Infection-related stones represent 10-15% of human kidney stones, are difficult to prevent and are known to have high recurrence rates.1 They typically are composed of magnesium ammonium phosphate (struvite) or calcium phosphate (apatite). However, the factors that result in either struvite or apatite formation have not been fully elucidated. In addition, multiple urinary modulators such as osteopontin, polyaspartic acid, glycosaminoglycans and inorganic pyrophosphate have been proposed to impact the growth of infection-based stones. Our study aimed to develop and validate an experimental model for infectious stones that could be utilized to test numerous potential compounds to identify novel preventative strategies.

Multiple urine media including Griffith’s artificial urine, Brooks’ artificial urine, pooled human urine and human urine from a non-stone former were tested using a wide range of urease concentrations and analyzed in a microplate spectrophotometer to quantitate crystal precipitation. Based on the results, we adjusted our choice of medium and urease concentrations on subsequent experiments to maximize crystal yield. The supernatant of the reaction was analyzed with scanning electron microscopy and X-ray diffraction (SEM-EDX) to determine crystal structure and composition.

Griffith’s artificial urine with a urease concentration of 0.075M showed the most consistent results with spectrophotometry (Figure 1). A Tris buffer was added to maintain a pH of 8.0. SEM-EDX confirmed that normal Griffith’s produced predominantly calcium phosphate crystals compared to a low calcium Griffith’s medium which produced struvite crystals (Figure 2).

We were able to develop a highly reproducible model that successfully creates both calcium phosphate and struvite crystals and can be utilized to analyze multiple urinary modulators in a high-throughput fashion.  Further investigation employing this model will be conducted to test potential preventative agents.