Ultrasensitive sensing urinary cystatin C via an interface-engineered graphene extended-gate field-effect transistor for non-invasive diagnosis of chronic kidney disease

Early chronic kidney disease (CKD) has strong concealment and lacks an efficient, non-invasive, and lable-free detection platform. Cystatin C (Cys C) in urine is closely related to the progress of CKD (especially at the early stage), which is an ideal endogenous marker to evaluate the impairment of renal function. Thus, the accurate detection of urinary Cys C (u-Cys C) is great significant for early prevention and treatment and delaying the course of the disease of CKD patients. Herein, we developed an extended-gate field-effect transistor (EG-FET) sensor for ultrasensitive detection of u-Cys C, which consists of a monolithic interface-engineered graphene EG electrode array and a commercially available MOSFET. Laser-induced graphene (LIG) loaded with sputtered Au NPs in the presence of adhesive Cr (Au NPs/Cr/LIG) boosts the electrical performance of the EG electrode. Meanwhile, Au NPs also serve as linkers to immobilize papain that can selectively form protein complexes with Cys C. Supported by the synergistic effect of multilevel interface-engineered graphene, our sensor exhibits a good linear correlation within the u-Cys C concentration range of 5 ag/μL to 50 ng/μL with low detection limit of 0.05 ag/μL. Our work makes accurate, specific and rapid detection of u-Cys C feasible and promising for early screening for CKD.

Urinary cystatin C: pediatric reference intervals and comparative assessment as a biomarker of renal injury among children in the regions with high burden of CKDu in Sri Lanka

BACKGROUND

Cystatin C (Cys-C) is an emerging biomarker of renal diseases and its clinical use, particularly for screening the communities affected by chronic kidney disease of unknown etiology (CKDu), is hindered due to the lack of reference intervals (RIs) for diverse ethnic and age groups. The present study aimed to define RIs for urinary Cys-C (uCys-C) for a healthy pediatric population in Sri Lanka and in turn compare the renal function of the residential children in CKDu endemic and non-endemic regions in Sri Lanka.

METHODS

A cross-sectional study was conducted with 850 healthy children (10-17 years) from selected locations for reference interval establishment, while a total of 892 children were recruited for the comparative study. Urine samples were collected and analyzed for Cys-C, creatinine (Cr) and albumin. Cr-adjusted uCys-C levels were partitioned by age, and RIs were determined with quantile regression (2.5th, 50th and 97.5th quantiles) at 90% confidence interval.

RESULTS

The range of median RIs for uCys-C in healthy children was 45.94-64.44 ng/mg Cr for boys and 53.58-69.97 ng/mg Cr for girls. The median (interquartile range) uCys-C levels of children in the CKDu endemic and non-endemic regions were 58.18 (21.8-141.9) and 58.31 (23.9-155.3) ng/mg Cr with no significant difference (P = 0.781). A significant variation of uCys-C was noted in the children across age.

CONCLUSIONS

Notably high uCys-C levels were observed in children with elevated proteinuria. Thus, uCys-C could be a potential biomarker in identifying communities at high risk of CKDu susceptibility.

Development and Evaluation of Europium-Based Quantitative Lateral Flow Immunoassay for the Chronic Kidney Disease Marker Cystatin-C

This study aimed to establish a Europium label time-resolved fluorescence immunoassay (TRFIA) to detect the chronic kidney disease (CKD) biomarker Cystatin-C. An Europium based Time resolved fluorescence immunoassay was developed to detect the concentration of Cystatin-C in a urine sample to increase the sensitivity with captured anti-Cystatin-C antibodies immobilized on nitrocellulose membrane and then bonded with detection anti-Cystatin-C labelled with CM-EU, followed by fluorescence measurement using time-resolved fluorometry in 15 min. The performance of this TRFIA was evaluated using the clinical urine serum and compared with the ELISA assays. The linear calibration range was 0.015-32 µg/ml, and the limit of detection (LOD) quantified was 0.0001 µg/ml. This current work has improved the LOD of our previous work from 0.013 µg/ml to 0.001 µg/ml. These results indicated that the CM-EU nanoparticle-based LFIA is rapid, more sensitive, reliable, and reproducible for point-of-care testing of Cys-C concentrations in urine.

Serum and urinary biomarkers for early detection of acute kidney injury following Hypnale spp. envenoming

Background

Hump-nosed pit viper (HNV; Hypnale spp.) bites account for most venomous snakebites in Sri Lanka. Acute kidney injury (AKI) is the most serious systemic manifestation (1–10%) following HNV envenoming. We aimed to identify the value of functional and injury biomarkers in predicting the development of AKI early following HNV bites.

Methods

We conducted a prospective cohort study of patients with confirmed HNV envenoming presenting to two large tertiary care hospitals in Sri Lanka. Demographics, bite details, clinical effects, complications and treatment data were collected prospectively. Blood and urine samples were collected from patients for coagulation and renal biomarker assays on admission, at 0-4h, 4-8h, 8-16h and 16-24h post-bite and daily until discharge. Follow-up samples were obtained 1 and 3 months post-discharge. Creatinine (sCr) and Cystatin C (sCysC) were measured in serum and kidney injury molecule-1 (uKIM-1), clusterin (uClu), albumin (uAlb), β2-microglobulin (uβ2M), cystatin C (uCysC), neutrophil gelatinase associated lipocalin (uNGAL), osteopontin (uOPN) and trefoil factor-3 (uTFF-3) were measured in urine. Definite HNV bites were based on serum venom specific enzyme immunoassay. Kidney Disease: Improving Global Outcomes (KDIGO) criteria were used to stage AKI. Two patients had chronic kidney disease at 3 month follow-up, both with pre-existing abnormal sCr, and one developed AKI following HNV envenoming.

Results

There were 52 patients with confirmed HNV envenoming; median age 48y (Interquartile range [IQR]:40-59y) and 29 (56%) were male. Median time to admission was 1.87h (IQR:1–2.75h). Twelve patients (23%) developed AKI (AKI stage 1 = 7, AKI stage 2 = 1, AKI stage 3 = 4). Levels of five novel biomarkers, the functional marker serum Cystatin C and the damage markers urinary NGAL, cystatin C, β2-microglobulin and clusterin, were elevated in patients who developed moderate/severe acute kidney injury. sCysC performed the best at 0–4 h post-bite in predicting moderate to severe AKI (AUC-ROC 0.95;95%CI:0.85–1.0) and no biomarker performed better than sCr at later time points.

Conclusions

sCysC appears to be a better marker than sCr for early prediction of moderate to severe AKI following HNV envenoming.

Snakebite is a major public health problem associated with considerable morbidity and mortality worldwide. Acute kidney injury is one of the major systemic complications of snakebites. Its pathophysiology is poorly understood and the diagnosis is often delayed due to lack of sensitive biomarkers. We aimed to investigate the value of selected biomarkers in the early diagnosis of acute kidney injury following hump-nosed pit viper (Hypnale spp.) envenoming. In a group of 52 patients with confirmed hump-nosed pit viper envenoming acute kidney injury was found to be common and was associated with severe disease in some. Levels of five novel biomarkers, the functional marker serum Cystatin C and the damage markers urinary NGAL, cystatin C, β2-microglobulin and clusterin, were elevated in patients who developed moderate/ severe acute kidney injury. Serum Cystatin C performed better than serum creatinine in early prediction of moderate/severe acute kidney injury. Serum Cystatin C appears to be a promising novel biomarker in diagnosing acute kidney injury in the setting of hump-nosed pit viper envenoming.

Urinary cystatin C as a biomarker of early renal dysfunction in type 2 diabetic patients

AIMS

We aimed to evaluate urinary CysC (cystanin c) as an early marker of diabetic nephropathy in patients with type 2 diabetes and investigate the correlation of urinary CysC with albuminuria and GFR.

METHODOLOGY

This case-controlled study was conducted on 66 type 2 diabetic patients who were classified according to albuminuria into 3 groups and consisting of 20 healthy subjects as the control group. We assessed urinary CysC, urinary albumin excretion rate (UACR).

RESULTS

Urinary CysC levels were significantly higher in normoalbuminuric diabetic compared with healthy control and there was a progressive linear increase in urinary CysC levels with increasing albuminuria in the diabetic patients. Despite insignificant deference in creatinine between participants groups, we observed significant differences between these groups as regard eGFR, urinary CysC, and UACR. Urinary CysC did not have significant correlations with any clinical or biochemical parameters. Moreover, urinary CysC had a statistically significant association with albuminuria and eGFR.

CONCLUSION

Urinary CysC levels correlated with UACR and GFR. It is linked to subclinical tubular injury and can be an earlier marker of kidney involvement, even before albuminuria and it is less influenced by non-renal factors. Therefore, Urinary CysC is useful biomarker for early diagnosis of diabetic nephropathy.

Kidney involvement and associated risk factors in children with Duchenne muscular dystrophy

BACKGROUND

Kidney dysfunction is a common complication in adults with Duchenne muscular dystrophy (DMD); however, little attention has been paid to kidney function in pediatric patients.

METHODS

Medical records of patients with DMD who were followed up for ≥ 12 months were retrospectively reviewed. Inclusion criteria were (i) aged 5-18 years, (ii) proven mutations in the dystrophin gene, and (iii) absence of structural anomalies of the kidney and urinary tract. Serum creatine kinase (CK) was used as an indirect marker of muscle destruction.

RESULTS

Forty-four patients (mean age, 10.9 ± 3.3 years) were included. Blood pressure was evaluated by 24-h ambulatory blood pressure monitoring in 28 patients. Hypertension was found in 9 (32.1%), eight of whom were using steroids. Mild proteinuria, hypercalciuria, hypocalciuria, and hyperphosphaturia in 24-h urine collection (n = 36) were detected in 3 (8.3%), 5 (13.9%), 7 (19.7%), and 6 (16.7%) patients, respectively. Twenty-one (58.3%) demonstrated hyperuricosuria, associated with hyperuricemia in 4. Logarithmic cystatin C (CysC) had a positive correlation to creatinine (Cr) (p = 0.001, r = 0.54), CK (p = 0.048, r = 0.30), and parathormone (PTH) (p = 0.001, r = 0.49). Moreover, the patients were divided into two groups according to median CysC value: group 1 (n = 20, CysC ≤ 0.76 mg/l) and group 2 (n = 24, CysC > 0.76 mg/l). Mean CK, PTH, and Cr levels were significantly elevated in group 2 compared with group 1 (p = 0.010, 0.033, and 0.023, respectively).

