The authors have declared that no competing interests exist.
Conceived and designed the experiments: KMC CYS. Performed the experiments: KMC CHC. Analyzed the data: KMC CCL CYS. Contributed reagents/materials/analysis tools: KMC CYS CHC. Wrote the paper: CYS.
Neutrophil gelatinase-associated lipocalin (NGAL) and liver-type fatty acid binding protein (L-FABP) are emerging as excellent biomarkers in the urine and plasma for the early prediction of acute and chronic kidney injury. The aims of this prospective study were to determine the role of albuminuria, and that of serum and urine levels of NGAL and L-FABP as predictors of a decline in the glomerular filtration rate (GFR) in patients with type 2 diabetes.
A longitudinal cohort study with one hundred forty type 2 diabetic patients was conducted. Serum and urine levels of NGAL and L-FABP, and the urine albumin excretion rate were determined. The correlation between the kidney injury biomarkers and rate of GFR decline was analyzed.
The eGFR of study subjects decreased significantly as the study progressed (86.4±31.1
Tubular markers, such as NGAL and L-FABP, may not be predictive factors associated with GFR decline in type 2 diabetic patients.
Diabetes mellitus is the leading cause of chronic kidney disease (CKD)
Neutrophil gelatinase-associated lipocalin (NGAL) and liver-type fatty acid binding protein (L-FABP) are emerging as excellent biomarkers in the urine and plasma for the early prediction of acute kidney injury
The aims of this prospective study were to determine the role of albuminuria, and serum and urine levels of NGAL and L-FABP as predictors of decline in the glomerular filtration rate (GFR) of patients with type 2 diabetes.
Prevalent type 2 diabetic patients who attended an outpatient clinic from October 2009 to Novenber 2011 were recruited into the study. The inclusion criterion was adults aged >18 but <80 years. Patients were excluded from the study if they had cardiovascular disease (coronary artery disease, myocardial ischaemia, cerebrovascular disease or peripheral artery disease) in the past 3 months, infections requiring admission in the past 3 months, uncontrolled hypertension, or unwillingness to participate in the study. A total of 140 patients were enrolled into the study and gave their informed written consent. All the study subjects were treated according to the ADA diabetes mellitus treatment guideline
The demographic and clinical laboratory data were collected at baseline and the end of the study. The estimated GFR was calculated using the abbreviated Modification of Diet in Renal Disease equation. The GFR decline rate was calculated with the following equation: (GFR at the study end – baseline GFR)/(baseline GFR x follow-up duration). The urine albumin excretion rate was determined as the albumin amount of a 24-h urine collection. Microalbuminuria was diagnosed based on a 24-hour urine collection (from 30–300 mg/day). A urine albumin level above 300 mg/day was defined as macroalbuminuria. The renal injury markers, NGAL (human NGAL ELISA kit, Abnova Co., CA, US), and L-FABP (human L-FABP ELISA Kit, Hycult Biotech Inc., NL, US), were measured in one venous blood sample and one 24 h urine sample at baseline and at the end of the study. Each NGAL and L-FABP reaction was performed in duplicate, according to product recommendations; the mean value of each reaction was used for further statistical analysis.
Descriptive statistics are expressed as means ± standard deviation or percentage frequency, as appropriate. Paired
One hundred forty type 2 diabetic patients were included in this study. The study subjects were followed up for 20.31±2.15 months. The general characteristics and laboratory data of the study subjects are listed in
Initial (n = 140) | Follow-up (n = 140) |
|
|
|
56.6±9.8 | 58.5±9.8 | |
|
72/68 | 72/68 | |
|
86.0±71.2 | 110.1±71.2 | |
|
136.0±14.3 | 133.8±16.9 | |
|
75.1±8.9 | 77.6±9.4 | |
|
27.6±4.5 | 27.7±6.8 | |
|
150.1±47.9 | 149.8±45.5 | |
|
7.8±1.6 | 7.8±1.4 | |
|
178.1±38.6 | 173.0±36.0 | |
|
181.1±134.4 | 188.8±161.7 | |
|
39.9±11.6 | 41.7±12.2 | |
|
102.7±39.2 | 98.0±28.5 | |
|
2.8±6.6 | 3.1±6.4 | |
|
17.4±8.8 | 18.5±11.6 | |
|
1.2±1.4 | 1.4±1.3 | |
|
86.4±31.1 | 74.4±27.3 | <0.001 |
|
264.9±1060.3 | 557.7±2092.5 | 0.009 |
|
70.0±35.7 | 90.6±55.6 | 0.001 |
|
6810.3±5450.5 | 7657.7±4733.2 | |
|
18.3±58.2 | 23.3±21.0 | |
|
7431.6±13761.8 | 8445.1±11858.8 | |
|
21.4 | 20.7 | |
|
53.6 | 66.2 | 0.003 |
|
62.3 | 60.4 | |
|
9.4 | 9.4 | |
|
13.0 | 11.5 | |
|
18.8 | 21.8 |
Abrreviations:
DM: diabettes mellitus.
SBP: systolic blood pressure.
DBP: diastolic blood pressure.
BMI: body mass index.
