Cell lipid alterations resulting from prolonged exposure to dimethylaminoethylmethacrylate

Cytotoxicity and genotoxicity of DMABEE, a co-photoinitiator of resin polymerization, on CHO-K1 cells: Role of redox and carboxylesterase

The 4-dimethylaminobenzoic acid ethyl ester (DMABEE) is an important co-initiator for resin polymerization in dental resinous materials. As a radical forming chemical with high lipophilicity, the genotoxicity and cytotoxicity of DMABEE deserve prudent investigation. In this study, we found that DMABEE reduced the viability and proliferation of Chinese hamster ovary (CHO-K1) cells in a dose-dependent manner, and altered cell morphology at higher concentrations. G0/G1 cell cycle arrest was induced by DMABEE at 0.25-0.75 mM, and cell proportion of sub-G0/G1 phase was significantly elevated at 1 mM while cell apoptosis was observed. Genotoxic effect was noted when cells were treated by 0.1 mM DMABEE, as revealed by increase of micronucleus formation. Reactive oxygen species overproduction was observed as cells treated with 0.75 and 1 mM, while elevation of intracellular glutathione was noticeable since 0.1 mM. Contrary to our expectation, pretreatment by N-acetyl-l-cysteine enhanced the toxicity of DMABEE on CHO-K1 cells. Catalase mildly reduced the toxic effect and carboxylesterase showed obvious ability to reverse the toxicity of DMABEE. These findings highlight the mechanism of DMABEE toxicity and provide clues for safety improvement of its application in clinical dental treatment.

Development of a calcium-chelating hydrogel for treatment of superficial burns and scalds

Aims: Superficial burns and scalds are usually managed conservatively with traditional dressings. Failure to heal within 3 weeks leads to their management by skin grafting. Our aim was to develop a biomaterial to actively promote keratinocyte migration in superficial burns by modulating local cation concentrations to accelerate keratinocyte migration and deter wounds from contracting, thus potentially reducing the number of such wounds requiring grafting. Materials & methods: We investigated polymeric hydrogels for their Ca2+ chelating properties and enhancement of keratinocyte migration in human tissue-engineered skin models. Results: Dimethylaminoethyl methacrylate:methacrylic acid hydrogel coupled with elevated [Mg2+] reduced media [Ca2+], potentiating keratinocyte migration in tissue-engineered skin models, it also significantly reduced wound model contraction. Conclusion: Dimethylaminoethyl methacrylate:methacrylic acid hydrogels could promote wound healing and reduce wound contraction, a significant complication in burn wound healing.

Apoptosis induced by the monomers HEMA and TEGDMA involves formation of ROS and differential activation of the MAP-kinases p38, JNK and ERK

OBJECTIVES

Cytotoxic methacrylate monomers have been identified in aqueous extracts of freshly cured compomers. Some of these compounds, including HEMA and TEGDMA, induce apoptosis and necrosis in vitro. The aim of the present study was to elucidate possible signaling pathways involved in apoptosis following exposure to HEMA or TEGDMA in a salivary gland cell line.

METHODS

The cells were exposed to various concentrations of HEMA or TEGDMA. ROS formation was determined by dichlorofluorescein assay. Phosphorylated MAP-kinases ERK1/2, p38 and JNK, as well as specific caspases were identified by Western blotting. Apoptosis was assayed by fluorescence microscopy.

RESULTS

HEMA or TEGDMA exposure resulted in ROS formation and concentration-dependent apoptosis as well as phosphorylation of ERK. Phosphorylation of JNK and p38 was induced by HEMA. Selective inhibitors of ERK and JNK modified the apoptotic response after HEMA and TEGDMA exposure, whereas p38 inhibition modified the apoptotic response only after HEMA exposure. Vitamin C reduced HEMA-induced apoptosis.

SIGNIFICANCE

ROS formation and differential MAP kinase activation appear to be involved in the apoptotic response following exposure to HEMA and TEGDMA.

(Meth)acrylate monomer-induced cytotoxicity and intracellular Ca2+ mobilization in human salivary gland carcinoma cells and human gingival fibroblast cells related to monomer hydrophobicity

To elucidate a possible link between the cytotoxicity and Ca(2+) mobilization by (meth)acrylates, we investigated the cell survival of and change in [Ca(2+)](i) in human salivary gland (HSG) cells (salivary gland carcinoma cell line) and human gingival fibroblasts (HGF) cells treated separately with 9 (meth)acrylate monomers used in dentistry. The cell survival was determined by the MTT method, and the [Ca(2+)](i) changes after the stimulation with the (meth)acrylate monomers were measured in floating indo-1/AM-loaded cells in Ca(2+)-free medium. For both HSG and HGF cells, the cytotoxicity of the monomers was approximately proportional to their hydrophobicity (logP). No increase in [Ca(2+)](i) was found with hydrophilic monomers, even with 10mm stimulation. [Ca(2+)](i) elevation by hydrophobic monomers occurred in a dose- and hydrophobic-dependent manner. The [Ca(2+)](i) change in HSG cells appeared as twin peaks, i.e., an initial sharp peak followed by a delayed broad one; whereas with the HGF cells only a single broad peak was seen, possibly dependent on their membrane quality. Pretreatment with n-butanol or methylmethacrylate enhanced the butylmethacrylate-induced [Ca(2+)](i) elevation, suggesting the [Ca(2+)](i) elevation by (meth)acrylate may be related to monomer hydrophobicity and cell type. The causal link between the cytotoxicity and [Ca(2+)](i) mobilization of monomers is discussed.

