Urinary liver-type fatty acid binding protein is a biomarker reflecting renal damage and the ameliorative effect of drugs at an early stage of histone-induced acute kidney injury

AIM

Circulated histones play a crucial role in the pathogenesis of infectious diseases and severe trauma, and it is one of the potential molecular targets for therapeutics. Recently, we reported that histone is one of the causative agents for urinary L-FABP increase. However, the mechanism is still unclear, especially in severe cases. We further investigated the mechanism of urinary L-FABP increase using a more severe mouse model with histone-induced kidney injury. This study also aims to evaluate the therapeutic responsiveness of urinary L-FABP as a preliminary study.

METHODS

Human L-FABP chromosomal transgenic mice were administrated 30 mg/kg histone from a tail vein with a single dose. We also performed a comparative study in LPS administration model. For the evaluation of the therapeutic responsiveness of urinary L-FABP, we used heparin and rolipram.

RESULTS

The histological change with cast formation as a characteristic of the models was observed in proximal tubules. Urinary L-FABP levels were significantly elevated and these levels tended to be higher in those with more cast formation. Heparin and rolipram had the ameliorative effect of the cast formation induced by histone and urinary L-FABP levels significantly decreased.

CONCLUSION

Histone is one of the causative agents for the increase of urinary L-FABP at an early stage of AKI. In addition, it suggested that urinary L-FABP may be useful as a subclinical AKI marker reflecting kidney damage induced by histone. Furthermore, urinary L-FABP reflected the degree of the damage after the administration of therapeutic agents such as heparin and PDE4 inhibitor.

Clinical usefulness of urinary biomarkers for early prediction of acute kidney injury in patients undergoing transaortic valve implantation

This study aimed to reveal the clinical usefulness of urinary biomarkers for the early prediction of AKI onset after transcatheter aortic valve implantation (TAVI) (n = 173). In this study, 22 (12.7%) patients had AKI, of which 21 had mild AKI and 1 had moderate AKI. Higher levels of urinary liver-type fatty acid binding protein (L-FABP), [tissue inhibitor of metalloproteinases-2] × [insulin-like growth factor-binding protein 7], clusterin and urinary albumin before, after and 4 h after TAVI were associated with AKI onset. However, the time point of higher urinary N-acetyl-β-D-glucosaminidase levels related to AKI onset was only before TAVI. No significant differences were found in the area under the receiver-operator characteristic curves (AUC) for predicting AKI onset between urinary biomarkers before TAVI. After TAVI, the AUC (0.81) of urinary albumin was significantly higher than those of any other urinary biomarkers. The sensitivity (0.86) in urinary albumin after TAVI and specificity (0.98) in urinary L-FABP before TAVI were the highest among urinary biomarkers. In conclusion, urinary biomarkers may be clinically useful for early differentiation of patients with a higher or lower risk for AKI onset or early prediction of post-TAVI onset of AKI.

Urinary liver-type fatty acid binding protein is increased in the early stages of the disease with a risk of acute kidney injury induced by histone

AIM

Urinary liver-type fatty acid binding protein (L-FABP) has potential utility as an early prognostic biomarker ahead of traditional severity scores in coronavirus disease 2019 and sepsis, however, the mechanism of elevated urinary L-FABP in the disease has not been clearly elucidated. We investigated the background mechanisms of urinary L-FABP excretion through non-clinical animal model focusing on histone, which is one of the aggravating factors in these infectious diseases.

METHODS

Male Sprague-Dawley rats were placed in central intravenous catheters, and these rats were given a continuous intravenous infusion of 0.25 or 0.5 mg/kg/min calf thymus histones for 240 min from caudal vena cava.

RESULTS

After the administration of histone, urinary L-FABP and gene expression of an oxidative stress marker in the kidney increased in a histone dose-dependent manner before increased serum creatinine. Upon further investigation, fibrin deposition in the glomerulus was observed and it tended to be remarkable in the high dose administrated groups. The levels of coagulation factor were significantly changed after the administration of histone, and these were significantly correlated with the levels of urinary L-FABP.

CONCLUSIONS

Firstly, it was suggested that histone is one of the causative agents for the urinary L-FABP increase at an early stage of the disease with a risk of acute kidney injury. Secondly, urinary L-FABP could be a marker reflecting the changes of coagulation system and microthrombus caused by histone in the early stage of acute kidney injury before becoming severely ill and maybe a guide to early treatment initiation.

Mechanism for exercise-mediated prevention against muscle wasting on extensor digitorum longus muscle in Spontaneously Diabetic Torii fatty rats

We previously reported the significant increase in limb muscle strength and cross-sectional area of the type IIb muscle fibers in the extensor digitorum longus (EDL) muscle in a type 2 diabetic animal model, with Spontaneously Diabetic Torii (SDT) fatty rats (n = 6) undergoing regular treadmill exercise from 8 to 16 weeks of age compared with sedentary SDT fatty rats (n = 6). This study investigated the mechanism by which exercise training prevented skeletal muscle wasting in the EDL muscle of the SDT fatty rats. The endurance exercise for 8 weeks downregulated the expression of muscle RING-finger protein-1 (an E3 ubiquitin ligase) and upregulated the expression of CD31, insulin receptor substrate-2, and phosphorylated endothelial nitric oxide synthase in the EDL muscle of 16-week-old SDT fatty rats.Endurance exercise training might reduce muscle wasting by preventing muscle degradation and increasing the angiogenic response in the EDL muscle in type 2 diabetes.

Angiotensin II type 1a receptor deficiency alleviates muscle atrophy after denervation

The study aim was to determine if suppressed activation of angiotensin II type 1 receptor (AT1) prevents severe muscle atrophy after denervation. The sciatic nerves in right and left inferior limbs were cut in AT1a knockout homo (AT1a^-/-) male mice and wild-type (AT1a^+/+) male mice. Muscle weight and cross-sectional areas of type IIb muscle fibers in gastrocnemius muscle decreased at 7 and 21 days postdenervation in both AT1a^-/- mice and AT1a^+/+ mice, and the reduction was significantly attenuated in the denervated muscles of AT1a^-/- mice compared to the AT1a^+/+ mice. Gene expressions in the protein degradation system [two E3 ubiquitin ligases (muscle RING-finger protein-1 and Atrogin-1)] upregulated at 7 days postdenervation in all denervated mice were significantly lower in AT1a^-/- mice than in AT1a^+/+ mice. Activations of nuclear factor κB and Forkhead box subgroup O1, and protein expression of monocyte chemoattractant protein-1 were significantly suppressed in the AT1a^-/- mice compared with those in the AT1a^+/+ mice. In addition, suppressed apoptosis, lower infiltration of M1 macrophages, and higher infiltration of M2 macrophages were significantly observed at 21 days postdenervation in the AT1a^-/- mice compared with those in the AT1a^+/+ mice. In conclusion, the AT1 receptor deficiency retarded muscle atrophy after denervation.

