Validation of cell-cycle arrest biomarkers for acute kidney injury using clinical adjudication

Serial Urinary Tissue Inhibitor of Metalloproteinase-2 and Insulin-Like Growth Factor-Binding Protein 7 and the Prognosis for Acute Kidney Injury over the Course of Critical Illness

INTRODUCTION

Over the course of critical illness, there is a risk of acute kidney injury (AKI), and when it occurs, it is associated with increased length of stay, morbidity, and mortality. The urinary cell-cycle arrest markers tissue inhibitor of metalloproteinase-2 (TIMP-2) and insulin-like growth factor binding protein 7 (IGFBP7) have been utilized to predict the risk of AKI over the next 12 h from the time of sampling. The aim of this analysis was to evaluate the utility of [TIMP-2] × [IGFBP7] measured serially to anticipate the occurrence of AKI over the first 7 days of critical illness.

METHODS

This analysis is from a prospective, blinded, observational, international study of patients admitted to intensive care units. We designed the analysis to emulate a clinician-driven serial testing strategy. Urine samples collected every 12 h up to 3 days from 530 patients were considered for analysis. We evaluated [TIMP-2] × [IGFBP7] results for the first 3 measurements (baseline, 12 and 24 h) and continued to evaluate additional results if any of the first 3 were positive >0.3 (ng/mL)2/1,000. Patients were stratified by number of [TIMP-2] × [IGFBP7] results >0.3 (ng/mL)2/1,000 and number of results >2.0 (ng/mL)2/1,000. The primary endpoint was AKI stage 2-3 defined by the Kidney Disease: Improving Global Outcomes (KDIGO) criteria.

RESULTS

The median (interquartile range) age was 64 (53-74) years, 61% were men, and 79% were Caucasian. The median APACHE III score was 71 (51-93), and 82% required mechanical ventilation. Baseline serum creatinine was 0.8 mg/dL and 164/530 (31%) developed the primary endpoint by day 7 with a median time from baseline to stage 2/3 AKI of 26 (8-56) h. In patients with negative values for the first 3 tests (≤0.3 (ng/mL)2/1,000), the cumulative incidence of the primary endpoint at 7 days was 13.0%. Conversely, for those with one, two, or three strongly positive values (>2.0 (ng/mL)2/1,000), the cumulative incidence for the primary endpoint at 7 days was 57.7, 75.0, and 94.4%, respectively, p < 0.001 for trend. There were 3.4% with test results between 0.3 and 2.0 (ng/mL)2/1,000 at all measurements; one third of those patients developed the primary endpoint. We observed a graded increase in the primary endpoint in Kaplan-Meier plots for successively positive test results over time.

CONCLUSION

Serial urinary [TIMP-2] × [IGFBP7] at baseline, 12 and 24 h, and up through 3 days are prognostic for the occurrence of stage 2/3 AKI over the course of critical illness. Three consecutive negative values (≤0.3 (ng/mL)2/1,000) are associated with very low (13.0%) incidence of stage 2/3 AKI over the course of 7 days. Conversely, emerging or persistent, strongly positive results [>2.0 [ng/mL]2/1,000] predict very high incidence rates (up to 94.4%) of stage 2/3 AKI. There was a low rate of test results between 0.3 and 2.0 (ng/mL)2/1,000, where the primary endpoint was observed in a third of cases.

Found in Translation: Reasons for Optimism in the Pursuit to Prevent Chronic Kidney Disease After Acute Kidney Injury

Purpose of review:

The current review will discuss on the progress of studying the transition phase between acute kidney injury (AKI) and chronic kidney disease (CKD) through improved animal models, common AKI and CKD pathways, and how human studies may inform different translational approaches.

Sources of information:

PubMed and Google Scholar.

Methods:

A narrative review was performed using the main terms “acute kidney injury,” “chronic kidney disease,” “end-stage renal disease,” “animal models,” “review,” “decision-making,” and “translational research.”

Key findings:

The last decade has shown much progress in the study of AKI, including evidence of a pathophysiological link between AKI and CKD. We are now in a phase of redesigning animal models and discovering mechanisms that can replicate the pathological conditions of the AKI-to-CKD continuum. Translating these findings into the clinic is a barrier that must be overcome. To this end, current efforts include prediction of AKI onset and maladaptive repair, detecting patients susceptible to the progression of chronic maladaptive repair, and understanding shared signaling mechanisms between AKI and CKD.

