The effects of dental resin polymerization initiators on cell lipid metabolism

Abstract

Benzoyl peroxide and camphorquinone, initiators of heat and light polymerized dental resins, are considered cytotoxic ~d the mech~ism of cytotoxicity suggested is lipid I I peroxidation-induced membrane damage. The mechanism of such damage is not clear. ! The objectives of our current study were ~) To study the effects of the various . . I concentrations of initiators benzoyl peroxi~e and camphorquinone on cell lipid I metabolism, 2) To study the effects of peroxiJation-inducing concentrations of benzoyl I I , peroxide on turnover of major lipids, 3) To stqdy the effects of the materials on the lipid I second messenger ceramide and on apoptotic r~sponses in cells. I Methods. Lipid metabolism i.e. synthesis as /well as turnover, was measured using 14C . I acetate in HCP and THP-1 cells. The lipid~ were extracted using the Bligh & Dyer method of lipid ~xtraction and separated Jsing one and two-dimensional thin-layer I chromatography. The lipid peroxidation was ~easured using thio-barbituric acid reactive . i substance (T -BARS) produced in response /to benzoyl peroxide combined with ferric . I chloride and camphorquinone with, or withoLt activation with light, when combined with an enhancer dimethylaminoethyl ethyl methacrylate (DMAEMA). Ceraniides were detected by extracting neutral lipids using chloroform/methanol extraction and separated by high performance thin-layered chromatjgraphy (HPTLC). DNA fragmentation assay ) was used to detect apoptosis. Results. Benzoyl peroxide and ,camphorquinone /at minimally inhibitory concentrations induced similar chang:e s in neutral "lipid.s such ~I incre.a sed .tr igly.ce rides and decrea.s ed cholesterol synthesis. Sphingomyelin changes 'o/ere specific to HCP cells exposed to camphorquinone. The changes were mostly rtlat~d to altered synthesis rather than turnover. The· changes were also cell-type specific. Toxic concentrations induced peroxidation as measured by T -BARS in a time and dose dependent manner only in HCP cells while THP-1 showed different responses. Major lipid profiles were unaltered at peroxidation-inducing concentrations. Sub-toxic concentrations of benzoyl peroxide : induced ceramide elevation at 24 hours, after ~n initial inhibition at 10 minutes, in both cell types. DNA fragmentation was, however,.' evident only in THP-1 cells at sub-toxic concentration. Conclusion. Both initiators, benzoyl peroxide and camphorquinone, induced changes in neutral lipids. Their mechanism of peroxidation-inducing membrane damage was not dependent on the quantitative alteration in major polar.lipids. Benzoyl peroxide induced changes in ceramides in both HCP and THP-1 cells. Induction of apoptosis was clearly seen only in THP-1 cells in response to benzoyl peroxide while HCP cells lacked this response.