Glucagon-like peptide-1 receptor agonist, liraglutide, attenuated retinal thickening in spontaneously diabetic Torii fatty rats

BACKGROUND

This study aims to investigate the effect of the glucagon-like peptide-1 (GLP-1) receptor agonist (GLP-1RA) liraglutide on retinal pathological findings as compared with insulin and hydralazine using an animal model of type 2 diabetes with obesity, hypertension, and hyperlipidemia.

METHODS

Male spontaneously diabetic Torii (SDT) fatty rats at 8 weeks of age were randomly assigned to three groups: the liraglutide group (SDT-lira, n = 6) received a subcutaneous injection of liraglutide from the age of 8 to 16 weeks, the SDT-ins-hyd group (n = 6) was provided both insulin against hyperglycemia and hydralazine against hypertension to match levels of both blood glucose and blood pressure to those of the liraglutide group, and the control group of SDT fatty rats (SDT-vehicle, n = 7) and a nondiabetic control group of Sprague-Dawley rats (SD, n = 7) were injected with vehicle only. Both eyeballs of all groups were collected at the age of 16 weeks.

RESULTS

Retinal thickness, which was found in the SDT-vehicle group, was significantly prevented to similar levels in both the SDT-lira and SDT-ins-hyd groups. Immunohistological analysis revealed that GLP-1 receptor was not expressed in the retina of all rats. The ocular protein expression of monocyte chemoattractant protein-1, which causes a proinflammatory situation, was significantly upregulated in all SDT fatty rats as compared to SD rats, but the expression levels were similar between all SDT fatty rats. With regard to neovascularization in the eyes, there were no significant differences in protein expressions of vascular endothelial growth factor, CD31, or endothelial nitric oxide synthase in all rats.

CONCLUSIONS

The present study indicates that liraglutide prevents retinal thickening, dependent on blood glucose and blood pressure levels in SDT fatty rats without ocular neovascularization. However, the effects did not improve the ocular proinflammatory state.

Effect of GLP-1 receptor agonist, liraglutide, on muscle in spontaneously diabetic torii fatty rats

This study investigated the effect of liraglutide, a glucagon-like peptide-1 receptor agonist, on skeletal muscles in rats with type 2 diabetes. Male SDT fatty rats (8-week-old) were provided liraglutide, or insulin-hydralazine for 8 weeks; control SDT fatty rats and SD rats were administered a vehicle. At 16 weeks of age, muscle strength of limbs was significantly lower in all SDT fatty rats compared to SD rats. While cross-sectional areas of type IIb muscle fibers in extensor digitorum longus muscle were significantly lower in SDT fatty rats than in SD rats, those of type I muscle fibers in soleus were similar in all rats. In the soleus of SDT fatty rats, liraglutide led to greater citrate synthase activity and cytochrome c oxidase subunit 5 B protein expression, independently of blood glucose and blood pressure levels. Liraglutide may contribute to preservation of mitochondrial content on soleus muscle in type 2 diabetes.

Endurance exercise training-attenuated diabetic kidney disease with muscle weakness in spontaneously diabetic Torii fatty rats

Background The aim of this study was to evaluate protective effects of endurance exercise training against diabetic kidney disease (DKD) with muscle weakness by using male spontaneously diabetic Torii (SDT) fatty rats as type 2 diabetic animal models with obesity, hypertension, and hyperlipidemia. Methods Eight-week-old SDT fatty rats (n = 12) and Sprague-Dawley (SD) rats (n = 10) were randomly divided into exercise (Ex; SDT-Ex: n = 6, SD-Ex: n = 5) and sedentary groups (SDT-Cont: n = 6, SD-Cont: n = 5), respectively. Each group underwent regular treadmill exercise four times a week from ages 8 to 16 weeks. Results The exercise attenuated hypertension and hyperlipidemia and prevented increases in renal parameter levels without affecting blood glucose levels. In the SDT fatty rats, it prevented induction of renal morphological abnormalities in the interstitium of the superficial and intermediate layers of the cortex. Downregulated expression of endothelial nitric oxide synthase in the glomerulus of the SDT fatty rats was significantly upregulated by the exercise. The exercise upregulated the renal expressions of both medium-chain acyl-CoA dehydrogenase and peroxisome proliferator-activated receptor γ coactivator-1α related to fatty acid metabolism. It increased muscle strength and both muscle weight and cross-sectional area of type IIb muscle fibers in the extensor digitorum longus muscle in the SDT fatty rats. Conclusion Endurance exercise training in type 2 diabetes ameliorates DKD by improving endothelial abnormality and enhancing fatty acid metabolism in addition to attenuated hypertension, hyperlipidemia, and muscle weakness independently of blood glucose levels.

Spontaneous Remission of Thrombospondin Type-1 Domain-Containing-Associated Membranous Nephropathy

Membranous nephropathy often achieves spontaneous remission. However, there are scarce reports of spontaneous remission of thrombospondin type-1 domain-containing 7A (THSD7A)-associated membranous nephropathy. A 64-year-old female presented with nephrotic syndrome and edema of the lower extremities. We diagnosed membranous nephropathy by kidney biopsy and confirmed positive THSD7A on immunofluorescence using frozen sections; serum THSD7A antibodies were also detected. Thirty-four months after the initial diagnosis, she achieved a spontaneous complete remission without immunosuppressive therapy. With the complete remission, no serum THSD7A levels were detected. In this study, we describe serial examinations of kidney biopsies and serum THSD7A antibodies.

Clinical Utility of Urinary Biomarkers for Prediction of Acute Kidney Injury and Chronic Renal Dysfunction After Open Abdominal Aortic Aneurysm Repair

Purpose

We examined the clinical utility of perioperative monitoring of urinary liver-type fatty acid binding protein (L-FABP), neutrophil gelatinase-associated lipocalin (NGAL), and albumin, for prediction of acute kidney injury (AKI) and prediction of chronic renal dysfunction in patients undergoing open surgical repair (OSR) of an abdominal aortic aneurysm.

Patients and Methods

Urine and serum samples were obtained perioperatively from 64 such patients (n=64). Patients in whom OSR-related AKI (defined by the Kidney Disease Improving Global Outcomes criteria) occurred were identified. Renal function was evaluated 3 years after OSR in patients with OSR-related AKI.

