Are Urinary Tubular Injury Markers Useful in Chronic Kidney Disease? A Systematic Review and Meta Analysis

Clinical Impacts of Urinary Neutrophil Gelatinase-Associated Lipocalin in Patients With Chronic Kidney Disease Undergoing Percutaneous Coronary Intervention

BACKGROUND

Chronic kidney disease (CKD) is associated with poor prognosis in patients undergoing percutaneous coronary intervention (PCI). Urinary neutrophil gelatinase-associated lipocalin (NGAL) is a biomarker for renal injury. However, the association between urinary NGAL concentrations and renal and cardiovascular events in patients with CKD undergoing PCI has not been elucidated. This study investigated the clinical impact of urinary NGAL concentrations on renal and cardiovascular outcomes in patients with non-dialysis CKD undergoing PCI.

METHODS AND RESULTS

We enrolled 124 patients with non-dialysis CKD (estimated glomerular filtration rate <60 mL/min/1.73 m2) undergoing elective PCI. Patients were divided into low and high NGAL groups based on the median urinary NGAL concentration measured the day before PCI. Patients were monitored for renal and cardiovascular events during the 2-year follow-up period. Kaplan-Meier analyses showed that the incidence of renal and cardiovascular events was higher in the high than low NGAL group (log-rank P<0.001 and P=0.032, respectively). Multivariate Cox proportional hazards analyses revealed that urinary NGAL was an independent risk factor for renal (hazard ratio [HR] 4.790; 95% confidence interval [CI] 1.537-14.924; P=0.007) and cardiovascular (HR 2.938; 95% CI 1.034-8.347; P=0.043) events.

CONCLUSIONS

Urinary NGAL could be a novel and informative biomarker for predicting subsequent renal and cardiovascular events in patients with CKD undergoing elective PCI.

External Validation of a Urinary Biomarker Risk Score for the Prediction of Steroid Responsiveness in Adults With Nephrotic Syndrome

Introduction

In idiopathic nephrotic syndrome, response to corticosteroids remains the best indicator of prognosis. Noninvasive markers to predict a patient's response to steroids would allow improved prognostication and a more personalized approach to management. We have previously derived a urinary biomarker risk score which can differentiate steroid sensitive nephrotic syndrome (SSNS) from steroid resistant nephrotic syndrome (SRNS) in children. The goal of this study was to validate this previously derived biomarker risk score in a cohort of steroid-naïve adult patients, to determine whether the panel could be used to predict steroid responsiveness at the time of initial diagnosis.

Methods

In this external validation study, clinical data, and urinary specimens (obtained before initiation of steroid treatment) from adult patients were used in the Nephrotic Syndrome Study Network (NEPTUNE) cohort. A panel of 5 previously identified and validated urinary biomarkers, including neutrophil gelatinase-associated lipocalin (NGAL), vitamin D binding protein (VDBP), Fetuin-A (FetA), Transthyretin (TTR), and alpha-1 acid glycoprotein 2 (AGP2) was measured. A summary risk score for steroid resistance was calculated based on biomarker concentrations. Receiver operating characteristic curves were created for each log-transformed biomarker concentration and for the individual and combined biomarker risk score.

Results

The urine biomarker risk score predicted development of steroid resistance, with optimal sensitivity and specificity of 0.74, and area under the receiver operating characteristic curve (AUC) of 0.79 using both absolute and creatinine-corrected concentrations.

Conclusion

This study validates the previously derived urinary biomarker risk score to predict steroid resistance in adult patients with nephrotic syndrome at initial diagnosis.

