Collagen synthesis and collagenase activity of cryopreserved heart valves

Durability of the valve seems to be dependent on the remodeling ability of the valve itself, which is controlled by both collagen synthesis and collagenolytic activity of valvular fibroblasts and endothelial cells. However, the balance of collagen synthesis and collagenolysis of the cryopreserved valve has not yet been clearly revealed. Thus, we assessed the collagen synthesis and collagenolysis ability of the cryopreserved valve.

Twelve valves were divided into 2 groups: freshly harvested valves (n = 6) and cryopreserved valves (n = 6). We measured the collagen content using Sirius red, a dye selective to the collagen. Collagen synthesis was evaluated by means of the tritiated proline incorporation method. Noncollagenase-digestible counts, which represent protein synthesis, and collagenase-digestible counts, which represent collagen synthesis, were estimated. Collagenase activity of the valves was assessed by gelatin zymography.

The collagen content of the cryopreserved group was maintained. The noncollagenase-digestible counts of the cryopreserved group decreased from 3862 +/- 1180 counts/mg to 1174 +/- 1362 counts/mg, and the collagenase-digestible counts of the cryopreserved group were 831 +/- 762 counts/mg compared with the value of 1062 +/- 136 counts/mg for the freshly harvested group. The collagenase activity of the cryopreserved group was observed at the same level as that of the freshly harvested group, despite the serious endothelial damage of the cryopreserved valves.

Although the collagen synthesis of cryopreserved valves was relatively maintained, the protein synthesis was highly diminished, and the collagenolysis ability was activated immediately after the thawing process. These results imply that the cryopreservation procedure itself may cause the collagen metabolism to be on the degradable side, which will lead to valve failure.