Effects of phytate and pyrophosphate on brushite and hydroxyapatite crystallization: Comparison with the action of other polyphosphates

Abstract

This is a comparative study of the effects of phytate and pyrophosphate and other polyphosphates on the crystallization of hydroxyapatite and brushite, the most frequent calcium phosphates involved in calcium oxalate urolithiasis. Brushite and hydroxyapatite crystal formation was studied in synthetic urine, through kinetic-turbidimetric measurements that allowed evaluation of the inhibitory effects on crystallization of insoluble salts. The effectiveness in preventing brushite crystallization decreases in the sequence phytate > polyphosphate > EDTPO > etidronate > pyrophosphate > triphosphate > medronate; whereas the order of effectiveness in preventing hydroxyapatite crystallization was EDTPO > etidronate = pyrophosphate > triphosphate > medronate > polyphosphate > phytate. Phytate, a natural inhibitor in urine, most effectively blocked brushite precipitation (1.21·10-5 M prevented crystallization during time periods of at least 1 h), and pyrophosphate was the natural inhibitor that most effectively blocked hydroxyapatite precipitation (2.87·10-6 M prevented crystallization during time periods of at least 1 h). This demonstrates that low excretion of these substances would pose a risk of renal lithiasis.