Nasal cytology and genotoxic damage in nasal epithelium and leukocytes: asthmatics versus nonasthmatics

Epithelial cells as alternative human biomatrices for comet assay

The comet assay is a valuable experimental tool aimed at mapping DNA damage in human cells in vivo for environmental and occupational monitoring, as well as for therapeutic purposes, such as storage prior to transplant, during tissue engineering, and in experimental ex vivo assays. Furthermore, due to its great versatility, the comet assay allows to explore the use of alternative cell types to assess DNA damage, such as epithelial cells. Epithelial cells, as specialized components of many organs, have the potential to serve as biomatrices that can be used to evaluate genotoxicity and may also serve as early effect biomarkers. Furthermore, 80% of solid cancers are of epithelial origin, which points to the importance of studying DNA damage in these tissues. Indeed, studies including comet assay in epithelial cells have either clear clinical applications (lens and corneal epithelial cells) or examine genotoxicity within human biomonitoring and in vitro studies. We here review improvements in determining DNA damage using the comet assay by employing lens, corneal, tear duct, buccal, and nasal epithelial cells. For some of these tissues invasive sampling procedures are needed. Desquamated epithelial cells must be obtained and dissociated prior to examination using the comet assay, and such procedures may induce varying amounts of DNA damage. Buccal epithelial cells require lysis enriched with proteinase K to obtain free nucleosomes. Over a 30 year period, the comet assay in epithelial cells has been little employed, however its use indicates that it could be an extraordinary tool not only for risk assessment, but also for diagnosis, prognosis of treatments and diseases.

Use of nasal cells in micronucleus assays and other genotoxicity studies

Genotoxicity experiments with exfoliated nasal mucosa cells are a promising minimally invasive approach for the detection of DNA-damaging compounds in ambient air. Results of single cell gel electrophoresis (SCGE) assays with individual cells and organ cultures from bioptic material show that DNA damage caused by compounds such as nitrosamines, polycyclic aromatic hydrocarbons and pesticides can be detected. Biochemical studies indicate that enzymes involved in the metabolism of environmental mutagens are represented in nasal cells. Several protocols for experiments with nasal cells have been developed and it was shown that formaldehyde, metals, styrene and crystalline silica induce DNA damage in SCGE and/or in micronucleus studies; furthermore, it was also found that polluted urban air causes DNA instability in nasal epithelial cells. Comparisons of these data with results obtained in lymphocytes and buccal cells indicate that nasal cells are in general equally sensitive. Broad variations in the baseline levels, differences of results obtained in various studies as well as the lack of information concerning the impact of confounding factors on the outcome of experiments with these cells indicate the need for further standardisation of the experimental protocols.

Gamma-tocopherol attenuates ozone-induced exacerbation of allergic rhinosinusitis in rats

Compared to healthy subjects, individuals with allergic airway disease (e.g., asthma, allergic rhinitis) have enhanced inflammatory responses to inhaled ozone. We created a rodent model of ozone-enhanced allergic nasal responses in Brown Norway rats to test the therapeutic effects of the dietary supplement gamma-tocopherol (gammaT). Ovalbumin (OVA)-sensitized rats were intranasally challenged with 0% or 0.5% OVA (in saline) on Days 1 and 2, and then exposed to 0 or 1 ppm ozone (eight hours/day) on Days 4 and 5. Rats were also given 0 or 100 mg/kg gammaT (p.o., in corn oil) on days 2 through 5, beginning twelve hours after the last OVA challenge. On Day 6, nasal tissues were collected for histological evaluation and morphometric analyses of intraepithelial mucosubstances (IM) and eosinophilic inflammation. Nasal septal tissue was microdissected and analyzed by reverse transcriptase polymerase chain reaction (RT-PCR) for mucin glycoprotein 5AC (MUC5AC) expression levels. Histological analysis revealed mild to moderate eosinophil influx in the mucosa lining the nasal airways and maxillary sinus of OVA-challenged rats (eosinophilic rhinosinusitis). Ozone exposure of allergic rats further increased eosinophils in the maxillary sinus (400%), nasolacrimal duct (250%), and proximal midseptum (150%). Storage of intraepithelial mucosubstances (IM) was not significantly affected by OVA challenge in filtered air-exposed rats, but it was increased by ozone in the septum (45%) and maxillary sinus (55%) of allergic compared to control rats. Treatment with gammaT attenuated the ozone/ OVA-induced synergistic increases in IM and mucosal eosinophils in both nasal and paranasal airways. gamma-Tocopherol also blocked OVA and ozone-induced MUC5AC gene expression. Together, these data describe a unique model of ozone enhancement of allergic rhinosinusitis and the novel therapeutic efficacy of a common supplement, gammaT, to inhibit ozone exacerbation of allergic airway responses.