Laura H. Mariani

Tissue transcriptome-driven identification of epidermal growth factor as a chronic kidney disease biomarker

Renal and urinary EGF can serve as biomarkers for prediction of outcomes in chronic kidney disease. Urine marker to the rescue Chronic kidney disease is a common medical problem worldwide, but it is difficult to predict which patients are more likely to progress to end-stage disease and need aggressive management. Ju et al. have now drawn on four independent cohorts totaling hundreds of patients from around the world to identify the expression of epidermal growth factor (EGF) in the kidneys as a marker of kidney disease progression. Moreover, the authors demonstrated that the amount of EGF in the urine is just as useful, providing a biomarker that can be easily tracked over time without requiring invasive biopsies. Chronic kidney disease (CKD) affects 8 to 16% people worldwide, with an increasing incidence and prevalence of end-stage kidney disease (ESKD). The effective management of CKD is confounded by the inability to identify patients at high risk of progression while in early stages of CKD. To address this challenge, a renal biopsy transcriptome-driven approach was applied to develop noninvasive prognostic biomarkers for CKD progression. Expression of intrarenal transcripts was correlated with the baseline estimated glomerular filtration rate (eGFR) in 261 patients. Proteins encoded by eGFR-associated transcripts were tested in urine for association with renal tissue injury and baseline eGFR. The ability to predict CKD progression, defined as the composite of ESKD or 40% reduction of baseline eGFR, was then determined in three independent CKD cohorts. A panel of intrarenal transcripts, including epidermal growth factor (EGF), a tubule-specific protein critical for cell differentiation and regeneration, predicted eGFR. The amount of EGF protein in urine (uEGF) showed significant correlation (P < 0.001) with intrarenal EGF mRNA, interstitial fibrosis/tubular atrophy, eGFR, and rate of eGFR loss. Prediction of the composite renal end point by age, gender, eGFR, and albuminuria was significantly (P < 0.001) improved by addition of uEGF, with an increase of the C-statistic from 0.75 to 0.87. Outcome predictions were replicated in two independent CKD cohorts. Our approach identified uEGF as an independent risk predictor of CKD progression. Addition of uEGF to standard clinical parameters improved the prediction of disease events in diverse CKD populations with a wide spectrum of causes and stages.

KDOQI US Commentary on the 2012 KDIGO Clinical Practice Guideline for Glomerulonephritis

Glomerulonephritis (GN) is an important cause of morbidity and mortality in patients of all ages throughout the world. Because these disorders are relatively rare, it is difficult to perform randomized clinical trials to define optimal treatment for many of the specific glomerulopathies. In the absence of high-grade evidence to guide the care of glomerular diseases, in June 2012, KDIGO (Kidney Disease: Improving Global Outcomes) published an international clinical guideline for GN. The Work Group report represents an important review of the literature in this area and offers valid and useful guidelines for the most common situations that arise in the management of patients with glomerular disease. This commentary, developed by a panel of clinical experts convened by the National Kidney Foundation, attempts to put the GN guideline into the context of the US health care system. Overall, we support the vast majority of the recommendations and highlight select areas in which epidemiological factors and medical practice patterns in this country justify modifications and adjustments in order to achieve favorable outcomes. There remain large gaps in our knowledge of the best approaches to treat glomerular disease and we strongly endorse an expanded clinical research effort to improve the health and long-term outcomes of children and adults with GN.

A reassessment of soluble urokinase-type plasminogen activator receptor in glomerular disease

It has been suggested that soluble urokinase receptor (suPAR) is a causative circulating factor for and a biomarker of focal and segmental glomerulosclerosis (FSGS). Here we undertook validation of these assumptions in both mouse and human models. Injection of recombinant suPAR in wild-type mice did not induce proteinuria within 24 hours. Moreover, a disease phenotype was not seen in an inducible transgenic mouse model that maintained elevated suPAR concentrations for 6 weeks. Plasma and urine suPAR concentrations were evaluated as clinical biomarkers in 241 patients with glomerular disease from the prospective, longitudinal multi-center observational NEPTUNE cohort. The serum suPAR concentration at baseline inversely correlated with estimated glomerular filtration rate (eGFR) and the urine suPAR/creatinine ratio positively correlated with the urine protein/creatinine ratio. After adjusting for eGFR and urine protein, neither the serum nor urine suPAR level was an independent predictor of FSGS histopathology. A multivariable mixed-effects model of longitudinal data evaluated the association between the change in serum suPAR concentration from baseline with eGFR. After adjusting for baseline suPAR concentration, age, gender, proteinuria and time, the change in suPAR from baseline was associated with eGFR, but this association was not different for patients with FSGS as compared to other diagnoses. Thus, these results do not support a pathological role for suPAR in FSGS.

