RESUMO
Photoactivated methylene blue was used to damage purified DNA and the mitochondrial DNA (mtDNA) of human fibroblasts in culture. The primary product of this reaction is the DNA lesion 7-hydro-8-oxo-deoxyguanosine (8-oxo-dG). The DNA damage was quantitated using Escherichia coli formamidopyrimidine DNA glycosylase (Fpg) in a gene-specific damage and repair assay. Assay conditions were refined to give incision at all enzyme-sensitive sites with minimal non-specific cutting. Cultured fibroblasts were exposed to photoactivated methylene blue under conditions that would produce an average of three oxidative lesions per double-stranded mitochondrial genome. Within 9 h, 47% of this damage had been removed by the cells. This removal was due to repair rather than to replication, cell loss or degradation of damaged genomes. The rate of repair was measured in both DNA strands of the frequently transcribed ribosomal region of the mitochondrial genome and in both strands of the non-ribosomal region. Fpg-sensitive alkali-resistant oxidative base damage was efficiently removed from human mtDNA with no differences in the rate of repair between strands or between two different regions of the genome that differ substantially with regard to transcriptional activity.
Assuntos
Dano ao DNA , Reparo do DNA , DNA Mitocondrial/efeitos dos fármacos , Proteínas de Escherichia coli , Oxigênio/farmacologia , 8-Hidroxi-2'-Desoxiguanosina , Linhagem Celular , DNA Mitocondrial/química , DNA Mitocondrial/metabolismo , DNA-Formamidopirimidina Glicosilase , Desoxiguanosina/análogos & derivados , Desoxiguanosina/química , Embrião de Mamíferos , Escherichia coli/enzimologia , Fibroblastos , Humanos , Luz , Azul de Metileno/química , Azul de Metileno/farmacologia , N-Glicosil Hidrolases/metabolismo , Oxigênio SingleteRESUMO
The diffusion through dentine by a number of biological and synthetic molecules, including resins and dyes, is reported. In vitro measurements were derived by experiments with a modified 'split-chamber device'. Diffusion was found to be indirectly proportional to dentine thickness for all molecules. Permeability of water-soluble molecules and ethanol-soluble molecules was proportional to the molecular weights, except for fluorescein, hydrogen peroxide (H2O2) and urethane dimethacrylate. The resin components tested are not soluble enough in an aqueous medium to diffuse through 0.5 mm dentine at sufficient concentrations to cause cytotoxicity to pulpal cells.
Assuntos
Permeabilidade da Dentina , Proteínas Sanguíneas/química , Difusão , Cultura em Câmaras de Difusão , Etanol , Fluoresceínas/química , Humanos , Peróxido de Hidrogênio/química , Peso Molecular , Fenóis/química , Resinas Sintéticas/química , Solubilidade , Espectrofotometria , ÁguaRESUMO
Until adhesiveness of dentin bonding agents and other restorative materials to dental structures can be assured, microleakage into resulting "gaps" and dentin permeability will remain major concerns in cases of pulpal irritation. The objectives of the present study were to (a) delineate the kinds and levels of metabolic cytotoxicity of the GLUMA and Scotchbond 2 systems as well as glutaraldehyde and 2-hydroxyethylmethacrylate, and (b) compare the effects of these same materials after diffusion through dentin discs approximately 0.5-mm thick. In monolayer cultures, glutaraldehyde was much more cytotoxic than 2-hydroxyethylmethacrylate. However, GLUMA sealer and Scotchbond 2 adhesive exhibited similar cytotoxicity in monolayer cultures. After diffusion through dentin, glutaraldehyde and 2-hydroxyethylmethacrylate effects were diluted 14.7 and 26.7 times, respectively. The postdiffusional effects of the GLUMA and Scotchbond 2 systems were not significantly different and less than those effects in monolayer cultures. This study should help in the evaluation of possible causes of pulpal irritation following restorative procedures.
