Michael Haase

Discovery and validation of cell cycle arrest biomarkers in human acute kidney injury

IntroductionAcute kidney injury (AKI) can evolve quickly and clinical measures of function often fail to detect AKI at a time when interventions are likely to provide benefit. Identifying early markers of kidney damage has been difficult due to the complex nature of human AKI, in which multiple etiologies exist. The objective of this study was to identify and validate novel biomarkers of AKI.MethodsWe performed two multicenter observational studies in critically ill patients at risk for AKI - discovery and validation. The top two markers from discovery were validated in a second study (Sapphire) and compared to a number of previously described biomarkers. In the discovery phase, we enrolled 522 adults in three distinct cohorts including patients with sepsis, shock, major surgery, and trauma and examined over 300 markers. In the Sapphire validation study, we enrolled 744 adult subjects with critical illness and without evidence of AKI at enrollment; the final analysis cohort was a heterogeneous sample of 728 critically ill patients. The primary endpoint was moderate to severe AKI (KDIGO stage 2 to 3) within 12 hours of sample collection.ResultsModerate to severe AKI occurred in 14% of Sapphire subjects. The two top biomarkers from discovery were validated. Urine insulin-like growth factor-binding protein 7 (IGFBP7) and tissue inhibitor of metalloproteinases-2 (TIMP-2), both inducers of G1 cell cycle arrest, a key mechanism implicated in AKI, together demonstrated an AUC of 0.80 (0.76 and 0.79 alone). Urine [TIMP-2]·[IGFBP7] was significantly superior to all previously described markers of AKI (P <0.002), none of which achieved an AUC >0.72. Furthermore, [TIMP-2]·[IGFBP7] significantly improved risk stratification when added to a nine-variable clinical model when analyzed using Cox proportional hazards model, generalized estimating equation, integrated discrimination improvement or net reclassification improvement. Finally, in sensitivity analyses [TIMP-2]·[IGFBP7] remained significant and superior to all other markers regardless of changes in reference creatinine method.ConclusionsTwo novel markers for AKI have been identified and validated in independent multicenter cohorts. Both markers are superior to existing markers, provide additional information over clinical variables and add mechanistic insight into AKI.Trial registrationClinicalTrials.gov number NCT01209169.

Neutrophil gelatinase-associated lipocalin as a biomarker of acute kidney injury: a critical evaluation of current status

Background The early prediction of acute kidney injury (AKI) by current clinical and laboratory methods remains inadequate. Neutrophil gelatinase-associated lipocalin (NGAL) has emerged as a promising non-invasive biomarker of kidney injury. We systematically reviewed the utility of plasma and urine NGAL measurements for the prediction of AKI in humans. Methods We searched MEDLINE, PubMed and EMBASE for human biomarker studies that included NGAL (January 2005 to October 2013). Studies reporting on the use of NGAL for the early prediction and prognosis of AKI were analysed in three common clinical settings: cardiac surgery, critical illness and kidney transplantation. Results We identified 58 manuscripts that met our inclusion and exclusion criteria, reporting on more than 16,500 patients. Following cardiac surgery, NGAL measurement in over 7000 patients was predictive of AKI and its severity, with an overall area under the receiver operator characteristic curve (AUC) of 0.82–0.83. Similar results were obtained in over 8500 critically ill patients. In over 1000 patients undergoing kidney transplantation, NGAL measurements predicted delayed graft function with an overall AUC of 0.87. In all three settings, NGAL significantly improved the prediction of AKI risk over the clinical model alone. Conclusions We identified several studies that collectively strongly support the use of NGAL as a biomarker for the prediction of AKI. However, we noted some limitations, including lack of published studies that adhere to diagnostic study guidelines, heterogeneity in AKI definition, the lack of uniformly applicable cut-off values and variability in the performance of commercially available NGAL assays.

Prophylactic Perioperative Sodium Bicarbonate to Prevent Acute Kidney Injury Following Open Heart Surgery: A Multicenter Double-Blinded Randomized Controlled Trial

In a double-blinded randomized controlled trial, Anja Haase-Fielitz and colleagues find that an infusion of sodium bicarbonate during open heart surgery did not reduce the risk for acute kidney injury, compared with saline control.

