Urinary Liver-Type Fatty Acid Binding Protein, a Biomarker for Disease Progression, Dialysis and Overall Mortality in Chronic Kidney Disease

Chronic kidney disease (CKD) is a major public health concern with an increasing proportion of sufferers progressing to renal replacement therapy (RRT). Early identification of those at risk of disease progression could be key in improving outcomes. We hypothesise that urinary liver-type fatty acid binding protein (uL-FABP) may be a suitable biomarker for CKD progression and can add value to currently established biomarkers such as the urinary protein-to-creatinine ratio (uPCR). A total of 583 participants with CKD 1-5 (not receiving renal replacement therapy) entered a 2 yr prospective longitudinal study. UPCR and uL-FABP were measured at baseline and CKD progression was defined as either (i) a decline in eGFR of >5 mL/min/1.73 m2 or an increase in serum creatinine by 10% at 1 yr; (ii) a decline in eGFR of >6 mL/min/1.73 m2 or an increase in serum creatinine by 20% at 2 yrs; or (iii) the initiation of RRT. A combined outcome of initiating RRT or death was also included. Approximately 40% of participants showed CKD progression. uL-FABP predicted CKD progression at both years 1 and 2 (OR 1.01, p < 0.01). Sensitivity and specificity were comparable to those of uPCR (AUC 0.623 v 0.706) and heat map analysis suggested that uL-FABP in the absence of significant proteinuria can predict an increase in serum creatinine of 10% at 1 yr and 20% at 2 yrs. The risk of the combined outcome of initiating RRT or death was 23% higher in those with high uL-FABP (p < 0.01) independent of uPCR. uL-FABP appears to be a highly sensitive and specific biomarker of CKD progression. The use of this biomarker could enhance the risk stratification of CKD and its progression and should be assessed further.

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.

Clinical significance of urinary liver-type fatty acid binding protein at various stages of nephropathy

This cross-sectional study was to evaluate the levels of urinary liver-type fatty acid binding protein (u-LFABP pg/mg urine creatinine ratio) at different stages of diabetic nephropathy and to see its correlation with other clinical parameters in South Indian patients with type 2 diabetes mellitus (T2DM). A total of 65 (M: F; 42:23) T2DM subjects were divided into three groups, and were compared with 13 (M: F; 3:10) nondiabetic controls. The study groups were as follows: normoalbuminuric (n = 22), microalbuminuric (n = 22) and macroalbuminuric (n = 21). Estimated glomerular filtration rate (eGFR) was calculated using Cockcroft and Gault formula. u-LFABP levels in spot urine samples were measured with a solid phase enzyme linked immunosorbent assay. This study showed that u-LFABP levels were undetectable in healthy controls and was very low in the normoalbuminuric subjects. Elevated levels of u-LFABP are evident from the microalbuminuric stage indicating tubular damage. The levels of u-LFABP increased gradually with declining renal function. Geometric mean (95% confidence interval) for normoalbuminuria was 0.65 (0.47–0.97), microalbuminuria was 0.99 (0.55–1.97) and macroalbuminuria was 5.16 (1.8–14.5), (P = 0.005). In conclusion, u-LFABP levels were elevated in patients with reduced eGFR and showed a positive correlation with systolic blood pressure and protein to creatinine ratio in the total study subjects.

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.

Urinary ACE2 is associated with urinary L-FABP and albuminuria in patients with chronic kidney disease

AIM

Angiotensin-converting enzyme 2 (ACE2) is expressed in the kidney and may be a renoprotective enzyme since it converts angiotensin (Ang) II to Ang-(1-7). In addition, ACE2 has been detected in urine from patients with chronic kidney disease (CKD). The aim of this study was to determine the urinary ACE2 levels in patients with various stages of CKD and to identify the factors associated with the presence of ACE2.

METHODS

We assessed 152 patients with CKD stage G1-G4. The patients were classified according to the presence or absence of diabetes mellitus (DM) (DM group, n = 72; non-DM group, n = 80) and according to the estimated glomerular filtration rate (CKD stage G1/2 group, n = 40; CKD stage G3 group, n = 74; and CKD stage G4 group, n = 38). Parameters were urinary ACE2, urinary albumin/ creatinine ratio (UACR), urinary liver-type fatty acid binding protein (L-FABP), estimated glomerular filtration rate, and other factors determined to be associated with elevated urinary ACE2.

RESULTS

Urinary ACE2 was significantly higher in patients with diabetes (p = 0.01) and in patients with CKD stage G4 compared with stages G1-G3 (p < 0.0001). Multivariable regression analysis revealed that urinary L-FABP and UACR were significantly associated with urinary ACE2 levels, indicating that urinary ACE2 is increased in patients with diabetes and advanced stage CKD.

CONCLUSION

ACE2 might continuously protect from both glomerular and tubulointerstitial injury during CKD progression. Taken together, urinary ACE2 might be a marker of kidney renin-angiotensin system activation in such patients.