CONCLUSIONS

Long-term exposure to the excessive burden of intracellular components released from damaged muscles may be associated with an increased risk over time of chronic kidney impairment in pediatric DMD patients. Graphical abstract.

NGAL, albumin and cystatin C during cisplatin therapy

Cisplatin is a commonly used chemotherapeutic drugs. It is known for its nephrotoxic side effects with an increased risk of acute kidney injury. Finding of clinically feasible cisplatin nephrotoxicity markers is of importance. In our study, we compared neutrophil gelatinase-associated lipocalin (NGAL) in serum and urine, the estimated glomerular filtration rate (based on serum cystatin C) and urine albumin as markers of nephrotoxicity. The study involved 11 men and 9 women (mean ± SD age 58.2±9.5 years) with different malignancies treated with cisplatin in four cycles of chemotherapy (I - IV). Samples 0-4 were taken before, immediately after, in 3, 6 and 24 hours after administering chemotherapy. We detected significant increase of ACR in Sample 2 (p=0.03) and decrease of eGFR in Sample 4 (p=0.03) up to 24 hours after cisplatin administration in the first chemotherapy cycle only. When cumulative effect of cisplatin was assessed, significantly increased values of urine albumin (vs cycle I) were found in Sample 0 (p=0.00058), 1 (p=0.00256), 2 (p=0.00456), 3 (p=0.00006) and 4 (p=0.00319) in cycles II to IV. We found a correlation between values of urine NGAL and urine albumin (r=0.68, p<0.0001). In conclusion, urine albumin was the only measured marker that consistently and statistically significantly increased after cisplatin containing chemotherapy cycles.

Determination of Cystatin C in human urine by isotope dilution tandem mass spectrometry

This work presents the development of a methodology for the accurate and precise quantification of the renal biomarker Cystatin C in human urine by Isotope Dilution Mass Spectrometry (IDMS). The procedure is based on the addition of a known quantity of the proteotypic peptide ALDFAVG*EYNK labelled with ¹³C₂-glycine to the urine sample followed by protein hydrolysis using trypsin. Then, preconcentration and purification of the isotope diluted peptide was carried out by a selective monoclonal antibody bound to magnetic beads and final measurement was done after injection of the sample in a HPLC-MS/MS triple quadrupole instrument. The isotopic distribution of the isotope diluted proteotypic peptide was measured by low resolution selected reaction monitoring. Using this aquisition mode, the bandpass of the first quadrupole was widened (FWHM =13 u) so the whole isotopic clusters for both the natural abundance and the labelled peptides entered the collision cell. The proposed acquisition mode provided similar accuracy and precision than the regular SRM mode (FWHM =0.7 u) but a higher sensitivity was observed. The purification of the sample by antibody based enrichment of the target peptide was shown to remove interfering compounds more efficiently in comparison with a sample purification based on semipreparative liquid chromatography. Using 5 ng of the labelled peptide it was possible to quantify Cystatin C in human urine in patients with normal and impaired renal function. Recoveries from 100 to 104% were obtained in samples containing from 90 to 700 μg L^-1 of Cystatin C with relative standard deviations from 0.5 to 6%. The stability of Cystatin C in urine samples was evaluated under different storage conditions showing that only when the urine samples were stored at room temperature during more than 10 days, a significant degradation of Cystatin C was observed.

Urinary biomarkers of tubular injury to predict renal progression and end stage renal disease in type 2 diabetes mellitus with advanced nephropathy: A prospective cohort study

BACKGROUND

Novel potential tubular biomarkers in diabetic nephropathy could improve risk stratification and prediction. The study aimed to evaluate the association of tubular damage markers with rapid renal progression and incidence of end stage renal disease (ESRD) in type 2 diabetes (T2DM).

METHODS

A prospective cohort study, involving a total of 257 patients with T2DM, was included. The baseline values of urine albumin, cystatin-C, angiotensinogen, kidney injury molecule-1 (KIM-1) and neutrophil-gelatinase associated lipocalin (NGAL) were measured. The composite outcomes included a rapid glomerular filtration rate (GFR) decline or incident of ESRD at 3-year follow-up.

MAIN FINDINGS

The composite outcomes were noted in 26.1%. Using univariate followed by multivariate COX proportional hazard regression analysis, the patients with highest quartiles of urine cystatin-C (HR 2.96, 95% CI, 1.38-6.35), urine angiotensinogen (HR 2.93, 95% CI, 1.40- 6.13) urine KIM-1 (HR 2.77, 95% CI, 1.27-6.05) and urine NGAL (HR 2.53, 95% CI, 1.11-5.76) were significantly associated with rapid renal progression when compared with the patients with the lowest quartiles of all tubular biomarkers.

CONCLUSIONS

Patients with T2DM with high levels of baseline urine tubular biomarkers (cystatin-C, angiotensinogen, KIM-1 and NGAL) had a greater incidence of ESRD and rapid GFR decline.

Biomarkers of Drug-Induced Kidney Toxicity

Blood urea nitrogen and serum creatinine are imperfect markers of kidney function because they are influenced by many renal and nonrenal factors independent of kidney function. A biomarker that is released directly into the blood or urine by the kidney in response to injury may be a better early marker of drug-induced kidney toxicity than blood urea nitrogen and serum creatinine. Urine albumin and urine protein, as well as urinary markers kidney injury molecule-1 (KIM-1), β2-microglobulin (B2M), cystatin C, clusterin, and trefoil factor-3 (TFF-3) have been accepted by the Food and Drug Administration and European Medicines Agency as highly sensitive and specific urinary biomarkers to monitor drug-induced kidney injury in preclinical studies and on a case-by-case basis in clinical trials. Other biomarkers of drug-induced kidney toxicity that have been detected in the urine of rodents or patients include IL-18, neutrophil gelatinase-associated lipocalin, netrin-1, liver-type fatty acid-binding protein (L-FABP), urinary exosomes, and TIMP2 (insulin-like growth factor-binding protein 7)/IGFBP7 (insulin-like growth factor-binding protein 7), also known as NephroCheck, the first Food and Drug Administration-approved biomarker testing platform to detect acute kidney injury in patients. In the future, a combined use of functional and damage markers may advance the field of biomarkers of drug-induced kidney toxicity. Earlier detection of drug-induced kidney toxicity with a kidney-specific biomarker may result in the avoidance of nephrotoxic agents in clinical studies and may allow for earlier intervention to repair damaged kidneys.

Urinary biomarkers for early detection of platinum based drugs induced nephrotoxicity

BACKGROUND

Nephrotoxicity is a major hazard complicating the use of platinum based drugs (PBD), which can hinder using higher doses protocols to maximize the therapeutic gain. Shortage of serum creatinine level as an accurate biomarker for acute kidney injuries (AKI) necessitates searching for novel biomarkers with better sensitivity and specificity in patients on PBD.

METHODS

In a prospective cohort design, 132 patients receiving PBD were selected for the study. AKI was diagnosed by continuous follow up of serum creatinine level according to Kidney Disease: Improving Global Outcomes (KDIGO) guidelines 2012. Serum creatinine and urinary biomarkers (KIM-1, NGAL and cystatin C) was measured in the day of treatment and for 3 days after PBD cycle.

RESULTS

AKI occurred in 35 patients (26.52% of patients). KIM-1, Cystatin C, and NGAL showed significant increase in samples collected in the day of AKI in comparison to their corresponding basal levels (P <  0.0001). In addition, significant increase in urinary levels of the biomarkers in samples collected 1 day before AKI in comparison to their basal levels (P <  0.0001, P <  0.0001, and P = 0.013 for KIM-1, NGAL and Cystatin C respectively). Furthermore KIM-1 data showed a significant increase 2 days before serum creatinine rise in comparison to the corresponding KIM-1 levels in patients who developed AKI (P = 0.001).

CONCLUSIONS

Urinary KIM-1, Cystatin C and NGAL can predict PBD induced AKI in earlier stages than serum createnine. KIM-1 is the most sensitive biomarker for early detection of AKI in patients receiving PBD.

Utility of urinary biomarkers as a diagnostic tool for early diabetic nephropathy in patients with type 2 diabetes mellitus

INTRODUCTION

Renal tubulo-interstitial damage has an important role in the pathogenesis of early diabetic nephropathy. Urinary biomarkers can help in the detection of early nephropathy in type 2 diabetic patients. The aim of this study was to estimate the levels of urinary neutrophil gelatinase associated lipocalin (NGAL) and cystatin-C in type 2 diabetic patients with early diabetic nephropathy & to compare them with diabetic patients without nephropathy and to correlate urinary NGAL and cystatin-C levels with microalbuminuria in them.

STUDY DESIGN

Cross-sectional comparative study.

MATERIAL AND METHODS

The study was conducted on 126 patients with type 2 diabetes along with 30 control subjects attending the outpatient care department of a tertiary care teaching hospital. There were 3 study groups-diabetic patients with microalbuminuria, diabetic patients without albuminuria and control subjects who were non-diabetic without any renal disease. Details on duration of diabetes and glycemic status were obtained from the patients. Urine examination was done for subjects in all the groups to look for microalbuminuria along with estimation of NGAL and cystatin-C levels. Samples were stored at -20 °C in the deep freezer.

RESULTS

Urinary NGAL and cystatin-C levels were significantly elevated in patients with microalbuminuria (228.18 & 3.23 ng/ml) as compared to those without albuminuria (146.12 & 2.61 ng/ml) and in control subjects (26.56 & 0.30 ng/ml). Urinary NGAL and cystatin-C levels showed a linear correlation with microalbuminuria in diabetic patients.

CONCLUSION

Urinary NGAL and cystatin-C levels were increased in type 2 diabetic patients with early diabetic nephropathy as compared to patients without nephropathy. Urine NGAL and cystatin-C levels also showed a positive correlation with microalbuminuria (urine albumin-creatinine ratio) in patients with type 2 diabetes mellitus.

Combining GFR estimates from cystatin C and creatinine-what is the optimal mix?

BACKGROUND

Combining estimated glomerular filtration rate (eGFR) equations based on creatinine and cystatin C has been shown to improve the accuracy of GFR estimation. This study aims to optimize this strategy for height-independent GFR estimation in children.

METHODS

Retrospective study of 408 inulin clearance tests with simultaneous International Federation of Clinical Chemistry-calibrated measurements of creatinine, cystatin C, and urea in children (mean age 12.5 years, GFR 91.2 ml/min/1.73m²) comparing the arithmetic (mean_arith) and geometric means (mean_geom) of a height-independent creatinine-based (full age spectrum, based on age (FASage)) and a cystatin C-based equation (FAScys), with the complex height-dependent CKiD3 equation incorporating gender, height, cystatin C, creatinine, and urea.

