Effect of 2-hydroxyethyl methacrylate on antioxidant responsive element-mediated transcription: a possible indication of its cytotoxicity

Investigation of biological effects of HEMA in 3D-organotypic co-culture models of normal and malignant oral keratinocytes

Several in vitro studies utilizing 2-dimensional (2D) cell culture systems have linked 2-hydroxyethyl methacrylate (HEMA) with cytotoxic effects in oral mucosa and dental pulp cells. Although such studies are invaluable in dissecting the cellular and molecular effects of HEMA, there is a growing interest in the utilization of appropriate 3-dimensional (3D) models that mimic the structure of oral mucosa. Using a previously characterized 3D-organotypic co-culture model, this study aimed to investigate the cellular and molecular effects of HEMA on a 3D-co-culture model consisting of primary normal oral keratinocyte (NOK) grown directly on top of collagen I gel containing primary oral fibroblasts (NOF). The second aim was to examine the suitability of a 3D-co-culture system consisting of oral squamous cell carcinoma (OSCC) cells as a model system to investigate the biological effects of HEMA. We demonstrated that HEMA treatment led to reduced viability of NOK, NOF and OSCC-cell lines in 2D-culture. The keratinocytes in 3D-co-cultures of NOK and OSCC-cells reacted similarly with respect to cell proliferation and activation of autophagy flux, to HEMA treatment. Nevertheless, NOK was found to be more susceptible to apoptosis following HEMA treatment than OSCC in 3D-co-cultures. These results indicate that 3D-organotypic co-cultures of NOK might represent an appropriate model system for the investigation of the biological effects of HEMA and other dental biomaterials. Given the challenges in obtaining primary cultures of NOK and issues associated with their rapid differentiation in culture, the possible use of OSCC cells as an alternative to NOK for 3D models represents an area for future research.

Intracellular stress caused by composite resins: An in vitro study using a bioluminescent antioxidant-responsive element reporter assay

Context

Elucidating the effects of leachates from composite resins (CRs) on cells by examining the transcription level of detoxification genes and the antioxidant-responsive element (ARE), would be helpful in clinical practice.

Aims

The aim of the study is to investigate the cytotoxicity of commercially available CRs, we used a reporter assay system to evaluate intracellular stress based on ARE-mediated transcription.

Setting and Design

The study design was an in vitro study.

Materials and Methods

Seven kinds of CRs were each placed in four-well plates to which culture medium was added and then light-cured. The prepared samples were used either immediately (sample A) or after incubation at 37°C for 24 h (sample B) in the subsequent ARE-luciferase reporter assay, in which HepG2 cells stably expressing an ARE-regulated luciferase reporter gene (HepG2-AD13 cells) were cultured for 6 h in culture media with the CR eluate (samples A or B) or without (control) (n = 4). In the cell viability assay, cell viability in various solutions with the same incubation time was confirmed by MTT assay (n = 4). Statistical analysis was performed using the paired t-test and one-way analysis of variance.

Results

All CR solutions showed an increase in ARE activation rate; a CR with spherical nanofillers showed the highest ARE activation rate of 108.5-fold in sample A. Cell viability was not significantly reduced for any of the CRs in sample A. However, the CR-containing bisphenol A-glycidyl methacrylate (Bis-GMA) caused a significant decrease in cell viability in sample B.

Conclusions

The intracellular stress in the viable cells differed among the CRs, depending on the type of monomer used. In particular, Bis-GMA-containing hydroxyl groups showed high cytotoxicity.

Anthracene dimer cross-linked, washing- and sterilization-free hydrogel films for multicellular spheroid generation

Three-dimensional multicellular spheroids are better in vitro cell models than two-dimensional cell monolayers; however, their applications are limited by their difficult production. PHEMA hydrogel films with honeycomb-like wrinkled patterns have been developed for high-throughput generation of multicellular spheroids with a uniform shape and size; however, the films are prepared by polymerization of the HEMA monomer, and should be washed extensively before use. Here to synthesize washing-free PHEMA hydrogel films, linear anthracene-functionalized PHEMA polymers were first synthesized by the free-radical copolymerization of HEMA and an anthracene-containing vinyl monomer. Smooth films were then prepared from the linear polymers in the wells of cell culture plates by solution casting. They were cross-linked via photo-dimerization of anthracene groups by exposing to 365 nm UV light, and patterned spontaneously by adding water to swell them. The swelling degree of the films and hence the shape of the wrinkled patterns could be facilely adjusted by adjusting the anthracene content in the linear polymers. If necessary, the cross-link density of the film and thus the shape of the wrinkled patterns could be callbacked by irradiating with 254 nm UV light, thanks to the reversibility of the photo-dimerization of anthracene. The as-prepared films exhibit a high biocompatibility and support cell growth well even without washing and sterilization. The high biocompatibility is attributed to the facts that no low molecular weight monomer, crosslinker and initiator were involved in the film preparation, and the photo-dimerization of anthracene groups produces no by-products. The films are sterilized simultaneously when cross-linked with UV irradiation, thus avoiding an additional sterilization step. PHEMA films with long-range ordered hexagonal wrinkled patterns were selected to generate multicellular spheroids of tumor cell lines. The resulting spheroids exhibit a narrow size distribution and high cell viability. Preliminary tests demonstrated their potential in the screening of anti-cancer drugs.

