Cytotoxicity and phospholipid-liposome phase-transition properties of 2-hydroxyethyl methacrylate (HEMA)

To elucidate the cytotoxic induction mechanisms of the hydrophilic HEMA, the comparative cytotoxic activities of HEMA and the hydrophobic monomers TEGDMA and MMA were studied, using erythrocytes, gingival fibroblasts and a salivary gland carcinoma cell line. Also, the gel-to-fluid phase transition properties (i.e. temperature, Tm; cooperativity, H/HHW; enthalpy, deltaH) of dipalmitoylphosphatidylcholine (DPPC) and DPPC/cholesterol (CS) liposomes (as a model for biological membranes) induced by methacrylates were investigated, using differential scanning calorimetry (DSC). In addition, the methacrylate-chemical-shifts in DPPC liposomes were assayed using NMR spectroscopy. Both the hemo lytic and cytotoxic activity declined in the order: TEGDMA> HEMA>MMA. The changes in Tm increased in the order: HEMA >TEGDMA, while in contrast, that of HEMA was slightly increased without changes in the deltaH. The DSC changes in DPPC/CS liposomes with HEMA were the largest of those recorded. The cytotoxicity of HEMA may be induced by the hydrophobic interaction derived from the molecular association of OH groups of HEMA and, in addition, by the preferential interaction with CS.