Expression of 3-nitrotyrosine, a marker for peroxynitrite, in nasal polyps of nonatopic patients

Several works have reported that nitric oxide and free oxygen radicals are up-regulated in nasal polyposis. This study aimed to assess the distribution of peroxynitrite in nasal polyps from nonatopic patients. Occurrence of peroxynitrite also was analyzed in relation with eosinophil infiltration and epithelial alterations.

Hematoxylin and eosin staining was used for histologic study. Peroxynitrite was assessed by 3-nitrotyrosine immunohistochemistry. Quantitative evaluation was done by measuring the total number of eosinophils, the number of 3-nitrotyrosine-positive eosinophils, and the extension of the various epithelial alterations.

Hematoxylin and eosin staining showed that the nasal polyp epithelium is characterized by progressive disruption or squamous metaplasia. In both cases, infiltrating eosinophils were found in the epithelium and lamina propria. The regions featuring epithelial disruption exhibited 3-nitrotyrosine immunostaining in eosinophils and epithelial cells; hematoxylin-and-eosin - stained eosinophils and 3-nitrotyrosine - positive eosinophils showed conspicuous variations in number. Within the regions featuring squamous metaplasia, 3-nitrotyrosine-positive eosinophils were rarely found, and the epithelium exhibited 3-nitrotyrosine only in the superficial cells. In these regions, hematoxylin-eosin - stained eosinophils showed slight variations in number.

Peroxynitrite plays a pivotal role in the pathophysiology of nasal polyps. In fact, strong expression of peroxynitrite is associated with epithelial disruption, while poor expression of peroxynitrite is associated with squamous metaplasia. Peroxynitrite could influence afflux of eosinophils in the nasal mucosa; moreover, the total number of eosinophils is not critical in generating alterations of nasal polyp mucosa.