The Review of Current Knowledge on Neutrophil Gelatinase-Associated Lipocalin (NGAL)

Neutrophil gelatinase-associated lipocalin (NGAL) is a 25-kDa protein that is secreted mostly by immune cells such as neutrophils, macrophages, and dendritic cells. Its production is stimulated in response to inflammation. The concentrations of NGAL can be measured in plasma, urine, and biological fluids such as peritoneal effluent. NGAL is known mainly as a biomarker of acute kidney injury and is released after tubular damage and during renal regeneration processes. NGAL is also elevated in chronic kidney disease and dialysis patients. It may play a role as a predictor of the progression of renal function decreases with complications and mortality due to kidney failure. NGAL is also useful in the diagnostic processes of cardiovascular diseases. It is highly expressed in injured heart tissue and atherosclerostic plaque; its serum concentrations correlate with the severity of heart failure and coronary artery disease. NGAL increases inflammatory states and its levels rise in arterial hypertension, obesity, diabetes, and metabolic complications such as insulin resistance, and is also involved in carcinogenesis. In this review, we present the current knowledge on NGAL and its involvement in different pathologies, especially its role in renal and cardiovascular diseases.

Effects of dietary phosphorus concentration and phosphate salt form on renal tubule function in unilateral nephrectomized rats

Background: Excessive consumption of phosphorus (P) impairs renal tubule function; however, the effects of different dietary phosphate salts on chronic kidney disease (CKD) are unclear. Aim: To examine the effects of potassium dihydrogen phosphate (KH2PO4) and potassium tripolyphosphate (K5P3O10) and P concentration on renal function in a rat model of early CKD. Methods: Male sham-operated Sprague-Dawley rats were fed a diet containing KH2PO4 with a normal P level. Kidney injury was induced by unilateral nephrectomy (UNx), and the rats were divided into four groups fed dietary KH2PO4 or K5P3O10 with a normal (UNx-NKH, UNx-NKP) or high (UNx-HKH, UNx-HKP) P concentration, respectively, for 21 days. Results: UNx-NKH rats showed significantly lower creatinine clearance (CCr) and higher albumin (ALB) compared with those of sham rats, confirming UNx-induced kidney injury. The urinary levels of liver-type fatty acid-binding protein (L-FABP) and ALB were significantly higher in UNx-HKP rats than in UNx-HKH rats. However, other markers of renal tubule function, such as CCr, serum creatinine (CRE), calcium (Ca), and hormones, only differed among groups according to the P concentration and not the dietary phosphate salt form. Histological examination showed higher incidence and severity of tubulointerstitial lesions, tubule regeneration, tubule dilation, and calcification in the high-phosphorus than in the normal-phosphorus UNx groups. These changes were more severe in the UNx-HKP group compared with the UNx-HKH group. Conclusion: This study highlights the importance of controlling dietary P intake in terms of both concentration and source to prevent the progression of CKD.

Nonsteroidal Mineralocorticoid Receptor Antagonism by Finerenone-Translational Aspects and Clinical Perspectives across Multiple Organ Systems

Perception of the role of the aldosterone/mineralocorticoid receptor (MR) ensemble has been extended from a previously renal epithelial-centered focus on sodium and volume homeostasis to an understanding of their role as systemic modulators of reactive oxygen species, inflammation, and fibrosis. Steroidal MR antagonists (MRAs) are included in treatment paradigms for resistant hypertension and heart failure with reduced ejection fraction, while more recently, the nonsteroidal MRA finerenone was shown to reduce renal and cardiovascular outcomes in two large phase III trials (FIDELIO-DKD and FIGARO-DKD) in patients with chronic kidney disease and type 2 diabetes, respectively. Here, we provide an overview of the pathophysiologic role of MR overactivation and preclinical evidence with the nonsteroidal MRA finerenone in a range of different disease models with respect to major components of the aggregate mode of action, including interfering with reactive oxygen species generation, inflammation, fibrosis, and hypertrophy. We describe a time-dependent effect of these mechanistic components and the potential modification of major clinical parameters, as well as the impact on clinical renal and cardiovascular outcomes as observed in FIDELIO-DKD and FIGARO-DKD. Finally, we provide an outlook on potential future clinical indications and ongoing clinical studies with finerenone, including a combination study with a sodium-glucose cotransporter-2 inhibitor.

