Molecular interactions of dental resins with human oral and intestinal cells

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Organic components are released from many resin-based restorative materials. Contrary to the rapid increase in their clinical use, very little is known about the biological effects and the cellular mechanisms of substances released at low concentrations during their long-term clinical service on primary target tissues, such as the oral mucosa. Comonomers, like 2-hydroxyethyl methacrylate (HEMA), and (photo)initiators of the polymerization reaction, like camphorquinone (CQ) and dibenzoyl peroxide (DBPO), induce intracellular redox homeostasis strain in various cell types. Our results showed that CQ induces apoptosis and CQ and DBPO generate oxidative damages in genomic DNA of human oral keratinocytes. Moreover, both initiators affect the cellular metabolism involving the redox sensitive transcription factor Nrf2 (low level effect). We postulate, that such a modification of the cellular redox homeostasis influences the composition of the extra cellular matrix (ECM) and, therefore, potentially the tissue homeostasis. Purpose of our proposal is to investigate, (1) whether human keratinocytes treated with dental materials show differences in gene expression of proteins involved in oxidative stress response and in ECM composition between cells cultured in monolayers (2D) and in co-culture with fibroblasts using a 3D (three dimensional)-ECM model of the oral mucosa and (2) whether and to what extent a material-induced activation of redox sensitive transcription factors influences the expression of components of the ECM. Therefore, we will compare the effects of CQ, DBPO, and HEMA on relevant parameters of tissue homeostasis between human cells of the oral mucosa (keratinocytes, fibroblasts), cultivated in monolayers and in a 3D-ECM-model. We will use well-established methods to investigate cell proliferation, differentiation, and apoptosis. The expression of molecular components of the ECM (e.g., membrane receptors, matrix metalloproteinases and their inhibitors, cytokines) and oxidative stress pathways (Nrf2, NFkappaB, and target genes) will be analyzed by real time PCR and protein analysis (western blot, ELISA, activity assays). Our results will provide valuable data concerning the material-modulated oxidative cellular metabolism and its significance for tissue homeostasis. This study will significantly extend our body of knowledge about the toxicological effects of dental resins and will generate important data for the risk assessment of present materials and the development of new biocompatible materials in restorative dentistry.