Results

The urinary biomarkers examined increased to maximum levels by 2 hours after aortic cross-clamping (AXC), regardless of whether AKI occurred. Notably, the serum creatinine (Cr) levels increased significantly immediately after OSR in patients with AKI (n=19) (vs that in patients without AKI). In patients with AKI, the increased serum Cr elevation rate, the urinary L-FABP levels 2 hours after AXC and immediately after OSR, and a reduction in eGFR documented 3 years after OSR were significantly greater in patients who underwent suprarenal AXC (n=11) than in those who underwent infrarenal AXC (n=8). Furthermore, urinary L-FABP levels 2 hours after AXC correlated significantly with the reductions in eGFR 3 years after OSR in patients with AKI.

Conclusion

Urinary L-FABP, NGAL and albumin concentrations 2 hours after AXC may be useful for early detection of OSR-related AKI. Furthermore, the increase in urinary L-FABP 2 hours after AXC may be predictive of chronic renal dysfunction in patients with OSR-related AKI.

Renoprotective effect of GLP-1 receptor agonist, liraglutide, in early-phase diabetic kidney disease in spontaneously diabetic Torii fatty rats

BACKGROUND

The aim of this study is to investigate the renoprotective effect of the GLP-1 receptor agonist, liraglutide, in early-phase diabetic kidney disease (DKD) using an animal model of type 2 diabetes with several metabolic disorders.

METHODS

Male 8-week-old spontaneously diabetic Torii (SDT) fatty rats (n = 19) were randomly assigned to three groups. The liraglutide group (n = 6) was injected subcutaneously with liraglutide. Another treatment group (n = 6) received subcutaneous insulin against hyperglycemia and hydralazine against hypertension for matching blood glucose levels and blood pressure with the liraglutide group. The control groups of SDT fatty (n = 7) and non-diabetic Sprague-Dawley rats (n = 7) were injected only with a vehicle.

RESULTS

The control group of SDT fatty rats exhibited hyperglycemia, obesity, hypertension, hyperlipidemia, glomerular sclerosis, and tubulointerstitial injury with high urinary albumin and L-FABP levels. Liraglutide treatment reduced body weight, food intake, blood glucose and blood pressure levels, as well as ameliorated renal pathologic findings with lower urinary albumin and L-FABP levels. Liraglutide increased expressions of phosphorylated (p)-eNOS and p-AMPK in glomeruli, downregulated renal expression of p-mTOR, and increased renal expressions of LC3B-II, suggesting activation of autophagy. However, these effects were not caused by the treatments with insulin and hydralazine, despite comparable levels of hyperglycemia and hypertension to those achieved with liraglutide treatment.

CONCLUSIONS

Liraglutide may exert a renoprotective effect via prevention of glomerular endothelial abnormality and preservation of autophagy in early-phase DKD, independent of blood glucose, and blood pressure levels.

Oral administration of melatonin contained in drinking water increased bone strength in naturally aged mice

Melatonin has recently been found to be a possible new regulator of bone metabolism. However, the influence of melatonin in natural age-related osteoporosis has not been fully elucidated yet, although there have been some reports regarding postmenopausal osteoporosis with melatonin treatments. The present study investigated the effects of long-term melatonin administration during the aging process on bone metabolism. Using quantitative computed tomography methods, we found that the total bone density of both the femur metaphysis and diaphysis decreased significantly in 20-month-old male mice. In the metaphysis, both trabecular bone mass and Polar-Strength Strain Index (SSI), which is an index of bone strength, decreased significantly. Judging from bone histomorphometry analysis, trabecular bone in 20-month-old male mice decreases significantly with age and is small and sparse, as compared to that of 4-month-old male mice. Loss of trabecular bone is one possible cause of loss of bone strength in the femoral bone. In the metaphysis, the melatonin administration group had significantly higher trabecular bone density than the non-administration group. The Polar-SSI, cortical area, and periosteal circumference in the diaphysis was also significantly higher with melatonin treatments. Since the melatonin receptor, MT2, was detected in both osteoblasts and osteoclasts of the femoral bone of male mice, we expect that melatonin acts on osteoblasts and osteoclasts to maintain the bone strength of the diaphysis and metaphysis. Thus, melatonin is a potential drug for natural age-related osteoporosis.

Incremental short maximal exercise increases urinary liver-type fatty acid-binding protein in adults without CKD

Exercise-induced redistribution of tissue blood flow decreases the renal blood flow in an exercise intensity-dependent manner. However, the acute effects of incremental short maximal exercise on renal tubular conditions remain unknown. The purpose of this study was to investigate the acute effects of incremental short maximal exercise on the urinary liver-type fatty acid-binding protein, which is a highly sensitive tubular biomarker that correlates excellently with peritubular capillary blood flow. A total of 116 adults (aged 24-83 years) without chronic kidney disease performed the incremental short maximal exercise using a cycling ergometer, wherein the exercise sequence consisted of commencing with a 2-min workout period at 20 W (as a warm-up period) and then followed by a 10-20 W increase every 1 minute until termination criteria were reached. Urinary samples were gathered before and immediately after the exercise to evaluate the concentrations of urinary creatinine, albumin, and liver-type fatty acid-binding protein. Urinary excretion levels of albumin and liver-type fatty acid-binding protein were significantly increased post-exercise (P < .001 and P = .008, respectively). Furthermore, the % change in urinary liver-type fatty acid-binding protein levels after exercise was found to correlate independently with age, estimated glomerular filtration rate at baseline, and the % change in urinary albumin (Model R²  = 0.451, P < .001). Our findings suggest that incremental short maximal exercise may lead to acute slightly adverse effects on tubular conditions, especially in young adults or adults with lower renal function, even without chronic kidney disease.

Relationship between Urinary Liver-Type Fatty Acid-Binding Protein (L-FABP) and Sarcopenia in Spontaneously Diabetic Torii Fatty Rats

BACKGROUND

Type 2 diabetes (T2D) is a known risk factor for diabetic kidney disease (DKD) and sarcopenia in older patients. Because there may be an interaction between DKD and sarcopenia, the aim of the present study is to investigate the relationship between urinary levels of liver-type fatty acid-binding protein (L-FABP) and sarcopenia using a novel rat model of T2D.

