Factors affecting struvite (MgNH4PO4·6H2O) crystallization in feline urine

Factors affecting struvite, a magnesium-ammonium-phosphate complex (MgNH4PO46H2O), in feline urine were evaluated. Incubation of just “urine mineral (UM)” solution, in which mineral concentrations are compatible with those in feline urine, for 4 h at 37 °C did not induce the formation of crystals. Similarly, incubation of urine alone did not produce crystals. However, struvite crystals were formed by the addition of urine to UM solution. Mg, NH3 and P were all required for urine-induced struvite crystallization. The lower molecular weight (LMW) fraction of urine was essential for struvite crystal formation, and the higher molecular weight (HMW) fraction enhanced formation of LMW-induced struvite crystals. The effects of urine proteins further fractionated by column chromatography were examined. A protein at > 250 kDa and cauxin, a major urine protein recently identified as a regulator of felinine production, potentiated struvite crystal formation induced by the LMW fraction. In contrast, Tamm-Horsfall glycoprotein, a urine protein thought to promote struvite crystallization, did not have this activity. The present study reveals a novel mechanism of feline struvite crystallization.