it was considered that HEMA might have originated from decomposition of diurethane dimethacrylate (UDMA) in the GC-injector. For Theracal, additives associated with light curing (DMABEE and CQ) were detected in higher amounts (4.11 and 19.95 μg mm^-2 ) than in the other materials. Pores were quantified in all samples by micro-computed tomography (micro-CT) analysis, which could influence leaching. The organic substances in the investigated materials might affect their clinical suitability as capping agents, especially for direct capping procedures.

HEMA enhances IgG1 production by human B-cells in vitro

We have previously shown that the resin monomer 2-hydroxyethylmethacrylate (HEMA) affects mouse B-lymphocyte activity, leading to increased IgG1 antibody production in vivo. In the present study, we tested, in vitro, the hypothesis that HEMA also affects human B-lymphocyte activity. The in vitro production of IgG1, IgM, and IgA in supernatants from purified human CD19+ B-lymphocyte cultures, containing different concentrations of HEMA, was assayed with ELISA. Proliferation was measured by [methyl-(3)H] thymidine incorporation. Of the different HEMA concentrations used, the lower concentrations caused a significant increase in IgG1 production, but not in IgM or IgA production, in vitro. The lower HEMA concentrations did not significantly change B-cell proliferation. At the highest concentration, HEMA significantly suppressed IgG1 and IgM production, as well as B-cell proliferation, in vitro. In conclusion, HEMA can, at certain concentrations, selectively enhance human B-lymphocyte IgG1 production.

ABBREVIATIONS

2-hydroxyethylmethacrylate (HEMA), Dulbecco's Modified Eagle's Medium supplemented with heat-inactivated fetal bovine serum, gentamycin, penicillin, and streptomycin (D-MEM++++), Enzyme-linked Immuno-sorbent Assay (ELISA), phosphate-buffered saline (PBS), ovalbumin (OVA), pokeweed mitogen (PWM), counts per minute (CPM).