Nitrative and oxidative DNA damage in cervical intraepithelial neoplasia associated with human papilloma virus infection

Recently, it was proposed that inflammation plays an integral role in the development of human papilloma virus (HPV)-induced cervical cancer. The present study sought to examine if 8-nitroguanine, a mutagenic nitrative DNA lesion formed during inflammation, contributes to cervical carcinogenesis. We obtained biopsy specimens from 30 patients with cervical intraepithelial neoplasia (CIN)1 (n = 9), CIN2 (n = 10), CIN3 (n = 6) and condyloma acuminatum (n = 5). We used immunohistochemistry to detect the formation of 8-nitroguanine and 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG), an oxidative DNA lesion, and compared it with the expression of the cyclin-dependent kinase inhibitor p16, which is considered to be a biomarker for cervical neoplasia. Double immunofluorescence labeling revealed that 8-nitroguanine and 8-oxodG were colocalized in cervical epithelial cells. Samples from CIN2-3 patients, most of whom were infected with high-risk HPV subtypes, exhibited significantly more intense staining for 8-nitroguanine than those with condyloma acuminatum. 8-Nitroguanine and 8-oxodG immunoreactivities correlated significantly with the CIN grade. We observed the expression of inducible nitric oxide synthase in epithelial and inflammatory cells from CIN lesions. Proliferating cell nuclear antigen was expressed specifically in dysplastic epithelial cells, but not in those of condyloma acuminatum. There were no statistically significant differences in p16 expression between CIN and condyloma acuminatum samples. These results suggest that high-risk HPV types promote inducible nitric oxide synthase-dependent DNA damage, which leads to dysplastic changes and carcinogenesis; in contrast, p16 appears to be merely a marker of HPV infection. Thus, 8-nitroguanine is a more suitable and promising biomarker for evaluating the risk of inflammation-mediated cervical carcinogenesis than p16.