Limitations:

This is a narrative review of the literature that is partially influenced by the knowledge, perspectives, and experiences of the authors and their research background.

Implications:

Overall, this new knowledge from the AKI-to-CKD continuum will help bridge the discontinuity that exists between animal models and patients, resulting in more effective translational biomarkers and therapeutics to test in known AKI pathologies thereby preventing the chronicity of kidney injury progression.

Postreperfusion plasma endothelial activation markers are associated with acute kidney injury after lung transplantation

Acute kidney injury (AKI) is common after lung transplantation, but molecular markers remain poorly studied. The endothelial activation markers soluble thrombomodulin (sTM), protein C, and plasminogen activator inhibitor-1 (PAI-1) are implicated in kidney microcirculatory injury in animal models of AKI. We tested the association of 6-hour postreperfusion plasma levels of these markers with posttransplant AKI severity in patients enrolled in the Lung Transplant Outcomes Group prospective cohort study at the University of Pennsylvania during two eras: 2004-06 (n = 61) and 2013-15 (n = 67). We defined AKI stage through postoperative day 5 using Kidney Disease Improving Global Outcomes creatinine criteria. We used multivariable ordinal logistic regression to determine the association of each biomarker with AKI, adjusted for primary graft dysfunction and extracorporeal life support. AKI occurred in 57 (45%) patients across both eras: 28 (22%) stage 1, 29 (23%) stage 2-3. Higher sTM and lower protein C plasma levels were associated with AKI stage in each era and remained so in multivariable models utilizing both eras (sTM: OR 1.76 [95% CI 1.19-2.60] per standard deviation, P = .005; protein C: OR 0.54 [1.19-2.60], P = .003). We conclude that 6-hour postreperfusion plasma sTM and protein C levels are associated with early postlung transplant AKI severity.

Urinary [TIMP-2] × [IGFBP-7] for predicting acute kidney injury in patients undergoing orthotopic liver transplantation

BACKGROUND

The product of the concentrations of urinary tissue inhibitor of metalloproteinases-2 and insulin-like growth factor binding protein-7 (urinary [TIMP-2] × [IGFBP-7]) has been suggested as biomarker for early detection of acute kidney injury (AKI) in various clinical settings. However, the performance of urinary [TIMP-2] × [IGFBP-7] to predict AKI has never been assessed in patients undergoing orthotopic liver transplantation (OLT). Thus, the aim of this study was to assess the early predictive value of urinary [TIMP-2] × [IGFBP-7] for the development of AKI after OLT.

METHODS

In this observational study, urinary [TIMP-2] × [IGFBP-7] was measured in samples from adult OLT patients. AKI was diagnosed and classified according to KDIGO criteria. Areas under the receiver operating curves (AUC) were calculated to assess predictive values of urinary [TIMP-2] × [IGFBP-7] for the development of AKI.

RESULTS

Forty patients (mean age 55 ± 8 years) were included. Twenty-eight patients (70%) developed AKI stage 1, 2, or 3 within 48 h after OLT. Urinary [TIMP-2] × [IGFBP-7] was not predictive for AKI at the end of OLT (AUC: 0.54, CI [0.32-0.75], P = 0.72), at day 1 (AUC: 0.60, CI [0.41-0.79], P = 0.31), or day 2 after OLT (AUC: 0.63, CI [0.46-0.8], P = 0.18).

CONCLUSION

Based on our results, routine clinical use of urinary [TIMP-2] × [IGFBP-7] cannot be recommended for risk assessment of AKI in patients undergoing OLT.

New Insights Into Mechanisms of Acute Kidney Injury in Heart Disease

Acute kidney injury is a frequent occurrence in patients with heart disease, and is associated with higher risk of adverse outcomes, including mortality. In the setting of decompensated heart failure, acute kidney injury can occur from hemodynamic and neurohormonal activation, venous congestion, and nephrotoxic medications. Certain medications, such as loop diuretics, renin angiotensin system blockers, and mineralocorticoid antagonists can seemingly cause acute kidney injury. However, this increase in creatinine level is not always associated with adverse outcomes and should be carefully differentiated so as to allow deliberate continuation of these cardio- and nephroprotective agents. In other settings such as cardiac surgery, acute kidney injury can occur from factors related to the cardiopulmonary bypass, renal hypoperfusion, or other perioperative factors. Last, patients with heart disease commonly undergo imaging procedures that require contrast administration. Contrast can indeed cause acute kidney injury, but these interventional procedures also can result in kidney injury from atheroembolic phenomena. This is well documented by the recent data reporting a higher risk of acute kidney injury from femoral compared with radial access. The advent of biomarkers of kidney injury present an opportunity for early detection, accurate differential diagnosis, as well as potentially designing innovative biomarker-enriched adaptive clinical trials.