METHODS

Male spontaneously diabetic Torii (SDT) fatty rats (n = 5) at 16 weeks of age were used as an animal model of T2D. Age- and sex-matched Sprague-Dawley (SD) rats (n = 7) were used as controls. Urine samples were obtained from the rats, and muscle strength was evaluated with the use of the forelimb grip test at 16, 20, and 24 weeks of age. Serum, kidney, soleus, and extensor digitorum longus (EDL) muscle samples were collected at 24 weeks of age. Urinary L-FABP levels were measured using dedicated enzyme-linked immunosorbent assays.

RESULTS

Increased urinary L-FABP levels, focal glomerular sclerosis, moderate interstitial inflammation and fibrosis, and accumulation of renal oxidative proteins were significantly observed in the SDT fatty rats, compared to the SD rats. Muscle weight, muscle strength, cross-sectional areas of both type I and type IIb muscle fibers, and increasing rate of muscle strength were significantly decreased in the SDT fatty rats compared to the SD rats at 24 weeks. Urinary L-FABP levels at 20 and 24 weeks were significantly negatively correlated with muscle strength. Urinary L-FABP levels at 16 weeks were significantly negatively correlated with the increasing rate of muscle strength.

CONCLUSIONS

Urinary L-FABP reflects the degree of muscle strength and weight, as well as cross-sectional areas of muscle fibers. Although further clinical study is needed, urinary L-FABP may be useful to monitor the progression of sarcopenia and DKD in T2D patients.

The Possibility of Urinary Liver-Type Fatty Acid-Binding Protein as a Biomarker of Renal Hypoxia in Spontaneously Diabetic Torii Fatty Rats

BACKGROUND

Renal hypoxia is an aggravating factor for tubulointerstitial damage, which is strongly associated with renal prognosis in diabetic kidney disease (DKD). Therefore, urinary markers that can detect renal hypoxia are useful for monitoring DKD.

OBJECTIVE

To determine the correlation between urinary liver-type fatty acid-binding protein (L-FABP) and renal hypoxia using a novel animal model of type 2 diabetes.

METHODS

Male spontaneously diabetic Torii (SDT) fatty rats (n = 6) were used as an animal model of type 2 diabetes. Age- and sex-matched Sprague-Dawley (SD) rats (n = 8) were used as controls. Body weight, systolic blood pressure, and blood glucose levels were measured at 8, 12, 16, and 24 weeks of age. Urine samples and serum and kidney tissues were collected at 24 weeks of age. Microvascular blood flow index (BFI) was measured using diffuse correlation spectroscopy before sampling both the serum and kidneys for the evaluation of renal microcirculation at the corticomedullary junction.

RESULTS

Obesity, hyperglycemia, and hypertension were observed in the SDT fatty rats. Focal glomerular sclerosis, moderate interstitial inflammation, and fibrosis were significantly more frequent in SDT fatty rats than in SD rats. While the frequency of peritubular endothelial cells and phosphoendothelial nitric oxide synthase levels were similar in both types of rats, the degree of renal hypoxia-inducible factor-1α (HIF-1α) expression was significantly higher (and with no change in renal vascular endothelial growth factor expression levels) in the SDT fatty rats. Urinary L-FABP levels were significantly higher and renal microvascular BFI was significantly lower in the SDT fatty rats than in the SD rats. Urinary L-FABP levels exhibited a significant positive correlation with renal HIF-1α expression and a significant negative correlation with renal microvascular BFI.

CONCLUSIONS

Urinary L-FABP levels reflect the degree of renal hypoxia in DKD in a type 2 diabetic animal model. Urinary L-FABP may thus prove useful as a renal hypoxia marker for monitoring DKD in patients with type 2 diabetes in clinical practice.

Urinary Level of Liver-Type Fatty Acid Binding Protein Reflects the Degree of Tubulointerstitial Damage in Polycystic Kidney Disease

BACKGROUND/AIMS

Polycystic kidney disease (PKD) is a common, progressive, and heritable type of kidney disease. Although certain imaging modalities are useful for the diagnosis and staging of PKD, they cannot adequately monitor the severity of interstitial inflammation and fibrosis. Therefore, the present study evaluated the urinary level of liver-type fatty acid binding protein (L-FABP) as a marker of interstitial inflammation and fibrosis in PKD.

METHODS

Male PCK/CrljCrl-Pkhd1pck/Crl (PCK) rats (n = 34) were used as an animal model of the PKD. Age-and sex-matched Sprague-Dawley rats (SD) (n = 34) were used as controls. Urine samples were obtained from the rats at 8, 12, 16, 20, and 24 weeks of age, and the sera and kidney tissues were obtained at 8, 16, 20, and 24 weeks of age.

RESULTS

All PCK rats developed cysts, and the degrees of tubular epithelial cell proliferation and interstitial inflammation increased linearly with age in these model rats relative to the controls. Interstitial fibrosis tended to increase in the PCK rats from 8 to 20 weeks of age, and revealed a peak level at 20 weeks. The urinary L-FABP levels increased linearly with age in the PCK rats, and the levels at 12, 16, 20, and 24 weeks were significantly higher than those in the controls. The urinary levels of L-FABP in the PCK rats correlated significantly with the severity of tubulointerstitial damage; specifically, we observed a significant correlation of the urinary levels at 16 weeks of age with the total kidney volume at 20 weeks. In contrast, both PCK and SD rats exhibited similar serum levels of L-FABP.

CONCLUSION

Urinary L-FABP reflects the progression of tubulointerstitial damage, and therefore, may be a useful marker for monitoring the progression of PKD.

Utility of urinary tubular markers for monitoring chronic tubulointerstitial injury after ischemia-reperfusion

AIM

The aim of this study was to elucidate whether urinary tubular markers during the chronic phase of acute kidney injury (AKI) are associated with chronic tubulointerstitial damage.

METHODS

Male human L-type fatty acid binding protein (L-FABP) chromosomal transgenic (Tg) mice underwent ischaemic reperfusion (I/R) injury via renal pedicle clamping for either 10 min or 20 min. Contralateral nephrectomy was performed at the time of tissue reperfusion. The kidneys were analyzed 20 days after the last I/R.

RESULTS

Serum creatinine levels 20 days post-I/R were significantly higher in the 20 min I/R than in the 10 min I/R and control groups and were similar between the 10 min I/R and control groups. The degree of tubulointerstitial damage 20 days post-I/R was significantly more severe in the 20 min I/R than in the 10 min I/R and control groups, as well as in the 10 min I/R than in the control group. Urinary levels of human L-FABP, albumin, and kidney injury molecule-1 (KIM-1) 20 days post-I/R were significantly higher in the 20 min I/R than in the control group, whereas urinary L-FABP was significantly higher in the 10 min I/R than in the control group. Conversely, urinary neutrophil gelatinase-associated lipocalin levels did not significantly differ between the three groups. Finally, the urinary levels of human L-FABP, albumin, and KIM-1 levels 20 days post-I/R were significantly correlated with the degree of renal damage.