Physical Performance and Frailty in Chronic Kidney Disease

Background: Poor physical performance and frailty are associated with elevated risks of death and disability. Chronic kidney disease (CKD) is also strongly associated with these outcomes. The risks of poor physical performance and frailty among CKD patients, however, are not well established. Methods: We measured the Short Physical Performance Battery (SPPB; a summary test of gait speed, chair raises and balance; range 0-12) and the five elements of frailty among 1,111 Chronic Renal Insufficiency Cohort participants. Adjusting for demographics and multiple comorbidities, we fit a linear regression model for the outcome of SPPB score and an ordinal logistic regression model for frailty status. Results: Median (interquartile range, IQR) age was 65 (57-71) years, median estimated glomerular filtration rate (eGFR) for non-dialysis patients was 49 (36-62) ml/min/1.73 m2, and median SPPB score was 9 (7-10). Seven percent of participants were frail and 43% were pre-frail. Compared with the SPPB score for eGFR >60 ml/min/1.73 m2, the SPPB was 0.51 points lower for eGFR 30-59; 0.61 points lower for eGFR 15-29, and 1.75 points lower for eGFR <15 (p < 0.01 for all comparisons). eGFR 30-59 (odds ratio, OR 1.45; p = 0.024), eGFR 15-29 (OR 2.02; p = 0.002) and eGFR <15 (OR 4.83; p < 0.001) were associated with worse frailty status compared with eGFR >60 ml/min/1.73 m2. Conclusions: CKD severity was associated with poor physical performance and frailty in a graded fashion. Future trials should determine if outcomes for CKD patients with frailty and poor physical performance are improved by targeted interventions.

Integrative Genomics Identifies Novel Associations with APOL1 Risk Genotypes in Black NEPTUNE Subjects

APOL1 variants have been associated with renal phenotypes in blacks. To refine clinical outcomes and discover mechanisms of APOL1-associated kidney injury, we analyzed clinical and genomic datasets derived from 90 black subjects in the Nephrotic Syndrome Study Network (NEPTUNE), stratified by APOL1 risk genotype. Ninety subjects with proteinuria ≥0.5 g/d were enrolled at first biopsy for primary nephrotic syndrome and followed. Clinical outcomes were determined, and renal histomorphometry and sequencing of Mendelian nephrotic syndrome genes were performed. APOL1 variants were genotyped, and glomerular and tubulointerstitial transcriptomes from protocol renal biopsy cores were analyzed for differential and correlative gene expression. Analyses were performed under the recessive model (high-risk genotype defined by two risk alleles). APOL1 high-risk genotype was significantly associated with a 17 ml/min per 1.73 m(2) lower eGFR and a 69% reduction in the probability of complete remission at any time, independent of histologic diagnosis. Neither APOL1 risk group was enriched for Mendelian mutations. On renal biopsy, high-risk genotype was associated with increased fractional interstitial area, interstitial fibrosis, and tubular atrophy. Risk genotype was not associated with intrarenal APOL1 mRNA expression levels. Differential expression analysis demonstrated an increased steady-state level of five genes associated with the high-risk genotype (CXCL9, CXCL11, and UBD in glomerulus; SNOR14B and MUC13 in tubulointerstitium). APOL1 tubulointerstitial coexpression analysis showed coexpression of APOL1 mRNA levels with a group of intrarenal transcripts that together were associated with increased interstitial fibrosis and tubular atrophy. These data indicate the high-risk APOL1 genotype confers renal risk across histopathologic diagnoses.

