Factors affecting the regrowth of renal stones in vitro: A contribution to the understanding of renal stone development

Abstract

Objective The exact mechanism of renal stone formation is still not totally understood. Thus, the role of crystallization inhibitors at different stages of stone development, the influence of preexisting solid particles and the effects of variations in urine composition require further clarification. The aim of this paper is to clarify some of these questions by studying the regrowth achieved by real spontaneously passed post-extracorporeal shock wave lithotripsy (post-ESWL) fragments of calcium oxalate monohydrate (COM) renal calculi. Material and methods An in vitro system was used to study the regrowth of post-ESWL fragments of COM calculi, which was defined as the relative increase in weight of the fragments. Results It was found that new columnar zones of COM crystals were formed under normal calcium and oxalate urinary conditions and no calcium phosphates were observed, in spite of the urinary pH being >6. The presence of 3.03 μM phytate totally blocked these crystal growth processes. When hypercalciuric urine was used at a pH of 6.5, large brushite crystals and zones totally covered by hydroxyapatite were observed for short periods, and zones containing calcium oxalate dihydrate crystals could be observed for longer periods. In such cases, 9.09 μM phytate totally blocked the growth processes, 69.0 μM pyrophosphate caused a reduction in calculi growth of 93% and 5.35 mM citrate caused no inhibitory effects. Conclusion The results show that when crystallization inhibitors were absent, the growth of calcium oxalate calculi fragments took place even under normal urine conditions, clearly demonstrating the importance of crystallization inhibitors in avoiding or delaying calculi development.

• Calcium oxalate monohydrate
• citrate
• phytate
• pyrophosphate
• renal stones