Triethylene glycol dimethacrylate (TEGDMA) is a dentin-bonding agent and a major component of various dental restorative biomaterials. TEGDMA monomers are released from dental resins and induce dental pulp inflammation and necrosis. In this study, we have investigated the mechanism of TEGDMA-induced cytotoxicity of fibroblasts. Treatment of cultured human gingival and pulpal fibroblasts with 0.1-3 mM of TEGDMA for 24 h induced a concentration-dependent and variable cytotoxic effect. Fifty percent of toxicity (TC(50)) was obtained with 1.2 +/- 0.9 and 2.6 +/- 1.1 mM of TEGDMA for gingival and pulpal fibroblasts, respectively. Moreover, TEGDMA-induced cytotoxicity was associated with an early and drastic depletion of cellular glutathione (GSH), which started at 15-30 min and was almost complete at 4-6 h. Antioxidants, such as Trolox (0.01 mM), ascorbate (0.2 mM), and N-acetylcysteine (NAC) (5 mM) prevented the TEGDMA-induced cytotoxicity while GSH depletion was partially inhibited. Finally, a late production of reactive oxygen species (ROS) occurred in fibroblasts treated with TEGDMA for 3-4 h, as determined by 2',7'-dichlorofluorescein fluorescence, and was completely inhibited by Trolox (5 microM). The data show that TEGDMA induced a drastic GSH depletion followed by production of ROS, which may contribute to the toxicity of gingival and pulpal fibroblasts. Antioxidants, such as NAC, ascorbate, and particularly Trolox, appear useful in preventing cell damage mediated by resin-containing dental restorative materials.

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Abstract. Oral mucosal melanoma (OMM) is a fatal sarcoma of unknown etiology. Histological morphology and genetic events are distinct from those of its cutaneous counterpart. Mutation and up-regulation of c-kit has been identified in OMM which may activate downstream molecules such as RAS and RAF. These molecules are involved in the mitogenactivated protein kinase (MAPK) pathway leading to tremendous cell proliferation and survival. NRAS and BRAF mutation and protein expression have been studied in other melanoma subtypes. The purpose of this study was to determine RAS protein expression and NRAS and BRAF mutation in 18 primary OMM cases using immunohistochemistry and mutation analysis. Results showed that RAS is intensely expressed in both in situ and invasive OMMs. However, NRAS mutation was only observed in 2/15 polymerase chain reaction (PCR) amplified cases both of which were silent mutations. On the other hand, BRAF missense mutations were observed only in 1/15 cases with PCR amplification. NRAS and BRAF mutations were independent from previously reported c-kit mutations. The classical V600E BRAF mutation was not found; instead a novel V600L was observed suggesting that the oncogenic event in OMM is different from that in skin melanoma. The low frequency of NRAS and BRAF mutations indicate that these genes are not common, but probable events in OMM pathogenesis, most likely independent of c-kit mutation. IntroductionOral mucosal melanoma (OMM) is a malignant tumor in the oral cavity characterized by adjoining proliferation of atypical melanocytes and alteration of their normal functions. Although OMM is a rare tumor observed in 0.5% of oral malignancies and 0.2-8% of all melanomas, it has an aggressive behavior with poor prognosis (1,2). Precursor lesions have not been clearly elucidated but the onset of atypical melanocytic proliferation may be the earliest indication of its development (1,3). OMM based on histological examination can be classified as in situ, invasive and the combination of both, the latter being the most commonly observed (1,4).Mitogen-activated protein kinase (MAPK) is the most common pathway described in oncogenic events during the progression of melanoma (5-8). One of the molecules that participate in this signal transduction cascade is RAS encoded by the RAS gene consisting of HRAS, KRAS and NRAS. Another molecule that leads to the activation of MAPK is RAF consisting of ARAF, BRAF and CRAF. Frequent mutations in NRAS and BRAF have been observed in cutaneous melanoma (9-11). The MAPK pathway together with the phosphoinositide 3-kinase cascade (PI3K) can be triggered by activation of c-kit leading to the recruitment of signaling proteins involved in tremendous cell proliferation and survival (12). Mutations in c-kit have been identified in mucosal melanomas rendering c-kit as a promising molecular target (13)(14)(15).NRAS and BRAF mutations have been reported in subsets of mucosal melanomas, but most reports focused on combined mucosal sites (9,(16)(17)(18)(19). Most reports have cla...

Dickkopf (Dkk)-3, an inhibitor of the Wnt/β-catenin pathway, is reported as a potential tumor suppressor gene in many cancers. To gain a better comprehension of the mechanisms involved in the carcinogenesis of oral squamous epithelium, protein expression and localization of Dkk-3 and β-catenin was investigated in normal epithelium, dysplasias and squamous cell carcinoma (SCC). An increase in β-catenin and Ki-67 expressions was observed from dysplasias to poorly differentiated SCC. Interestingly, an increase in Dkk-3 positive cells was also noted, which was correlated to the cancer progression step. A change in Dkk-3 localization during the transformation of normal oral epithelium to SCC was clearly observed. Dkk-3 was localized in the cell membrane in normal oral epithelium and in dysplasias, whereas that was localized in both cell membrane and cytoplasm in SCC. These results suggest that Dkk-3 is involved in the carcinogenesis of SCC with a distinct function from those in other cancers.

Abstract. Head and neck squamous cell carcinoma (HNSCC) is one of the most frequently occurring types of cancer worldwide. We focused on the fact that the aberrant function of Wnt/β-catenin signaling is a frequent event in malignancies. Dickkopf (Dkk)-3 is a major negative regulator of Wnt/β-catenin signaling, which is a known tumor suppressor and is down-regulated in various types of cancer. However, the expression profile of the Dkk-3 protein in HNSCC has not yet been reported. The present study was conducted to investigate Dkk-3 protein expression in 90 cases of HNSCC tissue samples and HNSCC-derived cell lines. In contrast to findings available on other types of cancer, the Western blot analysis revealed that HNSCC cell lines expressed the Dkk-3 protein. In immunohistochemistry, 76 cases (84.4%) out of 90 tissue samples were Dkk-3-positive, whereas only 14 cases (15.6%) were negative. Notably, survival analysis showed that the Dkk-3 (-) group exhibited significantly longer disease-free survival (p=0.038), metastasis-free survival (p=0.013) and longer overall survival (p=0.155). The results showed that the Dkk-3 protein was dominantly expressed and may be involved in carcinogenesis and metastasis in HNSCC. Moreover, the findings suggest that the function of Dkk-3 differs depending on the tissue of origin, and that it may exert an oncogenic function in HNSCC.