Xanthine oxidase/dehydrogenase is present in human placenta

Xanthine dehydrogenase/oxidase (XDH, EC 1.1.1.204, XO, EC 1.2.3.2) produces uric acid, and in the oxidase form also generates the free radical superoxide. Previous reports failed to demonstrate XDH/XO activity in human placenta. Our objective was to determine evidence of XDH/XO in human placenta. We developed a cDNA probe for human XDH/XO and used it to detect mRNA by Northern hybridization. Immunohistochemical localization of the enzyme in placental tissue was performed using a specific antibody for XDH/XO and ABC-peroxidase. Enzyme activity assay was determined by the conversion of [C-14] xanthine to [C-14] uric acid. mRNA was detected in all placental samples (n=4). Villous and non-villous trophoblast cells expressed immunohistochemical staining for XOD (n=4). Enzyme activity was detected in all placentae (n=6). Despite previous reports, we found mRNA, XDH/XO protein and enzyme activity in human placenta localized to trophoblast cells. Enzyme activity was much lower than in liver. Several conditions in the maternal-fetal unit could potentially increase XDH/XO activity and conversion of the enzyme to its oxidase form. (C) 1996 W. B. Saunders Company Ltd