Tissue Inhibitor Metalloproteinase-2 (TIMP-2)⋅IGF-Binding Protein-7 (IGFBP7) Levels Are Associated with Adverse Long-Term Outcomes in Patients with AKI

Tissue inhibitor metalloproteinase-2 (TIMP-2) and IGF-binding protein-7 (IGFBP7) have been validated for risk stratification in AKI. However, the association of urinary TIMP-2 and IGFBP7 with long-term outcomes is unknown. We evaluated the 9-month incidence of a composite end point of all-cause mortality or the need for RRT in a secondary analysis of a prospective observational international study of critically ill adults. Two predefined [TIMP-2]⋅[IGFBP7] cutoffs (0.3 for high sensitivity and 2.0 for high specificity) for the development of AKI were evaluated. Cox proportional hazards models were used to determine risk for the composite end point. Baseline [TIMP-2]⋅[IGFBP7] values were available for 692 subjects, of whom 382 (55.2%) subjects developed stage 1 AKI (defined by Kidney Disease Improving Global Outcomes guidelines) within 72 hours of enrollment and 217 (31.4%) subjects met the composite end point. Univariate analysis showed that [TIMP-2]⋅[IGFBP7]>2.0 was associated with increased risk of the composite end point (hazard ratio [HR], 2.11; 95% confidence interval [95% CI], 1.37 to 3.23; P<0.001). In a multivariate analysis adjusted for the clinical model, [TIMP-2]⋅[IGFBP7] levels>0.3 were associated with death or RRT only in subjects who developed AKI (compared with levels≤0.3: HR, 1.44; 95% CI, 1.00 to 2.06 for levels>0.3 to ≤2.0; P=0.05 and HR, 2.16; 95% CI, 1.32 to 3.53 for levels>2.0; P=0.002). In conclusion, [TIMP-2]⋅[IGFBP7] measured early in the setting of critical illness may identify patients with AKI at increased risk for mortality or receipt of RRT over the next 9 months.

Pilot double‐blind, randomized controlled trial of short‐term atorvastatin for prevention of acute kidney injury after cardiac surgery

Aim:  To test whether short‐term perioperative administration of oral atorvastatin could reduce incidence of postoperative acute kidney injury (AKI) in cardiac surgical patients.

A prospective evaluation of urine microscopy in septic and non-septic acute kidney injury

BACKGROUND Sepsis is the most common trigger for acute kidney injury (AKI) in critically ill patients. We sought to determine whether there are unique patterns to urine sediment in septic compared with non-septic AKI. METHODS Prospective two center cohort study of adult critically ill patients with septic and non-septic AKI, defined by the RIFLE criteria. Eligible patients had clinical, physiologic and laboratory data extracted. Blood and urine were sampled for urine biochemistry, microscopy and neutrophil gelatinase-associated lipocalin (NGAL). A urine microscopy score (UMS) was derived based on the observed quantification of renal tubular cells and casts in the sediment. The UMS was compared between septic and non-septic AKI and correlated with NGAL, worsening AKI, renal replacement therapy (RRT) and hospital mortality. RESULTS Eighty-three patients were enrolled. Mean (SD) age was 64.3 (16.6) years, 60.2% were male, Charlson comorbidity score was 3.3 (2.8) and Acute Physiology and Chronic Health Evaluation II score was 21.4 (7.6). Septic AKI was present in 43 patients (51.8%). RIFLE class at enrollment was not different between groups (P = 0.43). Septic AKI was associated with higher UMS compared with non-septic AKI (P = 0.001). There was no correlation between UMS and fractional excretion of sodium (FeNa) or fractional excretion of urea (FeU). Elevated urine NGAL (uNGAL) correlated with higher UMS (P = 0.0003), while correlation with plasma NGAL was modest (P = 0.05). Worsening AKI occurred in 22.9% with no difference between septic and non-septic groups. A UMS score ≥ 3 was associated with increased odds of worsening AKI [adjusted odds ratio 8.0; 95% confidence intervals (CI), 1.03-62.5, P = 0.046]. For a UMS ≥3, sensitivity and specificity were 0.67 (95% CI, 0.39-0.86) and 0.95 (0.84-0.99) and positive and negative predictive values we re 0.80 (0.49-0.94) and 0.91 (0.78-0.96) for detecting worsening AKI, respectively. While there were no differences between septic and non-septic AKI, higher UMS correlated with need for RRT (15.7%, P = 0.02) and in-hospital death (30.1%, P = 0.01); however, this did not persist in multivariable analysis. CONCLUSIONS Septic AKI is associated with greater urine microscopy evidence of kidney injury compared with non-septic AKI, despite similar severity of AKI. A UMS ≥ 3 correlated with higher uNGAL and was predictive of worsening AKI. Urine microscopy may have a complementary role for discerning septic from non-septic AKI, discriminating severity and predicting worsening AKI in critically ill patients.

