Atsuko Kamijo-Ikemori

Clinical Significance of Urinary Liver-Type Fatty Acid Binding Protein in Diabetic Nephropathy of Type 2 Diabetic Patients

OBJECTIVE Urinary liver-type fatty acid–binding protein (L-FABP) is a promising indicator of tubular but not glomerular damage. The aim of this study was to evaluate the clinical usefulness of urinary L-FABP as a prognostic biomarker in impaired diabetic nephropathy in type 2 diabetes. RESEARCH DESIGN AND METHODS This investigation involved a cross-sectional and longitudinal analysis of the relationship between urinary L-FABP levels and progressive nephropathy. Urinary L-FABP was measured with enzyme-linked immunosorbent assay. In the cross-sectional analysis, the association of urinary L-FABP, with the severity of diabetic nephropathy, was investigated in 140 patients with type 2 diabetes and in 412 healthy control subjects. Of the patients in the former study, 104 have been followed for 4 years. The progression of diabetic nephropathy was defined as progressive albuminuria, end-stage renal disease, or induction of hemodialysis. RESULTS Urinary L-FABP levels were progressively increased in subjects with normo-, micro-, or macroalbuminuria and further increased in patients with end-stage renal disease. In the longitudinal analysis, high urinary L-FABP levels were associated with the increase in albuminuria, progression to end-stage renal disease, or induction of hemodialysis. This was particularly demonstrated in the subgroup of patients without renal dysfunction (n = 59), where high urinary L-FABP levels were associated with the progression of diabetic nephropathy. CONCLUSIONS Urinary L-FABP accurately reflected the severity of diabetic nephropathy in type 2 diabetes, and its level was high in the patients with normoalbuminuria. Moreover, higher urinary L-FABP was a risk factor for progression of diabetic nephropathy.

Urinary Excretion of Liver Type Fatty Acid Binding Protein Accurately Reflects the Degree of Tubulointerstitial Damage

To investigate the relationship between liver-type fatty acid-binding protein (L-FABP), a biomarker of chronic kidney disease, in the kidney and the degree of tubulointerstitial damage, folic acid (FA)-induced nephropathy was studied in a mouse model system. As renal L-FABP is not expressed in wild-type mice, human L-FABP (hL-FABP) transgenic mice were used in this study. hL-FABP is expressed in the renal proximal tubules of the transgenic mice that were injected intraperitoneally with FA in NaHCO3 (the FA group) or only NaHCO3 (the control group) and oral saline solution daily during the experimental period. The FA group developed severe tubulointerstitial damage with the infiltration of macrophages and the deposition of type I collagen on days 3 and 7 and recovered to the control level on day 14. The gene and protein expression levels of hL-FABP in the kidney were significantly enhanced on days 3 and 7. Urinary hL-FABP in the FA group was elevated on days 3 and 7 and decreased to the control level on day 14. The protein expression levels of hL-FABP in both the kidney and urine significantly correlated with the degree of tubulointerstitial damage, the infiltration of macrophages, and the deposition of type I collagen. In conclusion, renal expression and urinary excretion of hL-FABP significantly reflected the severity of tubulointerstitial damage in FA-induced nephropathy.

Urinary Fatty Acids and Liver-Type Fatty Acid Binding Protein in Diabetic Nephropathy

Background: The aims of this clinical study were to investigate the associations of urinary free fatty acid (FFA) levels with tubulointerstitial damage, and to determine the clinical significance of urinary liver-type fatty acid binding protein (L-FABP) in diabetic nephropathy. Methods: Fifteen patients with nephrotic syndrome due to diabetic nephropathy and 12 patients with minimal-change nephrotic syndrome (MCNS) were studied. Urinary and serum FFA concentrations (palmitic, oleic, linoleic, and arachidonic acids) were measured by gas chromatography, and urinary L-FABP levels were quantified using an ELISA technique. Tubulointerstitial damage was assessed using renal biopsy specimens. Results: The levels of urinary linoleic and arachidonic acids were significantly elevated in diabetic nephropathy compared to MCNS patients, though serum FFA levels were lower in diabetic nephropathy than MCNS patients. The degree of tubulointerstitial damage was significantly severer in the patients with diabetic nephropathy than MCNS. Urinary L-FABP and 8-OHdG (8-hydroxydeoxyguanosine) concentrations were significantly higher in the diabetic nephropathy subjects. Conclusion: Elevated urinary excretion of FFA may be a reflection of FFA overload in the proximal tubules, and FFA may be an important promoter of tubulointerstitial damage in diabetic nephropathy patients. Urinary L-FABP levels may reflect the stress induced by FFA to the proximal tubules, leading to severe tubulointerstitial damage.