CONCLUSIONS

Urinary levels of human L-FABP, albumin and, KIM-1 may be useful for monitoring AKI-to-CKD transition in clinical practice.

Habitual exercise decreases plasma xanthine oxidoreductase activity in middle-aged and older women

The aim of present study was to investigate the association between plasma xanthine oxidoreductase activity, which has gained attention as a novel preventive target of cardiovascular disease, and various physiological parameters and was to determine the effects of habitual exercise on plasma xanthine oxidoreductase activity in middle-aged and older women. In the cross-sectional study, we investigated the association between plasma xanthine oxidoreductase activity and various physiological parameters in 94 middle-aged and older women. In the interventional study, subjects (n = 22) were divided into two groups: exercise (n = 12) or the control group (n = 10), whereby we examined the effect of 12-week aerobic exercise training on plasma xanthine oxidoreductase activity in middle-aged and older women. The cross-sectional study demonstrated that plasma xanthine oxidoreductase activity was significantly associated with various physiological parameters, including visceral fat and daily step counts. In the interventional study, the plasma xanthine oxidoreductase activity significantly decreased after the 12-week aerobic exercise training, its changes were inversely associated with the changes in daily step counts. Our results revealed that the plasma xanthine oxidoreductase activity was associated with visceral fat accumulation and lack of exercise, and it was decreased by the aerobic exercise training.

Role of bardoxolone methyl, a nuclear factor erythroid 2-related factor 2 activator, in aldosterone- and salt-induced renal injury

The aim of this study was to investigate the renoprotective effect of bardoxolone methyl (BM), a nuclear factor erythroid 2-related factor 2 (Nrf2) activator with an antioxidant effect, in a salt-sensitive hypertension model induced by aldosterone (Ald) and salt. Tubulointerstitial damage with urinary liver-type fatty acid-binding protein (L-FABP) was evaluated using human L-FABP chromosomal transgenic (L-FABP^+/-) male mice. The mice in the Ald group (n=7) received systemic Ald infusions via an osmotic minipump and were given 1% NaCl water for 35 days. Those in the Ald-BM group (n=8) were administered BM intraperitoneally in addition to an injection of Ald and salt. The dose of BM was gradually increased every 7 days up to 10 mg kg^-1 per day, which was maintained for 14 days. The administration of BM significantly increased renal expression of the Nrf2 target antioxidant gene. Tubulointerstitial damage was significantly ameliorated in the Ald-BM group compared to the Ald group. The increase in reactive oxygen species (ROS) and upregulation of angiotensinogen expression in the kidneys of the Ald group was significantly prevented in the Ald-BM group. The upregulation of human L-FABP expression induced in the kidneys and increase in urinary L-FABP in the Ald group were significantly suppressed by BM administration. In conclusion, BM ameliorated tubulointerstitial damage in the Ald- and salt-induced hypertension model through suppression of both ROS production and intrarenal renin-angiotensin system activation. Urinary L-FABP may be a useful marker reflecting the therapeutic efficacy of BM.

Urinary liver-type fatty acid-binding protein is associated with subendocardial viability ratio in middle- and older-aged adults

BACKGROUND

To identify one of the physiological underlying mechanisms of the predictive effects of urinary liver-type fatty acid-binding protein (L-FABP) for the onset of cardiovascular disease (CVD), we investigated the relationship between urinary L-FABP levels and subendocardial viability ratio (SEVR), a marker of myocardial perfusion, in middle- and older-aged adults.

METHODS

This was a cross-sectional study of 249 middle- and older-aged adults (aged 46-83 years). We measured urinary L-FABP levels and central hemodynamic parameters, including SEVR, calculated by pulse wave analysis using an applanation tonometry.

RESULTS

In the participants stratified in accordance with the tertiles of urinary L-FABP levels, SEVR decreased in a stepwise fashion with increasing tertiles (p < 0.001). Furthermore, this association remains significant after the consideration of various confounders. On the contrary, urinary albumin levels were not independently related with SEVR.

CONCLUSION

Our results demonstrated that urinary L-FABP levels were independently associated with the SEVR of the middle- and older-aged adults. This result suggests that the increase in urinary L-FABP levels even within the normal range might be related to the decrease in myocardial perfusion (SEVR).

Renoprotective effect of the xanthine oxidoreductase inhibitor Topiroxostat under decreased angiotensin II type 1a receptor expression

The aim of this study was to confirm the renoprotective effect of xanthine oxidoreductase (XOR) inhibitor, topiroxostat, compared with another XOR inhibitor, febuxostat, under decreased angiotensin II type 1_a (AT1_a) receptor expression in the model of renal injury caused by adenine. To evaluate the degree of tubular damage using urinary liver-type fatty acid-binding protein (L-FABP) under decreased AT1_a expression, we used AT1_a receptor knockdown hetero and human L-FABP chromosomal transgenic (Tg) mice (AT1_a^+/-L-FABP^+/-). Male AT1_a^+/-L-FABP^+/- mice were divided into two groups: the adenine diet group (n = 40) was given a diet containing only 0.2% w/w adenine, and the normal diet group (n = 5) was given a normal diet. When renal dysfunction was confirmed in the adenine diet group 4 weeks after starting the diet, the adenine diet group was further divided into five groups. The adenine diet group (n = 8) was continuously given only the adenine diet. Each group receiving high-dose (3mg/kg) or low-dose (1mg/kg) topiroxostat (Topiroxostat-H group, n = 8, Topiroxostat-L group, n = 8) or febuxostat (Febuxostat-H group, n = 8, Febuxostat-L group, n = 8) was given the adenine diet including the drug for another 4 weeks. The levels of renal XOR, renal dysfunction, urinary L-FABP, tubulointerstitial damage, hypoxia, and oxidative stress were decreased or attenuated after treatment with topiroxostat or febuxostat compared with the adenine diet group. Furthermore, antioxidant capacity was maintained owing to these treatments. In conclusion, topiroxostat and febuxostat attenuated renal damage under decreased AT1_a expression in the adenine-induced renal injury model.

