Takeo W. Tsutsui

Comparison of Stem-cell-mediated Osteogenesis and Dentinogenesis

The difference between stem-cell-mediated bone and dentin regeneration is not yet well-understood. Here we use an in vivo stem cell transplantation system to investigate differential regulation mechanisms of bone marrow stromal stem cells (BMSSCs) and dental pulp stem cells (DPSCs). Elevated expression of basic fibroblast growth factor (bFGF) and matrix metalloproteinase 9 (MMP-9, gelatinase B) was found to be associated with the formation of hematopoietic marrow in BMSSC transplants, but not in the connective tissue of DPSC transplants. The expression of dentin sialoprotein (DSP) specifically marked dentin synthesis in DPSC transplants. Moreover, DPSCs were found to be able to generate reparative dentin-like tissue on the surface of human dentin in vivo. This study provided direct evidence to suggest that osteogenesis and dentinogenesis mediated by BMSSCs and DPSCs, respectively, may be regulated by distinct mechanisms, leading to the different organization of the mineralized and non-mineralized tissues.

In vitro chromosome aberration tests using human dental pulp cells to detect the carcinogenic potential of chemical agents

To examine if human dental pulp cells are useful for assessing the carcinogenic potential of chemical agents, we cultured human dental pulp cells from adults and studied the ability of chemical agents known to be carcinogenic to induce chromosome aberrations in these cells. We confirmed that human dental pulp cells in primary or secondary cultures had the capability of accumulating calcium in vitro as detected by Alizarin red staining and generating dentin-like tissue in immunocompromised mice. These phenotypes were maintained even in cells at seven passages. Next, we examined if chromosome aberrations were induced by exposure of human dental pulp cells (designated here as D824 cells) at seven to nine passages to chemical agents with carcinogenic activity. Statistically significant increases in the frequencies of chromosome aberrations were induced in D824 cells treated with a direct-acting carcinogen, mitomycin C, for 3 h. Chromosome aberrations were also induced at statistically significant levels in D824 cells treated with an indirect-acting carcinogen, cyclophosphamide, for 2 h in the presence of exogenous metabolic activation with rat liver postmitochondrial supernatant. Cyclophosphamide failed to induce chromosome aberrations in the absence of exogenous metabolic activation. Although the reliability of chromosome aberration tests using human dental pulp cells remains to be validated by studying the ability of various other chemical agents with or without carcinogenic activity to induce chromosome aberrations, this chromosome aberration test system may be useful for carcinogenic risk assessment in the target cells.To examine if human dental pulp cells are useful for assessing the carcinogenic potential of chemical agents, we cultured human dental pulp cells from adults and studied the ability of chemical agents known to be carcinogenic to induce chromosome aberrations in these cells. We confirmed that human dental pulp cells in primary or secondary cultures had the capability of accumulating calcium in vitro as detected by Alizarin red staining and generating dentin-like tissue in immunocompromised mice. These phenotypes were maintained even in cells at seven passages. Next, we examined if chromosome aberrations were induced by exposure of human dental pulp cells (designated here as D824 cells) at seven to nine passages to chemical agents with carcinogenic activity. Statistically significant increases in the frequencies of chromosome aberrations were induced in D824 cells treated with a direct-acting carcinogen, mitomycin C, for 3 h. Chromosome aberrations were also induced at statistically significant levels in D824 cells treated with an indirect-acting carcinogen, cyclophosphamide, for 2 h in the presence of exogenous metabolic activation with rat liver postmitochondrial supernatant. Cyclophosphamide failed to induce chromosome aberrations in the absence of exogenous metabolic activation. Although the reliability of chromosome aberration tests using human dental pulp cells remains to be validated by studying the ability of various other chemical agents with or without carcinogenic activity to induce chromosome aberrations, this chromosome aberration test system may be useful for carcinogenic risk assessment in the target cells.

