OSTEOPONTIN IS ASSOCIATED WITH BIOPROSTHE TIC HEART-VALVE CALCIFICATION IN HUMANS

Calcification of non-osseous tissues such as heart valves or vessels i s a major concern in clinical practice. The exact mechanism is still u nknown. Numerous studies have shown that mineral deposits of crystalli ne hydroxyapatite within these tissues were associated with increased non-collagenous protein content. More recently osteopontin was found t o be associated with calcification in living tissues such as vessels a nd native human aortic valves. The aim of this study was to determine whether or not non-collagenous proteins can also be found in non-livin g tissues such as glutaraldehyde-pretreated porcine valves after impla ntation in humans. Thirty-eight glutaraldehyde pretreated porcine biop rostheses were studied: 16 not implanted and 22 after 11 years of impl antation in the aortic and mitral valve position in humans In areas of calcification vizualized by Von Kossa staining and microradiography, immunostaining using polyclonal antibodies against calcium-binding pro teins showed osteopontin staining for osteocalcin, bone sialoprotein o r osteonectin. In uncalcified areas and in non-implanted valves, stain ing for osteopontin or other calcium-binding proteins was negative. We stern blot analysis of macroscopically calcified and uncalcified areas showed that several proteins were adsorbed in implanted valves and co nfirmed the presence of osteopontin in the calcified areas, while no i mmunolabelling was found in non-calcified areas, in uncalcified valves and in non-implanted valves. Thus the presence of osteopontin in the calcified areas of bioprosthetic heart valves implanted in human indic ates that this protein is associated with bioprosthetic valvular calci fication. Since these valves are made of non-living connective tissue, and no cell immunostained for osteopontin was found around the calcif ied area, this study suggests that a non-cellular mediated mechanism i nvolving protein adsorption may play a role in bioprosthetic valvular calcification.