Alterations of cell lipids by metal salts

Metallic medical devices undergo degradation in vivo and the degradation products affect the chemistry and biological responses of cells and tissues in the immediate vicinity. The responses vary with the metal and cell type. In the current study, we examined the effects of several metals on a human monocytic cell line. Monocytes are important effector cells capable of responding rapidly to inflammatory and immune stimuli in a variety of ways, including production of inflammatory proteins, differential expression of surface adhesion molecules, enhanced phagocytic activity, and activation and differentiation to macrophages. Cells were exposed in the presence of (14)C-acetate to titanium, nickel, chromium, copper, or cobalt or vanadium at concentrations that were subinhibitory or inhibitory based on cellular mitochondrial dehydrogenase activity. Cell lipids were then extracted, separated by thin layer chromatography, and quantitated by liquid scintillation spectrometry. Total cell protein also was measured. Titanium reduced cell protein content at concentrations that were noninhibitory to mitochondrial dehydrogenase activity, whereas neither chromium nor cobalt affected protein amounts at dehydrogenase-inhibitory concentrations. In cells exposed to vanadium, the protein- and dehydrogenase-inhibitory concentrations were similar. The major effects on cell lipids appeared to occur in the neutral lipids, although chromium, cobalt, and titanium produced changes in some major phospholipids. These results suggest that metals differentially affect various metabolic pathways in THP-1 cells, perhaps related to their abilities to enter the cells or interact with the membrane. These alterations to the cells may affect the cells' abilities to respond to various stimuli that can damage the tissues.

Effects of DMAEMA and 4-methoxyphenol on gingival fibroblast growth, metabolism, and response to interleukin-1

Some components of resins used in restorative dentistry have been shown to alter metabolism in cultured oral epithelial cells. Here we have extended such studies to the underlying supportive tissue, composed of gingival fibroblasts (GF). Primary cultures of human GF were transferred to serum-free, defined medium and exposed to either 2-(dimethylamino)ethyl methacrylate (DMAEMA) or 4-methoxyphenol (MEHQ) for 24-72 h. At a DMAEMA concentration of 6.4 mM, which was well tolerated by epithelial cells, GF numbers, as estimated by crystal violet, and metabolic activity, as indicated by MTT, were reduced at least 60% within 24 h of exposure. Between 1.6 and 6.4 mM, there were dose-related reductions in cell numbers; however, at lower doses (0.32-0.64 mM), proliferation was stimulated. MEHQ, between 8 and 16 microM, did not stimulate cellular protein production. To examine the capacity of GF to respond to an inflammatory stimulus, interleukin-6 (IL-6) production by confluent cells was estimated without or with these compounds. DMAEMA (1.6- 6.4 mM) virtually eliminated the acute IL-6 response of these cells to an interleukin-1beta challenge; only at 0.32 mM DMAEMA was the response restored. MEHQ (1.6-16 microM) reduced the IL-6 response by >50%. In summary, both growth and the innate immune responsivity of GF were affected by DMAEMA and MEHQ in vitro; thus, these compounds deserve careful evaluation for biocompatibility.

The induction of micronuclei in vitro by unpolymerized resin monomers

Components of resin materials may damage DNA, leading to genetic alterations in mammalian cells. Here, monomers were analyzed for the induction of chromosomal aberrations indicated by micronuclei induced in V79 cells. A dose-related increase in the numbers of micronuclei was observed with triethyleneglycol dimethacrylate (TEGDMA), 2-hydroxyethyl methacrylate (HEMA), and glycidyl methacrylate (GMA). These effects were reduced, however, by a metabolically active microsomal fraction from rat liver. The very low activity of Bis-GMA and UDMA and the elevated numbers of micronuclei caused by high concentrations of methyl methacrylate and bisphenol A were associated with cytotoxicity. Our findings provide evidence for the induction of micronuclei by TEGDMA, HEMA, and GMA under physiological conditions, indicating clastogenic activity of these chemicals in vitro. Since it has been shown that TEGDMA also caused gene mutations and DNA sequence deletions in mammalian cells, the activity of this substance should be analyzed in vivo.

