H2O2 oxidative damage in cultured oral epithelial cells: the effect of short-term vitamin C exposure

Smoking is the main etiology of oral cancer and generates oxygen free radicals in the oral cavity. Free radicals have been implicated in apoptosis and in DNA damage inducing alteration of the cell cycle. The antioxidant vitamin C (VC) is reported to inhibit damage induced by free radicals. We exposed cultures of normal human oral epithelial cells to hydrogen peroxide (H2O2) in the presence and absence of VC. Generation of hydroxyl radicals was measured by electron paramagnetic resonance (EPR), cell cycle alterations by flow cytometry, cell death by SYTO 11 and morphology by organotypic culture. Human primary cell culture was given four treatments - control, VC alone, H2O2 alone and VC followed by H2O2. Cell cycle analysis indicated cultures treated with H2O2 had fewer cells in G1 phase (26%) and higher number of cells in S phase (44%) compared to the control (G1 70% & S 14%). Cell cycle of 48 hour VC treatment followed by H2O2 was similar to H2O2 alone. SYTO 11 showed 22% cell death when treated with H2O2 alone compared to 9% of normal control. By organotypic culture H2O2 alone induced a two-fold cell proliferation, loss of maturation, nuclear hyperchromatism and nuclear crowding. Our results suggest that H2O2 is capable of altering the cell cycle and morphology of cultured normal human oral epithelial cells. Forty-eight hour exposure to Vitamin C does not prevent the cell cycle changes caused by hydroxyl radicals.

Effect of brief exposure to mitomycin C on cultured human nasal mucosa fibroblasts

PURPOSE

To observe the effect of mitomycin C (MMC) on cultured human nasal mucosa fibroblasts.

METHODS

Cultured human nasal mucosa fibroblasts were exposed to MMC (0.1-0.4 mg/ml) for 1 to 5 minutes. The viability of the fibroblasts was determined by MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide) assay; DNA fragmentation (apoptosis) by terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL); apoptotic percentage by flow cytometry; and morphology by light microscopy.

RESULTS

A portion of the fibroblasts survived the mitomycin treatment and showed evidence of regrowth within 2 to 3 days. These cells reached confluence in 5 to 7 days. The inhibition rates by MTT assay of 0.4 mg/ml MMC for 5-minute exposures was 31.3%. Dose-response effect was noted with the lower concentrations and shorter exposure times where the inhibition rates were lower (but not significantly so). DNA fragmentation was observed in fibroblasts 24 hours after MMC exposure (0.4 mg/ml) for 5 minutes compared with normal control. The apoptotic rate of fibroblasts treated by 0.4 mg/ml MMC was significantly higher than the control (p < 0.05).

CONCLUSIONS

Short MMC exposure times have a variable cytotoxic effect and inhibit proliferation of cultured nasal mucosa fibroblasts. MMC also can induce apoptosis with a 5-minute exposure time. Therefore, it is possible that MMC has a complex effect in dacryocystorhinostomy.

Response of human oral epithelial cells to oxidative damage and the effect of vitamin E

Smoking and periodontal inflammation are various conditions with the potential to induce oxidative stress and thus DNA damage in the oral cavity. In cellular defense systems, vitamin E is considered the most powerful lipid-soluble antioxidant. To investigate whether oxygen-free radicals alter normal progression of the cell cycle and whether vitamin E prevents this damage, we exposed cultured normal human oral epithelial cells to hydrogen peroxide (H2O2) in the presence or absence of vitamin E. Two primary cell lines were analyzed for the presence of hydroxyl radical, cell cycle distribution and morphology. Each cell line received five treatments: control, ethanol only, vitamin E only, H2O2 only or vitamin E followed by H2O2. Degradation of hydroxyl radicals was detected by electron paramagnetic resonance analysis, cell cycle by flow cytometry and morphology by organotypic technique. Hydroxyl radicals were generated in H2O2-treated cells at an initial concentration, which decreased over a period of time. Cell cycle analysis showed that H2O2-treated cells differed from normal cells in that the percentage of cells in the G1 phase decreased markedly (34.3 vs. 61.2% in control) and the S phase increased (35.5 vs. 15.6% in control). Organotypic cultures treated with H2O2 demonstrated nuclear hyperchromatism, loss of maturation and prominent nucleoli, features consistent with premalignant epithelial transformation. In conclusion, our data suggest that H2O2 produced hydroxyl radicals and altered the cell cycle. Also, vitamin E may have the potential to reduce oxidative damage caused by hydroxyl radicals.