RESULTS

Mean_geom had a P₃₀ accuracy of 89.2% compared to mean_arith 87.7% (p = 0.030) as well as lower bias and %precision error and performed almost as well as CKiD3 (P₃₀ accuracy 90.9%). Modifying the weight of FASage and FAScys when calculating the means showed that an equal contribution was most accurate in most patients. In spina bifida patients, FAScys alone outperformed any combination. Malignancy or nephritis patients had slightly higher accuracy with weighted means favoring cystatin C or creatinine, respectively. Disagreement between FAScys and FASage was inversely correlated with the accuracy of mean_geom. When disagreement exceeded 40%, application of weighted means based on diagnosis improved the performance of eGFR.

CONCLUSIONS

In the absence of height data, the optimal strategy for estimating GFR in children is by using the geometric mean of FASage and FAScys. When there is large disagreement between the two, weighted means based on diagnosis improve accuracy.

Combination of pediatric and adult formulas yield valid glomerular filtration rate estimates in young adults with a history of pediatric chronic kidney disease

As patients with chronic kidney disease (CKD) transition from pediatric nephrology care to adult care, their kidney function is clinically assessed by estimated glomerular filtration rate (eGFR) using both pediatric and adult equations, which may not be congruent. Here we evaluated commonly used eGFR equations and directly measured iohexol GFR (iGFR) among participants between ages 18 and 26 with a diagnosis of pediatric CKD in the Chronic Kidney Disease in Children (CKiD) cohort. The bedside serum creatinine (SCr)-only equation (CKiDSCr), the SCr-only CKD-EPI (CKD-EPISCr), the cystatin C (Cys)-only CKD-EPI (CKD-EPICys) and the combined SCr and Cys CKD-EPI (CKD-EPISCr-Cys) were compared with a) 279 measured iGFRs obtained from 187 participants and b) 548 eGFRs from the SCr and Cys-based CKiD equation (CKiDSCr-Cys) obtained from 219 participants. Among emerging adults with a median iGFR of 49 ml/min/1.73m2, the CKiDSCr-Cys equation had low bias (+1.5 ml/min/1.73m2) and high correlation (0.94), while CKiDSCr underestimated iGFR and CKiDSCr-Cys (-5.6 and -7.4 ml/min/1.73m2, respectively) and CKD-EPISCr had an overestimation bias (+8.2 and +6.1 ml/min/1.73m2, respectively). However, the CKD-EPICys and CKD-EPISCr-Cys exhibited strong agreement with both iGFR and CKiDSCr-Cys. GFR may also be validly estimated in this population by taking the simple average of CKiDSCr and CKD-EPISCr (average bias +1.3 compared to iGFR and -0.6 compared to CKiDSCr-Cys). Clinicians should be aware that individually the pediatric and adult SCr-based estimates of GFR had large discrepancies among emerging adults with pediatric CKD. Thus, when cystatin C is not available, we recommend the average of pediatric and adult SCr-based eGFR as a valid tool for clinical use.

Impact of acute versus repetitive moderate intensity endurance exercise on kidney injury markers

Exercise may lead to kidney injury through several mechanisms. Urinary Kidney Injury Molecule-1 (uKIM1) and Neutrophil Gelatinase-Associated Lipocalin (uNGAL) are known biomarkers for acute kidney injury, but their response to repetitive exercise remains unknown. We examined the effects of a single versus repetitive bouts of exercise on markers for kidney injury in a middle-aged population. Sixty subjects (aged 29-78 years, 50% male) were included and walked 30, 40 or 50 km for three consecutive days. At baseline and after exercise day 1 and 3, a urine sample was collected to determine uNGAL and uKIM1. Furthermore, urinary cystatin C, creatinine, and osmolality were used to correct for dehydration-related changes in urinary concentration. Baseline uNGAL was 9.2 (5.2-14.7) ng/mL and increased to 20.7 (11.0-37.2) ng/mL and 14.2(8.0-26.3) ng/mL after day 1 and day 3, respectively, (P ≤ 0.001). Baseline uKIM1 concentration was 2.6 (1.4-6.0) ng/mL and increased to 5.2 (2.4-9.1) ng/mL (P = 0.002) after day 1, whereas uKIM1 was not different from baseline at day 3 (2.9 [1.4-6.4] ng/mL (P = 0.52)). Furthermore, both uNGAL and uKIM1 levels were higher after day 1 compared to day 3 (P < 0.01). When corrected for urinary cystatin C, creatinine, and osmolality, uNGAL demonstrated a similar response compared to the uncorrected data, whereas differences in uKIM1 between baseline, day 1 and day 3 (Ptime = 0.63) were no longer observed for cystatin C and creatinine corrected data. A single bout of prolonged exercise significantly increased uNGAL concentration, whereas no changes in uKIM1 were found. Repetitive bouts of exercise show that there is no cumulative effect of kidney injury markers.

Clinical benefits of using inulin clearance and cystatin C for determining glomerular filtration rate in HIV-1-infected individuals treated with dolutegravir

INTRODUCTION

Dolutegravir may inhibit creatinine transporters in renal tubules and elevate serum creatinine levels. We investigated the usefulness of glomerular filtration rate (GFR) measured using inulin clearance (Cin), creatinine clearance (Ccr), and estimated GFR based on both serum creatinine (eGFRcre) and serum cystatin C (eGFRcys).

PATIENTS & METHODS

HIV-1-infected Japanese patients with suppressed viremia and whose antiretroviral drug was switched to dolutegravir from other drugs were included (n = 108, Study 1). We compared eGFRcre and eGFRcys at the start and after 48 weeks of dolutegravir administration. For the patients providing consent, we measured Cin and Ccr (n = 15, Study 2). We assessed biases and accuracy and compared Cin with eGFRcre, eGFRcys, and Ccr.

RESULTS

There were no differences in serum cystatin C and eGFRcys between baseline and at 48 weeks. Moreover, eGFRcre was significantly less accurate (within 30% of measured GFR) than both eGFRcys and Ccr (40% accuracy compared to 93% and 93%, respectively). eGFRcys was significantly less biased than eGFRcre and Ccr (p < 0.0001, p = 0.00036, respectively). No significant difference between Cin and eGFRcys was observed. eGFRcys was significantly correlated with Cin (γ = 0.85, p < 0.0001).

CONCLUSIONS

eGFRcys provided the most precise estimate and most closely approximate Cin in HIV-1-infected Japanese patients with suppressed viremia treated with dolutegravir. We demonstrated clinical benefits of inulin clearance and eGFRcys. This is the first study performing inulin clearance for HIV-1-infected individuals and to show data for eGFRcys from a large cohort following a switch to dolutegravir from other antiretroviral agents.

Evaluation of neutrophil gelatinase-associated lipocalin and cystatin C as early markers of diabetic nephropathy

INTRODUCTION

Diabetes mellitus (DM) is a major cause of concern because of its increasing prevalence rate and related microvascular as well as macrovascular complications, including kidney disease. Microalbuminuria has been accepted as the earliest marker for diabetic nephropathy; however, a large proportion of renal impairment occurs in nonalbuminuric state. We planned to investigate the serum and urinary levels of the tubular damage markers (neutrophil gelatinase-associated lipocalin [NGAL] and cystatin C [Cys C]) in patients of type 2 diabetes to detect early kidney injury.

MATERIALS AND METHODS

This cross-sectional hospital-based study included 180 patients with type 2 DM according to the American Diabetes Association criteria. Serum NGAL (S.NGAL) and urine NGAL (U.NGAL) and Cys C were measured in all study participants and investigated for correlation with microalbuminuria.

RESULTS

Our results showed that U.NGAL and S.NGAL levels were significantly high in patients with microalbuminuria as compared to normoalbuminuric controls. Serum Cys C was also higher in microalbuminuric patients than who had normoalbuminuria. A positive correlation of urinary albumin excretion with S.NGAL and U.NGAL was noted. U.NGAL also showed positive correlation with duration of diabetes, glycated hemoglobin, and dyslipidemia. Receiver operating characteristic curve analysis showed that the area under the curve for U.NGAL and S.NGAL were 1 and 0.8, respectively, which indicates that they are sensitive markers for early renal damage.

CONCLUSION

Urinary biomarkers were significantly elevated in normoalbuminuric type 2 diabetic patients compared with nondiabetic controls and could be used as markers of nephropathy at a very early stage even before the development of microalbuminuria, the current gold standard for early diagnosis. Despite the promise of these new biomarkers, further large, multicenter prospective studies are still needed.

Megalin dependent urinary cystatin C excretion in ischemic kidney injury in rats

Background

Cystatin C, a marker of kidney injury, is freely filtered in the glomeruli and reabsorbed by the proximal tubules. Megalin and cubilin are endocytic receptors essential for reabsorption of most filtered proteins. This study examines the role of these receptors for the uptake and excretion of cystatin C and explores the effect of renal ischemia/reperfusion injury on renal cystatin C uptake and excretion in a rat model.

Methods

Binding of cystatin C to megalin and cubilin was analyzed by surface plasmon resonance analysis. ELISA and/or immunoblotting and immunohistochemistry were used to study the urinary excretion and tubular uptake of endogenous cystatin C in mice. Furthermore, renal uptake and urinary excretion of cystatin C was investigated in rats exposed to ischemia/reperfusion injury.

Results

A high affinity binding of cystatin C to megalin and cubilin was identified. Megalin deficient mice revealed an increased urinary excretion of cystatin C associated with defective uptake by endocytosis. In rats exposed to ischemia/reperfusion injury urinary cystatin C excretion was increased and associated with a focal decrease in proximal tubule endocytosis with no apparent change in megalin expression.

Conclusions

Megalin is essential for the normal tubular recovery of endogenous cystatin C. The increase in urinary cystatin C excretion after ischemia/reperfusion injury is associated with decreased tubular uptake but not with reduced megalin expression.

Short-Term Non-Steroid Anti-Inflammatory Drug Use in Spondyloarthritis Patients Induces Subclinical Acute Kidney Injury: Biomarkers Study

BACKGROUND

Non-steroid anti-inflammatory drug (NSAID) usage is associated with kidney injury. Rise in serum creatinine (sCr) often represents irreversible process. Thus to assess the early effects of regular NSAID use, we studied sensitive serum and urine biomarkers of kidney injury.

