Return
to Table of Contents
068
BONE TYPE ALKALINE PHOSPHATASE IS EXPRESSED BY CALCIFIED HOMOGRAFTS
P Mathieu, A Pépin, J Perron, F Dagenais, R Baillot
Sainte-Foy, Quebec
OBJECTIVES: Calcification of valve allografts (VA) is associated with early graft degeneration and failure. Mechanisms leading to calcification of VA leaflets are still poorly understood. Osseous calcification is closely associated with alkaline phosphatase (ALP) activity. Therefore, we tested the hypothesis that bone type ALP activity might be implicated in the calcification process of VA leaflets.
METHODS: Human valve were obtained from calcified explanted VA (n=8), and normal aortic valve (control) from transplant explanted hearts (n=12).
RESULTS: Von Kossa staining showed that explanted VA were mostly calcified at the junction of leaflets with either the aortic wall or the septal muscle, whereas free margin of leaflets were free of calcification. Explanted VA expressed the bone glycoprotein, osteonectin, indicating an osteoblastic activity. Calcified VA were found to express an enzymatic activity for ALP, and immnohistochemistry studies showed that bone type specific ALP was expressed within calcified areas. To further elucidate the role of bone type ALP activity in the calcification process of VA, leaflets interstitial cells (ICs) were isolated and cultured from all calcified VA. ICs did not calcify sponteanously, however when the growth medium was supplemented with
CONCLUSIONS: Therefore, calcification of VA is closely associated with bone type specific ALP activity, and furthermore, in vitro data suggest that ALP activity is an essential step leading to calcification of valve ICs.
DNC