Kidney Injury Molecule 1 (KIM-1): a Multifunctional Glycoprotein and Biological Marker (Review)

KIM-1 (kidney injury molecule 1) is a transmembrane glycoprotein also known as HAVcr-1 and TIM-1 belongs to the T-cell immunoglobulin and mucin domain family (TIM) of proteins. TIM glycoproteins are presented on the immune cells and participate in the regulation of immune reactions. KIM-1 differs from other members of its family in that it is expressed not only by immunocompetent cells but epithelial cells as well. Cellular and humoral effects mediated by KIM-1 are involved in a variety of physiological and pathophysiological processes.

Current understanding of the mechanisms determining the participation of KIM-1 in viral invasion, the immune response regulation, adaptive reactions of the kidney epithelium to acute ischemic or toxic injury, in progression of chronic renal diseases, and kidney cancer development have been presented in this review. Data of clinical researches demonstrating the association of KIM-1 with viral diseases and immune disorders have also been analyzed. Potential application of KIM-1 as urinary or serological marker in renal and cardiovascular diseases has been considered.

Evaluation of Radiographic Contrast-Induced Nephropathy by Functional Diffusion Weighted Imaging

Contrast-induced nephropathy (CIN) resembles an important complication of radiographic contrast medium (XCM) displayed by a rise in creatinine levels 48-72 h after XCM administration. The purpose of the current study was to evaluate microstructural renal changes due to CIN in high-risk patients by diffusion weighted (DWI) and diffusion tensor imaging (DTI). Fifteen patients (five CIN and ten non-CIN) scheduled for cardiological intervention were included in the study. All patients were investigated pre- and post-intervention on a clinical 3T scanner. After anatomical imaging, renal DWI was performed by a paracoronal echo-planar-imaging sequence. Renal clinical routine serum parameters and advanced urinary injury markers were determined to monitor renal function. We observed a drop in cortical and medullar apparent diffusion coefficient (ADC) and fractional anisotropy (FA) before and after XCM administration in the CIN group. In contrast, the non-CIN group differed only in medullary ADC. The decrease of ADC and FA was apparent even before serum parameters of the kidney changed. In conclusion, DWI/DTI may be a useful tool for monitoring high-risk CIN patients as part of multi-modality based clinical protocol. Further studies, including advanced analysis of the diffusion signal, may improve the identification of patients at risk for CIN.

Dickkopf 3-a novel biomarker of the 'kidney injury continuum'

Chronic kidney disease (CKD) is a global public health problem accompanied by substantial comorbidities and reduced life expectancy. In this respect, progressive CKD leading to uraemia can be seen as a systemic disease with a critical impact on virtually all organ systems. Therefore, it is of particular importance to identify patients with ongoing CKD progression, which is challenging, because the individual course of CKD is difficult to predict. Patterns of progression in CKD patients include linear and non-linear trajectories of GFR loss, but kidney function can also remain stable for years. Moreover, a substantial GFR decline may occur in the absence of higher-grade albuminuria (non-proteinuric CKD), rendering the measurement of albuminuria less reliable for progression prediction in such individuals. In the present review, we focus on the recently identified glycoprotein Dickkopf-3 (DKK3) as a stress-induced, renal tubular epithelial cell-derived, pro-fibrotic molecule. In experimental CKD models, DKK3 promoted renal tubulointerstitial fibrosis through modulation of the canonical Wnt/β-catenin signalling pathway. In clinical studies, increased urinary DKK3 levels identified patients at high risk for short-term CKD progression, regardless of the cause of kidney disease, baseline kidney function and albuminuria. Moreover, increased urinary DKK3 levels are associated with a high risk for acute kidney injury and the subsequent loss of kidney function after cardiac surgery. These findings highlight DKK3 as a mediator of renal tubular cell damage in kidney injury and short-term progression of kidney disease, with potential therapeutic implications.

