The incidence of calcium oxalate (CaOx) uroliths is increasing in humans and cats. The food discussed in this study had previously been demonstrated to significantly reduce the urine saturation of CaOx crystals. The same urine collected for that study was used to test for the concentrations of glycosaminoglycans (GAGs), Tamm-Horsfall glycoproteins (THP), and nephrocalcin, which are common, natural inhibitors of CaOx formation. Ten client-owned cats with CaOx urolithiasis were fed either food consumed before urolith detection followed by urolith prevention food or urolith prevention food followed by the diet consumed before detection. Urine was collected for 72 hours after the trial food was consumed for 8 weeks. In addition to reducing CaOx supersaturation, the urolith prevention food altered urinary concentrations of some organic matrices that can influence crystal nucleation and growth. While no effect was seen in the amounts of THP and nephrocalcin in the urine, there was significantly higher concentration of GAGs. About half of human patients with CaOx uroliths have reduced concentrations of GAGs compared with the concentration in nonurolith formers. GAGs in the urine may be an important factor for preventing CaOx urolith formation. Supported in part by an educational grant from Hill’s Pet Nutrition.

Commentary
Approximately 40% of feline uroliths are CaOx and the prevalence of these stones may be increasing. Since CaOx uroliths cannot be dissolved medically, preventing of recurrence after surgical removal is important. Previous dietary trials evaluating a CaOx prevention diet (Hill’s Prescription Diet c/d Multicare Feline, HillsVet.com) in cats that had undergone cystotomy for CaOx stone removal showed that urine supersaturation with CaOx could be reduced by 59%. Increased urine concentrations of GAGs were observed following 8 weeks of feeding this prevention diet. Increased urine GAG concentrations may be beneficial because of the potential to reduce CaOx crystal aggregation and growth and decrease crystal adherence to uroepithelial cells.—Gregory F. Grauer, DVM, MS, DACVIM

Source
Effects of a urolith prevention diet on urine compositions of glycosaminoglycans, Tamm-Horsfall glycoprotein, and nephrocalcin in cats with calcium oxalate urolithiasis. Lulich JP, Osborne CA, Carvalho M, Nakagawa Y. AM J VET RES 73:447-451, 2012.