Metabolic effects of dental resin components in vitro detected by NMR spectroscopy

Earlier studies have shown that the comonomer triethyleneglycol-dimethacrylate (TEGDMA) and the photostabilizer 2-hydroxy-4-methoxybenzophenone (HMBP) are cytotoxic and inhibit cell growth. It was the aim of this study to elucidate the underlying metabolic effects of TEGDMA and HMBP on immortal contact-inhibited Swiss albino mouse embryo cells (3T3 fibroblasts) by nuclear magnetic resonance (NMR) spectroscopy. Cell extracts and culture media were analyzed by NMR spectroscopy for metabolic changes after incubation for 24 hours with ED20-concentrations of TEGDMA and HMBP. TEGDMA could be detected in all fractions (cytosol, lipid fractions, and culture media) of 3T3 cells, while HMBP was found only in the lipid fraction accumulated at a maximum rate (51 nmol/mg DNA) compared with TEGDMA (27 nmol/mg DNA). TEGDMA increased the concentration of phosphomonoesters to 180+/-36% and decreased the phosphodiesters to 65+/-5% of controls (control = 100%). Thus, the turnover of phospholipids was enhanced, whereas content and composition of phospholipids of membranes did not alter markedly. Additionally, TEGDMA changed the metabolic state of cells, indicated by slight decreases of nucleoside triphosphates and an increase in the ratio of nucleoside diphosphates to nucleoside triphosphates, while HMBP had no effect. The most remarkable effect of TEGDMA was a nearly complete decline of the intracellular glutathione levels. Analysis of our data shows that NMR spectroscopy of cell-material interactions may reveal metabolic effects of organic test substances which are not detectable by standard in vitro assays. The comonomer TEGDMA affected the metabolism of the cells on different levels, while HMBP accumulated in the lipid fraction and induced significantly fewer effects on cell metabolism.

Effects of BisGMA and TEGDMA on proliferation, migration, and tenascin expression of human fibroblasts and keratinocytes

Previous studies have documented a marked cytotoxic potency of BisGMA and TEGDMA. The purpose of this investigation was to determine if these substances also affect proliferation, migration, and tenascin expression of primary human gingival fibroblasts (HGF) and immortalized human keratinocytes (HaCaT). These parameters play an important role in healing wounds. HGF and HaCaT cultures were incubated with TEGDMA and BisGMA. Cell proliferation (BrdU-assay) and migration (Boyden method) were determined 24 h after incubation. Tenascin expression was investigated four and seven days after treatment. Results were statistically evaluated by ANOVA using the Wilcoxon-Mann-Whitney test (p < 0.05). Proliferation of both cell types was significantly inhibited at concentrations > or = 0.25 mM (TEGDMA) or > or = 0.01 mM (BisGMA). Migration of HaCaT was significantly increased after incubation with BisGMA for 24 h. TEGDMA did not alter migration of HGF and HaCaT. In addition, TEGDMA had no effect on tenascin expression of both cell cultures. After 4 days of incubation, BisGMA (at a concentration of 0.01 mM) significantly reduced tenascin production of HaCaT cultures related to cell number. However, 7 days after treatment, BisGMA significantly increased tenascin expression of HGF and HaCaT cultures. Altogether, our results indicate that BisGMA can affect migration of keratinocytes and alters the expression of the extracellular matrix component tenascin. Thus, BisGMA may significantly influence the healing of injured oral tissues.

Changes in cell phospholipid metabolism in vitro in the presence of HEMA and its degradation products

OBJECTIVES

Diacylglycerol-kinase (DAG-kinase) is an enzyme that phosphorylates diacylglycerol (DAG) to phosphatidic acid (PA), which serves as a precursor to phosphoglycerides involved in cell signaling or as cell membrane structural components. DAG-kinase can be inhibited by diacylethylene glycols (DAEG). We hypothesize that 2-hydroxyethyl methacrylate (HEMA) may alter phosphorylation of DAG to PA following intracellular formation of DAEG.

METHODS

Cultured rabbit kidney (RK13) epithelial cells were treated with HEMA, EG, or known inhibitors of DAG-kinase for 24 h, then exposed to [32P]O4- in the presence of a synthetic diacylglycerol for 2 h. Other cultures were radiolabeled with [3H]-oleic acid for 24 h, then exposed to HEMA for an additional 24 h. The cells were harvested and the lipids extracted. Radioactive lipids were separated by thin layer chromatography, located by autoradiography, and quantitated as cpm/ug protein. Cell cultures treated with HEMA were homogenized and the DAG-kinase activity was assayed and expressed as cpm/ug protein. Data were analyzed by one-way ANOVA and Newman-Keuls Multiple Comparison Test.

RESULTS

Cultures exposed to HEMA or known DAG-kinase inhibitors exhibited reduced incorporation of radioactivity in the PA fraction compared to control cultures. Direct assays of DAG-kinase activity from cells exposed to HEMA demonstrated decreased enzyme activity. Evaluation of cell phospholipid synthesis showed altered formation of phosphatidylethanolamine and phosphatidylcholine.

SIGNIFICANCE

Results suggest that HEMA impairs formation of PA, possibly by acylation of EG released by hydrolysis of the HEMA and resultant production of the inhibitor DAEG. The decreased availability of PA may alter PA-dependent cell structural lipid pathways and lipid-dependent signaling pathways, altering cell growth.