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. 2020 Mar;34(2):761-769.
doi: 10.1111/jvim.15721. Epub 2020 Feb 22.

Renal expression and urinary excretion of liver-type fatty acid-binding protein in cats with renal disease

Affiliations

Renal expression and urinary excretion of liver-type fatty acid-binding protein in cats with renal disease

Masaaki Katayama et al. J Vet Intern Med. 2020 Mar.

Abstract

Background: Liver-type fatty acid-binding protein (L-FABP) is a biomarker for early detection of renal disease in humans. Liver-type fatty acid-binding protein is cytotoxic oxidation products secreted from proximal tubules under ischemia and oxidative stress.

Objective: To examine renal expression and quantify urinary excretion of L-FABP in catswith renal disease.

Animals: One hundred and thirty-four client-owned cats including 34 cats with serum creatinine (sCre) values >1.6 mg/dL and 10 other cats that died in clinics.

Methods: Tissue expressions of L-FABP were examined by reverse transcription polymerase chain reaction and Western blotting. Urinary L-FABP (uL-FABP) and serum L-FABP (sL-FABP) levels were determined by enzyme-linked immunosorbent assay. Anti-liver-type fatty acid-binding protein antibody immunostained renal sections.

Results: Feline kidneys express L-FABP. Strong L-FABP signals were observed in the lumens of proximal tubular cells in 5 cats with high uL-FABP excretion, but not in 5 cats with low uL-FABP excretion. In 9 normal cats, uL-FABP index was <1.2 μg/g urinary creatinine (uCre). High uL-FABP indexes (>10.0 μg/g uCre) were detected in 7 of 100 cats with low sCre (<1.6 mg/dL) and 18 of 44 cats with high sCre (>1.6 mg/dL). There was a weak correlation between L-FABP index and sCre, serum symmetric dimethylarginine (SDMA), or blood urea nitrogen (BUN), and these correlation coefficients were increased by analyzing only data of cats with sCre >1.6 mg/dL. There was a weak correlation between u L-FABP index and sL-FABP in all tested cats, but not in cats with high sCre.

Conclusions and clinical importance: This study demonstrates correlations between L-FABP and current renal biomarkers for chronic kidney disease in cats, such as sCre and SDMA. Liver-type fatty acid-binding protein may be a potential biomarker to predict early pathophysiological events in feline kidneys.

Keywords: acute kidney injury; biomarker; chronic kidney disease; kidney.

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Conflict of interest statement

Tsuyoshi Oikawa, Keiichi Ohata, and Takeshi Sugaya are senior scientists of CMIC Holdings Co. Ltd (Tokyo, Japan), a company that produced the high sensitivity L‐FABP ELISA kits for L‐FABP analysis. No other potential conflicts of interest relevant to this article are reported.

Figures

Figure 1
Figure 1
Expression of L‐FABP in feline kidneys. A, RT‐PCR for amplification of feline L‐FABP and GAPDH was performed with kidney and liver mRNAs from a normal male cat. The feline L‐FABP gene (amplicon size 321 bp) and GAPDH gene (amplicon size 452 bp) were amplified from renal and liver cDNAs using specific primers. B, Western blotting of proteins (aliquots of 30 μg) extracted from cat kidneys and livers was performed using anti‐L‐FABP antibodies. An arrow indicates an signal of 14‐kDa L‐FABP. L, liver, K, kidney; M, marker (Figure 1A, 100‐bp ladder marker). L‐FABP, liver‐type fatty acid‐binding protein; RT‐PCR, reverse transcription polymerase chain reaction
Figure 2
Figure 2
Urinary excretion of L‐FABP in cats. A, Western blotting of urine (aliquots of 10 μL) collected from 9 cats with CKD was performed using anti‐L‐FABP antibody. Other detail information of the 9 cats is described in Table S1. B, Correlation between urinary L‐FABP contents quantified by L‐FABP ELISA and density of the L‐FABP band detected in Figure 2A. CKD, chronic kidney disease; ELISA, enzyme‐linked immunosorbent assay; L‐FABP, liver‐type fatty acid‐binding protein
Figure 3
Figure 3
Representative immunohistochemical images of L‐FABP in paraffin‐embedded renal sections of 10 cats. A‐E and F‐J are renal sections of 5 cats with low urinary L‐FABP index and 5 cats with high uL‐FABP index, respectively. Their individual information, urinary L‐FABP indexes, pathological diagnosis, and clinical history are described in Table S2. L‐FABP, liver‐type fatty acid‐binding protein; uL‐FABP, urinary L‐FABP
Figure 4
Figure 4
Correlations between serum and urinary L‐FABP in cats. The correlation between Log serum L‐FABP and Log urinary L‐FABP index was examined in 108 cats including 12 cats with high sCre (>1.6 mg/dL). Asterisks indicate cats with low sCre (<1.6 mg/dL). L‐FABP, liver‐type fatty acid‐binding protein; sCre, serum creatinine
Figure 5
Figure 5
Correlations between urinary L‐FABP, sCre, or BUN in cats. The correlation between Log uL‐FABP index and Log sCre (A) or Log BUN (B) was examined in 134 cats including 24 cats with high sCre (>1.6 mg/dL). Asterisks indicate cats with low sCre (<1.6 mg/dL). C. Log uL‐FABP indexes are shown inbox and whisker plot, and their significant differences between IRIS stages were evaluated by nonparametric Wilcoxon matched‐pair signed ranks tests. BUN, blood urea nitrogen, L‐FABP, liver‐type fatty acid‐binding protein; sCre, serum creatinine; uL‐FABP, urinary L‐FABP
Figure 6
Figure 6
Correlations between serum SDMA and urinary L‐FABP or sCre in cats. The correlation between Log serum SDMA and Log sCre (A) or urinary L‐FABP index (B) was examined in 106 cats including 13 cats with high sCre (>1.6 mg/dL). Asterisks indicate cats with low sCre (<1.6 mg/dL). L‐FABP, liver‐type fatty acid‐binding protein; sCre, serum creatinine; SDMA, serum symmetric dimethylarginine

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