Comparison of urine proteomes from healthy and CKD cats

In veterinary medicine there is an increasing interest in the application of proteomic techniques to investigate protein patterns in healthy and diseased animals; however, data on urine proteome are still limited. The aims of this study were to identify a urine protein profile in healthy cats and to compare it with those obtained in patients affected by chronic kidney disease (CKD). Urine samples were collected by cystocentesis from 23 healthy and 18 CKD cats. Urinalysis was performed and urine protein to creatinine ratio (UPC) was calculated. Urine proteins were separated by SDS-PAGE on 4-12% gels, 20 different protein bands were cut, reduced, alkylated and digested by trypsin before ESIQ-TOF mass spectrometry analysis; protein identification was performed using MASCOT science search engine. CKD cats had significantly higher UPC (median 0.9, P < .01) and significantly lower urine specific gravity (USG, median 1.014, P < .01) than healthy cats (UPC 0.1; USG 1.070). SDS-PAGE allowed visualization of qualitative and quantitative differences in protein profiles. CKD cats had significantly less bands (P < .01), particular at molecular weight (MW) > 100 kDa (P < .01). Eleven different proteins were identified by mass spectrometry in cat urine. In CKD a2-macroglobulin (168 kDa) and uromodulin (90 kDa) disappeared, while albumin (64 kDa), retinol-binding protein (RBP, 22 kDa) and cystatin (16 kDa) were enhanced. Cauxin (carboxylesterase 5A, 61 kDa), transferrin (80 kDa), angiotensin-converting enzyme 2 (93 kDa), inter-a-trypsin inhibitor heavy chain H4 (103 kDa), albumin- (55 kDa) and cauxin- (40 kDa) fragments, haptoglobin (45 kDa) and immunoglobulin light chains (24 kDa) were also identified. In conclusion, proteomic techniques were successfully used to investigate urine proteins, revealing different patterns between healthy and CKD cats; some of these proteins could be considered as promising biomarkers of chronic renal damage in feline patients.