| Formaldehyde (FA) is cytotoxic and carcinogenic in the nasal respiratory epithelium of rats and mice. Human exposure to formaldehyde is either occupational or environmental. However, there is little evidence directly linking formaldehyde to human cancer. Glutaraldehyde (GA) is also cytotoxic to the respiratory epithelium inducing similar tissue responses, including respiratory dysplasia, goblet cell hypertrophy, and squamous metaplasia but not cancer. Both chemicals induce regenerative cell proliferation and similar microscopic lesions after four weeks or less of treatment. Little is known about the levels of cell death induced by exposure. I hypothesized that FA induced less apoptosis than GA. This hypothesis was tested through the use of gene expression analysis. F344 male rats received formaldehyde (400mM), glutaraldehyde (20mM), or water by intranasal instillation 5 days a week for 1, 5, or 28 days. Respiratory and transitional epithelium was isolated from the nose after euthanasia and Trizol™ infusion. Total RNA was recovered, then cDNA probes were generated and hybridized to Clontech™ Rat Toxicology II macroarrays, followed by phosphoimaging, and analysis of differential gene expression. Multiple approaches were used to analyze the data. 80 genes were identified that best fit an ANOVA model. Thirty-seven of the 80 were associated with subchronic (28 days) exposure and 43 were associated with acute toxicity (1 and 5 days). When comparing formaldehyde to glutaraldehyde, 49 genes were significantly altered (p < 0.05) and were represented by 3 functional categories: DNA repair, apoptosis, and xenobiotic metabolism. Expression after FA treatment could be completely discriminated from GA at 5 days. GA treatment resulted in higher expression of proapoptotic genes but lower expression of DNA repair and metabolism genes than FA. These data suggest that FA and GA induce similar phenotypic expression of toxicity, however, FA induced greater expression of DNA repair genes but less expression of apoptotic genes than GA. Less apoptosis would mean that FA-damaged cells could survive accounting for FA's ability to induce nasal cancer in the rodent. |