A review of early warning systems for prompt detection of patients at risk for clinical decline

Early Warning Scores (EWS) are a composite evaluation of a patient's basic physiology, changes of which are the first indicators of clinical decline and are used to prompt further patient assessment and when indicated intervention. These are sometimes referred to as "track and triggers systems" with tracking meant to denote periodic observation of physiology and trigger being a predetermined response criteria. This review article examines the most widely used EWS, with special attention paid to those used in military and trauma populations.The earliest EWS is the Modified Early Earning Score (MEWS). In MEWS, points are allocated to vital signs based on their degree of abnormality, and summed to yield an aggregate score. A score above a threshold would elicit a clinical response such as a rapid response team. Modified Early Earning Score was subsequently followed up with the United Kingdom's National Early Warning Score, the electronic cardiac arrest triage score, and the 10 Signs of Vitality score, among others.Severity of illness indicators have been in military and civilian trauma populations, such as the Revised Trauma Score, Injury Severity Score, and Trauma and Injury Severity. The sequential organ failure assessment score and its attenuated version quick sequential organ failure assessment were developed to aggressively identify patients near septic shock.Effective EWS have certain characteristics. First, they should accurately capture vital signs information. Second, almost all data should be derived electronically rather than manually. Third, the measurements should take into consideration multiple organ systems. Finally, information that goes into an EWS must be captured in a timely manner. Future trends include the use of machine learning to detect subtle changes in physiology and the inclusion of data from biomarkers. As EWS improve, they will be more broadly used in both military and civilian environments. LEVEL OF EVIDENCE: Review article, level I.

Urinary mitochondrial DNA copy number identifies renal mitochondrial injury in renovascular hypertensive patients undergoing renal revascularization: A Pilot Study

AIMS

Patients with renovascular hypertension (RVH) exhibit elevated urinary mtDNA copy numbers, considered to constitute surrogate markers of renal mitochondrial injury. The modest success of percutaneous transluminal renal angioplasty (PTRA) in restoring renal function in RVH has been postulated to be partly attributable to acute reperfusion injury. We hypothesized that mitoprotection during revascularization would ameliorate PTRA-induced renal mitochondrial injury, reflected in elevated urinary mtDNA copy numbers and improve blood pressure and functional outcomes 3 months later.

METHODS

We prospectively measured urinary copy number of the mtDNA genes COX3 and ND1 using qPCR in RVH patients before and 24 hrs after PTRA, performed during IV infusion of vehicle (n = 8) or the mitoprotective drug elamipretide (ELAM, 0.05 mg/kg/h, n = 6). Five healthy volunteers (HV) served as controls. Urinary mtDNA levels were also assessed in RVH and normal pigs (n = 7 each), in which renal mitochondrial structure and density were studied ex-vivo.

RESULTS

Baseline urinary mtDNA levels were elevated in all RVH patients vs HV and directly correlated with serum creatinine levels. An increase in urinary mtDNA 24 hours after PTRA was blunted in PTRA+ELAM vs PTRA+Placebo. Furthermore, 3-months after PTRA, systolic blood pressure decreased and estimated glomerular filtration rate increased only in ELAM-treated subjects. In RVH pigs, mitochondrial damage was observed using electron microscopy in tubular cells and elevated urinary mtDNA levels correlated inversely with renal mitochondrial density.

CONCLUSIONS

PTRA leads to an acute rise in urinary mtDNA, reflecting renal mitochondrial injury that in turn inhibits renal recovery. Mitoprotection might minimize PTRA-associated mitochondrial injury and improve renal outcomes after revascularization.

