DNA damage in human nasal mucosa and environmental pollution: a study in the city of Florence

The aim of this work was to evaluate the genotoxic effects of urban air pollutants in the human nasal mucosa. DNA damage was studied from June 2001 to January 2002 by means of the alkaline comet assay in the nasal mucosa of 102 subjects living in the city of Florence. A control group of subjects living in a city with a lower level of urban pollution (Sassari), was also analysed for comparison. Nasal mucosa cells were harvested from the medium and lower turbinates by means of a non-invasive procedure (brushing) involving the use of a bronchial cytology nylon brush. Half of the harvested cells were transferred to agarose-coated slides to be run through the comet assay. The rest of the cells were fixed on histology slides, stained with Papanicolau’s solution and analysed for morphological alterations. The results showed that in the subjects living in Florence the levels of DNA damage in the nasal mucosa were considerably higher (+73%) than those measured in the subjects living in Sassari. These higher levels of DNA damage appeared to be related partly to increased incidence of inflammatory pathologies of the upper respiratory tract in the Florentine group and partly to high levels of ozone in the Florentine air. Furthermore, the concentration of ozone in the air was positively correlated with the incidence of respiratory inflammatory pathologies in Florence. None of the other major urban air pollutants was significantly correlated with DNA damage in nasal mucosa. DNA damage in the nasal mucosa was also correlated with some morphological alterations. In fact, the samples exhibiting higher levels of DNA damage also displayed a reduced ability to form cellular clusters, possibly indicating a dysfunction in the intercellular junctions and in the ability to maintain the normal epithelial structure. A correlation between DNA damage and morphological signs of cell death was also found. At variance with the Sassari group, in most of the Florentines morphological evidence of squamous metaplasia was found, which did not correlate with DNA damage and was interpreted as a plastic phenotypic response to environmental pollution. In conclusion, these indicate a major role of ozone pollution in inducing genotoxic effects in the upper respiratory tract. Furthermore, this study shows that the comet assay, in association with the morphological analysis of human nasal mucosa samples obtained with the simple brushing procedure, might be used as a screening test to evaluate the effects of environmental pollution in humans.