Evaluation of the repeated-dose liver, bone marrow and peripheral blood micronucleus and comet assays using kojic acid.

The repeated-dose liver micronucleus assay has the potential to detect liver carcinogens and could be integrated into general toxicological studies. To assess the performance of this assay, kojic acid was tested in 14-day and 28-day liver micronucleus assays. We evaluated the incidence of micronucleated cells in liver, bone marrow and peripheral blood and performed comet assays in both the liver and peripheral blood (comet assay was performed only for 14-days). Kojic acid, a skin-whitening agent used in cosmetic products, was orally dosed in six-week-old male rats at 250, 500 and 1000mg/kg/day for 14 days, and at 125, 250 and 500mg/kg/day for 28 days. Organ weight and histopathology were examined at the end of the experiment. Neither a clear, positive response in micronucleus (MN) incidence nor changes in the percent of tail DNA in the comet assays was noted in liver and bone marrow. An increase of relative liver weight was observed in 1000mg/kg/day for 14 days. In histopathology, minimal hypertrophy of hepatocytes was found at 1000mg/kg/day for 14 days. The results of both the micronucleus assay and the comet assay indicate that 14-day and 28-day repeated dosing of kojic acid are non-genotoxic in the liver and bone marrow. Kojic acid has been known to act as a tumor-promoter in thyroid carcinogenesis but has not been shown to have initiation activities in liver carcinogenesis. Findings in this study are consistent with the evidence that kojic acid is not an apparent initiator of liver carcinogenesis. Therefore, the liver micronucleus assay is simple and sensitive to detect genotoxic liver carcinogens.

Human papillomavirus and p53 mutations in head and neck squamous cell carcinoma among Japanese population.

We aimed to reveal the prevalence and pattern of human papillomavirus (HPV) infection and p53 mutations among Japanese head and neck squamous cell carcinoma (HNSCC) patients in relation to clinicopathological parameters. Human papillomavirus DNA and p53 mutations were examined in 493 HNSCCs and its subset of 283 HNSCCs. Oropharyngeal carcinoma was more frequently HPV-positive than non-oropharyngeal carcinoma (34.4% vs 3.6%, P < 0.001), and HPV16 accounted for 91.1% of HPV-positive tumors. In oropharyngeal carcinoma, which showed an increasing trend of HPV prevalence over time (P < 0.001), HPV infection was inversely correlated with tobacco smoking, alcohol drinking, p53 mutations, and a disruptive mutation (P = 0.003, <0.001, <0.001, and <0.001, respectively). The prevalence of p53 mutations differed significantly between virus-unrelated HNSCC and virus-related HNSCC consisting of nasopharyngeal and HPV-positive oropharyngeal carcinomas (48.3% vs 7.1%, P < 0.001). Although p53 mutations were associated with tobacco smoking and alcohol drinking, this association disappeared in virus-unrelated HNSCC. A disruptive mutation was never found in virus-related HNSCC, whereas it was independently associated with primary site, such as the oropharynx and hypopharynx (P = 0.01 and 0.03, respectively), in virus-unrelated HNSCC. Moreover, in virus-unrelated HNSCC, G:C to T:A transversions were more frequent in ever-smokers than in never-smokers (P = 0.04), whereas G:C to A:T transitions at CpG sites were less frequent in ever-smokers than in never-smokers (P = 0.04). In conclusion, HNSCC is etiologically classified into virus-related and virus-unrelated subgroups. In virus-related HNSCC, p53 mutations are uncommon with the absence of a disruptive mutation, whereas in virus-unrelated HNSCC, p53 mutations are common, and disruptive mutagenesis of p53 is related with oropharyngeal and hypopharyngeal carcinoma.

Optimum design for glass fiber-reinforced composite clasps using nonlinear finite element analysis.