Development and validation of quick Acute Kidney Injury-score (q-AKI) to predict acute kidney injury at admission to a multidisciplinary intensive care unit

AKI is associated with increased risk of death, prolonged length of stay and development of de-novo chronic kidney disease. The aim of our study is the development and validation of prediction models to identify the risk of AKI in ICU patients up to 7 days. We retrospectively recruited 692 consecutive patients admitted to the ICU at San Bortolo Hospital (Vicenza, Italy) from 1 June 2016 to 31 March 2017: 455 patients were treated as the derivation group and 237 as the validation group. Candidate variables were selected based on a literature review and expert opinion. Admission eGFR< 90 ml/min /1.73 mq (OR 2.78; 95% CI 1.78–4.35; p<0.001); SOFAcv ≥ 2 (OR 2.23; 95% CI 1.48–3.37; p<0.001); lactate ≥ 2 mmol/L (OR 1.81; 95% CI 1.19–2.74; p = 0.005) and (TIMP-2)•(IGFBP7) ≥ 0.3 (OR 1.65; 95% CI 1.08–2.52; p = 0.019) were significantly associated with AKI. For the q-AKI score, we stratified patients into different AKI Risk score levels: 0–2; 3–4; 5–6; 7–8 and 9–10. In both cohorts, we observed that the proportion of AKI patients was higher in the higher score levels.

Acute kidney injury from sepsis: current concepts, epidemiology, pathophysiology, prevention and treatment

Sepsis-associated acute kidney injury (S-AKI) is a frequent complication of the critically ill patient and is associated with unacceptable morbidity and mortality. Prevention of S-AKI is difficult because by the time patients seek medical attention, most have already developed acute kidney injury. Thus, early recognition is crucial to provide supportive treatment and limit further insults. Current diagnostic criteria for acute kidney injury has limited early detection; however, novel biomarkers of kidney stress and damage have been recently validated for risk prediction and early diagnosis of acute kidney injury in the setting of sepsis. Recent evidence shows that microvascular dysfunction, inflammation, and metabolic reprogramming are 3 fundamental mechanisms that may play a role in the development of S-AKI. However, more mechanistic studies are needed to better understand the convoluted pathophysiology of S-AKI and to translate these findings into potential treatment strategies and add to the promising pharmacologic approaches being developed and tested in clinical trials.

Urine Klotho Is Lower in Critically Ill Patients With Versus Without Acute Kidney Injury and Associates With Major Adverse Kidney Events

Supplemental Digital Content is available in the text.

Klotho and fibroblast growth factor-23 were recently postulated as candidate biomarkers and/or therapeutic targets in acute kidney injury. We examined whether urine Klotho and serum intact fibroblast growth factor-23 levels were differentially and independently associated with major adverse kidney events in critically ill patients with and without acute kidney injury.

Identifying KDIGO Trajectory Phenotypes Associated with Increased Inpatient Mortality

Acute kidney injury (AKI) is a complex systemic syndrome associated with high morbidity and mortality and risk for the subsequent development of renal and non-renal complications. Nearly 50% of patients in the ICU experience AKI. AKI severity is a key metric for evaluating patients risk of hospital mortality. Current AKI stratification is based on absolute changes in Serum Creatinine (SCr) and the maximal increase relative to the patients baseline value. However, such measurement does not consider either the progression or duration of AKI, both of which are associated with adverse outcomes post-AKI. In this article, by leveraging a large volume of SCr temporal variabilities, we present a novel model called Trajectory of Acute Kidney Injury (TAKI) for the identification of AKI trajectory subtypes. Experimental results demonstrate that TAKI is better than the existing trajectory subtyping methods on both the inpatient mortality stratification and the post-7-day AKI progression estimation. With TAKI, it is found that the trend of KDIGO trajectory appears to be more highly associated with inpatient mortality rates than the maximum KDIGO score.

Comparison of urinary TIMP-2 and IGFBP7 cut-offs to predict acute kidney injury in critically ill patients: A PRISMA-compliant systematic review and meta-analysis

BACKGROUND

Tissue inhibitor of metalloproteinase-2 (TIMP-2) and insulin-like growth factor binding protein 7 (IGFBP7) are recently identified urinary biomarkers of acute kidney injury (AKI) in critically ill patients. Because their predictive accuracies vary widely, a meta-analysis was performed to evaluate the accuracy of previously reported urinary TIMP-2 and IGFBP7 cut-offs for predicting AKI.

