DIFFERENTIAL IMMUNOHISTOCHEMICAL LOCALIZATION OF XANTHINE-OXIDASE IN NORMAL AND NEOPLASTIC HUMAN BREAST EPITHELIUM

Xanthine oxidase (XO) and xanthine dehydrogenase (XDH) are alternate e nzymatic forms of the XO/XDH protein that catalyzes the oxidation of h ypoxanthine to xanthine, and xanthine to uric acid, and in the process XO/XDH generates reactive oxygen species (ROS) such as superoxide, hy drogen peroxide, and hydroxyl radicals. We hypothesize that XO/XDH, wh ich is expressed in mammary epithelium, contributes to the development of breast cancers by virtue of its ability to generate genotoxic ROS. In this study, we produced human XO/XDH protein at high levels in Spo doptera frugiperda (Sf9) insect cells using the baculovirus vector to confirm the specificity of antibodies used for immunostaining of human breast tissues. Immunoblot analysis demonstrated that the full length 143 kDa polypeptide was partially processed into a 87 kDa and 59 kDa fragments. The overexpressed XO/XDH protein was identified in the cyto plasm of insect cells by immunofluorescence staining. Using these anti bodies we analyzed normal and neoplastic breast epithelium for the pre sence of XO/XDH. Immunohistochemical analysis of normal human breast r evealed the presence of XO/XDH in the cytoplasm of epithelium lining t erminal ducts. The intensity of XO/XDH staining was markedly enhanced in alveolar epithelium of lactating mammary lobules. In contrast, no i mmunohistochemically detectable XO/XDH was observed in intraductal in situ carcinomas and in invasive carcinomas of the breast. Further stud ies are necessary to confirm the utility of the loss of XO/XDH express ion as a marker for neoplastic change in the breast and investigate th e functional role of this enzyme in the pathogenesis of breast cancer.