Expression of inducible nitric oxide synthase in human oral premalignant epithelial lesions

Increased expression of inducible nitric oxide synthase (iNOS) has been found at the protein level in human oral epithelial dysplasias, but, a corresponding expression at the mRNA level has not been demonstrated. The purpose here was to assess the expression of iNOS mRNA and its correlation with the expression of the enzyme protein in human buccal premalignant epithelial lesions. Activities for iNOS protein (57/80, 64%) and mRNA (53/80, 53%) were detected in the specimens examined. Cytoplasmic and/or nuclear staining for iNOS protein was detected immunohistochemically in a number of mild oral epithelial dysplasias (16/20, 80%), moderate to severe oral epithelial dysplasias (14/20, 70%), submucous fibrosis (14/20, 70%) and verrucous hyperplasia (13/20, 65%). Upon in situ reverse transcription-polymerase chain reaction (RT-PCR), the cellular location of iNOS mRNA was compatible with the immunohistochemical findings. Furthermore, iNOS mRNA was found in 15 specimens of mild oral epithelial dysplasia (15/20, 75%), 13 specimens of moderate to severe oral epithelial dysplasia (13/20, 65%), 13 specimens of submucous fibrosis (13/20, 65%) and 12 specimens of verrucous hyperplasia (12/20, 60%). No iNOS protein or mRNA was found in samples of normal buccal mucosa, or in negative controls. Further studies on the characteristics of iNOS-positive cells and more long-term clinical follow-up data are needed.