Detection of xanthine oxidase in human atherosclerotic specimens and arterialized vein grafts

Xanthine oxidase is an essential enzyme in the formation of uric acid and has been previously identified by immunohistochemistry in liver, intestine and capillary endothelial cells. The purpose of this study was to investigate the presence of xanthine oxidase in human atherosclerotic plaques. Atherosclerotic plaques from carotid endarterectomy pathology specimens were snap frozen in liquid nitrogen, placed in an OCT block, and cut to a thickness of 6 microns with a cryotome. Slides were stored at -120° C until ready for staining Immunohistochemical staining, using a polyclonal rabbit anti-xanthine oxidase antibody (Fitzgerald, Concord MA), was performed on 17 specimens which included 14 carotid endarterectomy plaques, 2 transplant donors and 1 arterialized saphenous vein graft. The staining for xanthine oxidase was found to be positive in carotid artery from transplant donors, carotid artery plaques and the arterialized vein graft. The carotid artery of donors was found to have positive staining in the intima that was less than the staining of smooth muscle cells in the media. Occasional cells the adventitia also stained positive. The carotid plaques were found to be irregularly stained, with endothelial cells and smooth muscle cells staining positive in the intima. The thickened intimal and medial areas of the plaques had cholesterol clefts whose periphery stained more intensively than the rest of the plaque. Additional staining using an antibody against uric acid crystals was, likewise, positive in these areas. In the arterialized vein graft, endothelial cells and smooth muscle cells, likewise, stained positive for xanthine oxidase in the thickened intima. The layers beyond the elastic lamina were negative. These results suggest that xanthine oxidase is expressed in smooth muscle cells and endothelial cells. The identification of xanthine oxidase in the plaque of disease arteries and arterialized vein graft suggest a possible relationship between the presence of xanthine oxidase and the development of atherosclerosis and/or intimai hyperplasia.