Amelioration of diabetic tubulointerstitial damage in liver-type fatty acid-binding protein transgenic mice

BACKGROUND Renoprotection of liver-type fatty acid binding protein (L-FABP) was demonstrated in a streptozotocin (STZ)-induced diabetic mouse model. METHODS Established human L-FABP (hL-FABP) transgenic (Tg) mice and wild-type (WT) mice were divided into two groups: diabetic mice were uninephrectomized and injected with STZ; control mice were uninephrectomized and injected with a citrate buffer alone. Although mouse L-FABP was not expressed in WT mice, hL-FABP was expressed in the proximal tubules of the diabetic Tg mice and in the control Tg mice at 8 and 14 weeks after these injections. RESULTS The expression of renal hL-FABP increased significantly in diabetic Tg mice compared to control Tg mice. A number of macrophages (F4/80) infiltrating the interstitium, the gene expressions of MCP-1, MCP-3, TGF-beta, Fas, Bax and RAGE were significantly lower in diabetic Tg kidneys compared with diabetic WT kidneys. In the diabetic Tg kidneys, the degree of the tubulointerstitial injury and the deposition of type IV collagen were significantly lower than that of diabetic WT kidneys. The expressions of catalase and glutathione peroxidase-1 were significantly lower in diabetic Tg kidneys compared with diabetic WT kidneys. CONCLUSIONS Renal L-FABP ameliorated the tubulointerstitial damage of type 1 diabetic mice.

Roles of human liver type fatty acid binding protein in kidney disease clarified using hL‐FABP chromosomal transgenic mice

Kidney disease develops to renal failure over a period of days, months or years, hence, clinical markers that indicate the real‐time renal pathophysiological conditions is important. Liver type fatty acid binding protein (L‐FABP) is a 14 kDa molecule predominantly expressed in human proximal tubules. Clinical studies demonstrate that urinary excretion of L‐FABP derived from the proximal tubules is an excellent biomarker for predicting and monitoring deterioration of renal function or for early detection of kidney disease. However, in order to clarify the pathophysiological roles or dynamics of renal L‐FABP in diseased settings, in vivo experimental studies of kidney diseases are indispensable. Since L‐FABP is not endogenously expressed in murine kidneys, a transgenic (Tg) mouse model with expression of the human L‐FABP gene was established. This review article summarizes the findings on the pathophysiological roles and dynamics of renal human L‐FABP in the recent experimental studies performed using this Tg mouse model.

Urinary liver type fatty acid binding protein in diabetic nephropathy.

Deterioration of diabetic nephropathy (DN) is largely determined by the degree of tubulointerstitial changes rather than the extent of histological changes in the glomeruli. Therefore, a tubular marker that accurately reflects tubulointerstitial damage may be an excellent biomarker for early detection or prediction of DN. Liver-type fatty-acid binding protein (L-FABP) is a 14 kDa small molecule that is expressed in the cytoplasm of human proximal tubules. In vivo experimental studies revealed that renal L-FABP gene expression was up-regulated by various stresses that cause tubulointerstitial damage, such as massive proteinuria, hyperglycemia, hypertension, ischemia and toxins, and that urinary excretion of L-FABP was increased. Recent clinical studies of patients with type 1 or type 2 diabetes demonstrated that urinary excretion of L-FABP derived from proximal tubules is a suitable biomarker for predicting and monitoring deterioration of renal function in DN. Moreover, therapeutic interventions with renoprotective effects reduced urinary L-FABP concentrations. Therefore, urinary L-FABP measured using the Human L-FABP ELISA Kit developed by CMIC Co., Ltd. (Tokyo, Japan) was confirmed as a newly established tubular biomarker by the Ministry of Health, Labour and Welfare in Japan in 2010. This review article summarizes the clinical significance of urinary L-FABP in DN.

Renal Liver-Type Fatty Acid Binding Protein Attenuates Angiotensin II–Induced Renal Injury

To investigate the role of human liver-type fatty acid binding protein (hL-FABP) in angiotensin (Ang) II–induced renal injury, Ang II was infused systemically into hL-FABP chromosomal transgenic (Tg) and wild-type (WT) mice (Tg-Ang II and WT-Ang II) for 28 days. Control mice were injected with saline only (Tg-control and WT-control). hL-FABP was expressed in proximal tubules of Tg mice. After a high-dose injection of Ang II, renal gene and protein expressions of hL-FABP in Tg-Ang II mice increased significantly compared with Tg-control mice. Urinary excretion of L-FABP was significantly greater in Tg-Ang II than in Tg-control mice. Blood pressure levels in both groups increased to a similar extent. Upregulation of monocyte chemoattractant protein 1 expression, macrophage infiltration in the interstitium, tubulointerstitial damage, and depositions of type I and III collagens were observed in both Tg-Ang II and WT-Ang II mice. However, these effects were less pronounced in Tg-Ang II compared with WT-Ang II mice. The level of renal N-(hexanoyl)lysine, an oxidative stress marker, was significantly higher in WT-Ang II than in Tg-Ang II mice. In conclusion, renal hL-FABP reduced oxidative stress in Ang II–induced renal injury and attenuated tubulointerstitial damage.

