Electron spin resonance spin trapping assay and immunohistochemical localization of superoxide dismutases in the rat nasal mucosa

The immunohistochemical method and electron spin resonance (ESR) spin trapping assay were employed to detect the localization and biochemical activity of superoxide dismutases (SODs) in the rat nasal mucosa. Manganese SOD and copper-zinc SOD were immunohistochemically illustrated to be richly expressed in the epithelial cells and the subepithelial glands of nasal mucosa. The olfactory vesicles also showed positive immunostaining for manganese SOD and copper-zinc SOD. ESR spin trapping assay revealed that SOD activity in the mucosa of olfactory areas was significantly higher than in the mucosa of respiratory areas; however, the ratio of SOD activity in the mitochondrial fraction to SOD activity in the cytosolic fraction was similar, approximating 17: 83 in the mucosa of both the olfactory and respiratory areas. The predominant localization of SODs in epithelial cells of nasal mucosa suggests the importance of mucosal epithelium in protecting nasal mucosa against cytotoxic superoxide (O₂) radicals. Epithelial goblet cells and the connective tissue of lamina propria, which showed no positive immunostaining for SODs, are considered to be vulnerable to oxidative insults implicated in the generation of O₂ radicals. The higher SODs activity in the mucosa of olfactory areas implies that there is a different requirement of SOD in mucosa of the respiratory and olfactory areas on scavenging microenvironmental O₂ radicals.