Precision medicine in diabetic nephropathy and chronic kidney disease

Progressive chronic kidney disease (CKD) in individuals with type 2 diabetes mellitus is a global public health problem accompanied by substantial comorbidities and reduced life expectancy. In this respect, CKD leading to uremia can be seen as a systemic disease with a critical impact on virtually all organ systems. Thus it is of particular importance to identify patients with incipient CKD and ongoing CKD progression, but the individual course of CKD is challenging to predict. Patterns of progression in persons with CKD include linear and nonlinear trajectories of glomerular filtration rate (GFR) loss. Kidney function can also remain stable for years, especially in the elderly. In particular, one-fifth of individuals show a substantial GFR decline in the absence of high albuminuria (nonproteinuric CKD), rendering albuminuria less suitable for predicting the progression in such individuals.

Kidney function and markers of renal damage after renal denervation. Does method of measurement matter? The Reshape CV-Risk Study

Data suggest that renal denervation (RDN) in treatment‐resistant hypertension (TRHT) is safe in terms of renal function. However, most studies report kidney function as creatinine‐based estimated glomerular filtration rate (eGFR), which may be biased by non‐renal factors. Damage markers other than albuminuria have never been evaluated after RDN. In this non‐randomized RDN trial, we studied changes in kidney function, assessed as measured GFR (mGFR) and various GFR estimates, six months and two years after RDN. We also examined changes in albuminuria and a biomarker of tubular dysfunction. Adult non‐diabetic patients with TRHT and eGFR ≥45 ml/min/1.73 m² were recruited from hypertension clinics. Before bilateral RDN, mGFR was measured by iohexol clearance. We estimated eGFR from serum creatinine and cystatin C (eGFR_crea, eGFR_cys, and eGFR_creacys), and albumin‐creatinine ratio (ACR) and N‐acetyl‐β‐D‐glucosaminidase (NAG)‐creatinine ratio (NAG‐CR) were measured in spot urines. All measurements were repeated after six and twenty‐four months.

Twenty patients, mean age 54 (±9) years and baseline mGFR 83 (±20) ml/min/1.73 m² underwent RDN. After six months, mGFR fell, eGFR_crea remained unchanged, whereas eGFR_cys and eGFR_creacys increased. At 2 years’ follow‐up, eGFR_creacys was significantly lower than at baseline. mGFR was 78 (±28) ml/min/1.73 m². Change in ambulatory systolic BP predicted change in eGFR_crea. Urinary NAG‐CR, but not ACR, increased during follow‐up.

Different GFR assessments gave diverging results after RDN. Therefore, care should be taken to method when evaluating kidney function after RDN. Increases in a tubular dysfunction biomarker suggest that kidney damage may occur. Long‐term renal follow‐up is needed after RDN.

A Review of Specific Biomarkers of Chronic Renal Injury and Their Potential Application in Nonclinical Safety Assessment Studies

A host of novel renal biomarkers have been developed over the past few decades which have enhanced monitoring of renal disease and drug-induced kidney injury in both preclinical studies and in humans. Since chronic kidney disease (CKD) and acute kidney injury (AKI) share similar underlying mechanisms and the tubulointerstitial compartment has a functional role in the progression of CKD, urinary biomarkers of AKI may provide predictive information in chronic renal disease. Numerous studies have explored whether the recent AKI biomarkers could improve upon the standard clinical biomarkers, estimated glomerular filtration rate (eGFR), and urinary albumin to creatinine ratio, for predicting outcomes in CKD patients. This review is an introduction to alternative assays that can be utilized in chronic (>3 months duration) nonclinical safety studies to provide information on renal dysfunction and to demonstrate specific situations where these assays could be utilized in nonclinical drug development. Novel biomarkers such as symmetrical dimethyl arginine, dickkopf homolog 3, and cystatin C predict chronic renal injury in animals, act as surrogates for GFR, and may predict changes in GFR in patients over time, ultimately providing a bridge from preclinical to clinical renal monitoring.