2-hydroxyethyl methacrylate-derived reactive oxygen species stimulate ATP release via TRPA1 in human dental pulp cells

Extracellular ATP (adenosine triphosphate) and transient receptor potential ankyrin 1 (TRPA1) channels are involved in calcium signaling in odontoblasts and dental pain. The resin monomer 2-hydroxyethyl methacrylate (HEMA), used in dental restorative procedures, is related to apoptotic cell death via oxidative stress. Although the TRPA1 channel is highly sensitive to reactive oxygen species (ROS), the effect of HEMA-induced ROS on ATP release to the extracellular space and the TRPA1 channel has not been clarified in human dental pulp. In this study, we investigated the extracellular ATP signaling and TRPA1 activation by HEMA-derived ROS in immortalized human dental pulp cells (hDPSC-K4DT). Among the ROS-sensitive TRP channels, TRPA1 expression was highest in undifferentiated hDPSC-K4DT cells, and its expression levels were further enhanced by osteogenic differentiation. In differentiated hDPSC-K4DT cells, 30 mM HEMA increased intracellular ROS production and ATP release, although 3 mM HEMA had no effect. Pretreatment with the free radical scavenger PBN (N-tert-butyl-α-phenylnitrone) or TRPA1 antagonist HC-030031 suppressed HEMA-induced responses. These results suggest that ROS production induced by a higher dose of HEMA activates the TRPA1 channel in human dental pulp cells, leading to ATP release. These findings may contribute to the understanding of the molecular and cellular pathogenesis of tertiary dentin formation and pain in response to dental biomaterials.

Diels-Alder Cross-Linked, Washing-Free Hydrogel Films with Ordered Wrinkling Patterns for Multicellular Spheroid Generation

Three-dimensional (3D) multicellular spheroids are a new generation in vitro cell model, however, their applications are severely limited by difficulties in their generation. Here patterned poly(2-hydroxyethyl methacrylate) (PHEMA) hydrogel films were synthesized for their generation. Instead of polymerization of HEMA monomers in the presence of a cross-linker, here the PHEMA films were synthesized by cross-linking furan-functionalized linear PHEMA, PHEMA-furan, and maleimide-functionalized linear PHEMA, PHEMA-mal, via Diels-Alder (DA) reaction between furan and maleimide groups. A thermal treatment temperature of 75 °C was chosen for the cross-linking reaction. The occurrence of DA reaction was confirmed by IR spectra. Using this method, cross-linked PHEMA films with smooth surface were successfully synthesized in situ in the well of cell culture plates. The films were then patterned by simply adding water to swell them. Highly ordered, honeycomb-like wrinkling patterns were successfully obtained by adjusting the furan and maleimide contents in the precursor linear polymers. The patterned hydrogel films were used to generate multicellular spheroids. Guided by the patterns, 3D spheroids with narrow size distribution, tunable size, and high cell viability were successfully obtained. The patterned PHEMA films reported here exhibited a lot of advantages. The patterning method was quite simple and required no template or special equipment. They were synthesized in situ in commercial cell culture plates. Particularly, thanks to the clean nature of the DA reaction, no low molecular weight monomer, cross-linker, initiator, or catalyst, which were potentially cytotoxic, was involved in the film synthesis, and no byproduct was produced and left in the film. The resulting films presented a high biocompatibility, allowing the avoidance of the tedious washing step. The films synthesized here were expected to have high potential for massive production of well-defined multicellular spheroids.

Polymethyl methacrylate does not adversely affect the osteogenic potential of human adipose stem cells or primary osteoblasts

Custom-made polymethyl methacrylate (PMMA) bone cement is used to treat cranial bone defects but whether it is cytotoxic is still unsure. Possible PMMA-induced adverse effects in vivo affect mesenchymal stem cells and osteoblasts at the implant site. We aimed to investigate whether PMMA affects osteogenic and osteoclast activation potential of human mesenchymal stem cells and/or osteoblasts. Immediately after polymerization, PMMA was added to cultured human adipose stem cells (hASCs) or human osteoblasts (hOBs). Medium lactate dehydrogenase was measured (day 1), metabolic activity, proliferation, osteogenic and osteoclast-activation marker expression (day 1 and 7), and mineralization (day 14). PMMA did not affect lactate dehydrogenase, KI67 gene expression, or metabolic activity in hASCs and hOBs. PMMA transiently decreased DNA content in hOBs only. PMMA increased COL1 gene expression in hASCs, but decreased RUNX2 in hOBs. PMMA did not affect osteocalcin or alkaline phosphatase (ALP) expression, ALP activity, or mineralization. Only in hOBs, PMMA decreased RANKL/OPG ratio. In conclusion, PMMA is not cytotoxic and does not adversely affect the osteogenic potential of hASCs or hOBs. Moreover, PMMA does not enhance production of osteoclast factors by hASCs and hOBs in vitro. Therefore, PMMA bone cement seems highly suitable to treat patients with cranial bone defects.