Immortalization of normal human gingival keratinocytes and cytological and cytogenetic characterization of the cells

Most in vitro studies of oral carcinogenesis in human cells are carried out with oral keratinocytes immortalized by human papillomavirus type 16 DNA. However, because various etiological factors for oral cancer are known, it is important to establish new human keratinocyte cell lines useful for studying the mechanism of oral carcinogenesis. Normal human gingival keratinocytes in secondary cultures grown in serum-free medium were either transfected with origin (−) SV40 DNA or sequentially transfected with origin (−) SV40 DNA and human c-fos. The transfected cells were continually passaged and analyzed for cytological and cytogenetic characterizations. Four immortal cell lines were grown for over 1100 days in culture and maintained a vigorous growth for over 250 population doublings. They expressed SV40 T antigen, cytokeratins 8 and 18, and E-cadherin, and overexpressed the c-Fos protein. The immortal cell lines had telomerase activity but lacked transformed phenotypes on soft agar or in nude mice. Each cell line had nonrandom chromosomal abnormalities and minisatellite alterations. One of the immortal cell lines, NDUSD-1, retained the capability to deposit calcium, which was also demonstrated in normal human gingival keratinocytes by alizarin red staining, indicating the possibility that NDUSD-1 cells may retain some natural characteristics of normal gingival keratinocytes. Because the oral ectoderm plays an important role in tooth development, these immortal cell lines may be useful in various experimental models for investigations of oral biology and oral carcinogenesis.

Effects of a catechol-O-methyltransferase inhibitor on catechol estrogen-induced cellular transformation, chromosome aberrations and apoptosis in Syrian hamster embryo cells

To examine a possible mechanism of endogenous estrogen‐induced carcinogenesis, we studied the effect of the catechol‐O‐methyltransferase (COMT) inhibitor Ro 41‐0960 on cell transforming and clastogenic activities of 2 catechol estrogens 2‐ and 4‐hydroxyestrone (2‐ or 4‐OHE1) using Syrian hamster embryo (SHE) cells. COMT activity was assayed by determining the methylation of 2‐ or 4‐OHE1 using gas chromatography. The production of 2‐methoxyestrone in cultures treated with 2‐OHE1 was approximately 2‐fold that of 4‐methoxyestrone in cultures treated with 4‐OHE1. 4‐OHE1 induced morphological transformation at a higher frequency than 2‐OHE1 did and the frequencies of cell transformation and chromosome aberrations were not significantly changed in cells treated with 4‐OHE1 in the presence of Ro 41‐0960. In contrast, the frequencies of cell transformation and chromosome aberrations were markedly increased in cells treated with 2‐OHE1 along with Ro 41‐0960 when compared to cells treated with 2‐OHE1 alone. In addition, both catechol estrogens induced P53 protein expression and apoptosis. The frequencies of apoptotic cells induced by the catechol estrogens were modified by the COMT inhibition in a manner similar to those observed with the chromosome aberrations assay and the cell transformation assay, indicating that each effect by the catechol estrogens at the three measured endpoints might be caused by a mechanism similar to the others. Our findings indicate that COMT activity has an influence on cell transforming activity and its related genetic effects of catechol estrogens in SHE cells, which implies that an individual activity of COMT may be one of the etiological factors in endogenous estrogen‐induced carcinogenesis.

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.

Expression status of mRNA for sex hormone receptors in human dental pulp cells and the response to sex hormones in the cells

OBJECTIVES Sex hormone receptors are reported to be present in human dental pulp (HDP) cells. The purpose of this study was to examine the biological significance of oestrogen and androgen receptors (ER and AR, respectively) in HDP cells. DESIGN We isolated HDP cells expressing ER- and AR-mRNAs and investigated the expression status of the receptors and the response to sex hormones in the cells. RESULTS HDP cells expressing ER- and/or AR-mRNAs had the ability to form alizarin red S-positive nodules in which calcium and phosphorus were deposited in vitro and to differentiate into odontoblasts-like cells and dentine-like tissue in vivo. Individual clones isolated from HDP cells exhibited a different expression pattern of mRNA for ER and AR. Some clones expressed ERα- and/or ERβ-mRNAs and the others coexpressed ER- and AR-mRNAs. Using the Ingenuity software, we found that 17β-estradiol (E2) and dihydrotestosterone (DHT) could act directly on HDP cells through ER-or androgen signalling-mediated mechanisms. E2 or DHT stimulated the mRNA expression for genes related to odontogenesis of dentine-containing teeth and odontoblast differentiation, suggesting that ER and AR in HDP cells may be involved in dentinogenesis. CONCLUSIONS Our findings provide new insights into the biological significance of sex hormone receptors in HDP cells.