Urine Neutrophil Gelatinase-associated Lipocalin (NGAL) for Prediction of Persistent AKI and Major Adverse Kidney Events

We aimed to determine whether urinary neutrophil gelatinase-associated lipocalin (uNGAL) can accurately predict persistent AKI, major adverse kidney events at 30 days (MAKE30) and 365 days (MAKE365) in hospitalized AKI patients. This is a retrospective study of adult patients who were admitted at King Chulalongkorn Memorial Hospital. We performed multivariable logistic regression for persistent AKI, MAKE30, and MAKE365. We developed equations for predicting MAKE30 and MAKE365 and divided the dataset into derivation and validation cohorts. uNGAL performance and predictive models were assessed using the area under the receiver operating characteristic curve (AROC). Among 1,322 patients with AKI, 76.9%, 45.1%, and 61.7% had persistent AKI, MAKE30, and MAKE365. The AROC were 0.75 (95% confidence interval[CI] 0.70–0.80), 0.66 (95%CI 0.61–0.71), and 0.64 (95%CI 0.59–0.70) for prediction of persistent AKI, MAKE30, and MAKE365 by uNGAL. The AROC in the validation dataset combining uNGAL with clinical covariates were 0.74 (95%CI 0.69–0.79) and 0.72 (95%CI 0.67–0.77) for MAKE30 and MAKE365. We demonstrated an association between uNGAL and persistent AKI, MAKE30, and MAKE365. Prediction models combining uNGAL can modestly predict MAKE30 and MAKE365. Therefore, uNGAL is a useful tool for improving AKI risk stratification.

Rapid Progression of Autosomal Dominant Polycystic Kidney Disease: Urinary Biomarkers as Predictors

BACKGROUND

Markers currently used to predict the likelihood of rapid disease progression in patients with autosomal dominant polycystic kidney disease (ADPKD) are expensive and time consuming to assess and often have limited sensitivity. New, easy-to-measure markers are therefore needed that alone or in combination with conventional risk markers can predict the rate of disease progression. In the present study, we investigated the ability of tubular damage and inflammation markers to predict kidney function decline.

METHODS

At baseline, albumin, immunoglobulin G, kidney injury molecule 1, β2 microglobulin (β2MG), heart-type fatty acid-binding protein, neutrophil gelatinase-associated lipocalin, and monocyte chemotactic protein-1 -(MCP-1) were measured in 24-h urine samples of patients participating in a study investigating the therapeutic efficacy of lanreotide in ADPKD. Individual change in estimated glomerular filtration rate (eGFR) during follow-up was calculated using mixed-model analysis taking into account 13 -eGFRs (chronic kidney disease EPIdemiology) per patient. Logistic regression analysis was used to select urinary biomarkers that had the best association with rapidly progressive disease. The predictive value of these selected urinary biomarkers was compared to other risk scores using C-statistics.

RESULTS

Included were 302 patients of whom 53.3% were female, with an average age of 48 ± 7 years, eGFR of 52 ± 12 mL/min/1.73 m2, and a height-adjusted total kidney volume (htTKV) of 1,082 (736-1,669) mL/m. At baseline, all urinary damage and inflammation markers were associated with baseline eGFR, also after adjustment for age, sex and baseline htTKV. For longitudinal analyses only patients randomized to standard care were considered (n = 152). A stepwise backward analysis revealed that β2MG and MCP-1 showed the strongest association with rapidly progressive disease. A urinary biomarker score was created by summing the ranking of tertiles of β2MG and MCP-1 excretion. The predictive value of this urinary biomarker score was higher compared to that of the Mayo htTKV classification (area under the curve [AUC] 0.73 [0.64-0.82] vs. 0.61 [0.51-0.71], p = 0.04) and comparable to that of the predicting renal outcomes in -ADPKD score (AUC 0.73 [0.64-0.82] vs. 0.65 [0.55-0.75], p = 0.18). In a second independent cohort with better kidney function, similar results were found for the urinary biomarker score.

CONCLUSION

Measurement of urinary β2MG and MCP-1 excretion allows selection of ADPKD patients with rapidly progressive disease, with a predictive value comparable to or even higher than that of TKV or PKD mutation. Easy and inexpensive to measure urinary markers therefore hold promise to help predict prognosis in ADPKD.