Pathogenesis of Cardiorenal Syndrome Type 1 in Acute Decompensated Heart Failure: Workgroup Statements from the Eleventh Consensus Conference of the Acute Dialysis Quality Initiative (ADQI)

Pathophysiological mechanisms of cardiorenal syndromes (CRS) types 1-5 are still sparsely characterized. In an attempt to address this issue, a consensus conference on CRS was held in Venice, Italy, in November 2012 under the auspices of the Acute Dialysis Quality Initiative (ADQI). Working group 1 discussed monodirectional mechanisms of CRS type 1 which is characterized by a rapid worsening of cardiac function leading to acute kidney injury (AKI). Pre-conference we performed a systematic search and review of the available literature using a modified Delphi analysis. Hereby identified and in this review discussed questions were: (i) What are the predominant pathophysiologic mechanisms of CRS type 1 in acute decompensated heart failure? (ii) Could biomarker profiling identify pathomechanisms or hemodynamic phenotype of patients with CRS type 1? Could predictive biomarkers improve renal safety of therapy in CRS type 1? (iii) How do the timing, severity and duration relate to the mechanisms and outcomes of CRS type 1? In summary, after discussion and appraisal of the best available evidence, working group 1 makes consensus recommendations for future research on pathologic mechanisms of CRS type 1 and recommendations for clinical practice where treatment is in either proof or disproof of a mechanism.

Urine hepcidin has additive value in ruling out cardiopulmonary bypass-associated acute kidney injury: an observational cohort study.

IntroductionConventional markers of acute kidney injury (AKI) lack diagnostic accuracy and are expressed only late after cardiac surgery with cardiopulmonary bypass (CPB). Recently, interest has focused on hepcidin, a regulator of iron homeostasis, as a unique renal biomarker.MethodsWe studied 100 adult patients in the control arm of a randomized, controlled trial http://www.clinicaltrials.gov/NCT00672334 who were identified as being at increased risk of AKI after cardiac surgery with CPB. AKI was defined according to the Risk, Injury, Failure, Loss, End-stage renal disease classification of AKI classification stage. Samples of plasma and urine were obtained simultaneously (1) before CPB (2) six hours after the start of CPB and (3) twenty-four hours after CPB. Plasma and urine hepcidin 25-isoforms were quantified by competitive enzyme-linked immunoassay.ResultsIn AKI-free patients (N = 91), urine hepcidin concentrations had largely increased at six and twenty-four hours after CPB, and they were three to seven times higher compared to patients with subsequent AKI (N = 9) in whom postoperative urine hepcidin remained at preoperative levels (P = 0.004, P = 0.002). Furthermore, higher urine hepcidin and, even more so, urine hepcidin adjusted to urine creatinine at six hours after CPB discriminated patients who did not develop AKI (area under the curve (AUC) receiver operating characteristic curve 0.80 [95% confidence interval (95% CI) 0.71 to 0.87] and 0.88 [95% CI 0.78 to 0.97]) or did not need renal replacement therapy initiation (AUC 0.81 [95% CI 0.72 to 0.88] 0.88 [95% CI 0.70 to 0.99]) from those who did. At six hours, urine hepcidin adjusted to urine creatinine was an independent predictor of ruling out AKI (P = 0.011). Plasma hepcidin did not predict no development of AKI. The study findings remained essentially unchanged after excluding patients with preoperative chronic kidney disease.ConclusionsOur findings suggest that urine hepcidin is an early predictive biomarker of ruling out AKI after CPB, thereby contributing to early patient risk stratification.