METHODS

This meta-analysis was reported following the guideline of PRISMA. Four databases, PubMed, the Cochrane Library, the ISI Web of Knowledge, and Embase, were systematically searched from inception to June 2018 by 2 investigators, who independently selected studies, extracted relevant data, and evaluated study quality. A bivariate model was used to calculate the pooled estimates.

RESULTS

The search identified 5 studies with 1619 critically ill patients. Urinary TIMP-2 and IGFBP7 cut-off points of 0.3 (ng/ml)/1000 had a sensitivity of 0.89 [95% confidence interval (CI) 0.85-0.93], a specificity of 0.48 (95% CI 0.45-0.51) and a diagnostic odds ratio (DOR) of 8.33 (95% CI 5.55-12.52). The area under the curve (AUC) estimated by the summary receiver operating characteristic (SROC) curve was 0.748. Based on 891 critically ill patients from 4 studies, urinary TIMP-2 and IGFBP7 cut-off points of 2.0 (ng/ml)/1000 had a sensitivity of 0.45 (95% CI 0.37-0.53), a specificity of 0.93 (95% CI 0.91-0.95) and a DOR of 11.43 (95% CI 7.43-17.57). The AUC estimated by SROC was 0.844.

CONCLUSION

Cut-off values around 0.3 (ng/ml)/1000 (high sensitivity) and 2.0 (ng/ml)/1000 (high specificity) could be accurate surrogate biomarkers predicting AKI in critically ill patients. The urinary TIMP-2 and IGFBP7 cut-off point of 2.0 (ng/mL)/1000 appears to have the highest overall accuracy.

TRIAL REGISTRATION

PROSPERO registration number 2018: CRD42018084457 Registered on 11 February 2018.

Plasma Biomarkers in Predicting Renal Recovery from Acute Kidney Injury in Critically Ill Patients

BACKGROUND

Numerous studies have suggested a possible role for acute kidney injury (AKI) biomarkers in predicting renal recovery both before and after renal replacement therapy (RRT). However, definitions for recovery and whether to include patients dying but free of RRT may influence results.

OBJECTIVES

To validate plasma neutrophil gelatinase-associated lipocalin (pNGAL) as a useful biomarker for predicting or improving the ability of clinical predictors alone to predict recovery following AKI, including in our model plasma B-type natriuretic peptide (pBNP) to account for cardiovascular events.

METHODS

We analyzed 69 patients enrolled in the Acute Renal Failure Trial Network study. pNGAL and pBNP were measured on days 2, 7, and 14. We analyzed their predictive ability for subsequent recovery, defined as alive and independent from dialysis in 60 days. In sensitivity analyses, we explored changes in results with alternative definitions of recovery.

RESULTS

Twenty-nine patients (42%) recovered from AKI. Neither pNGAL nor pBNP, alone or in combination, was accurate predictors of renal recovery-the best area under the receiver-operating characteristics curve (AUC) was for pNGAL using the largest relative change (AUC 0.59, 95% CI 0.45-0.74). The best clinical model achieved superior performance to biomarkers (AUC 0.69, 95% CI 0.56-0.81). The AUC was greatest (0.75, 95% CI 0.60-0.91) when pNGAL + pBNP on day 14 were added to the clinical model but this increase did not achieve statistical significance. However, integrated discrimination improvement analysis showed that the addition of pNGAL and pBNP on day 14 to the clinical model significantly improved the prediction of renal recovery (p = 0.008).

CONCLUSIONS

pNGAL and pBNP can improve the accuracy of clinical parameters in predicting AKI recovery and a full model using biomarkers together with age achieved adequate discrimination.

