Abstract 1321: Decreased Activity Of Nucleotide Pyrophosphatase Phosphodiesterase-1 During Phosphate-induced Calcification Of Valve Interstitial Cells- New Insights At Understanding Valve Calcification In Patients With Chronic Kidney Disease
Introduction: Calcification of the aortic valve is accelerated in patients with chronic kidney disease (CKD). Elevated plasma concentration of phosphate in patients with CKD is a contributing factor promoting the calcification of valve interstitial cells (ICs). Tissue production of pyrophosphate (PPi) through the enzymatic activity of nucleotide pyrophosphatase phos-phodiasterase 1 (NPP1) is a critical regulator inhibiting mineralization. We hypothesized that phosphate-induced calcification of valve ICs would be associated with a decreased NPP activity.
Methods: Human aortic valve interstitial cells were isolated from explanted hearts during transplant procedures. Calcification was induced with Na2HPO4 and activity of NPP along with concentration of calcium and Pi, PPi levels were determined.
Results: Immuno-histochemistry studies and western blot analyses revealed that isolated valve ICs expressed NPP1. When Na2HPO4 was added to the growth medium it induced the formation of calcified nodules. Na2HPO4-induced calcification dose-dependently reduced NPP activity and the expression at the protein level. Phosphate-induced modulation of NPP was abolished by the sodium-phosphate cotransporter (Pit1) inhibitor, foscarnet. NPP activity was inversely correlated with calcium concentration (r=-0.39; p=0.0006). Na2HPO4 treated cells had decreased PPi levels whereas the Pi concentration was increased.
Conclusion: Elevated phosphate concentrations, such as those encountered in patients with CKD (≈2 mM), induced the calcification of valve fibroblasts through a mechanism involving the entry of Pi into the cell through a specific transporter (Pit1), which results in a decreased expression of NPP1. Thus intervention targeting enzymatic NPP activity in patients with CKD may contribute to decrease valvular calcification process.