IL-18, VCAM-1 and P-selectin as early biomarkers in normoalbuminuric Type 2 diabetes patients

Aim: To investigate the pathophysiological role of different biomarkers in diabetic kidney disease (DKD) among normoalbuminuric patients with a low-estimated glomerular filtration rate (eGFR). Methods: In this cross-sectional study of 200 normoalbuminuric Type 2 diabetes patients, 28 patients (14%) had a low eGFR. Results: The IL-18, VCAM-1 and P-selectin levels were significantly higher at a low eGFR. On analyzing the area under the receiver operating characteristic curve, these biomarkers had significant diagnostic value and have important pathophysiological role in the progression of DKD. Conclusion: Among normoalbuminuric Type 2 diabetes patients, IL-18, VCAM-1 and P-selectin may play a significant role in the prediction of early DKD. Further prospective studies need to be conducted to confirm this observation.

Urinary Biomarkers of Renal Fibrosis

Renal fibrosis is the common pathological pathway of progressive CKD. The commonly used biomarkers in clinical practice are not optimal to detect injury or predict prognosis. Therefore, it is crucial to develop novel biomarkers to allow prompt intervention. Urine serves as a valuable resource of biomarker discovery for kidney diseases. Owing to the rapid development of omics platforms and bioinformatics, research on novel urinary biomarkers for renal fibrosis has proliferated in recent years. In this chapter, we discuss the current status and provide basic knowledge in this field. We present novel promising biomarkers including tubular injury markers, proteins related to activated inflammation/fibrosis pathways, CKD273, transcriptomic biomarkers, as well as metabolomic biomarkers. Furthermore, considering the complex nature of the pathogenesis of renal fibrosis, we also highlight the combination of biomarkers to further improve the diagnostic and prognostic performance.

Novel glomerular filtration markers

Chronic kidney disease is currently assessed by estimated glomerular filtration rate, a mathematical construct based on creatinine or creatinine and cystatin concentration. Creatinine-based equations have improved with standardization efforts and the Modification of Diet in Renal Disease Study (MDRD) and CKD-Epidemiology Collaboration Study (CKD-EPI). Because the measurement of creatinine is subject to interference from non-GFR determinants, alternative markers have long been sought. These have included cystatin C and low molecular weight proteins like β2-microglobulin and beta trace protein. Tubular disease often occurs before glomerular filtration is impaired and investigators have investigated the excretion of other low molecular weight proteins such as Neutrophil Gelatinase-Associated Lipocalin (NGAL) and Kidney Injury Molecule-1 and N-acetyl-β-d-glucosaminidase. While preliminary, there is some evidence linking these analytes with GFR, disease stage and mortality. Although asymmetrical dimethyl arginine, an inhibitor of nitric oxide, has been shown to be associated with progression of renal disease, symmetric dimethyl arginine may be a better marker. Recent work has also explored the potential of microRNA (miRNA) analysis and metabolomics studies to further elucidate this complex pathophysiologic disease process. Investigators hope to improve our ability to detect CKD by the use of test panels, i.e., various marker combinations thereof. Unfortunately, most of these markers lack standardization unlike traditional measures that rely on creatinine and cystatin C measurement.

Prospective assessment of urinary neutrophil gelatinase-associated lipoprotein in living kidney donors: toward understanding differences between chronic kidney diseases of surgical and medical origin

OBJECTIVES

To evaluate the clinical implications of postoperative urinary neutrophil gelatinase-associated lipoprotein (NGAL) changes and the association between urinary NGAL (uNGAL) and renal function in living kidney donors.

SUBJECTS, PATIENTS AND METHODS

We included 76 healthy adults who underwent donor nephrectomy between December 2013 and November 2014. Perioperative serum creatinine (sCr), uNGAL, serum NGAL (sNGAL), and urinary microalbumin were prospectively measured until 6 months postoperatively. Patients with chronic kidney disease (CKD) due to medical disorders who visited our outpatient clinic during the same period were included for comparison.