IGFBP7 regulates sepsis-induced acute kidney injury through ERK1/2 signaling

IGFBP7 as an early biomarker has been used to identify patients at risk of developing acute kidney injury (AKI). Nevertheless, its role in AKI remains obscure. The aim of our study is to determine the role and mechanism of IGFBP7 in lipopolysaccharide (LPS)-induced HK-2 cells in vitro and on sepsis-induced AKI by cecal ligation and puncture (CLP) in vivo. Here, we identified that IGFBP7 expression was increased in patients with AKI and HK-2 cells with LPS (1, 2, and 5 μg/mL) induction. HK-2 cells with LPS induction showed cell cycle arrest at G1-G0 phases and cell apoptosis and activated ERK1/2 parallel with the changes in the proteins belonging to the ERK1/2 pathway, including Cyclin D1, P21, Bax, and Bcl-2, which were inhibited by the IGFBP7 knockdown. Moreover, IGFBP7 overexpression significantly induced cell cycle arrest at G1-G0 phases and cell apoptosis of HK-2 cells, which were inhibited by PD98509, an ERK1/2 signaling inhibitor. IGFBP7 knockdown effectively alleviated the severity of the renal injury, evidenced by decreases in the urinary levels of creatinine, blood urea nitrogen, and albumin, cell apoptosis, and activation of ERK1/2 signaling in CLP mice. Taken together, our findings indicate that IGFBP7 regulates sepsis-induced AKI through ERK1/2 signaling.

The future for diagnostic tests of acute kidney injury in critical care: evidence synthesis, care pathway analysis and research prioritisation

BACKGROUND

Acute kidney injury (AKI) is highly prevalent in hospital inpatient populations, leading to significant mortality and morbidity, reduced quality of life and high short- and long-term health-care costs for the NHS. New diagnostic tests may offer an earlier diagnosis or improved care, but evidence of benefit to patients and of value to the NHS is required before national adoption.

OBJECTIVES

To evaluate the potential for AKI in vitro diagnostic tests to enhance the NHS care of patients admitted to the intensive care unit (ICU) and identify an efficient supporting research strategy.

DATA SOURCES

We searched ClinicalTrials.gov, The Cochrane Library databases, Embase, Health Management Information Consortium, International Clinical Trials Registry Platform, MEDLINE, metaRegister of Current Controlled Trials, PubMed and Web of Science databases from their inception dates until September 2014 (review 1), November 2015 (review 2) and July 2015 (economic model). Details of databases used for each review and coverage dates are listed in the main report.

REVIEW METHODS

The AKI-Diagnostics project included horizon scanning, systematic reviewing, meta-analysis of sensitivity and specificity, appraisal of analytical validity, care pathway analysis, model-based lifetime economic evaluation from a UK NHS perspective and value of information (VOI) analysis.

RESULTS

The horizon-scanning search identified 152 potential tests and biomarkers. Three tests, Nephrocheck^® (Astute Medical, Inc., San Diego, CA, USA), NGAL and cystatin C, were subjected to detailed review. The meta-analysis was limited by variable reporting standards, study quality and heterogeneity, but sensitivity was between 0.54 and 0.92 and specificity was between 0.49 and 0.95 depending on the test. A bespoke critical appraisal framework demonstrated that analytical validity was also poorly reported in many instances. In the economic model the incremental cost-effectiveness ratios ranged from £11,476 to £19,324 per quality-adjusted life-year (QALY), with a probability of cost-effectiveness between 48% and 54% when tests were compared with current standard care.

LIMITATIONS

The major limitation in the evidence on tests was the heterogeneity between studies in the definitions of AKI and the timing of testing.

CONCLUSIONS

Diagnostic tests for AKI in the ICU offer the potential to improve patient care and add value to the NHS, but cost-effectiveness remains highly uncertain. Further research should focus on the mechanisms by which a new test might change current care processes in the ICU and the subsequent cost and QALY implications. The VOI analysis suggested that further observational research to better define the prevalence of AKI developing in the ICU would be worthwhile. A formal randomised controlled trial of biomarker use linked to a standardised AKI care pathway is necessary to provide definitive evidence on whether or not adoption of tests by the NHS would be of value.

STUDY REGISTRATION

The systematic review within this study is registered as PROSPERO CRD42014013919.

FUNDING

The National Institute for Health Research Health Technology Assessment programme.

Urinary TIMP2 and IGFBP7 Identifies High Risk Patients of Short-Term Progression from Mild and Moderate to Severe Acute Kidney Injury during Septic Shock: A Prospective Cohort Study

Background

To examine whether the new urinary biomarkers TIMP2 and IGFBP7 can predict progression within 24 hours and 72 hours from mild and moderate (KDIGO 1 or 2) to severe (KDIGO 3) AKI in patients with septic shock.

Methods

A prospective, multicenter observational study performed in three French ICUs. The urinary biomarkers TIMP2∗IGFBP7 were analyzed at the early phase (<6 hours) of patients admitted for septic shock with mild and moderate AKI.

