Sensitivity of human dental pulp cells to eighteen chemical agents used for endodontic treatments in dentistry.

To determine the adverse effects against human dental pulp tissue, the sensitivity of human dental pulp cells (D824 cells) to 18 chemical agents used for endodontic treatments in dentistry was examined. The cytotoxicity, as determined by a decrease in colony-forming ability of cells treated with the chemical agents, increased as the concentration increased. As a quantitative measure of the cytotoxic effect, LC(50), the concentration which induces a 50% lethality, was extrapolated from the concentration-response curves. The rank of the chemical agents according to their cytotoxic effect (LC(50)) was sodium arsenite > formaldehyde > hydrogen peroxide > zinc oxide > thymol ≈ iodoform ≈ eugenol > guaiacol > ethylenediaminetetraacetic acid ≈ iodine > procaine > lidocaine ≈ chloramphenicol ≈ m-cresol > calcium hydroxide ≈ sodium hypochlorite ≈ phenol ≈ p-phenolsulfonic acid. To compare the cytotoxicity and the levels of apoptosis and mRNA expression of five genes related to the function of dental pulp tissue, D824 cells treated with the LC(50) concentrations of chemical agents were assayed by the TUNEL method and quantitative reverse transcription polymerase chain reaction analysis, respectively. The inducibility of apoptotic cells and the level of mRNA expression of the genes varied with the chemical agents, indicating that both effects occurred independent of the rank of cytotoxic effect of the chemical agents. The results not only provide information concerning cytotoxicity of various chemical agents to human dental pulp cells, but also show an insight into the diversity of the pharmacodynamic action of the chemical agents.

Changes in expression of imprinted genes following treatment of human cancer cell lines with non-mutagenic or mutagenic carcinogens.

It remains possible that chemicals that act by mutagenic mechanisms as well as chemicals that do not induce gene mutations may affect epigenetic gene expression. To test the possibility, we investigated the ability of both types of chemicals to alter the expression of five imprinted genes, PEG3, SNRPN, NDN, ZAC and H19, using two human colon cancer cell lines and a human breast cancer cell line. The expression of imprinted genes was changed by some non-mutagenic and mutagenic carcinogens independent of their mutagenic activity. The genes most commonly exhibiting the changes in expression were SNRPN and PEG3. Alterations of the expression of NDN and ZAC were also observed in some conditions. Methylation-specific PCR and chromatin immunoprecipitation assays suggest the possibility that changes in the expression of SNRPN may be associated with DNA hypomethylation and histone acetylation of the promoters and euchromatinization of the heterochromatic domains of the promoters. Changes in expression of the imprinted genes, PEG3 and NDN, were also observed in cells immortalized by treatment of normal human fibroblasts with 4-nitroquinoline 1-oxide or aflatoxin B1. We previously demonstrated that expression of the cancer-related gene, INK4a, in these immortal cells was lost via epigenetic mechanisms. The results prove that, in cancer cells, some mutagenic or non-mutagenic carcinogens can epigenetically influence the transcription levels of imprinted genes and also suggest the possibility that some chemical carcinogens may have epigenetic carcinogenic effects in human cells.

Clastogenic activity of seven endodontic medications used in dental practice in human dental pulp cells.

Numerous and varied chemical agents are used for endodontic treatments in dental practice. Endodontic medications are administered directly to the teeth in relatively high concentrations and chemical agents applied to enamel or dentin can penetrate the dental pulp tissue and circulate through the body in the bloodstream. In the present study, to assess safety regarding mutagenicity, we investigated the ability of seven endodontic medications to induce chromosome aberrations in human dental pulp cells. Chromosome aberrations were induced in cells treated with each of six endodontic medications, eugenol, guaiacol, modified phenol, phenol, thymol, and zinc oxide. The other endodontic medication, zinc chloride, failed to induce chromosome aberrations in the presence or absence of exogenous metabolic activation. The percentages of cells with polyploid or endoreduplication were not enhanced by any of the endodontic medications tested. Our results indicate that the endodontic medications that exhibited a positive response are potentially mutagenic to human cells.

Ability of root canal antiseptics used in dental practice to induce chromosome aberrations in human dental pulp cells.

Root canal antiseptics are topically applied to root canals within the pulpless teeth to treat the root canal and periapical infections. Because the antiseptics that are applied to root canals can penetrate through dentin or leak out through an apical foramen into the periodontium and distribute by the systemic circulation, it is important to study the safety of these antiseptics. In the present study, we examined the ability to induce chromosome aberrations in human dental pulp cells of five root canal antiseptics, namely, carbol camphor (CC), camphorated p-monochlorophenol (CMCP), formocresol (FC), calcium hydroxide, and iodoform which are most commonly used in dental practice. Statistically significant increases in the levels of chromosome aberrations were induced by CC, FC, or iodoform in a concentration-dependent manner. Conversely, CMCP and calcium hydroxide failed to induce chromosome aberrations in the absence or presence of exogenous metabolic activation. The percentages of cells with polyploid or endoreduplication were enhanced by FC or iodoform. Our results indicate that the root canal antiseptics that exhibited a positive response are potentially genotoxic to human cells.

Assessment using human dental pulp cells of clastogenicity of antiseptics used in dental practice and agents for root canal enlargement and cleaning.

Numerous and varied chemical agents are used as topically applied drugs in dental practice. As they are administered directly to the oral cavity, it is important to study the safety of these agents. In the present study, to assess safety regarding mutagenicity, we investigated the abilities of six antiseptics to induce chromosome aberrations in human dental pulp cells. The antiseptics tested were benzalkonium chloride, benzethonium chloride, iodine glycerin, iodine tincture, oxydol, and povidone-iodine. In addition, we tested two agents used for root canal enlargement and cleaning, ethylenediaminetetraacetic acid and sodium hypochlorite. Chromosome aberrations were induced only in cells treated with the highest concentration of iodine tincture for 30 h. The other chemical agents failed to induce chromosome aberrations in the presence or absence of exogenous metabolic activation. The concentration of iodine tincture to which patients are exposed in dental practice is 1000-fold the concentration that induced chromosome aberrations in the present study. Our findings suggest that iodine tincture is mutagenic to human cells.