Dialysis versus Nondialysis in Patients with AKI: A Propensity-Matched Cohort Study

BACKGROUND AND OBJECTIVES The benefit of the initiation of dialysis for AKI may differ depending on patient factors, but, because of a lack of robust evidence, the decision to initiate dialysis for AKI remains subjective in many cases. Prior studies examining dialysis initiation for AKI have examined outcomes of dialyzed patients compared with other dialyzed patients with different characteristics. Without an adequate nondialyzed control group, these studies cannot provide information on the benefit of dialysis initiation. To determine which patients would benefit from initiation of dialysis for AKI, a propensity-matched cohort study was performed among a large population of patients with severe AKI. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS Adults admitted to one of three acute care hospitals within the University of Pennsylvania Health System from January 1, 2004, to August 31, 2010, who subsequently developed severe AKI were included (n=6119). Of these, 602 received dialysis. Demographic, clinical, and laboratory variables were used to generate a time-varying propensity score representing the daily probability of initiation of dialysis for AKI. Not-yet-dialyzed patients were matched to each dialyzed patient according to day of AKI and propensity score. Proportional hazards analysis was used to compare time to all-cause mortality among dialyzed versus nondialyzed patients across a spectrum of prespecified variables. RESULTS After propensity score matching, covariates were well balanced between the groups, and the overall hazard ratio for death in dialyzed versus nondialyzed patients was 1.01 (95% confidence interval, 0.85 to 1.21; P=0.89). Serum creatinine concentration modified the association between dialysis and survival, with a 20% (95% confidence interval, 9% to 30%) greater survival benefit from dialysis for each 1-mg/dl increase in serum creatinine concentration (P=0.001). This finding persisted after adjustment for markers of disease severity. Dialysis initiation was associated with more benefit than harm at a creatinine concentration ≥ 3.8 mg/dl. CONCLUSIONS Dialysis was associated with increased survival when initiated in patients with AKI who have a more elevated creatinine level but was associated with increased mortality when initiated in patients with lower creatinine concentrations.

Complete Remission in the Nephrotic Syndrome Study Network

BACKGROUND AND OBJECTIVES This analysis from the Nephrotic Syndrome Study Network (NEPTUNE) assessed the phenotypic and pathology characteristics of proteinuric patients undergoing kidney biopsy and defined the frequency and factors associated with complete proteinuria remission (CRever). DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS We enrolled adults and children with proteinuria ≥0.5 g/d at the time of first clinically indicated renal biopsy at 21 sites in North America from April 2010 to June 2014 into a prospective cohort study. NEPTUNE central pathologists assigned participants to minimal-change disease (MCD), FSGS, membranous nephropathy, or other glomerulopathy cohorts. Outcome measures for this analysis were (1) CRever with urine protein-to-creatinine ratio (UPC) <0.3 g/g with preserved native kidney function and (2) ESRD. Continuous variables are reported as median and interquartile range (IQR; 25th, 75th percentile). Cox proportional hazards modeling was used to assess factors associated with CRever. RESULTS We enrolled 441 patients: 116 (27%) had MCD, 142 (32%) had FSGS, 66 (15%) had membranous nephropathy, and 117 (27%) had other glomerulopathy. The baseline UPC was 4.1 g/g (IQR, 1.9, 7.7) and the eGFR was 81 ml/min per 1.73 m(2) (IQR, 50, 105). Median duration of observation was 19 months (IQR, 11, 30). CRever occurred in 46% of patients, and 4.6% progressed to ESRD. Multivariate analysis demonstrated that higher prebiopsy proteinuria (hazard ratio, 0.3; 95% confidence interval, 0.2 to 0.5) and pathology diagnosis (FSGS versus MCD; hazard ratio, 0.2; 95% confidence interval, 0.1 to 0.5) were inversely associated with CRever. The effect of immunosuppressive therapy on remission varied by pathology diagnosis. CONCLUSIONS In NEPTUNE, the high frequency of other pathology in proteinuric patients affirms the value of the diagnostic kidney biopsy. Clinical factors, including level of proteinuria before biopsy, pathology diagnosis, and immunosuppression, are associated with complete remission.

Defining Glomerular Disease in Mechanistic Terms: Implementing an Integrative Biology Approach in Nephrology

