Clinical evaluation of urinary liver-type fatty acid-binding protein for the diagnosis of renal diseases in dogs

Abstract

Liver-type fatty acid-binding protein (L-FABP) is a biomarker for the early detection of renal diseases in humans. L-FABP is a cytotoxic oxidation product secreted from the proximal tubules under ischemic and oxidative stress conditions. First, L-FABP gene expression in the kidney and liver was evaluated. Next, the urinary L-FABP concentrations in dogs with or without renal diseases were measured using a novel enzyme-linked immunosorbent assay kit. Urinary L-FABP was normalized relative to urinary creatinine (uCre) concentrations (µg/g uCre). Finally, the relationships between urinary L-FABP and renal biomarkers used in canine medicine or serum alanine transaminase (ALT) as an indicator of liver damage were examined. Serum and urine samples from 94 client-owned dogs including 23 dogs with renal diseases and 71 dogs without renal diseases were used for analysis. Relative L-FABP gene expression was confirmed both in the liver and kidney. Dogs with renal diseases had a significantly higher urinary L-FABP than those without, and its predictive cutoff value was 26 µg/g uCre. Urinary L-FABP was significantly correlated with serum creatinine (r=0.4674, P<0.01), urea nitrogen (r=0.4907, P<0.01), urine specific gravity (r=-0.5100, P<0.01), and urine protein/creatinine ratio (r=0.7216, P<0.01), but not with serum ALT. Hence, dogs with a high urinary L-FABP value were more likely to have renal diseases.

Keywords: dog; renal disease; urinary liver-type fatty acid-binding protein.

Fig. 1.

Liver-type fatty acid-binding protein (L-FABP) mRNA transcription levels in the liver and kidney of normal dogs. Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) mRNA was used as internal control. Data are normalized to GAPDH levels. The mean L-FABP mRNA was calculated from a standard curve. Error bars represent the S.D.

Fig. 2.

Urinary liver-type fatty acid-binding protein (L-FABP) in dogs with or without renal diseases. The triangle represents 24 dogs with renal diseases including chronic kidney disease (CKD, closed symbols, n=20) and acute kidney injury (AKI, open symbols, n=4). The circle represents 70 dogs without renal diseases including clinical healthy dogs (n=23), those with extrarenal urological disease (n=20), and those with non-urological diseases (n=27). The solid lines indicate median values (renal diseases: 238.3 µg/g uCre, clinically healthy: 1.9 µg/g uCre, extrarenal urological diseases: 4.0 µg/g uCre, and non- urological diseases: 3.2 µg/g uCre), and the dashed lines indicate the cutoff value for detecting renal diseases (26 µg/g uCre). *P<0.05 and **P<0.01.

Fig. 3.

Correlation between urinary liver-type fatty acid-binding protein (L-FABP) levels and serum creatinine (A), urea nitrogen (B), urine specific gravity (USG) (C), and urine protein/creatinine (UPC) ratio (D). The associations with urinary L-FABP were examined among serum creatinine, serum urea nitrogen and USG in 94 dogs. The relationship between urinary L-FABP and UPC ratio in 77 dogs without urinary sediment was examined.

Fig. 4.

Correlation between urinary liver-type fatty acid-binding protein (L-FABP) levels and serum alanine transaminase (ALT) levels in 94 dogs. There was no significant correlation between serum ALT and urinary L-FABP levels.