HbA1c: glycated hemoglobin.
HDL: high-density lipoprotein.
LDL: low-density lipoprotein.
HS-CRP: highly sensitive C-reactive protein.
eGFR: estimated glomerular filtration rate.
NGAL: neutrophil gelatinase-associated lipocalin.
L-FABP: liver-type fatty acid-binding protein.
ACEI: angiotensin-converting-enzyme inhibitor.
ARB: angiotensin receptor blocker.
Urine albumin | Baseline (n = 140) | End of study (n = 140) | |
|
52.90% | 39.29% | |
|
35.00% | 37.86% | |
|
12.10% | 22.86% |
eGFR | Baseline (n = 140) | End of study (n = 140) | |
≧ |
44.60% | 27.34% | |
< |
35.25% | 46.76% | |
< |
20.14% | 25.90% |
The results of Pearson correlation between baseline eGFR and the baseline levels of serum NGAL, serum L-FABP, urine NGAL, and urine L-FABP and the urine albumin excretion rate are plotted in
The results of correlation analysis for the correlations between baseline eGFR and the baseline levels of serum NGAL, serum L-FABP, urine NGAL, and urine L-FABP, and the urine albumin excretion rate are summarized in
Baseline eGFR | Standardized coefficients (beta) | t |
|
|
−0.251 | −2.985 | 0.003 |
|
−0.022 | −0.278 | 0.781 |
|
−0.221 | −2.481 | 0.014 |
|
−0.012 | −0.154 | 0.878 |
|
−0.126 | −1.437 | 0.153 |
Multiple regression analysis results.
Baseline eGFR | Spearman's rho |
|
|
−0.3416 | <0.001 |
|
−0.0152 | 0.858 |
|
−0.2814 | 0.001 |
|
−0.2313 | 0.006 |
|
−0.2547 | 0.002 |
Spearman's rank correlation coefficient analysis results.
Due to the distribution of baseline levels of serum NGAL, serum L-FABP, urine NGAL, and urine L-FABP and the urine albumin excretion rate were not normal by Shapiro-Wilk W test (P>0.05), Spearman's rank correlation coefficient was calculated. The results showed that baseline urine albumin excretion rate, urine NGAL, and serum/urine L-FABP levels were significantly correlated with baseline eGFR (P<0.05) (
Pearson correlations between the rate of eGFR decline and the baseline levels of serum NGAL, serum L-FABP, urine NGAL, and urine L-FABP and the daily urine albumin amount were analyzed (
The results of correlations between the rate of eGFR decline and the baseline levels of serum NGAL, serum L-FABP, urine NGAL, and urine L-FABP and the urine albumin excretion rate were summarized in
Rate of eGFR decline | Standardized coefficients (beta) | t |
|
|
−0.378 | −4.298 | <0.001 |
|
−0.101 | −1.238 | 0.218 |
|
0.108 | 1.226 | 0.222 |
|
−0.061 | −0.769 | 0.443 |
|
−0.065 | −0.726 | 0.469 |
Multiple regression analysis results.
Rate of eGFR decline | Spearman's rho |
|
|
−0.2732 | 0.001 |
|
−0.1014 | 0.233 |
|
0.0415 | 0.627 |
|
−0.0367 | 0.667 |
|
0.0193 | 0.821 |
Spearman's rank correlation coefficient analysis results.
The results of Spearman's rank correlation coefficient analysis for the correlations between the rate of eGFR decline and the baseline levels of kidney injury variables revealed that only the urine albumin excretion rate was significantly correlated with the eGFR decline rate (Spearman's rho: −0.2732; P = 0.001) (
The results of subgroup analysis according to the daily urine albumin excretion rate were listed in supplemental tables. In patients with daily urine albumin excretion rate less than 30 mg, all the kidney injury markers were not significantly correlated with the eGFR decline rate (
Diabetic nephropathy is currently the leading cause of CKD. It is also one of the most significant long-term complications in terms of morbidity and mortality for individual patients with diabetes
Tubulointerstitial and glomerular injuries have important roles in the pathogenesis of diabetic nephropathy
Albuminuria is a clinical biomarker for glomerular injury. According to the staging, initial changes in diabetic nephropathy include glomerular hyperfiltration. The phase following hyperfiltration is associated with subtle morphological changes, including thickening of the glomerular basement membrane, glomerular hypertrophy, mesangial expansion, and modest expansion of the tubulointerstitium. In the microalbuminuric phase, significant glomerular injury is often noted. In advanced diabetic nephropathy, nodular glomerulosclerosis is the most prominent pathological presentation
The results of this study are subject to some limitations. First, the sample number and unhomogenized characteristics of the study subjects might confound the study results. Second, this was a longitudinal observational study. The lack of a control group or effective intervention for comparison might limit the power of the study. Despite these limitations, the results of the cross-sectional analysis with baseline data were compatible with the longitudinal analysis results.
In conclusion, the results of this study suggest that tubular markers, such as NGAL and L-FABP, may not be predictive factors associated with GFR decline in type 2 diabetic patients. In addition, the urine albumin excretion rate was an independent factor associated with GFR decline rate in type 2 diabetic patients.
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