METHODS

In a protocol-based intervention study, 103 subjects were enrolled in 3 mutually exclusive groups. Group 1 included 37 healthy controls having minimal baseline NSAID exposure as per a definition, and group 2 had 41 spondyloarthritis (SpA) patients on regular NSAID therapy for >3 months. Group 3 included 25 SpA patients having minimal NSAID exposure at baseline. Blood and urine samples were collected from all the 3 groups at baseline. Furthermore, group 3 was started on 6-week regular NSAID therapy, and blood and urine samples were re-collected at 1, 6, and 12 weeks. Baseline normal kidney function as per the definition was ensured in all the subjects. Creatinine, neutrophil gelatinase-associated lipocalin (NGAL), kidney injury molecule-1 (KIM-1), cystatin-C, and microalbumin were measured in urine and serum samples to assess kidney injury.

RESULTS

Kidney injury biomarkers were 2-3-fold higher in SpA patients using regular NSAID therapy compared to healthy controls and SpA patients having minimal NSAID exposure (uKIM-1 and uNGAL p < 0.0001, sKIM-1 and sNGAL p = 0.001). There was no difference in sCr and estimated glomerular filtration rate using Cockcroft-Gault equation between the groups. In SpA patients started on 6 weeks of regular NSAID (group 3), biomarker levels started rising at week 1 and showed a significant rise at week 6. The levels in the patients that stopped NSAID use at 6 weeks showed reversibility at 12 weeks.

CONCLUSIONS

Regular NSAID use in SpA patients induces subclinical kidney injury represented by rise in biomarkers. These levels start rising as early as 7 days of regular NSAID use and are reversible on stopping the drug.

Acute Kidney Injury Urine Biomarkers in Very Low-Birth-Weight Infants

BACKGROUND AND OBJECTIVES

Serum creatinine (SCr)-based AKI definitions have important limitations, particularly in very low-birth-weight (VLBW) neonates. Urine biomarkers may improve our ability to detect kidney damage. We assessed the association between 14 different urine biomarkers and AKI in VLBW infants.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

We performed a prospective cohort study on 113 VLBW infants (weight ≤1200 g or <31 weeks' gestation) admitted to a regional neonatal intensive care unit at the University of Alabama at Birmingham between February 2012 and June 2013. SCr was measured on postnatal days 1, 2, 3, and 4 and was combined with clinically measured SCr to determine AKI according to Kidney Disease Improving Global Outcomes AKI definition (increase in SCr ≥0.3 mg/dl or ≥50% increase from previous lowest value). Urine was collected on the first 4 days (average number of urine collections, 3; range, 1-4). The maximum urine biomarkers and urine biomarker/creatinine levels were calculated for 12 urine biomarkers, and the minimum urine biomarker and biomarker/creatinine levels were assessed for two urine biomarkers. We compared these values between infants with and those without AKI. Ideal cutoffs, area under the receiver-operating characteristic curve , and area under the curve adjusted for gestational age were calculated.

RESULTS

Cumulative incidence of AKI during the first 2 postnatal weeks was 28 of 113 (25%). Infants with AKI had higher maximum levels of urine cystatin C, neutrophil gelatinase-associated lipocalin, osteopontin, clusterin, and α glutathione S-transferase (2.0, 1.8, 1.7, 1.7, and 3.7 times higher, respectively) than infants without AKI. In addition, infants with AKI had lower minimum levels of epithelial growth factor and uromodulin than those without AKI (1.4 and 1.6 times lower, respectively). Most but not all participants had their maximum (or minimum) biomarker values preceding AKI. These associations remained after adjustment for gestational age.

CONCLUSIONS

Urine biomarkers measured in the first 4 days of life are associated with AKI during the first postnatal weeks. Further evaluations are necessary to determine whether these biomarkers can predict important clinical outcomes. In addition, intervention studies that use biomarkers to stratify enrollment groups are needed before bedside evaluations can be incorporated into care.

Associations between urinary kidney injury biomarkers and cardiovascular mortality risk in elderly men with diabetes

AIM

Three urinary biomarkers, kidney injury molecule-1 (KIM-1), neutrophil gelatinase-associated lipocalin (NGAL), and cystatin C, have been suggested as clinically relevant highly specific biomarkers of acute kidney tubular damage. Yet, the utility of these biomarkers in the prognostication of diabetic nephropathy has been less studied. Therefore, we aimed to investigate the longitudinal association between these urinary biomarkers and cardiovascular mortality in patients with diabetes.

METHODS

The study sample consisted of participants with diabetes in the community-based Uppsala Longitudinal Study of Adult Men (n = 91; mean age 77.8 years). During follow-up (median 8.3 years, interval 0.7-13.4 years), 33 participants died of cardiovascular causes.

RESULTS

In a multivariable Cox regression model adjusting for age, glomerular filtration rate, and urinary albumin/creatinine ratio, higher urinary KIM-1/creatinine was associated with an increased risk for cardiovascular mortality (HR per SD increase 1.51, 95% confidence intervals 1.03-2.24, P = 0.03). Neither urinary NGAL/creatinine nor urinary cystatin C/creatinine were independently associated with an increased cardiovascular mortality risk.

CONCLUSION

In elderly men with diabetes, higher urinary KIM-1/creatinine was associated with an increased long-term risk of cardiovascular mortality independently of established markers of diabetic nephropathy. Our data provide support for kidney tubular damage as an important aspect of diabetic nephropathy that merits further investigation.

Association of Renal Stress/Damage and Filtration Biomarkers with Subsequent AKI during Hospitalization among Patients Presenting to the Emergency Department

BACKGROUND AND OBJECTIVES

Emergency departments (EDs) have a growing role in hospital admissions, but few studies address AKI biomarkers in the ED.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Patients admitted to the internal medicine service were enrolled during initial workup in the ED at Robert-Bosch-Hospital, Stuttgart, Germany. Daily serum creatinine (sCr) and urine output (UO) were recorded for AKI classification by Kidney Disease Improving Global Outcomes (KDIGO) criteria. Cystatin C, kidney injury molecule-1, liver-type fatty acid-binding protein, and neutrophil gelatinase-associated lipocalin were measured in blood and urine, and IL-18, insulin-like growth factor-binding protein 7 (IGFBP7), tissue inhibitor of metalloproteinases-2 (TIMP-2) and [TIMP-2]⋅[IGFBP7] were measured in urine collected at enrollment, after 6 hours, and the following morning. Association between these biomarkers and the end point of moderate-severe AKI (KDIGO stage 2-3) occurring within 12 hours of each sample collection was examined using generalized estimating equation logistic regression. Performance for prediction of the AKI end point using two previously validated [TIMP-2]-[IGFBP7] cutoffs was also tested.

RESULTS

Of 400 enrolled patients, 298 had sufficient sCr and UO data for classification by KDIGO AKI criteria: AKI stage 2 developed in 37 patients and AKI stage 3 in nine patients. All urinary biomarkers, sCr, and plasma cystatin C had statistically significant (P<0.05) odds ratios (ORs) for the AKI end point. In a multivariable model of the urine biomarkers and sCr, only [TIMP-2]⋅[IGFBP7] and sCr had statistically significant ORs. Compared with [TIMP-2]⋅[IGFBP7]<0.3 (ng/ml)(2)/1000, values between 0.3 and 2.0 (ng/ml)(2)/1000 indicated 2.5 (95% confidence interval [95% CI], 1.1 to 5.2) times the odds for the AKI end point and values >2.0 (ng/ml)(2)/1000 indicated 11.0 (95% CI, 4.4 to 26.9) times the odds. Addition of [TIMP-2]⋅[IGFBP7] to a clinical model significantly improved area under the receiver-operating characteristic curve from 0.67 (95% CI, 0.61 to 0.78) to 0.77 (95% CI, 0.72 to 0.86) (P<0.001); however, including both markers in the model was not significantly different from including either marker alone.

CONCLUSIONS

Urinary [TIMP-2]⋅[IGFBP7] with pre-established cutoffs provides valuable information about risk for imminent AKI in the ED that is complementary to sCr and clinical risk factors.

Estimated GFR and Subsequent Higher Left Ventricular Mass in Young and Middle-Aged Adults With Normal Kidney Function: The Coronary Artery Risk Development in Young Adults (CARDIA) Study

BACKGROUND

Left ventricular hypertrophy is common and is associated with cardiovascular events and death among patients with known chronic kidney disease. However, the link between reduced glomerular filtration rate (GFR) and left ventricular mass index (LVMI) remains poorly explored among young and middle-aged adults with preserved kidney function. In this study, we examined the association of cystatin C-based estimated GFR (eGFRcys) and rapid decline in eGFR with subsequent LVMI.

STUDY DESIGN

Observational study.

SETTING & PARTICIPANTS

We included 2,410 participants from the Coronary Artery Risk Development in Young Adults (CARDIA) cohort with eGFRcys > 60mL/min/1.73m(2) at year 15 and who had an echocardiogram obtained at year 25.

PREDICTOR

eGFRcys at year 15 and rapid decline in eGFRcys (defined as >3% per year over 5 years from years 15 to 20).

OUTCOME

LVMI measured at year 25.

MEASUREMENTS

We adjusted for age, sex, race, diabetes, body mass index, low- and high-density lipoprotein cholesterol levels, cumulative systolic blood pressure, and albuminuria.

RESULTS

Mean age was 40±4 (SD) years, 58% were women, and 43% were black. After 10 years of follow-up, mean LVMI was 39.6±13.4g/m(2.7). Compared with eGFRcys > 90mL/min/1.73m(2) (n = 2,228), eGFRcys of 60 to 75mL/min/1.73m(2) (n = 29) was associated with 5.63 (95% CI, 0.90-10.36) g/m(2.7) greater LVMI (P = 0.02), but there was no association of eGFRcys of 76 to 90mL/min/1.73m(2) (n = 153) with LVMI after adjustment for confounders. Rapid decline in eGFRcys was associated with higher LVMI compared with participants without a rapid eGFRcys decline (β coefficient, 1.48; 95% CI, 0.11-2.83; P = 0.03) after adjustment for confounders.

LIMITATIONS

There were a limited number of participants with eGFRcys of 60 to 90mL/min/1.73m(2).

CONCLUSIONS

Among young and middle-aged adults with preserved kidney function, eGFRcys of 60 to 75mL/min/1.73m(2) and rapid decline in eGFRcys were significantly associated with subsequently higher LVMI. Further studies are needed to understand the mechanisms that contribute to elevated LVMI in this range of eGFRcys.

