Substances that elute from dental resins and composite materials may alter the growth and metabolism of cells with which they come in contact. The substances themselves may affect the cells or they may be hydrolyzed by tissue enzymes and the products of hydrolysis affect the cells. The cell changes may relate to growth, membrane composition and membrane-related functions, many of which are related to cell sterol and phospholipid composition. Two widely used components of resins, dimethylaminoethyl methacrylate (DMAEMA) and hydroxyethyl methacrylate (HEMA), produce such changes and will serve as prototype compounds for the study. The former affects cell neutral lipid and phospholipid metabolism while the latter appears to only alter neutral lipid metabolism. In the case of neutral lipid metabolism, the major effects of both compounds are decreases in cholesterol and increase in cholesterol esters, with some changes in other neutral lipid classes. In the case of phospholipids, there are changes in phosphatidycholine (PC) and phosphatidylethanolamine (PE) with accumulation of a methylated precursor of PC, dimethylphosphatidylethanolamine (DMPE). Changes in sterols and levels of methylated phospholipid alter a variety of membrane-associated functions.
The specific aims of the current proposal are to examine 1) hydrolysis of the methacrylates and their effects on cell lipid metabolism of oral epithelial and connective tissue cells, as well as a non-keratinizing epithelial cell type and a non-oral fibroblast cell type, 2) cellular phospholipase activity, and 3) cell Ca2+ fluxes. Cultures of the various cells will be exposed to the methacrylates and the patterns of lipid metabolism analyzed by thin-layer chromatography. Alterations in the phospholipid pathways in response to DMAEMA will be examined biochemically, since the different cell types respond in a different manner quantitatively. The ability of cells and tissue esterases to hydrolyze the materials will also be assessed using cell homogenates and commercial tissue esterases. Since methylated phospholipids and cell sterol composition can affect calcium fluxes, changes in [CA2+]i response to the materials will be determined using spectrofluorimetery. Phospholipase A2, C and D( PLA2, PLC, PLD) activities are affected by methylated phospholipids and by cell calcium, and products of their activity can provide not only precursors for the methylated phospholipid, but also components of the intracellular cell signaling pathways. These activities will be measured using radiolabeled substrates. These studies will provide information concerning the mechanism by which cells metabolize methacrylates and how the compounds can affect cells.