Advances in biomedical research allow for the capture of an unprecedented level of genetic, molecular, and clinical information from large patient cohorts, where the quest for precision medicine can be pursued. An overarching goal of precision medicine is to integrate the large-scale genetic and molecular data with deep phenotypic information to identify a new mechanistic disease classification. This classification can ideally be used to meet the clinical goal of the right medication for the right patient at the right time. Glomerular disease presents a formidable challenge for precision medicine. Patients present with similar signs and symptoms, which cross the current disease categories. The diseases are grouped by shared histopathologic features, but individual patients have dramatic variability in presentation, progression, and response to therapy, reflecting the underlying biologic heterogeneity within each glomerular disease category. Despite the clinical challenge, glomerular disease has several unique advantages to building multilayered datasets connecting genetic, molecular, and structural information needed to address the goals of precision medicine in this population. Kidney biopsy tissue, obtained during routine clinical care, provides a direct window into the molecular mechanisms active in the affected organ. In addition, urine is a biofluid ideally suited for repeated measurement from the diseased organ as a liquid biopsy with potential to reflect the dynamic state of renal tissue. In our review, current approaches for large-scale data generation and integration along the genotype-phenotype continuum in glomerular disease will be summarized. Several successful examples of this integrative biology approach within glomerular disease will be highlighted along with an outlook on how achieving a mechanistic disease classification could help to shape glomerular disease research and care in the future.

Increasing Use of Vitamin D Supplementation in the Chronic Renal Insufficiency Cohort Study

OBJECTIVE This study examined rates and determinants of vitamin D supplementation among Chronic Renal Insufficiency Cohort (CRIC) participants and determined the association between dose and 25-hydroxyvitamin D (25(OH)D) level. The 2010 Institute of Medicine Report noted a significant increase in vitamin D supplementation in the general population, but use in chronic kidney disease (CKD) is unknown. METHODS CRIC is a multicenter prospective observational cohort study of 3,939 participants with a median baseline age of 60 and an estimated glomerular filtration rate (eGFR) of 42.1 mL/minute per 1.73 m2. Of the cohort, 54.9% was male, 42.1% were Black, and 48.4% were diabetic. Multivariable logistic generalized estimating equations were used to examine determinants of supplementation use assessed annually between 2003 and 2011. Cross-sectional linear regression models, based on a subset of 1,155 participants, assessed associations between supplement dose and 25(OH)D level, measured by high-performance liquid chromatography coupled with tandem mass spectrometry. RESULTS The proportion of participants reporting supplement use increased (P < .0001), from 10% at baseline to 44% at 7-year follow-up visits. This was largely due to initiation of products containing only ergocalciferol or cholecalciferol. The odds of supplementation were greater in older, female, non-Black, married participants with greater education and lower body mass index. Among participants taking supplementation, dose was positively associated with 25(OH)D level, adjusted for race, season, diabetes, dietary intake, eGFR, and proteinuria. Only 3.8% of non-Black and 16.5% of Black participants taking a supplement were deficient (<20 ng/mL), whereas 22.7% of non-Black and 62.4% of black participants not reporting supplement use were deficient. CONCLUSIONS Vitamin D supplementation rates rose significantly among CRIC participants over 7 years of follow-up and were associated with greater serum 25(OH)D levels. Studies of vitamin D levels on clinical outcomes in CKD and future vitamin D interventional studies should consider these changes in supplementation practices.

The chronic kidney disease outcomes and practice patterns study Brazil (CKDopps-Brazil): Design, data and methodology

INTRODUCTION The chronic kidney disease outcomes and practice patterns study (CKDopps) is an international observational, prospective, cohort study involving patients with chronic kidney disease (CKD) stages 3-5 [estimated glomerular filtration rate (eGFR) < 60 ml/min/1.73 m2, with a major focus upon care during the advanced CKD period (eGFR < 30 ml/min/1.73 m2)]. During a 1-year enrollment period, each one of the 22 selected clinics will enroll up to 60 advanced CKD patients (eGFR < 30 ml/min/1.73 m2 and not dialysis-dependent) and 20 earlier stage CKD patients (eGFR between 30-59 ml/min/1.73 m2). EXCLUSION CRITERIA age < 18 years old, patients on chronic dialysis or prior kidney transplant. The study timeline include up to one year for enrollment of patients at each clinic starting in the end of 2013, followed by up to 2-3 years of patient follow-up with collection of detailed longitudinal patient-level data, annual clinic practice-level surveys, and patient surveys. Analyses will apply regression models to evaluate the contribution of patient-level and clinic practice-level factors to study outcomes, and utilize instrumental variable-type techniques when appropriate. CONCLUSION Launching in 2013, CKDopps Brazil will study advanced CKD care in a random selection of nephrology clinics across Brazil to gain understanding of variation in care across the country, and as part of a multinational study to identify optimal treatment practices to slow kidney disease progression and improve outcomes during the transition period to end-stage kidney disease.