RESULTS

The mean (SD) preoperative uNGAL of donors was 5 (5.17) ng/mL. uNGAL (corrected for urinary creatinine) was maximal at 1-2 days postoperatively, decreased on postoperative day 3, and stabilised by 7 days after surgery. Postoperative uNGAL was not associated with sex, age, or preoperative renal function. When corrected for sNGAL to compensate for the systemic increase in NGAL with major surgery, uNGAL on days 1-3 postoperatively was negatively correlated with sCr. Postoperatively, donor uNGAL remained higher than preoperatively for up to 6 months but was significantly lower than in patients with medical CKD with similar glomerular filtration rates.

CONCLUSION

Acute kidney injury due to hyperfiltration of remnant kidney after donor nephrectomy was maximal within 1-2 days postoperatively. The rise in uNGAL during this period in donors was negatively correlated with postoperative sCr levels. Decreased renal function after nephrectomy differs from that of medical CKD.

Dickkopf-3 (DKK3) in Urine Identifies Patients with Short-Term Risk of eGFR Loss

BACKGROUND

The individual course of CKD may vary, and improved methods for identifying which patients will experience short-term eGFR loss are needed. Assessing urinary Dickkopf-3 (DKK3), a stress-induced tubular epithelia-derived profibrotic glycoprotein, may provide information about ongoing tubulointerstitial fibrosis and short-term eGFR loss.

METHODS

To investigate urinary DKK3's potential as a biomarker of short-term eGFR loss (over 12 months), we prospectively assessed eGFR and urinary DKK3 levels in patients with CKD of various etiologies at baseline and annual follow-ups. We also measured urinary DKK3 in a general population sample and patients with diagnostic kidney biopsies or IgA nephropathy under treatment.

RESULTS

Median urinary DKK3-to-creatinine concentration at baseline was significantly higher in patients with CKD than the general population sample (431 versus 33 pg/mg). In the CKD cohort, having a urinary DKK3-to-creatinine level >4000 pg/mg was independently and significantly associated after multiple adjustments with mean annual decline in eGFR of 7.6% over 12 months. Urinary DKK3 significantly improved prediction of kidney function decline compared with eGFR or albuminuria alone. Urinary DKK3-to-creatinine levels were related to the extent of tubulointerstitial fibrosis in kidney biopsies. In patients with IgA nephropathy, a rise in urinary DKK3 was associated with significant eGFR decline within 6 months, whereas stable or decreasing urinary DKK3 indicated a more favorable course.

CONCLUSIONS

Urinary DKK3 levels identify patients at high risk for eGFR decline over the next 12 months regardless of the cause of kidney injury and beyond established biomarkers, potentially providing a tool to monitor CKD progression and assess effects of interventions.

Urinary kidney injury molecule-1 in renal disease

Kidney injury molecule-1 (KIM-1), a type l transmembrane glycoprotein, is recognized as a potential biomarker for detection of tubular injury in the main renal diseases. Urinary KIM-1 increases rapidly upon the tubular injury, and its levels are associated with the degree of tubular injury, interstitial fibrosis, and inflammation in the injured kidney. Currently, the investigation of kidney diseases is usually performed through the assessment of serum creatinine and urinary albumin. However, these biomarkers are limited for the early detection of changes in renal function. Besides, the tubular injury appears to precede glomerular damage in the pathophysiology of renal diseases. For these reasons, the search for sensitive, specific and non-invasive biomarkers is of interest. Therefore, the purpose of this article is to review the physiological mechanisms of KIM-1, as well to present clinical evidence about the association between elevated urinary KIM-1 levels and the main renal diseases such as chronic kidney disease, diabetic kidney disease, acute kidney injury, and IgA nephropathy.

