Vitamin K-dependent Calcium Binding Proteins in Aortic Valve Calcification

The pathogenesis of valvar calcification, which complicates the course of cardiac valve disease and also affects tissue valve prostheses, is incompletely understood. The present work explores the possible role of the vitamin K-dependent, calcium-binding amino acid, γ-carboxyglutamic acid (Gla) in valve mineralization. Gla is normally found in the vitamin K-dependent clotting factor proteins, and is also present in unique calcium binding proteins in bone, kidney, and lung. Unique Gla-containing proteins have also been isolated from pathologic calcifications including calcium containing renal stones and calcified atherosclerotic plaque. Calcified valves including specimens with calcific aortic stenosis, calcified porcine xenograft valves, and a calcified aortic homograft valve were analyzed for Gla content, complete amino acid analysis, and tissue calcium and phosphorus levels. Normal porcine valves contained protein-bound Gla (2.0-10.6 Gla/10⁴ amino acids): no Gla was present in normal valve leaflets. Furthermore, Gla levels paralleled tissue calcium content in the calcified valves. In addition, complete amino acid analysis indicated a decline in valvar collagen content plus increased acidic proteins in conjunction with valvar calcification and the presence of Gla-containing proteins. These results suggest that calcific valvar disease may result in part from vitamin K-dependent processes.

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