Evaluation of cystatin C as an early biomarker of cadmium nephrotoxicity in the rat

Cadmium (Cd) is a nephrotoxic environmental pollutant that causes insidious injury to the proximal tubule that results in severe polyuria and proteinuria. Cystatin C is a low molecular weight protein that is being evaluated as a serum and urinary biomarker for various types of ischemic and nephrotoxic renal injury. The objective of the present study was to determine if cystatin C might be a useful early biomarker of Cd nephrotoxicity. Male Sprague-Dawley rats were given daily injections of Cd for up to 12 weeks. At 3, 6, 9 and 12 weeks, urine samples were analyzed for cystatin C, protein, creatinine, β2 microglobulin and kidney injury molecule-1. The results showed that Cd caused a significant increase in the urinary excretion of cystatin C that occurred 3-4 weeks before the onset of polyuria and proteinuria. Serum levels of cystatin C were not altered by Cd. Immunolabeling studies showed that Cd caused the relocalization of cystatin C from the cytoplasm to the apical surface of the epithelial cells of the proximal tubule. The Cd-induced changes in cystatin C labelling paralleled those of the brush border transport protein, megalin, which has been implicated as a mediator of cystatin C uptake in the proximal tubule. These results indicate that Cd increases the urinary excretion of cystatin C, and they suggest that this effect may involve disruption of megalin-mediated uptake of cystatin C by epithelial cells of the proximal tubule.

Relationship between Urinary N-Desmethyl-Acetamiprid and Typical Symptoms including Neurological Findings: A Prevalence Case-Control Study

Neonicotinoid insecticides are nicotinic acetylcholine receptor agonists used worldwide. Their environmental health effects including neurotoxicity are of concern. We previously determined a metabolite of acetamiprid, N-desmethyl-acetamiprid in the urine of a patient, who exhibited some typical symptoms including neurological findings. We sought to investigate the association between urinary N-desmethyl-acetamiprid and the symptoms by a prevalence case-control study. Spot urine samples were collected from 35 symptomatic patients of unknown origin and 50 non-symptomatic volunteers (non-symptomatic group, NSG, 4–87 year-old). Patients with recent memory loss, finger tremor, and more than five of six symptoms (headache, general fatigue, palpitation/chest pain, abdominal pain, muscle pain/weakness/spasm, and cough) were in the typical symptomatic group (TSG, n = 19, 5–69 year-old); the rest were in the atypical symptomatic group (ASG, n = 16, 5–78 year-old). N-desmethyl-acetamiprid and six neonicotinoids in the urine were quantified by liquid chromatography-tandem mass spectrometry. The detection of N-desmethyl-acetamiprid was the most frequent and highest in TSG (47.4%, 6.0 ppb (frequency, maximum)), followed by in ASG (12.5%, 4.4 ppb) and in NSG (6.0%, 2.2 ppb), however acetamiprid was not detected. Thiamethoxam was detected in TSG (31.6%, 1.4 ppb), in ASG (6.3%, 1.9 ppb), but not in NSG. Nitenpyram was detected in TSG (10.5%, 1.2 ppb), in ASG (6.3%, not quantified) and in NSG (2.0%, not quantified). Clothianidin was only detected in ASG (6.3%, not quantified), and in NSG (2.0%, 1.6 ppb). Thiacloprid was detected in ASG (6.3%, 0.1 ppb). The cases in TSG with detection of N-desmethyl-acetamiprid and thiamethoxam were aged 5 to 62 years and 13 to 62 years, respectively. Detection of N-desmethyl-acetamiprid was associated with increased prevalence of the symptoms (odds ratio: 14, 95% confidence interval: 3.5–57). Urinary N-desmethyl-acetamiprid can be used as a biomarker for environmental exposure to acetamiprid. Further multi-centered clinical research in larger patients groups with more metabolites analysis is needed.

Nanoparticle Detection of Urinary Markers for Point-of-Care Diagnosis of Kidney Injury

The high incidence of acute and chronic kidney injury due to various environmental factors such as heavy metals or chemicals has been a major problem in developing countries. However, the diagnosis of kidney injury in these areas can be more challenging due to the lack of highly sensitive and specific techniques that can be applied in point-of-care settings. To address this, we have developed a technique called ‘micro-urine nanoparticle detection (μUNPD)’, that allows the detection of trace amounts of molecular markers in urine. Specifically, this technique utilizes an automated on-chip assay followed by detection with a hand-held device for the read-out. Using the μUNPD technology, the kidney injury markers KIM-1 and Cystatin C were detected down to concentrations of 0.1 ng/ml and 20 ng/ml respectively, which meets the cut-off range required to identify patients with acute or chronic kidney injury. Thus, we show that the μUNPD technology enables point of care and non-invasive detection of kidney injury, and has potential for applications in diagnosing kidney injury with high sensitivity in resource-limited settings.

Mechanisms underlying early rapid increases in creatinine in paraquat poisoning

Background

Acute kidney injury (AKI) is common after severe paraquat poisoning and usually heralds a fatal outcome. The rapid large increases in serum creatinine (Cr) exceed that which can be explained by creatinine kinetics based on loss of glomerular filtration rate (GFR).

Methods and Findings

This prospective multi-centre study compared the kinetics of two surrogate markers of GFR, serum creatinine and serum cystatin C (CysC), following paraquat poisoning to understand and assess renal functional loss after paraquat poisoning. Sixty-six acute paraquat poisoning patients admitted to medical units of five hospitals were included. Relative changes in creatinine and CysC were monitored in serial blood and urine samples, and influences of non-renal factors were also studied.

Results

Forty-eight of 66 patients developed AKI (AKIN criteria), with 37 (56%) developing moderate to severe AKI (AKIN stage 2 or 3). The 37 patients showed rapid increases in creatinine of >100% within 24 hours, >200% within 48 hours and >300% by 72 hours and 17 of the 37 died. CysC concentration increased by 50% at 24 hours in the same 37 patients and then remained constant. The creatinine/CysC ratio increased 8 fold over 72 hours. There was a modest fall in urinary creatinine and serum/urine creatinine ratios and a moderate increase in urinary paraquat during first three days.

Conclusion

Loss of renal function contributes modestly to the large increases in creatinine following paraquat poisoning. The rapid rise in serum creatinine most probably represents increased production of creatine and creatinine to meet the energy demand following severe oxidative stress. Minor contributions include increased cyclisation of creatine to creatinine because of acidosis and competitive or non-competitive inhibition of creatinine secretion. Creatinine is not a good marker of renal functional loss after paraquat poisoning and renal injury should be evaluated using more specific biomarkers of renal injury.

Exploration of chronic kidney disease prevalence estimates using new measures of kidney function in the health survey for England

BACKGROUND

Chronic kidney disease (CKD) diagnosis relies on glomerular filtration rate (eGFR) estimation, traditionally using the creatinine-based Modification of Diet in Renal Disease (MDRD) equation. The Chronic Kidney Disease Epidemiology Collaboration (CKDEPI) equation performs better in estimating eGFR and predicting mortality and CKD progression risk. Cystatin C is an alternative glomerular filtration marker less influenced by muscle mass. CKD risk stratification is improved by combining creatinine eGFR with cystatin C and urinary albumin to creatinine ratio (uACR). We aimed to identify the impact of introducing CKDEPI and cystatin C on the estimated prevalence and risk stratification of CKD in England and to describe prevalence and associations of cystatin C.

METHODS AND FINDINGS

Cross sectional study of 5799 people in the nationally representative 2009 and 2010 Health Surveys for England.

PRIMARY OUTCOME MEASURES

prevalence of MDRD, CKDEPI and cystatin C-defined eGFR<60 ml/min/1.73 m(2); prevalence of CKD biomarker combinations (creatinine, cystatin C, uACR). Using CKDEPI instead of MDRD reduced the prevalence of eGFR<60 ml/min/1.73 m(2) from 6.0% (95% CI 5.4-6.6%) to 5.2% (4.7-5.8%) equivalent to around 340,000 fewer individuals in England. Those reclassified as not having CKD evidenced a lower risk profile. Prevalence of cystatin C eGFR<60 ml/min/1.73 m(2) was 7.7% and independently associated with age, lack of qualifications, being an ex-smoker, BMI, hypertension, and albuminuria. Measuring cystatin C in the 3.9% people with CKDEPI-defined eGFR<60 ml/min/1.73 m(2) without albuminuria (CKD Category G3a A1) reclassified about a third into a lower risk group with one of three biomarkers and two thirds into a group with two of three. Measuring cystatin C in the 6.7% people with CKDEPI eGFR >60 ml/min/1.73 m(2) with albuminuria (CKD Category G1-2) reclassified almost a tenth into a higher risk group.

LIMITATIONS

Cross sectional study, single eGFR measure, no measured ('true') GFR.

CONCLUSIONS

Introducing the CKDEPI equation and targeted cystatin C measurement reduces estimated CKD prevalence and improves risk stratification.

Evidence of uncoupling between renal dysfunction and injury in cardiorenal syndrome: insights from the BIONICS study

OBJECTIVE

The objective of the study was to assess urinary biomarkers of renal injury for their individual or collective ability to predict Worsening renal function (WRF) in patients with acutely decompensated heart failure (ADHF).

METHODS

In a prospective, blinded international study, 87 emergency department (ED) patients with ADHF were evaluated with biomarkers of cardiac stretch (B type natriuretic peptide [BNP] and its amino terminal equivalent [NT-proBNP], ST2), biomarkers of renal function (creatinine, estimated glomerular filtration rate [eGFR]) and biomarkers of renal injury (plasma neutrophil gelatinase associated lipocalin [pNGAL], urine kidney injury molecule-1 [KIM-1], urine N-acetyl-beta-D-glucosaminidase [NAG], urine Cystatin C, urine fibrinogen). The primary endpoint was WRF.

RESULTS

26% developed WRF; baseline characteristics of subjects who developed WRF were generally comparable to those who did not. Biomarkers of renal function and urine biomarkers of renal injury were not correlated, while urine biomarkers of renal injury correlated between each other. Biomarker concentrations were similar between patients with and without WRF except for baseline BNP. Although plasma NGAL was associated with the combined endpoint, none of the biomarker showed predictive accuracy for WRF.

CONCLUSIONS

In ED patients with ADHF, urine biomarkers of renal injury did not predict WRF. Our data suggest that a weak association exists between renal dysfunction and renal injury in this setting (Clinicaltrials.gov NCT#0150153).

