Urinary F(2)‐Isoprostanes in Cats with International Renal Interest Society Stage 1–4 Chronic Kidney Disease

BACKGROUND: F(2)‐isoprostanes, a biomarker of oxidant injury, increase with advancing chronic kidney disease (CKD) in humans. In cats, the relationship between CKD and oxidative stress is poorly understood. OBJECTIVES: To determine whether cats with advancing CKD have increasing urinary F(2)‐isoprostanes. ANIMALS: Control cats without evidence of CKD (≥6 years old; n = 11), and cats with IRIS stage 1 (n = 8), 2 (n = 38), 3 (n = 21), and 4 (n = 10) CKD. METHODS: This was a prospective observational study. Urinary F(2)‐isoprostanes (specifically free 15‐F(2t)‐isoprostanes) normalized to urine creatinine (IsoPs) were compared among groups and tested for correlations with blood pressure, proteinuria, serum creatinine concentration, and urine specific gravity. The IsoPs also were compared between cats with and without hypertension or proteinuria, and in cats fed predominantly standard versus renal diets. RESULTS: Urinary IsoPs were increased, but not significantly, in cats with stage 1 CKD (median 263 pg/mg creatinine; range, 211–380) compared to controls (182 pg/mg; range, 80–348) and decreased significantly from stage 1 through advancing CKD (stage 2, 144 pg/mg; range, 49–608; stage 3, 102 pg/mg; range, 25–158; stage 4, 67 pg/mg; range, 26–117; P < .01). Urinary IsoPs were inversely correlated with serum creatinine (r = −0.66, P < .0001). CONCLUSION AND CLINICAL IMPORTANCE: Urinary IsoPs are significantly higher in early CKD (stage 1) compared to cats with more advanced CKD. Additional studies are warranted to characterize oxidative stress in cats with stage 1 CKD and determine whether early antioxidant treatments have a protective effect on CKD progression.