Clinical utility of urinary liver-type fatty acid binding protein measured by latex-enhanced turbidimetric immunoassay in chronic kidney disease

BACKGROUND

Urinary liver-type fatty acid binding protein (L-FABP) measured by enzyme-linked immunosorbent assay method (ELISA) was approved as a clinical biomarker of tubular damage by the Japanese Ministry of Health, Labor and Welfare (MHLW) in 2011. We evaluated a new latex-enhanced immunoturbidimetric assay (LTIA) to evaluate the clinical utility of urinary L-FABP measured by LTIA versus an ELISA assay.

METHODS

LTIA with anti-human L-FABP mouse monoclonal antibodies was performed using an automated clinical chemistry analyzer. Five positive samples with low, medium and high L-FABP concentrations were analyzed to determine the within-run precision. In patients with chronic kidney disease (CKD) (n=91), urinary L-FABP levels were measured by ELISA and LTIA.

RESULTS

Measurement of urinary L-FABP revealed urinary L-FABP levels within 30 min. The within-run coefficient of variation was 10.0% for 1.4 ng/mL, 4.4% for 2.5 ng/mL, 3.2% for 9.8 ng/mL, 1.5% for 50.1 ng/mL, and 1.2% for 102.7 ng/mL. Concentrations of urinary L-FABP measured by LTIA were significantly correlated with those measured by ELISA (ρ=0.932). Proportional systematic error was almost within limits of agreement (LOA). Urinary L-FABP levels measured by LTIA were significantly correlated with urinary albumin (ρ=0.634), urinary NAG (ρ=0.688) and eGFR (ρ=-0.561).

CONCLUSIONS

Measurement of urinary L-FABP by LITA was simple, speedy, and similar in quality to ELISA results. Therefore, this method was approved as external body diagnosing medicines by the Japanese MHLW in 2014. Urinary L-FABP is expected to be widely used in various pathophysiological conditions by measuring urinary L-FABP using LTIA.

Role of angiotensin II type 1a receptor in renal injury induced by deoxycorticosterone acetate-salt hypertension

The aim of this study was to investigate the in vivo role of angiotensin II type 1a (AT1a) receptor in renal damage as a result of hypertension by using transgenic mice with AT1a receptor gene disruption. Transgenic mice that express human liver-type fatty acid binding protein (L-FABP) with or without disruption of the AT1a receptor gene (L-FABP^+/− AT1a^−/−, and L-FABP^+/− AT1a^+/+, respectively) were used with urinary L-FABP as an indicator of tubulointerstitial damage. Those female mice were administered subcutaneously deoxycorticosterone acetate (DOCA)–salt tablets plus drinking water that contained 1% saline for 28 d after uninephrectomy. In L-FABP^+/− AT1a^+/+ mice that received DOCA-salt treatment, hypertension was induced and slight expansion of glomerular area, glomerular sclerosis, and tubulointerstitial damage were observed. In L-FABP^+/− AT1a^−/− mice that received DOCA-salt treatment, hypertension was similarly induced and the degree of glomerular damage was significantly more severe than in L-FABP^+/− AT1a^+/+-DOCA mice. Urinary L-FABP levels were significantly higher in L-FABP^+/− AT1a^−/−-DOCA mice compared with those in L-FABP^+/− AT1a^+/+-DOCA mice. Hydralazine treatment significantly attenuated renal damage that was found in L-FABP^+/− AT1a^−/−-DOCA mice along with a reduction in blood pressure. In summary, activation of the AT1a receptor may contribute to maintenance of the glomerular structure against hypertensive renal damage.—Hisamichi, M., Kamijo-Ikemori, A., Sugaya, T., Ichikawa, D., Natsuki, T., Hoshino, S., Kimura, K., Shibagaki, Y. Role of angiotensin II type 1a receptor in renal injury induced by deoxycorticosterone acetate–salt hypertension.

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.

Does elevation of serum creatinine in patients with chronic hepatitis C under therapy of telaprevir mean renal impairment?

AIM

Treatment with telaprevir (TVR) entails adverse side-effects including anaemia and elevation of serum creatinine (SCr) level. Our purpose was to evaluate the effects of treatment with TVR on renal function in adults with chronic hepatitis C.

METHODS

Thirteen adult patients with HCV genotype 1b who were scheduled to be treated with TVR, pegylated interferon (PEG IFN), and ribavirin (RBV) were prospectively followed. Patients were divided into two groups: (i) patients with an increase in SCr during the treatment (n = 8), and (ii) patients without an increase in SCr (n = 5). Urine and serum parameters were evaluated.

RESULTS

Although there was no difference in SCr level between the two groups before HCV therapy, the SCr level was persistently high in the patients in the increase-in-SCr group during the triple therapy. The SCr level returned to the pre-treatment level after cessation of TVR. There were no differences in urinary L-FABP, NAG, serum cystatin C level and eGFRcys throughout the study between the two groups. The serum cystatin C level at pre-treatment tended to be higher in the increase-in-SCr group. Urinary L-FABP and NAG levels in these groups remained within normal limits during treatment. We found that the increase in SCr was not associated with the degree of renal impairment. The increase in SCr may have been induced as a result of a decrease in creatinine secretion from proximal tubules via inhibition of transporters of creatinine induced by TVR.

CONCLUSION

Elevation of SCr levels with TVR therapy may not suggest renal impairment.

Increase in urinary markers during the acute phase reflects the degree of chronic tubulointerstitial injury after ischemia-reperfusion renal injury

CONTEXT

Acute kidney injury (AKI) could lead to progressive chronic kidney disease (CKD).

OBJECTIVES

To demonstrate that urinary markers in AKI are associated with the degree of persistent renal injury.

MATERIAL AND METHODS

Human L-FABP chromosomal transgenic (T_g) mice were subjected to ischemia-reperfusion (I/R) clamping renal pedicle for 20 min or 30 min. Kidneys were obtained at one and 40 days after I/R.

RESULTS

Urinary L-FABP, NGAL, Kim-1 and albumin levels increased during the acute phase and were significantly correlated with the degree of tubulointerstitial fibrosis during the chronic phase.

DISCUSSION AND CONCLUSION

These markers could detect higher risk of progression to CKD.

Roles of layilin in TNF-α-induced epithelial-mesenchymal transformation of renal tubular epithelial cells

BACKGROUND

Tumor necrosis factor (TNF)-α is suggested to induce epithelial-mesenchymal transformation (EMT) of renal tubular epithelial cells that possibly exacerbates renal interstitial fibrosis in glomerulonephritis (GN). We here investigated whether layilin (LAYN), a c-type lectin-homologous protein, was involved in the EMT process.