The purpose of this study was to design an optimum glass fiber-reinforced composite (FRC) clasp. Three-dimensional finite element models were constructed of FRC circumferential clasp arms and an abutment tooth. The basic clasp arm was half-oval, without a taper, 2.60 mm wide and 1.30 mm thick. Four modified clasp arms were prepared by changing the width or thickness of the basic clasp (width/thickness: 2.60 mm/0.65 mm, 2.60 mm/1.95 mm, 1.30 mm/1.30 mm, and 3.90 mm/1.30 mm). Forced displacements of 5 mm in the removal direction were applied to the nodes at the base of the clasp arm. The retentive forces and maximum tensile stresses of the five FRC clasp arms ranged from 1.00-16.30 N and from 58.9-151 MPa, respectively. Results showed that an optimum FRC clasp was a circumferential clasp with 2.60 mm width and 1.30 mm thickness, which had sufficient retentive force and low risk of tensile failure.

DNA binding-dependent glucocorticoid receptor activity promotes adipogenesis via Krüppel-like factor 15 gene expression.

Glucocorticoids, such as dexamethasone, have been used as in vitro inducers of adipogenesis. However, the roles of the glucocorticoid receptor (GR) in adipogenesis have not been well characterized yet. Here, we show that inhibition of GR activity using the GR antagonist RU486 prevents human mesenchymal stem cell and mouse embryonic fibroblast (MEF) differentiation into adipocytes. Moreover, in MEFs isolated from GR knockout (GR(null)) and GR(dim) mice deficient in GR DNA-binding activity, adipogenesis was blocked. We identified glucocorticoid response element sites in the first intron of KLF15 by bioinformatical promoter analysis and confirmed their functional relevance by demonstrating GR interaction by chromatin immunoprecipitation. Moreover, transfection of MEFs with siRNA for KLF15 significantly attenuated the expressions of adipogenic-marker genes and the lipid accumulation. Our results provide a new mechanism for understanding glucocorticoids-dependent adipogenesis and that GR promotes adipogenesis via KLF15 gene expression as a transcriptional direct target.

Stress analysis of clasps made of glass fiber-reinforced composite material using three-dimensional finite element method: influence of shape in cross and longitudinal sections of circumferential clasp arms.

The purpose of this study was to investigate the effects of different cross-sectional shapes and presence of taper on stress distribution in clasp arms made of glass fiber-reinforced composite (FRC) material. Stress analysis of clasps was performed under a constant load (5 N) using a three-dimensional finite element method with due consideration to the anisotropy of unidirectional FRC material. Results were then compared with clasp arms made of metal- an isotropic material. It was found that both FRC clasps and metal clasps yielded similar results. As for the displacement of clasp arms with a basic cross-sectional shape under a load of 5 N, the amount of displacement showed that FRC clasps provided sufficient retentive force required for clinical application.

Hepatocyte growth factor attenuates airway hyperresponsiveness, inflammation, and remodeling.

Hepatocyte growth factor (HGF) is known to influence a number of cell types and their production of regulatory cytokines. We investigated the potential of recombinant HGF to regulate not only the development of allergic airway inflammation and airway hyperresponsiveness (AHR), but also airway remodeling in a murine model. Administration of exogenous HGF after sensitization but during ovalbumin challenge significantly prevented AHR, as well as eosinophil and lymphocyte accumulation in the airways; interleukin (IL)-4, IL-5, and IL-13 levels in bronchoalveolar lavage (BAL) fluid were also significantly reduced. Further, treatment with HGF significantly suppressed transforming growth factor-beta (TGF-beta), platelet-derived growth factor, and nerve growth factor levels in BAL fluid. The expression of TGF-beta, the development of goblet cell hyperplasia and subepithelial collagenization, and the increases in contractile elements in the lung were also reduced by recombinant HGF. Neutralization of endogenous HGF resulted in increased AHR as well as the number of eosinophils, levels of Th2 cytokines (IL-4, IL-5, and IL-13) and TGF-beta in BAL fluid. These data indicate that HGF may play an important role in the regulation of allergic airway inflammation, hyperresponsiveness, and remodeling.