Elevated urinary levels of cystatin C and neutrophil gelatinase-associated lipocalin in Henoch-Schönlein purpura patients with renal involvement

Henoch-Schönlein purpura (HSP) is a commonest systemic vasculitis in childhood. The long-term prognosis of HSP is determined by the degree of renal involvement. The aim of this study is to search novel clinically applicable biomarkers to evaluate renal involvement in HSP patients. 20 bio-indexes in urine samples were simultaneously screened by antibody array assay. We indicated that urinary levels of cystatin C (Cys C) and neutrophil gelatinase-associated lipocalin (NGAL) in HSP patients with renal involvement were significantly higher than those without renal involvement and healthy controls. Furthermore, ELISA was used to analyze urinary Cys C and NGAL levels in HSP patients with or without renal involvement, atopic dermatitis (AD) patients and healthy controls. Our results demonstrated that urinary Cys C and NGAL levels in HSP patients with renal involvement were significantly elevated, when compared with those without renal involvement, AD patients and control subjects. In addition, by receiver operating characteristic (ROC) curve analysis, we demonstrated that the area under the ROC curve of NGAL (0.789) was larger than that of Cys C (0.692). Taken together, we show firstly that urinary Cys C and NGAL levels is abnormally elevated in HSP patients with renal involvement. We suggest that urinary Cys C and NGAL are novel useful biomarkers of renal involvement in HSP patients.

Urinary cystatin C as an early biomarker of acute kidney injury after open and endovascular abdominal aortic aneurysm repair

BACKGROUND

Acute kidney injury (AKI) after open repair (OR) and endovascular repair (EVAR) of abdominal aortic aneurysm (AAA) is associated with increased mortality and hospital costs. Early detection of AKI is critical to prevent its progression. Recent findings demonstrate that elevated levels of urinary cystatin C (uCysC) may reflect tubular dysfunction. We prospectively evaluated whether uCysC can detect renal dysfunction earlier than serum creatinine (sCr).

METHODS

In a prospective study, 126 consecutive patients (mean age ± SD, 69.1 ± 8.66 years) with AAA (EVAR = 87, OR = 39) were enrolled. sCr and uCysC were measured preoperatively (baseline) and at 6, 24, and 48 hr postoperatively. A final measurement was made on day 5. AKI was defined according to Acute Kidney Injury Network criteria.

RESULTS

The incidence of AKI was significantly higher (χ(2) test, P < 0.05) in the OR group (n = 13, 33%) than in the EVAR group (n = 15, 17%). The baseline median (interquartile range) value of uCysC was significantly higher (t-test, P < 0.05) in patients of both groups (OR-EVAR) who developed AKI from those who did not (OR/AKI group: 0.06 [0.02-0.12] mg/L, EVAR/AKI group: 0.08 [0.05-0.11] mg/L versus no-AKI subjects: 0.04 [0.02-0.07] mg/L). Subsequent analysis showed that at 6 hr postoperatively, the patients who developed AKI increased their uCysC levels significantly from baseline (OR/AKI group: 0.58 [0.42-0.70] mg/L, EVAR/AKI group: 0.59 [0.30-1.07] mg/L). The median value of uCysC in AKI patients increased at 24 hr (OR/AKI group: 1.37 [0.78-3.40] mg/L, EVAR/AKI group: 2.11 [0.70-2.42] mg/L) and peaked at 48 hr (OR/AKI group: 6.16 [1.74-10.73] mg/L, EVAR/AKI group: 2.57 [1.21-7.40] mg/L), while no increase was observed among those who did not develop AKI at the same time points (0.06 [0.04-0.14] vs. 0.08 [0.04-0.19] mg/L). The diagnostic accuracy of uCysC at 6 hr post-surgery was excellent (area under the curve - receiver-operating characteristic [AUC-ROC] = 0.968), significantly higher than sCr (AUC-ROC = 0.844) and a cutoff value set at 0.30 mg/L can diagnose AKI with a sensitivity of 85.71% and a specificity of 98.97%.

CONCLUSIONS

uCysC is superior to sCr in the early diagnosis of AKI following open and endovascular AAA repair.

Urinary biomarkers and renal near-infrared spectroscopy predict intensive care unit outcomes after cardiac surgery in infants younger than 6 months of age

OBJECTIVE

To assess the ability of urinary acute kidney injury biomarkers and renal near-infrared spectroscopy (NIRS) to predict outcomes in infants after surgery for congenital heart disease.

METHODS

Urinary levels of neutrophil gelatinase-associated lipocalin (NGAL), interleukin-18 (IL-18), kidney injury molecule-1 (KIM-1), and cystatin C were measured preoperatively and postoperatively in 49 infants younger than 6 months of age. Renal NIRS was monitored for the first 24 hours after surgery. A composite poor outcome was defined as death, the need for renal replacement therapy, prolonged time to first extubation, or prolonged intensive care unit length of stay.

RESULTS

Forty-two (86%) patients had acute kidney injury as indicated by at least Acute Kidney Injury Network/Kidney Disease: Improving Global Outcomes (AKIN/KDIGO) stage 1 criteria, and 17 (35%) patients had poor outcomes, including 3 deaths. With the exception of KIM-1, all biomarkers demonstrated significant increases within 24 hours postoperatively among patients with poor outcomes. Low levels of NGAL and IL-18 demonstrated high negative predictive values (91%) within 2 hours postoperatively. Poor outcome infants had greater cumulative time with NIRS saturations less than 50% (60 vs 1.5 minutes; P = .02) in the first 24 hours.

CONCLUSIONS

Within the first 24 hours after cardiopulmonary bypass, infants at increased risk for poor outcomes demonstrated elevated urinary NGAL, IL-18, and cystatin C and increased time with low NIRS saturations. These findings suggest that urinary biomarkers and renal NIRS may differentiate patients with good versus poor outcomes in the early postoperative period, which could assist clinicians when counseling families and inform the development of future clinical trials.

Urinary biomarkers for early detection of recovery in patients with acute kidney injury

Urinary biomarkers of acute kidney injury (AKI) have been revealed recently to be useful for prior prediction of AKI. However, it is unclear whether these urinary biomarkers can also detect recovery from established AKI. Urinary biomarkers, including neutrophil gelatinase-associated lipocalin (NGAL) and cystatin C, were measured every 2 days for 8 days in 66 patients with AKI. At day 0, there were no significant differences in plasma creatinine, BUN, and urine cystatin C between AKI patients in the recovery (n = 33) and non-recovery (n = 33) groups. Plasma creatinine concentrations were significantly lower in the recovery group (3.0 ± 2.0 mg/dL) than in the non-recovery group (5.4 ± 1.9 mg/dL) on day 4 after AKI diagnosis (P < 0.001). In contrast, there were significant differences in urine NGAL between the two groups starting on day 0 (297.2 ± 201.4 vs 407.6 ± 190.4 ng/mL, P = 0.025) through the end of the study (123.7 ± 119.0 vs 434.3 ± 121.5 ng/mL, P < 0.001). The multiple logistic regression analysis showed that urine NGAL could independently predict recovery from AKI. Conclusively, this prospective observational study demonstrates that urine NGAL can be a highly versatile marker for early detection of the recovery phase in established AKI patients.

Biomarkers of acute kidney injury in pediatric cardiac surgery

OBJECTIVES

Acute kidney injury (AKI) is a significant problem in children undergoing cardiopulmonary bypass (CPB). The aims of this study were to assess the diagnostic validity of serum CysC (sCysC), serum neutrophil gelatinase lipocalin (sNGAL), urine neutrophil gelatinase lipocalin (uNGAL), urine kidney injury molecule (uKIM)-1, and urine liver fatty acid-binding protein (uL-FABP) to predict AKI presence and severity in children undergoing CPB.

DESIGN AND METHODS

We performed a prospective single-center evaluation of sCysC, sNGAL, uNGAL, uKIM-1 and uL-FABP at 0, 2, 6, 24 and 48 h postoperatively in children undergoing CPB during cardiac surgery. AKI was defined as ≥25% decrease in the estimated creatinine clearance (eCCl) from pre-operative baseline at 48h after surgery.

RESULTS

Of the 112 patients, 18 patients (16.1%) developed AKI; four of them needed acute dialysis treatment and three AKI patients died. In the AKI compared to the non-AKI group, sCysC at 2h, and uNGAL and uL-FABP at 2-48 h were significantly increased, as well as CPB, aortic cross clamp time and length of hospital stay. Biomarkers increased with worsening AKI severity. At 2h after CPB the best accuracy for diagnosis of AKI had uL-FABP and sCysC with area under the receiver operator curve (AUC) of 0.89 and 0.73, respectively. At 6 and 24h after CPB the best AUC was found for uL-FABP (0.75 and 0.87 respectively) and for uNGAL (0.70 and 0.93, respectively).

CONCLUSIONS

sCysC, uNGAL and uL-FABP are reliable early predictors for AKI after CPB. By allowing earlier timing of injury and earlier intervention, they could improve AKI outcome.

Urinary biomarkers in hydronephrosis

Hydronephrosis is diagnosed in 0.5-1% of all newborns, and ureteropelvic junction obstruction (UPJO) accounts for 35% of those cases. A urinary tract obstruction that occurs during early kidney development affects renal morphogenesis, maturation, and growth, and in the most severe cases, this will ultimately lead to progressive renal tubular atrophy and interstitial fibrosis with the loss of nephrons. The clinical management of these patients remains a controversial topic. The aim is to preserve renal function by identifying the 15-20% of children who require early surgical intervention from those for whom watchful waiting may be appropriate because of spontaneous resolving/stabilization without significant loss of renal function. Although the patients attend regular follow-ups, including repetitive blood tests, ultrasonographies, and the more invasive diuretic renograms, the surgeons still miss reliably biomarkers that could be used as predictors for renal parenchymal damage and decreased renal function, and thereby provide more clear indications for surgical intervention. The aim of this PhD thesis was to further elucidate the pathophysiology of obstructive nephropathy (study I) and to search for potential candidate biomarkers that may have a predictive and/or diagnostic value in the management of hydronephrosis (study II). Study I: Urine and kidney cytokine profiles in experimental unilateral acute and chronic hydronephrosis.

AIM

To study the dynamics of the urinary secretion of cytokines after the release of unilateral ureteral obstruction, and to study whether the urinary concentrations of these compounds reliably reflects changes in the renal parenchyma. This was tested in 2 experimental rat models: an acute obstruction model and a chronic obstruction model.