Cytotoxicity and Pro-inflammatory Properties of Aliphatic Alpha, Beta-unsaturated Acid and Ester Monomers in RAW264.7 Cells and Their Chemical Reactivity

BACKGROUND/AIM

α,β-Unsaturated ester monomers such as methyl methacrylates (MMA), 2-hydroxyethyl methacrylates (2-HEMA), ethyleneglycol dimethacrylate (EGDMA) and triethyleneglycol dimetacrylate (TEGDMA) have been widely used in dentistry as dental materials. The present study was designed to clarify the proinflammatory activity of monomers.

MATERIALS AND METHODS

The cytotoxicity of the monomers and their effects on the expression of cyclooxygenase-2 (Cox2), nitric oxide synthase 2 (Nos2) and heme oxygenase 1 (Ho-1) mRNAs in RAW264.7 cells were determined using a cell counting kit and real-time reverse transcriptase-polymerase chain reaction, respectively.

RESULTS

The cytotoxicity declined in the order n-butyl acrylate (nBA) > acrylic acid > TEGDMA > EGDMA > methacrylic acid ≈ 2-HEMA > lauryl methacrylate > nBMA > MMA. nBA and EGDMA at 1 mM up-regulated the expression of Cox2 mRNA. In contrast, 1 mM nBA and 10 mM 2-HEMA up-regulated the expression of Nos2 mRNA. Up-regulation of Ho-1 mRNA expression was found for 0.1 mM nBA, 1 mM EGDMA and 2 mM TEGDMA. The electrophilicity, ω was calculated on the basis of the density function theory BLYP/6-31G*.

CONCLUSION

nBA and EGDMA with high ω values exerted potent pro-inflammatory activities. nBA, EGDMA and TEGDMA upregulated Ho-1 gene expression. Ho-1 gene activation of monomers may promote resistance of chemical carcinogenesis in biological systems.

Structure-cytotoxicity relationship of methacrylate-based resin monomers as evaluated by an anti-oxidant responsive element-luciferase reporter assay

To investigate the chemical structure-cytotoxicity relationship of methacrylate-based resin monomers, we studied their effects on anti-oxidant responsive element (ARE)-mediated transcription. HepG2 cells stably expressing an ARE-regulated luciferase reporter gene were cultured for 6 h with various concentrations of several resin monomers and subjected to a luciferase assay. The doseresponse curves observed for hydrophobic monomers with different hydrocarbon chains (MMA, EMA, PMA and BMA) began to rise at concentrations between 0.5 and 1 mM; the curves rose as the monomer concentrations increased up to 5 (BMA), 10 (PMA), or 30 mM (MMA and EMA). In contrast, hydrophilic monomers having a hydroxyl group (HEMA and HPMA) showed bell-shaped curves, and stimulated the reporter expression more strongly than the hydrophobic monomers in a low concentration range (0.5-5 mM). The results suggest that introduction of a hydroxyl group in a methacrylate-based resin monomer increases its intracellular electrophilic reactivity and cytotoxicity.

RP-HPLC detection and dosage method for acrylic monomers and degradation products released from implanted medical devices

Acrylic copolymers are useful in medical therapeutics. As in dental implants or intraocular lenses, acrylics are present in many medical devices or drug adjuvants. Industrial using of acrylics is still important in painting or textile manufacturing. Scientific research background has proved that acrylic suffer for depolymerized and cross-linking mechanisms under heating and photo-oxidative conditions. Those aging processes could lead to release of unreacted monomers and degradation products. We developed a new RP-HPLC method with good resolution, recovery, linearity, detection and quantification limits that is efficient for acrylic monomers quantification in in vitro and in vivo saline solution matrices. This method allows the detection of copolymer and medical devices degradation products too. Both the limit of quantification and the limit of detection for monomers and degradation products are above cytotoxic concentrations for human epithelial cells. Those biological results confirm the interest of the method for dosage of unreacted acrylics after polymerization and for the research of degradation products in body fluids as aqueous humor.

Epigallocatechin-3-Gallate Reduces Cytotoxic Effects Caused by Dental Monomers: A Hypothesis

Resin monomers from dental composite materials leached due to incomplete polymerization or biodegradation may cause contact allergies and damage dental pulp. The cytotoxicity of dental resin monomers is due to a disturbance of intracellular redox equilibrium, characterized by an overproduction of reactive oxygen species (ROS) and depletion of reduced glutathione (GSH). Oxidative stress caused by dental resin monomers leads to the disturbance of vital cell functions and induction of cell apoptosis in affected cells. The nuclear factor-erythroid 2-related factor 2 (Nrf2) pathway plays a key role in the cellular defense system against oxidative and electrophilic stress. Epigallocatechin-3-gallate (EGCG) can activate the Nrf2 pathway and induce expression of a multitude of antioxidants and phase II enzymes that can restore redox homeostasis. Therefore, here, we tested the hypothesis that EGCG-mediated protection against resin monomer cytotoxicity is mediated by activation of the Nrf2 pathway. This study will help to elucidate the mechanism of resin monomer cytotoxicity and provide information that will be helpful in improving the biocompatibility of dental resin materials.