Urinary L-type fatty acid-binding protein can reflect renal tubulointerstitial injury

Abstract

This study aimed to elucidate the role of L-type fatty acid-binding protein (L-FABP) in renal tubulointerstitial injury using a mouse adenine-induced renal injury model. C57BL/6 mice fed excess dietary adenine for 6 weeks showed a gradual increase in levels of blood urea nitrogen (BUN). They also showed severe tubulointerstitial pathological findings, such as fibrosis and macrophage infiltration without glomerular damage, which were attenuated by treatment with either allopurinol or Y-700, a new xanthine dehydroxygenase inhibitor. Because renal expression of L-FABP is defective in C57BL/6 mice, human L-FABP transgenic mice were fed an adenine-containing diet. Transgenic mice showed lower BUN levels and lower levels of pathological injury compared with wild-type mice. On the other hand, urinary levels and renal expression of L-FABP in the adenine group was significantly increased and attenuated by treatment with either allopurinol or Y-700. Urinary L-FABP was positively correlated with BUN levels and pathological damages in the tubulointerstitium. No increases in urinary protein, albumin, or N-acetyl-beta-D-glucosaminidase levels were found for 6 weeks in any group. In conclusion, we demonstrated that urinary L-FABP levels can be used to monitor both dynamics and drug responses in a mouse adenine-induced tubulointerstitial injury model.

Figure 1

Renal pathological injury induced by excess dietary adenine. Renal histological changes of the 0.05% (A) and 0.2% (B) adenine diet groups are shown (Masson’s trichrome staining). The animals were sacrificed at 6 weeks. Original magnifications, ×40.

Figure 2

Time course of BUN levels in adenine-induced tubulointerstitial injury model. BUN was measured at 0, 2, 4, and 6 weeks in wild-type (A) and human L-FABP transgenic mice (B) (n = 5 in each group). *P < 0.05 versus adenine group, ^#P < 0.05 versus allopurinol group.

Figure 3

Pathological findings at 6 weeks in C57BL/6 mice. Renal histological changes stained with periodic acid-Schiff (A) and Masson’s trichrome (B) and immunohistochemistry of α-smooth muscle actin (C), and F4/80 (D) are shown. Original magnifications: ×600 (A and D, insets); ×200 (A, C, and D); ×100 (B).

Figure 4

Quantitative analyses of the pathological changes. Fibrotic area in Masson’s trichrome (A), positive staining of α-smooth muscle actin (B), and F4/80 (C) was quantified (n = 5 in each group). *P < 0.05 wild type (Wt) versus transgenic (Tg) mice, ^#P < 0.05 versus adenine group.

Figure 5

Quantitative analyses of mRNA expression. Transforming Growth Factor-β1 (A) and Monocyte Chemoattractant Protein-1 (B) expressions were evaluated by real-time PCR (n = 5 in each group). *P < 0.05 versus adenine group.

Figure 6

Expression of human L-FABP in the kidney. Immunohistochemistry (A), quantitative RT-PCR (B), and Western blotting analysis (C) showed an increased expression of human L-FABP in the adenine group (n = 5 in each group). *P < 0.05 versus normal diet, ^#< 0.05 versus adenine group.

Figure 7

Correlations between urinary markers [L-FABP (A), protein (B), albumin (C), and N-acetyl-β-d-glucosaminidase (D)] and BUN, fibrotic area, and F4/80 positively stained area. Urinary markers, BUN, and pathological changes were evaluated in human L-FABP transgenic mice of the adenine (filled square), allopurinol (open triangle), Y-700 (filled triangle), and normal diet (open circle) groups (n = 5 in each group).