Role of Kidney Biopsies for Biomarker Discovery in Diabetic Kidney Disease

Although estimated glomerular filtration rate and albuminuria are well-established biomarkers of diabetic kidney disease (DKD), additional biomarkers are needed, especially for the early stages of the disease when both albuminuria and estimated glomerular filtration rate may still be in the normal range and are less helpful for identifying those at risk of progression. Traditional biomarker studies for early DKD are challenging because of a lack of good early clinical end points, and most rely on changes in existing imprecise biomarkers to assess the value of new biomarkers. There are well-characterized changes in kidney structure, however, that are highly correlated with kidney function, always precede the clinical findings of DKD and, at preclinical stages, predict DKD progression. These structural parameters may thus serve as clinically useful end points for identifying new biomarkers of early DKD. In addition, investigators are analyzing tissue transcriptomic data to identify pathways involved in early DKD which may have associated candidate biomarkers measurable in blood or urine, and differentially expressed microRNAs and epigenetic modifications in kidney tissue are beginning to yield important observations which may be useful in identifying new clinically useful biomarkers. This review examines the emerging literature on the use of kidney tissue in biomarker discovery in DKD.

Analytical validation of Gentian NGAL particle-enhanced enhanced turbidimetric immunoassay (PETIA)

Objectives

This study was designed to validate the analytical performance of the new Gentian particle-enhanced enhanced turbidimetric immunoassay (PETIA) for measuring neutrophil gelatinase-associated lipocalin (NGAL) in serum samples.

Design and methods

Analytical validation of the Gentian NGAL assay was carried out on a Roche Cobas c501 and was based on assessment of limit of blank (LOB), limit of detection (LOD), functional sensitivity, imprecision, linearity and concordance with the BioPorto NGAL test.

Results

The LOB and LOD of Gentian NGAL were found to be 3.8 ng/mL and 6.3 ng/mL, respectively. An analytical coefficient of variation (CV) of 20% corresponded to a NGAL value of 10 ng/mL. The intra-assay and inter-assay imprecision (CV) was between 0.4 and 5.2% and 0.6 and 7.1% and the total imprecision (CV) was 3.7%. The linearity was optimal at NGAL concentrations between 37 and 1420 ng/mL (r=1.00; p<0.001). An excellent correlation was observed between values measured with Gentian NGAL and BioPorto NGAL in 74 routine serum samples (r=0.993). The mean percentage bias of the Gentian assay versus the Bioporto assay was +3.1% (95% CI, +1.6% to +4.5%).

Conclusions

These results show that Gentian NGAL may be a viable option to other commercial immunoassays for both routine and urgent assessment of serum NGAL.

Performance of urinary kidney injury molecule-1, neutrophil gelatinase-associated lipocalin, and N-acetyl-β-D-glucosaminidase to predict chronic kidney disease progression and adverse outcomes

Urinary biomarkers can predict the progression of chronic kidney disease (CKD). In this study, kidney injury molecule-1 (KIM-1), neutrophil gelatinase-associated lipocalin (NGAL), and N-acetyl-β-D-glucosaminidase (NAG) were correlated with the stages of CKD, and the association of these biomarkers with CKD progression and adverse outcomes was determined. A total of 250 patients, including 111 on hemodialysis, were studied. Urinary KIM-1, NGAL, and NAG were measured at baseline. Patients not on dialysis at baseline who progressed to a worse CKD stage were compared with those who did not progress. The association of each biomarker and selected covariates with progression to more advanced stages of CKD, end-stage kidney disease, or death was evaluated by Poisson regression. NGAL was moderately correlated (r^s=0.467, P<0.001) with the five stages of CKD; KIM-1 and NAG were also correlated, but weakly. Sixty-four patients (46%) progressed to a more advanced stage of CKD. Compared to non-progressors, those patients exhibited a trend to higher levels of KIM-1 (P=0.064) and NGAL (P=0.065). In patients not on dialysis at baseline, NGAL was independently associated with progression of CKD, ESKD, or death (RR=1.022 for 300 ng/mL intervals; CI=1.007-1.037, P=0.004). In patients on dialysis, for each 300-ng/mL increase in urinary NGAL, there was a 1.3% increase in the risk of death (P=0.039). In conclusion, urinary NGAL was associated with adverse renal outcomes and increased risk of death in this cohort. If baseline urinary KIM-1 and NGAL predict progression to worse stages of CKD is something yet to be explored.