Induction of mRNA expression of osteogenesis-related genes by guaiacol in human dental pulp cells

To investigate the stimulating effect of endodontic medications on the mRNA expression of some osteogenesis-related genes associated with reparative dentinogenesis and hard-tissue formation, human dental pulp cells (D824 cells) were treated with calcium hydroxide (Ca (OH)2), formocresol, or guaiacol. The effect on growth was determined by growth curves of D824 cells treated for 1–3 days with 0.03–0.3 mM Ca (OH)2, 0.0007%–0.0014% formocresol, or 0.24–2.43 mM guaiacol. The mitotic activity of individual cells and the mRNA expression of the osteogenesis-related genes for alkaline phosphatase (ALP), type I collagen (COL-1), and bone sialoprotein (BSP) in the cells treated for 24 h with the same concentrations of the medications as described above were determined by colony-forming efficiency and by real-time quantitative reverse transcription polymerase chain reaction (qRT-PCR) analysis, respectively. Cellular growth and mitotic activity were scarcely affected by Ca (OH)2, but were significantly reduced by formocresol or guaiacol. The mRNA expression of the osteogenesis-related genes was little affected by Ca (OH)2 or formocresol, but was significantly enhanced by guaiacol. The results indicate that guaiacol may stimulate the mRNA expression of genes associated with reparative dentinogenesis and hard-tissue formation in human dental pulp cells, suggesting that the novel property of guaiacol provides new insights into the utilization of guaiacol in endodontic therapy.

In Vivo Stem Cell Transplantation Using Reduced Cell Numbers

Dental pulp stem cell (DPSC) characterization is essential for regeneration of a dentin/pulp like complex in vivo. This is especially important for identifying the potential of DPSCs to function as stem cells. Previously reported DPSC transplantation methods have used with huge numbers of cells, along with hydroxyapatite/tricalcium phosphate (HA/TCP), gelatin and fibrin, and collagen scaffolds. This protocol describe a transplantation protocol that uses fewer cells and a temperature-responsive cell culture dish.

Modulation of Transforming and Clastogenic Activities of Catechol Estrogens by a Catechol-O-methyltransferase Inhibitor in Syrian Hamster Embryo Fibroblasts

Catechol estrogens (CEs) are considered critical intermediates in estrogen (E)-induced carcinogenesis. Previously, we demonstrated that estradiol (E2), estrone (E1), and four of their catechol estrogens, 2- and 4-OHE2 and 2- and 4-OHE1 induced morphological transformation in Syrian hamster embryo (SHE) cells, and their transforming activities varied as follows: 4-OHE1 > 2-OHE1 > 4-OHE2 > 2-OHE2 ≧ E1, E2, which are consistent with the genetic effects, i.e., chromosome aberrations and DNA adduct formation, of each E. To further elucidate the mechanism of hormonal carcinogenesis, we studied the effect of the catechol-O-methyltransferase (COMT) inhibitor Ro41-0960 on the transforming and clastogenic activities of the CEs using SHE cells. The frequencies of transformation and chromosome aberrations induced by 4-OHE1 were not affected by co-treatment with Ro-41-0960, but those induced by 2-OHE1 were markedly enhanced. The frequency of transformation induced by 4-OHE1 was markedly decreased by E2 in a concentration dependent manner, but this decrease was not inhibited by Ro41-0960. Cell treatment with E2, 2-OHE1, or 4-OHE1 alone induced apoptosis as detected by the TUNEL method. Additive effect on the induction of apoptosis was observed in cells treated with E2 + 2-OHE1 or 4-OHE1. The % apoptotic cells induced by E2 and 4-OHE1 decreased in the presence of Ro41-0960, while those induced by E2 and 2-OHE1 did not. These results suggest an important role of both the substrate specificity of COMT and the induction of apoptosis in CE-induced carcinogenesis.