Methacrylates Less Toxic than Acrylates in Correlating Cell Membrane Damage

Previous reports have shown that methacrylate monomers are less cytotoxic than acrylate monomers. Objectives: The objective was to evaluate cytotoxicity differences among acrylate and methacrylate monomers at the level of cell membrane disruption. Methods: Loss of cell viability of acrylate/methacrylate pairs were evaluated using L929 cell cultures with the neutral red uptake assay. Cell membrane disruption was measured with the calcein release assay, which measures calcein release from calcein-entrapped vesicles made of POPC/CS (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC)/cholesterol (CS). Using 96-well plate format, loss of cell viability in half the cell population (IC50) and calcein-release was measured after exposure of hydroxyethyl acrylate (HEA), hydroxyethyl methacrylate (HEMA), ethyl acrylate (EA) and ethyl methacrylate (EMA) to cells or vesicles for 24h at 37°C. Results: The IC50 of monomers with methacrylate function, HEMA and EMA, was at concentrations 71 and 27 fold larger than their un-methylated acrylate counterparts HEA (0.21mM) and EA (0.58mM), respectively, making these more cytotoxic than the methacrylate monomers (ANOVA, Bonferroni, p<0.05). Percent calcein release with 100mM HEA or EA was 3 and 5 fold higher than 100mM HEMA or EMA, respectively, indicating that the acrylates were more cell membrane damaging than methacrylates. Conclusion: Methylation of the acrylate moiety significantly attenuates cytotoxicity compared to their un-methylated counterparts and that these differences can be explained in part at the level of lipid cell membrane disruption. Study supported by NIH/NIDCR grant DE14379