RESULTS

The acute obstruction model demonstrated significant differences in the renal levels of IL-1β, IL-6, TNF-α, and IL-10 in comparison with controls, and these differences were associated with similar differences in their urinary excretion. Such results were not obtained in the chronic obstruction model in which significant differences were only demonstrated in the urinary concentrations of IL-6. Study II: Candidate urinary biomarkers in hydronephrosis - a clinical study.

AIM

To study the dynamics of the urinary excretion of selected potential biomarkers in children after the relief of UPJO, and to compare their findings with healthy controls.

RESULTS

Twenty-eight children with UPJO were included in the study from 2007-2011 together with 13 healthy children. Pre-, peri- and post-operatively (1 year) urine samples were collected. The median age of the patients was 8.1 (3.5-14.5) years. Five proteins (EGF, IP-10, MCP-1, RANTES, and MIP-1α) were examined in study IIa, and 4 proteins (NGAL, CyC, βM-2, and OPN) were examined in study IIb. In brief, significantly increased urinary concentrations of EGF and MCP-1 were demonstrated in children with UPJO compared to controls, which was followed by a decline in the post-operative period to levels similar to the controls. This indicates that the urinary concentrations of EGF and MCP-1 are regulated as a response to the obstruction, suggesting that they may have a potential as urinary biomarkers in hydronephrosis. In general, urine from the obstructed kidney exhibited higher concentrations of the proteins compared to urine from the nonobstructed kidney. Furthermore, CyC, β-2M, and OPN were negatively correlated with age, and IP-10 and MCP-1 were negatively correlated with DRF. In conclusion, this PhD study confirmed increased concentrations of selected proteins in urine from kidneys suffering from obstruction. Interestingly, it was observed that some urinary proteins had an age-dependent excretion. Further investigations are required to test the ability of the examined proteins to identify an obstruction and reveal disease progression and, thereby, be useful clinical tools.

α1-Microglobulin/albumin ratio may improve interpretation of albuminuria in statin-treated patients

BACKGROUND

Statins can cause tubular proteinuria by inhibiting tubular reabsorption of urinary proteins. To distinguish between microalbuminuria originating from glomerular leakage of albumin and tubular microalbuminuria due to statin therapy, the α1-microglobulin/albumin ratio is evaluated in patients taking statins and compared to untreated patients.

METHODS

Ten apparently healthy subjects were given 40 mg of simvastatin and tested for urinary α1-microglobulin, albumin, creatinine and cystatin C, up to 24 h after administration. Additionally, urine samples of 76 statin-treated and 456 untreated patients presenting with micro-albuminuria (albuminuria range between 20 and 200 mg/L) were tested for α1-microglobulin and albumin. α1-Microglobulin/albumin ratios were compared. Total cholesterol was measured in 50 patients on statin therapy.

RESULTS

In the 10 apparently healthy subjects, a significant temporary increase of α1-microglobulin, albumin and α1-microglobulin/albumin ratio was observed after statin intake. In the group of 532 patients showing micro-albuminuria, those treated with statins showed a significantly higher mean urinary α1-microglobulin/albumin ratio then untreated patients. Urinary albumin concentrations were significantly higher in patients taking simvastatin than in patients on rosuvastatin treatment and they were also higher in patients on statin therapy with a total serum cholesterol concentration below 3.88 mmol/L than in patients with a total serum cholesterol concentration above 5.17 mmol/L.

CONCLUSIONS

Tubular proteinuria, caused by the use of statins, can be distinguished from glomerular proteinuria by a higher urinary α1-microglobulin/albumin ratio.

[Diagnostic value of cystatin C and neutrophil gelatinase-associated lipocalin in primary glomerulopathies]

AIM

To study an association between clinical and morphological evidence and the serum and daily urinary levels of cystatin C (CysC) and neutrophil gelatinase-associated lipocalin (NGAL) in patients with primary glomerulopathies.

SUBJECTS AND METHODS

The investigation included 104 patients; morphological examination showed minimal change disease in 15 (14.4%) patients, focal segmental glomerulosclerosis in 24 (23.1%), membrane nephropathy in 32 (30.8%), and IgA nephropathy (mesangioproliferative glomerulonephritis) in 33 (31.7%). The investigators analyzed the clinical type of nephropathy, performed conventional laboratory and instrumental examinations, and determined the level of CysC (by immunoturbodimetry) and NGAL (by enzyme immunoassay) in the serum and daily urine taken before kidney biopsy. The degree of glomerulosclerosis, tubulointerstititial sclerosis, and tubular atrophy was semiquantitatively estimated.

RESULTS

Urinary CysC and NGAL excretion correlated with the degree of glomerulosclerosis and proteinuria and the reduced glomerular filtration rate (GFR) regardless of the method of its determination. The urinary level of NGAL positively correlated with the degree of tubular atrophy. The GFR value determined from serum CysC and creatinine levels more precisely reflected the degree of glomerulosclerosis.

CONCLUSION

The tubulointerstitial compartment in primary glomerulopathies should be determined not only by morphological changes, but also by tubular function parameters by estimating the urinary excretion of biomarkers. The urinary content of CysC reflects tubular epithelial dysfunction whereas that of NGAL also characterizes tubular atrophy. To estimate the degree of glomerulosclerosis, it is more preferable to use the GFR calculated from the blood concentrations of CysC and creatinine, by keeping in mind clinical findings (using Chronic Kidney Disease Epidemiology Collaboration formula, 2012).

Analytical and biological validation of a multiplex immunoassay for acute kidney injury biomarkers

BACKGROUND

Acute kidney injury (AKI) is a dynamic process that can involve inflammatory, hypoxic, and structural changes to the kidney. We evaluated a multiplex panel of markers representing different AKI mechanisms as a tool to provide integrated assessment of AKI status in a single assay.

METHODS

Urinary cystatin C (CysC), neutrophil gelatinase-associated lipocalin (NGAL), kidney injury molecule-1 (KIM-1) and interleukin-18 (IL-18) were measured by multiplex electrochemiluminescence immunoassay. Analytical performance was compared to the biological and pathological variation of these markers in human samples.

RESULTS

Linearity was established over a 3- to 4-log range for all markers, which spanned the reference ranges established from healthy donors. Imprecision was below 15%, comparing favorably with the observed biological variation of these markers. Control patients fell within donor-derived reference ranges for most markers, but a subset of patients showed CysC and KIM-1 elevations in the absence of documented AKI.

CONCLUSION

The multiplex assay is reliable for simultaneous quantitation of CysC, IL-18, KIM-1 and NGAL in human urine, and performs at levels sufficient for clinical application. The observed differences in biological variability and baseline levels suggest that clinical strategies to detect AKI will need to vary depending upon the specific markers used.

[Exploration of early assessment of renal impairment in multiple myeloma]

OBJECTIVE

To investigate the value of serum cystatin C (Cys-C), urinary Cys-C, urinary retinol binding protein (RBP) and urinary neutrophil gelatinase-associated lipocalin (NGAL) in the early assessment of multiple myeloma (MM) and their characteristic changes in different pathological types of renal impairment.

METHODS

According to glomerular filtration rate (eGFR), the patients were divided into two groups, of which marked group A with normal renal function, the other marked group B with abnormal renal function. Sixty healthy subjects were chosen as control. Detection of the serum Cys-C, urinary RBP, urinary Cys-C, urinary NGAL, serum creatinine (Scr), urinary microalbumin (MAU) and urinary α1-microglobulin (α1-MG) were performed. Renal biopsy was carried out for patients who had abnormal serum Cys-C, urinary Cys-C, urinary RBP, urinary NGAL and were willing to accept further test.

RESULTS

Compared with healthy controls, the serum Cys-C, urinary RBP, urinary Cys-C, urinary NGAL of group A were significantly higher than that of healthy controls. Six group A patients received renal biopsy, and varying degrees of renal damage were discovered. The serum Cys-C, urinary RBP, urinary Cys-C and urinary NGAL positive rate were 66.7%, 66.7%, 66.7% and 83.3%, respectively. Of twenty-four cases received biopsy after abnormal examination results were shown, six turned out to be amyloidosis, twelve cast nephropathy (CN) and 6 monoclonal immunoglobulin deposition disease (MIDD). Compared with MIDD and amyloidosis, the urinary Cys-C and NGAL of the CN group are significantly higher (P < 0.05). Compared with CN and amyloidosis, urinary RBP of MIDD is significantly higher (P = 0.043). Compared with MIDD and CN, the MAU of amyloidosis is significantly higher (P = 0.006).

CONCLUSION

Compared with the conventional indicators, serum Cys-C, urinary Cys-C, RBP and NGAL are more sensitive in early assessment of MM patients with renal damage. The MAU is higher in amyloid, the urinary Cys-C and urinary NGAL are significantly elevated in CN, the urinary RBP is significantly elevated in MIDD.

Biomarkers of diabetic nephropathy, the present and the future

Diabetic nephropathy (DN) is a leading cause of end-stage renal disease. Searching for the perfect biomarker of DN has become the holy grail of nephrology since the burden of this disease is untenable. The only feasible way to tackle this health care crisis is by prevention and treatment in a mechanistically rational approach. Therefore, the discovery of a specific, reliable diagnostic and prognostic biomarker for DN is imperative. Part of the difficulty in finding such a marker is the complex pathogenesis of DN; it is clearly multifactorial and involves multiple genes, proteins, metabolic pathways, and environmental factors. In this review, we will discuss the latest findings in the use of genetic, protein, and metabolic markers of DN. Particular attention will be paid to the urinary biomarker as a noninvasive method to detect either morphological or biochemical changes in DN. Urinary protein and mRNA studies have focused on either the glomerular (podocyte-specific) or tubular components (matrix or injury-related) of the nephron. The virtues and pitfalls of using the podocyte as a biomarker will be discussed. The systems biology approach of biomarker discovery in the studies of genomics, transcriptomics, proteomics, and metabolomics will be explored. Despite significant numbers of new biomarkers described, most studies are limited by either their small sample size or their cross-sectional nature, so that the ability to predict future and severity of DN is lacking. In order to successfully search for the ideal, validated biomarker, we need to conduct large, prospective, multi-center trials enlisting both Type 1 and Type II diabetic patients with and without nephropathy for at least two decades.

The levels of circulating and urinary monocyte chemoattractant protein-1 are associated with chronic renal injury in obese men

BACKGROUND

Monocyte chemoattractant protein-1 (MCP-1) is a vital inflammatory marker of obesity. Whether obesity by itself increases the risk of chronic kidney injury and accelerates its progression is unknown. More importantly, it is unknown whether obesity could induce kidney injury by MCP-1.

