Effects of an extract from Herniaria hirsuta on calcium oxalate crystallization in vitro

Objective. To evaluate the effectiveness of an extract obtained from Herniaria hirsuta on calcium oxalate crystallization in vitro. Materials and methods. An extract was prepared from H. hirsuta at different concentrations (0.0625-1 mg/mL). Crystallization was induced in whole normal human urine samples in the absence or presence of the extract. Crystals generated in the urine were harvested and analysed by scanning electron microscopy. The nucleation and aggregation of calcium oxalate crystals were measured separately using spectrophotometric methods. The nucleation rate was followed at 620 nm after mixing calcium chloride and sodium oxalate solution at 37°C, with stirring. The induction time in the presence of herb extract was compared with that of the control. The aggregation rate was also followed at 620 nm in a buffered solution containing calcium oxalate monohydrate crystals after stopping the stirring. The rate was evaluated by comparing the slope of turbidity in the presence of the extract with that of the control. Results. The herb extract promoted the precipitation of calcium oxalate particles in whole urine. SEM showed that there were more crystals with increasing concentration of extract but that they were proportionally smaller. Moreover, the presence of herb extract favoured the formation of calcium oxalate dihydrate rather than monohydrate crystals. The extract inhibited calcium oxalate crystal aggregation. In an independent experiment, the herb extract was dialysed and filtered before inducing crystallization, to eliminate any fibrous particles and oxalate. The treated herb extract promoted more crystallization, especially at high concentrations. Conclusion. An extract of H. hirsuta promoted the nucleation of calcium oxalate crystals, increasing their number but decreasing their size. It also promoted the formation of calcium oxalate dihydrate crystals, despite the presence of calcium oxalate monohydrate particles. The extract may contain substances that inhibit calcium oxalate crystal aggregation. These properties of H. hirsuta might be beneficial in preventing kidney stone formation.