Evaluation of vascular endothelial growth factor addition in vitro on mouse inner ear progenitor cell cultures.

We analyzed progenitor cell cultures of inner ear tissue from newborn mice, and found proliferating cells, morphologically differentiating cells and subpopulations of cells expressing either neuronal or glial markers. In addition, we observed the expression of fetal liver kinase-1, a receptor for the vascular endothelial growth factor in a subpopulation of the cultured cells. Consistent with the expression of fetal liver kinase-1, addition of vascular endothelial growth factor at a dose of 10 ng/ml increased the expansion rate of inner ear-derived progenitor cells. Together with other published data, these results suggest that the vascular endothelial growth factor might be involved in inducing or supporting cochlear repair processes.

The tobacco alkaloid nicotine demonstrates genotoxicity in human tonsillar tissue and lymphocytes.

Recent studies suggest a direct contribution of nicotine, the addictive component of tobacco and tobacco smoke, to human carcinogenesis. To assess the genotoxicity of nicotine, the DNA-damaging effect on human lymphocytes and target cells from lymphatic tissue of the palatine tonsils from 10 healthy patients was tested with the alkaline single-cell microgel electrophoresis (Comet) assay. The degree of DNA migration, a measure of possible DNA single strand breaks, alkali labile sites, and incomplete excision repair sites, was expressed as the Olive tail moment, the percentage of DNA in the tail, and the tail length. One hour exposure to nicotine at 0.125, 0.25, 0.5, 1, 2, and 4 mM induced a statistically significant dose-dependent increase of DNA migration up to 3.8-fold and 3.2-fold in tonsillar cells and lymphocytes, respectively. The lowest concentration eliciting significant DNA damage was 0.5 mM nicotine. The genotoxic effect was confirmed in a second series of experiments using nicotine of high purity from two different suppliers. There were no significant differences between the two series, excluding artifacts from the source of nicotine. Finally, DNA damage by nicotine was compared in cells incubated in medium strictly adjusted to neutral pH, with non-adjusted medium becoming alkaline with increasing nicotine concentrations. Again no differences in DNA migration were observed. The data indicate that nicotine expresses significant direct genotoxic effects in human target cells in vitro. However, no differences in DNA damage were observed in cells from smokers and nonsmokers incubated without nicotine. The lack of higher DNA damage in smokers compared to nonsmokers could be a question of nicotine dose, rapid DNA repair, or interactions with other smoke constituents. These results require further investigations on the contribution of nicotine to tobacco carcinogenesis.