Objective—To evaluate proteomic delineation of feline urine by mass spectrometry as a method for identifying biomarkers in cats at risk of developing azotemia.
Samples—Urine samples from geriatric cats (> 9 years old) with chronic kidney disease and nonazotemic cats that either remained nonazotemic (n = 10) or developed azotemia (10) within 1 year.
Procedures—Optimization studies with pooled urine were performed to facilitate the use of surface enhanced laser desorption-ionization time-of-flight mass spectrometry (SELDI-TOF-MS) for analysis of the urinary proteome of cats. Urine samples from nonazotemic cats at entry to the study were analyzed via SELDI-TOF-MS with weak cation exchange and strong anion exchange arrays. Spectral data were compared to identify biomarkers for development of azotemia.
Results—Low protein concentration in feline urine precluded direct application to array surfaces, and a buffer exchange and concentration step was required prior to SELDI-TOF-MS analysis. Three preparation conditions by use of weak cation and strong anion exchange arrays were selected on the basis of optimization studies for detection of biomarkers. Eight potential biomarkers with an m/z of 2,822, 9,886, 10,033, 10,151, 10,234, 11,653, 4,421, and 9,505 were delineated.
Conclusions and Clinical Relevance—SELDI-TOF-MS can be used to detect urinary low-molecular weight peptides and proteins that may represent biomarkers for early detection of renal damage. Further study is required to purify and identify potential biomarkers before their use in a clinical setting.
Objective—To evaluate urine cauxin immunoreactivity in geriatric cats with variable plasma creatinine concentrations and proteinuria and to assess urinary cauxin-to-creatinine concentration ratio (UC/C) as a predictor of developing azotemia.
Animals—188 client-owned geriatric (≥ 9 years of age) cats.
Procedures—A direct immunoassay was developed and validated for the quantification of urinary cauxin relative to a standard curve generated from a urine sample with high cauxin immunoreactivity. Relationships among UC/C, plasma creatinine concentration, and proteinuria were assessed. Nonazotemic cats were recruited and followed for 12 months. Urinary cauxin-to-creatinine concentration ratio was evaluated as a predictor of development of azotemia in these cats.
Results—No relationship was evident between UC/C and plasma creatinine concentration. A weak positive correlation was identified between UC/C and urine protein-to-creatinine concentration ratio (r = 0.212). At entry to the longitudinal study, those cats that later developed azotemia had a UC/C that was significantly higher than in those remaining nonazotemic after 12 months.
Conclusions and Clinical Relevance—The UC/C did not vary with severity of azotemia but appeared contributory to the feline urinary proteome. High UC/C values were predictive of the geriatric cats in our study developing azotemia. However, it seems unlikely that UC/C will provide additional information about the measurement of urine protein-to-creatinine concentration ratio as a biomarker for the development of azotemia in cats.