Novel Urinary Biomarkers in Early Diabetic Kidney Disease

In diabetic kidney disease, detection of urinary albumin is recommended to aid in diagnosis, evaluate disease severity, and determine effects of therapy. However, because typical histopathologic changes in diabetic kidney disease or early progressive renal decline may occur in patients with normoalbuminuria, urinary albumin may not be sufficient to identify patients with early-stage diabetic kidney disease or to predict its progression. Therefore, intensive efforts have been made to identify novel noninvasive urinary biomarkers to discriminate patients with a higher risk of end-stage renal failure. Because diabetic kidney disease progression is associated with the extent of histologic changes in the glomeruli and the degree of tubulointerstitial changes, urinary biomarkers that accurately reflect the degree of histopathologic damage may be excellent biomarkers. This review article summarizes the clinical significance of new urinary biomarkers in the early detection of diabetic kidney disease.

Renoprotective effect of the xanthine oxidoreductase inhibitor topiroxostat on adenine-induced renal injury

The aim of the present study was to reveal the effect of a xanthine oxidoreductase (XOR) inhibitor, topiroxostat (Top), compared with another inhibitor, febuxostat (Feb), in an adenine-induced renal injury model. We used human liver-type fatty acid-binding protein (L-FABP) chromosomal transgenic mice, and urinary L-FABP, a biomarker of tubulointerstitial damage, was used to evaluate tubulointerstitial damage. Male transgenic mice (n = 24) were fed a 0.2% (wt/wt) adenine-containing diet. Two weeks after the start of this diet, renal dysfunction was confirmed, and the mice were divided into the following four groups: the adenine group was given only the diet containing adenine, and the Feb, high-dose Top (Top-H), and low-dose Top (Top-L) groups were given diets containing Feb (3 mg/kg), Top-H (3 mg/kg), and Top-L (1 mg/kg) in addition to adenine for another 2 wk. After withdrawal of the adenine diet, each medication was continued for 2 wk. Serum creatinine levels, the degree of macrophage infiltration, tubulointerstitial damage, renal fibrosis, urinary 15-F2t-isoprostane levels, and renal XOR activity were significantly attenuated in the kidneys of the Feb, Top-L, and Top-H groups compared with the adenine group. Serum creatinine levels in the Top-L and Top-H groups as well as renal XOR in the Top-H group were significantly lower than those in the Feb group. Urinary excretion of L-FABP in both the Top-H and Top-L groups was significantly lower than in the adenine and Feb groups. In conclusion, Top attenuated renal damage in an adenine-induced renal injury model.

Renoprotective effect of renal liver-type fatty acid binding protein and angiotensin II type 1a receptor loss in renal injury caused by RAS activation

The aim of this study was to assess the renoprotective effect of renal human liver-type fatty acid binding protein (hL-FABP) and angiotensin II (ANG II) type 1A receptor (AT1a) loss in renal injury caused by renin-angiotensin system (RAS) activation. We established hL-FABP chromosomal transgenic mice (L-FABP(+/-)AT1a(+/+)), crossed the L-FABP(+/-)AT1a(+/+) with AT1a knockdown homo mice (L-FABP(-/-)AT1a(-/-)), and generated L-FABP(+/-)AT1a hetero mice (L-FABP(+/-)AT1a(+/-)). After the back-cross of these cubs, L-FABP(+/-)AT1a(-/-) were obtained. To activate the renal RAS, wild-type mice (L-FABP(-/-)AT1a(+/+)), L-FABP(+/-)AT1a(+/+), L-FABP(-/-)AT1a(+/-), L-FABP(+/-)AT1a(+/-), L-FABP(-/-)AT1a(-/-), and L-FABP(+/-)AT1a(-/-) were administered high-dose systemic ANG II infusion plus a high-salt diet for 28 days. In the L-FABP(-/-)AT1a(+/+), RAS activation (L-FABP(-/-)AT1a(+/+)RAS) caused hypertension and tubulointerstitial damage. In the L-FABP(+/-)AT1a(+/+)RAS, tubulointerstitial damage was significantly attenuated compared with L-FABP(-/-)AT1a(+/+)RAS. In the AT1a partial knockout (AT1a(+/-)) or complete knockout (AT1a(-/-)) mice, reduction of AT1a expression led to a significantly lower degree of renal injury compared with L-FABP(-/-)AT1a(+/+)RAS or L-FABP(+/-)AT1a(+/+)RAS mice. Renal injury in L-FABP(+/-)AT1a(+/-)RAS mice was significantly attenuated compared with L-FABP(-/-)AT1a(+/-)RAS mice. In both L-FABP(-/-)AT1a(-/-)RAS and L-FABP(+/-)AT1a(-/-)RAS mice, renal damage was rarely found. The degrees of renal hL-FABP expression and urinary hL-FABP levels increased by RAS activation and gradually decreased along with reduction of AT1a expression levels. In conclusion, in this mouse model, renal hL-FABP expression and a decrease in AT1a expression attenuated tubulointerstitial damage due to RAS activation.