Combination of biomarkers for diagnosis of acute kidney injury after cardiopulmonary bypass

Abstract Novel acute kidney injury (AKI) biomarkers offer promise of earlier diagnosis and risk stratification, but have yet to find widespread clinical application. We measured urinary α and π glutathione S-transferases (α-GST and π-GST), urinary l-type fatty acid-binding protein (l-FABP), urinary neutrophil gelatinase-associated lipocalin (NGAL), urinary hepcidin and serum cystatin c (CysC) before surgery, post-operatively and at 24 h after surgery in 93 high risk patient undergoing cardiopulmonary bypass (CPB) and assessed the ability of these biomarkers alone and in combination to predict RIFLE-R defined AKI in the first 5 post-operative days. Twenty-five patients developed AKI. π-GST (ROCAUC = 0.75), lower urine Hepcidin:Creatine ratio at 24 h (0.77), greater urine NGAL:Cr ratio post-op (0.73) and greater serum CysC at 24 h (0.72) best predicted AKI. Linear combinations with significant improvement in AUC were: Hepcidin:Cr 24 h + post-operative π-GST (AUC = 0.86, p = 0.01), Hepcidin:Cr 24 h + NGAL:Cr post-op (0.84, p = 0.03) and CysC 24 h + post-operative π-GST (0.83, p = 0.03), notably these significant biomarkers combinations all involved a tubular injury and a glomerular filtration biomarker. Despite statistical significance in receiver–operator characteristic (ROC) analysis, when assessed by ability to define patients to two groups at high and low risk of AKI, combinations failed to significantly improve classification of risk compared to the best single biomarkers. In an alternative approach using Classification and Regression Tree (CART) analysis a model involving NGAL:Cr measurement post-op followed by Hepcidin:Cr at 24 h was developed which identified high, intermediate and low risk groups for AKI. Regression tree analysis has the potential produce models with greater clinical utility than single combined scores.

Greater increase in urinary hepcidin predicts protection from acute kidney injury after cardiopulmonary bypass

BACKGROUND Acute kidney injury (AKI) is a common and serious complication of cardiopulmonary bypass (CPB) surgery. Hepcidin, a peptide hormone that regulates iron homeostasis, is a potential biomarker of AKI following CPB. METHODS We investigated the association between post-operative changes in serum and urinary hepcidin and AKI in 93 patients undergoing CPB. RESULTS Twenty-five patients developed AKI based on the Risk, Injury, Failure, Loss, End-stage kidney disease (RIFLE) criteria in the first 5 days. Serum hepcidin, urine hepcidin concentration, the urinary hepcidin:creatinine ratio and fractional excretion of hepcidin in urine rose significantly after surgery. However, urine hepcidin concentration and urinary hepcidin:creatinine ratio were significantly lower at 24 h in patients with RIFLE-Risk, Injury or Failure compared to those without AKI (P = 0.0009 and P < 0.0001, respectively). Receiver operator characteristic analysis showed that lower 24-h urine hepcidin concentration and urinary hepcidin:creatinine ratio were sensitive and specific predictors of AKI. The urinary hepcidin:creatinine ratio had an area under the curve for the diagnosis of RIFLE ≥ risk at 24 h of 0.77 and of 0.84 for RIFLE ≥ injury. Urinary hepcidin had similar predictive accuracy. Such predictive ability remained when patients with early creatinine increases were excluded. CONCLUSIONS Urinary hepcidin and hepcidin:creatinine ratio are biomarkers of AKI after CPB, with an inverse association between its increase at 24 h and risk of AKI in the first five post-operative days. Measuring hepcidin in the urine on the first day following surgery may deliver earlier diagnosis and interventions.