METHODS

Expression of LAYN was investigated in kidneys of mice administered with TNF-α and in a clear cell renal carcinoma cell line of KMRC-1 stimulated with TNF-α by quantitative polymerase chain reaction (qPCR) and/or western blotting. Expression of LAYN was assessed immunohistochemically in renal biopsy samples of patients with various types of GN. Changes of EMT markers and cell morphology by TNF-α and transforming growth factor (TGF)-β in LAYN-knocked down KMRC-1 cells were investigated by qPCR and immunocytochemistry.

RESULTS

Administration of TNF-α increased expression of LAYN in renal tubular epithelia in mice. TNF-α but not TGF-β increased expression of LAYN in KMRC-1 cells. Renal biopsy samples from the patients with GN showed high expression of LAYN in tubular epithelial cells. TNF-α induced up-regulation of vimentin, down-regulation of E-cadherin, and fibroblast-like morphological change in KMRC-1 cells, indicating occurrence of EMT. These changes were not observed in the LAYN-knocked down cells. In contrast, similarly occurred TGF-β-induced EMT was not affected by the LAYN knockdown.

CONCLUSION

Our data indicate that LAYN is involved in the TNF-α-induced EMT of renal tubular epithelial cells. LAYN may play roles in the generation of renal interstitial fibrosis in GN via TNF-α-induced EMT.

Elevation of urinary liver-type fatty acid binding protein after cardiac catheterization related to cardiovascular events

Purpose

Contrast medium (CM) induces tubular hypoxia via endothelial damage due to direct cytotoxicity or viscosity. Urinary liver-type fatty acid binding protein (L-FABP) increases along with tubular hypoxia and may be a detector of systemic circulation injury. The aim of this study was to evaluate the clinical usefulness of detecting increases in urinary L-FABP levels due to administration of CM, as a prognostic biomarker for cardiovascular disease in patients without occurrence of CM-induced nephropathy undergoing cardiac catheterization procedure (CCP).

Methods

Retrospective longitudinal analyses of the relationship between urinary L-FABP levels and occurrence of cardiovascular events were performed (n=29). Urinary L-FABP was measured by ELISA before CCP, and at 6, 12, 24, and 48 hours after CCP.

Results

Urinary L-FABP levels were significantly higher at 12 hours (P<0.05) and 24 hours (P<0.005) after CCP compared with before CCP, only in the patients with occurrence of cardiovascular events (n=17), but not in those without cardiovascular events (n=12). The parameter with the largest area under the curve (0.816) for predicting the occurrence of cardiovascular events was the change in urinary L-FABP at 24 hours after CCP. The difference in urinary L-FABP levels (ΔL-FABP ≥11.0 μg/g creatinine) between before CCP and at 24 hours after CCP was a risk factor for the occurrence of cardiovascular events (hazard ratio, 4.93; 95% confidence interval, 1.27–19.13; P=0.021).

Conclusion

Measurement of urinary L-FABP before CCP and at 24 hours after CCP in patients with mild to moderate renal dysfunction may be an important indicator for risk stratification of onset of cardiovascular events.

Distinct roles of urinary liver-type fatty acid-binding protein in non-diabetic patients with anemia

Background

Various stresses including ischemia are known to up-regulate renal L-FABP gene expression and increase the urinary excretion of L-FABP. In diabetic patients with anemia, the urinary excretion of L-FABP is significantly increased. We studied the clinical significance of urinary L-FABP and its relationship with anemia in non-diabetic patients.

Subjects and Methods

A total of 156 patients were studied in this retrospective cross-sectional analysis. The associations between anemia and urinary L-FABP levels, and the predictors of urinary L-FABP levels in non-diabetic patients were evaluated.

Results

Urinary L-FABP levels were significantly higher in patients with anemia compared to those in patients without anemia. Similarly, the urinary L-FABP levels were significantly higher in patients with albuminuria compared to those in patients without albuminuria. Urinary L-FABP levels correlated with urinary albumin-to-creatinine ratios, estimated glomerular filtration rates, body mass index, and hemoglobin levels. Multivariate linear regression analysis determined that hemoglobin levels (β = -0.249, P = 0.001) and urinary albumin-to-creatinine ratios (β = 0.349, P < 0.001) were significant predictors of urinary L-FABP levels.

Conclusions

Urinary L-FABP is strongly associated with anemia in non-diabetic patients.

Human liver-type fatty acid–binding protein protects against tubulointerstitial injury in aldosterone-induced renal injury

To demonstrate the renoprotective function of human liver-type fatty acid–binding protein (hL-FABP) expressed in proximal tubules in aldosterone (Aldo)-induced renal injury, hL-FABP chromosomal transgenic (Tg) and wild-type (WT) mice received systemic Aldo infusions (Tg-Aldo and WT-Aldo, respectively) were given 1% NaCl water for 28 days. In this model, elevation of systolic blood pressure, monocyte chemoattractant protein-1 expression, macrophage infiltration in the interstitium, tubulointerstitial damage, and depositions of type I and III collagens were observed. Elevation of systolic blood pressure did not differ in WT-Aldo vs. Tg-Aldo animals, however, renal injury was suppressed in Tg-Aldo compared with WT-Aldo mice. Dihydroethidium fluorescence was used to evaluate reactive oxidative stress, which was suppressed in Tg-Aldo compared with WT-Aldo mice. Gene expression of angiotensinogen in the kidney was upregulated, and excretion of urinary angiotensinogen was increased in WT-Aldo mice. This exacerbation was suppressed in Tg-Aldo mice. Expression of hL-FABP was upregulated in proximal tubules of Tg-Aldo mice. Urinary excretion of hL-FABP was significantly greater in Tg-Aldo than in Tg-control mice. In conclusion, hL-FABP ameliorated the tubulointerstitial damage in Aldo-induced renal injury via reducing oxidative stress and suppressing activation of the intrarenal renin-angiotensin system.

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.

Moderate-intensity single exercise session does not induce renal damage

BACKGROUND

The aim of this study was to determine whether a single moderate-intensity exercise session induces renal injury based on various parameters that reflect kidney dysfunction, including urinary L-type fatty acid-binding protein (L-FABP).

METHODS

Adult outpatients (n = 31) with chronic kidney disease (CKD) not receiving renal replacement therapy participated in this study. Urine was collected before and after a single 20-min moderate-intensity exercise session. Urinary levels of L-FABP, albumin, N-acetyl-β-d-glucosaminidase (NAG), and α1-microglobrin (α1MG) were measured. In addition, 12 patients with estimated glomerular filtration fraction less than 30 ml/min/1.73 ml(2) were selected from all patients and evaluated using the same analysis.

