Possible involvement of nitric oxide and peroxynitrite in the pathogenesis of human vocal polyps and nodules.

Nitric oxide (NO) is a molecule involved in multiple functions including vasodilatation, neural transmission, immune response and inflammation. However, the role of NO in the pathophysiology of vocal cord diseases is not clear. The present study investigated the possible involvement of NO and its toxic metabolite, peroxynitrite, in the pathogenesis of vocal polyps and nodules. Vocal polyps and nodules were obtained from patients receiving surgery for their conditions. Immunohistochemistry was applied to evaluate the expression of the inducible form of nitric oxide synthase (iNOS) as well as the production of peroxynitrite represented by the formation of its biological footprint, 3-nitrotyrosine (3-NT). Each section was given a score of 0 to 4 according to the labeling intensity seen, with the highest number representing the highest labeling intensity. The results showed that vocal polyp had an average iNOS labeling score of 3.2, which was significantly higher than the value of 1.9 in vocal nodules. The average labeling score of 3-NT was 2.8 in vocal polyps, which was also significantly higher than the value of 1.8 in vocal nodules. There was also a positive correlation between the level of iNOS expression and the extent of 3-NT formation. These results suggest that increased peroxynitrite production, resulting from increased iNOS expression and NO formation, may have an important pathogenic role in these vocal diseases.