METHODS

We enrolled 40 obese men and 26 healthy volunteers who served as controls. The degree of insulin resistance was evaluated by the homeostasis model assessment (HOMA-IR) method, and kidney function was determined based on the estimated glomerular filtration rate (eGFR), albuminuria, the concentration of serum cystatin C (S-CysC), and the urinary cystatin C to creatinine ratio (UCCR).

RESULTS

The obese subjects had significantly higher S-CysC concentration (1114±288 vs.962±169 mg/L, p=0.021) and a higher UCCR (3.5±1.6 vs. 2.5±0.8 μg/g, p=0.002) than those of controls. The concentration of circulating MCP-1 and the urinary MCP-1 to creatinine ratio (UMCR) were higher in the obese group and were correlated with fat mass and HOMA-IR. Using stepwise multiple linear regression analysis, circulating MCP-1 concentration was found to be independently associated with the amount of S-CysC. In addition, the UMCR was independently associated with the UCCR.

CONCLUSION

The concentrations of circulating and urinary monocyte chemoattractant protein-1 are associated with chronic renal injury in obese men.

Ubiquinone (coenzyme Q10) prevents renal mitochondrial dysfunction in an experimental model of type 2 diabetes

Cardiovascular benefits of ubiquinone have been previously demonstrated, and we administered it as a novel therapy in an experimental model of type 2 diabetic nephropathy. db/db and dbH mice were followed for 10 weeks, after randomization to receive either vehicle or ubiquinone (CoQ10; 10mg/kg/day) orally. db/db mice had elevated urinary albumin excretion rates and albumin:creatinine ratio, not seen in db/db CoQ10-treated mice. Renal cortices from db/db mice had lower total and oxidized CoQ10 content, compared with dbH mice. Mitochondria from db/db mice also contained less oxidized CoQ10(ubiquinone) compared with dbH mice. Diabetes-induced increases in total renal collagen but not glomerulosclerosis were significantly decreased with CoQ10 therapy. Mitochondrial superoxide and ATP production via complex II in the renal cortex were increased in db/db mice, with ATP normalized by CoQ10. However, excess renal mitochondrial hydrogen peroxide production and increased mitochondrial membrane potential seen in db/db mice were attenuated with CoQ10. Renal superoxide dismutase activity was also lower in db/db mice compared with dbH mice. Our results suggest that a deficiency in mitochondrial oxidized CoQ10 (ubiquinone) may be a likely precipitating factor for diabetic nephropathy. Therefore CoQ10 supplementation may be renoprotective in type 2 diabetes, via preservation of mitochondrial function.

Cystatin C in prediction of acute kidney injury: a systemic review and meta-analysis

BACKGROUND

Cystatin C (CysC) has been proposed as a filtration marker for the early detection of acute kidney injury (AKI); however, a wide range of its predictive accuracy has been reported.

STUDY DESIGN

Meta-analysis of diagnostic test studies.

SETTING & POPULATION

Various clinical settings of AKI, including patients after cardiac surgery, pediatric patients, and critically ill patients.

SELECTION CRITERIA

Computerized search of PubMed, Current Contents, CINAHL, and EMBASE from inception until November 15, 2010, was performed to identify potentially relevant articles. Inclusion criteria were studies investigating the diagnostic accuracy of CysC level to predict AKI. There were no language restrictions in the search.

INDEX TESTS

Increasing or increased serum CysC level or urinary CysC excretion.

REFERENCE TESTS

The outcome was the development of AKI, primarily based on serum creatinine level (definition varied across studies).

RESULTS

We analyzed data from 19 studies and 11 countries involving 3,336 patients. Of these studies, 13 could be included in the meta-analysis. Across all settings, the diagnostic OR for serum CysC level to predict AKI was 27.7 (95% CI, 12.8-59.8), with sensitivity and specificity of 0.86 and 0.82, respectively. The area under the receiver operating characteristic curve (AUROC) of serum CysC levelto predict AKI was 0.87 (95% CI, 0.81-0.93). In an analysis excluding studies that did not clearly define the measurement time point, early serum CysC (within 24 hours after renal insult or intensive care unit admission) remained of diagnostic value. For the diagnostic value of urinary CysC excretion, the diagnostic OR was 3.10 (95% CI, 2.00-4.81), with sensitivity and specificity of0.61 and 0.67, respectively. TheAUROC of urinary CysC excretion to predict AKI was 0.67 (95% CI, 0.63-0.71) [corrected].

LIMITATIONS

Variation in criteria for definitions of index and reference tests, absence of measured glomerular filtration rate in most studies.

CONCLUSION

Serum CysC appears to be a good biomarker in the prediction of AKI, whereas urinary CysC excretion has only moderate diagnostic value.

Biomarkers for early detection of sickle nephropathy

Renal complications affect nearly 30-50% of adults with sickle cell anemia (SCA), causing significant morbidity and mortality. Standard renal function tests like serum creatinine and glomerular filtration rate become abnormal in this disease only when renal damage has become extensive and largely irreversible. Moreover, not all patients develop sickle nephropathy (SN). Therefore, noninvasive biomarkers that predict early onset of SN are necessary. We performed a cross-sectional analysis for nephropathy in 116 patients with sickle cell disease, analyzing urinary kidney injury molecule-1 (KIM-1), liver-type fatty acid binding protein (L-FABP), N-acetyl-b-D-glucosaminidase (NAG), neutrophil gelatinase-associated lipocalin (NGAL) and transforming growth factor-β1 (TGF-β), together with conventional renal biomarkers (urine albumin and osmolality, and serum creatinine and cystatin C estimated GFR) during routine clinic visits when patients were at steady-state/baseline. We observed a distinct biomarker pattern: KIM-1 and NAG emerged as biomarkers with a strong association with albuminuria. Surprisingly, and in contrast to other acute/chronic renal disorders, NGAL, L-FABP, and TGF-β levels did not show any relationship with albuminuria in patients with SCA. Our study identifies potential biomarkers for SN, and suggests longitudinal validation of these biomarkers for early detection of SN, so that therapeutic interventions can be applied before renal damage becomes irreversible.

Urine cystatin C as a biomarker of proximal tubular function immediately after kidney transplantation

BACKGROUND/AIMS

Clinical methods to predict allograft function soon after kidney transplantation are ineffective.

METHODS

We analyzed urine cystatin C (CyC) in a prospective multicenter observational cohort study of deceased-donor kidney transplants to determine its peritransplant excretion pattern, utility for predicting delayed graft function (DGF) and association with 3-month graft function. Serial urine samples were collected for 2 days following transplant and analyzed blindly for CyC. We defined DGF as any hemodialysis in the first week after transplant, slow graft function (SGF) as a serum creatinine reduction < 70% by the first week and immediate graft function (IGF) as a reduction ≥ 70%.

RESULTS

Of 91 recipients, 33 had DGF, 34 had SGF and 24 had IGF. Urine CyC/urine creatinine was highest in DGF for all time-points. The area under the curve (95% CI) for predicting DGF at 6 h was 0.69 (0.57-0.81) for urine CyC, 0.74 (0.62-0.86) for urine CyC/urine creatinine and 0.60 (0.45-0.75) for percent change in urine CyC. On the first postoperative day, urine CyC/urine creatinine and percent change in urine CyC were associated with 3-month graft function.

CONCLUSION

Urine CyC on the day after transplant differs between degrees of perioperative graft function and modestly corresponds with 3-month function.

Urinary cystatin C as a biomarker for acute kidney injury and its immunohistochemical localization in kidney in the CDDP-treated rats

Cystatin C, a cysteine protease inhibitor, is a novel biomarker of renal damage. In the present study, we examined the urinary and plasma levels of cystatin C and how useful they are for the early detection of acute kidney injury (AKI) in CDDP-treated rats in comparison with other biomarkers (β2-microglobulin, calbindin, clusterin, EGF, GST-α, GST-μ, KIM-1, NGAL, osteopontin, TIMP-1, and VEGF). The urinary levels of cystatin C, GST-α, KIM-1, and EGF changed prior to proximal tubule damage and increases in plasma urea nitrogen and creatinine levels, suggesting their usefulness for predicting AKI. On the other hand, the plasma cystatin C level hardly changed. We also investigated the localization of cystatin C in the kidney according to the progression of renal damage. Cystatin C was predominantly localized in the proximal tubule of the cortex, and its immunohistochemical expression was not affected by CDDP treatment. In addition, cystatin C was observed in the lumen of the renal tubule in the cortex, cortico-medullary junction, and medulla during the progression of renal damage, although its immunoreactive area ratio was very low. In conclusion, urinary cystatin C measurements can detect CDDP-induced AKI as early as KIM-1, GST-α, and EGF in rats, although the change ratio of the cystatin C was smaller than others. Immunohistochemical cystatin C expression in the proximal tubule of the kidney was hardly changed by the CDDP treatment, but it was newly observed in the renal tubule lumen after CDDP treatment.

Cystatin C as an early biomarker of nephropathy in patients with type 2 diabetes

This study was done to evaluate clinical usefulness of cystatin C levels of serum and urine in predicting renal impairment in normoalbuminuric patients with type 2 diabetes and to evaluate the association between albuminuria and serum/urine cystatin C. Type 2 diabetic patients (n = 332) with normoalbuminuria (n = 210), microalbuminuria (n = 83) and macroalbuminuria (n = 42) were enrolled. Creatinine, urinary albumin levels, serum/urine cystatin C and estimated glomerular filtration rate (eGFR by MDRD [Modification of Diet in Renal Disease] and CKD-EPI [Chronic Kidney Disease Epidemiology Collaboration] equations) were determined. The cystatin C levels of serum and urine increased with increasing degree of albuminuria, reaching higher levels in macroalbuminuric patients (P < 0.001). In multiple regression analysis, serum cystatin C was affected by C-reactive protein (CRP), sex, albumin-creatinine ratio (ACR) and eGFR. Urine cystatin C was affected by triglyceride, age, eGFR and ACR. In multivariate logistic analysis, cystatin C levels of serum and urine were identified as independent factors associated with eGFR < 60 mL/min/1.73 m(2) estimated by MDRD equation in patients with normoalbuminuria. On the other hand, eGFR < 60 mL/min/1.73 m(2) estimated by CKD-EPI equation was independently associated with low level of high-density lipoprotein in normoalbuminuric patients. The cystatin C levels of serum and urine could be useful markers for renal dysfunction in type 2 diabetic patients with normoalbuminuria.