RESULTS

Urinary values of L-FABP, albumin, NAG, and α1MG did not increase significantly after exercise compared with before exercise (urinary L-FABP, from 8.3 to 9.4 μg/g of creatinine; urinary albumin, from 293.1 to 333.7 mg/g of creatinine; urinary NAG, from 9.2 to 8.2 U/g of creatinine; urinary α1MG, from 11.4 to 9.8 mg/g of creatinine, not significant). Similar findings were seen in all patients, regardless of degree of renal dysfunction.

CONCLUSIONS

A single session of moderate-intensity exercise was not associated with an increase in renal parameters used to assess renal damage.

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.

[L-type fatty acid binding protein (L-FABP) and kidney disease]

Liver-type fatty acid binding protein (L-FABP) is expressed in the cytoplasm of human renal proximal tubules. Renal L-FABP expression is up-regulated and urinary excretion of renal L-FABP is increased by various stressors, such as urinary protein, hyperglycemia, tubular ischemia, toxins, and salt-sensitive hypertension, which lead to the progression of kidney disease. Urinary L-FABP levels accurately reflect the degree of tubulointerstitial damage and are strongly correlated with the prognosis of chronic kidney disease (CKD) patients in clinical studies. In patients with type I or type II diabetes, urinary L-FABP levels were reported to be significantly higher in patients with normal levels of urinary albumin than in those with microalbuminuria. Urinary L-FABP may be useful for the early detection of diabetic nephropathy. Furthermore, in a longitudinal study, a higher level of urinary L-FABP was found to be a risk factor for the progression of diabetic nephropathy. With respect to acute kidney disease (AKI), urinary L-FABP facilitates the early detection of AKI before an increase in serum creatinine. Therefore, urinary L-FABP was approved as a new tubular biomarker by the Ministry of Health, Labour and Welfare of Japan.

[Urinary L-type fatty acid binding protein (L-FABP) as a new urinary biomarker promulgated by the Ministry of Health, Labour and Welfare in Japan]

Liver-type fatty acid binding protein (L-FABP) is a 14kDa protein found in the cytoplasm of human renal proximal tubules. Fatty acids are bound with L-FABP and transported to the mitochondria or peroxisomes, where fatty acids are beta-oxidized, and this may play a role in fatty acid homeostasis. Moreover, L-FABP has high affinity and capacity to bind long-chain fatty acid oxidation products, and may be an effective endogenous antioxidant. Renal L-FABP is rarely expressed in the kidneys of rodents. In order to evaluate the pathological dynamics of renal L-FABP in kidney disease, human L-FABP chromosomal transgenic mice were generated. Various stress, such as massive proteinuria, hyperglycemia, hypertension, and toxins overloaded in the proximal tubules were revealed to up-regulate the gene expression of renal L-FABP and increase the excretion of L-FABP derived from the proximal tubules into urine. In clinical studies of chronic kidney disease (CKD), urinary L-FABP accurately reflected the degree of tubulointerstitial damage and correlated with the rate of CKD progression. Furthermore, a multicenter trial has shown that urinary L-FABP is more sensitive than urinary protein in predicting the progression of CKD. With respect to diabetic nephropathy and acute kidney disease (AKI), urinary L-FABP is an early diagnostic of kidney disease or a predictive marker for renal prognosis. After many clinical studies, urinary L-FABP was approved as a new tubular biomarker promulgated by the Ministry of Health, Labour and Welfare in Japan.

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.

Usefulness of urinary biomarkers in early detection of acute kidney injury after cardiac surgery in adults

BACKGROUND

Acute kidney injury (AKI) is a common complication after cardiac surgery. Urinary liver-type fatty acid-binding protein (L-FABP) reflects the presence of renal tubular injury. The aim of the present study was to evaluate the utility of urinary L-FABP compared with other urinary biomarkers for the early detection of postoperative AKI among adult patients undergoing cardiac surgery.

METHODS AND RESULTS

Patients were divided into the AKI (n=48) and non-AKI groups (n=37) according to whether they developed postoperative AKI within 48h after surgery. Changes in various biomarkers were evaluated. Urine and serum samples were obtained from each patient at the following time points: before the operation, immediately after the operation, and 3, 6, 18, 24, and 48h postoperatively. The urinary L-FABP level was significantly higher in the AKI group than in the non-AKI group at every time point, while other biomarkers did not show such a tendency. The biomarker with the largest area under the curve at every time point for predicting the onset of AKI was urinary L-FABP. On multiple logistic regression analysis, the urinary L-FABP level before operation and within the first 6h after cardiac surgery was significantly associated with the onset of AKI.

CONCLUSIONS

Urinary L-FABP is a useful biomarker for early detection of AKI and is a good early predictor of the onset of AKI.

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.

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.

Clinical significance of tubular and podocyte biomarkers in acute kidney injury

BACKGROUND

Acute kidney injury (AKI) is a common complication in critically ill patients. Urinary excretion of liver-type fatty acid-binding protein (L-FABP), which is expressed in the proximal tubules, reflects the presence of tubular injury. Urinary excretion of podocalyxin (PCX), a glycoprotein prominently expressed on podocytes, is associated with podocyte injury. Our aims were to evaluate the utility of urinary L-FABP for the early detection of AKI and to examine whether podocyte injury is present in AKI patients using the biomarker of urinary PCX.

METHODS

Patients admitted to the intensive care unit (ICU) were divided into the AKI group (n = 14) and non-AKI group (n = 11), according to the occurrence of AKI during hospitalization in the ICU. Changes in various biomarkers were evaluated.

RESULTS

In the AKI group, elevation of urinary L-FABP level [maximum value of L-FABP, 199.0 (92.5-433.6) μg/g creatinine, median (25-75% interquartile range)], which reflects tubular injury (area under the curve 0.95, cut-off value 44.1 μg/g Cr), occurred between -30 and 0 h before the occurrence of AKI (i.e., the time at which serum creatinine peaked), and elevation of urinary PCX level [maximum value of PCX, 389.5 (267.0-501.0) μg/g creatinine; upper limit of reference value, 160 μg/g creatinine] occurred during the time of recovery from AKI when serum creatinine levels were decreasing between 34.0 and 72.0 h after the occurrence of AKI. Furthermore, a parameter with the primary large AUC for predicting the onset of AKI was urinary L-FABP.

CONCLUSIONS

Our study suggests that L-FABP is a useful biomarker for early detection of AKI and that podocyte injury was induced during the recovery phase of AKI.

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.