Aggregation of Calcium Phosphate and Oxalate Phases in the Formation of Renal Stones

Abstract

The majority of human kidney stones are comprised of multiple calcium oxalate monohydrate (COM) crystals encasing a calcium phosphate nucleus. The physiochemical mechanism of nephrolithiasis has not been well determined on the molecular level; this is crucial to the control and prevention of renal stone formation. This work investigates the role of phosphate ions on the formation of calcium oxalate stones; recent work has identified amorphous calcium phosphate (ACP) as a rapidly forming initial precursor to the formation of calcium phosphate minerals in vivo. The effect of phosphate on the nucleation of COM has been investigated using the constant composition (CC) method in combination with scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Our findings indicate COM nucleation is strongly promoted by the presence of phosphate; this occurs at relatively low phosphate concentrations, undersaturated with respect to brushite (dicalcium phosphate dehydrate, DCPD) formation. The results show that ACP plays a crucial role in the nucleation of calcium oxalate stones by promoting the aggregation of amorphous calcium oxalate (ACO) precursors at early induction times. The coaggregations of ACP and ACO precursors induce the multiple-point nucleation of COM. These novel findings expand our knowledge of urinary stone development, providing potential targets for treating the condition at the molecular level.

Abstract

In solutions that are supersaturated with respect to calcium oxalate, the presence of phosphate results in the initial formation of amorphous calcium phosphate clusters; these clusters were found to promote the aggregation of amorphous calcium oxalate complexes which induce the nucleation and growth of urinary stones.