Results

Among the 112 patients included, 45 (40%) progressed to the KDIGO 3 level 24 hours after inclusion (KDIGO 3 H24) and 47 (42%) 72 hours after inclusion (KDIGO 3 H72). The median urinary TIMP2∗IGFBP7 at inclusion (baseline) were higher in the KDIGO 3 group than in the KDIGO<3 group at H24 and H72. All covariates with a p value < 0.1 in the univariate analysis were included in stepwise multiple logistic regression models to identify factors independently associated with the risk of KDIGO 3 at H24 and H72. TIMP2∗IGFBP7 remained independently associated with KDIGO 3 at H24 and H72. Baseline posology of norepinephrine, baseline urine output, and baseline serum creatinine remained also significantly associated with progression to KDIGO 3 at H24. Baseline TIMP2∗IGFBP7 and baseline urinary output had the best AUC ROC. A baseline TIMP2∗IGFBP7 > 2.0 (ng/ml)²/1,000 identified the population at high risk of KDIGO 3 H24 (relative risk 4.19 (1.7-10.4)) with a sensitivity of 76% (60-87) and a specificity of 81% (69-89). But the diagnostic performance at H72 of baseline TIMP2∗IGFBP7 was poor (AUC: 0.69 (0.59-0.77)).

Conclusion

The urinary TIMP2∗IGFBP7 concentration and the urine output at the early phase of septic shock are independent factors to identify the population at high risk of progression from mild and moderate to severe AKI over the next 24 but not 72 hours. A TIMP2∗IGFBP7 concentration > 2.0 (ng/ml)²/1,000 quadruples the risk of KDIGO 3 AKI within 24 hours. This trial is registered with (NCT03547414).

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.

Tissue inhibitor metalloproteinase-2 (TIMP-2) • IGF-binding protein-7 (IGFBP7) levels are associated with adverse outcomes in patients in the intensive care unit with acute kidney injury

The G1 cell cycle inhibitors tissue inhibitor metalloproteinase-2 (TIMP-2) and insulin-like growth factor-binding protein 7 (IGFBP7) have been identified as novel biomarkers for the prediction of moderate to severe acute kidney injury (AKI) risk. However, the prognostic value of [TIMP-2]•[IGFBP7] in predicting adverse outcomes in intensive care unit (ICU) patients with AKI was not previously described. To evaluate this, we conducted a cohort study, measuring [TIMP2]•[IGFBP7] levels in critically ill patients admitted to the ICU and classified the patients as NephroCheck (NC) (+) or NC (-) according to [TIMP-2]•[IGFBP7] values and AKI (+) or AKI (-) according to Kidney Disease: Improving Global Outcomes (KDIGO) criteria. We then evaluated the incidence of continuous renal replacement therapy initiation, all-cause mortality and a composite endpoint of both in the four groups. Baseline [TIMP-2]•[IGFBP7] values were available for 719 patients, of whom 239 developed AKI and 151 met the composite endpoint. Compared to NC (-)/AKI (+) patients, NC (+)/AKI (+) patients had a significant risk of ICU mortality and the composite endpoint. Kaplan-Meier curves showed that the survival estimate for the composite endpoint of NC (+)/AKI (+) patients was 34.4%; significantly worse than NC (-)/AKI (+) patients (67.4%). Multivariate analyses showed strong association between NC positivity and the composite endpoint. The inflammatory marker, procalcitonin, was an additional prognostic biomarker to compare and confirm the incremental value of NephroCheck. No association between procalcitonin and the composite endpoint was found, especially in patients with AKI, suggesting that NephroCheck may be more kidney specific. Thus, the [TIMP-2]•[IGFBP7] values can serve to identify patients with AKI at increased risk for adverse outcomes in the ICU.

Impact of Recent Clinical Trials on Nephrology Practice: Are We in a Stagnant Era?

BACKGROUND

Although renal replacement therapy prevents death from uremia, survival among patients with acute and chronic kidney diseases (CKD) remains an imperative concern. The expected life span of US dialysis patients 60-64 years of age is approximately 4.5 years; this is similar to that of patients with lung cancer. Despite substantial progress in many medical specialties over the past decades (e.g., notable reductions in myocardial infarction, stroke, and mortality rates in the general population), survival among dialysis patients has not improved significantly over the same period. A few decades ago, HIV infection and AIDS were pretty much a death sentence. Because of progress in HIV treatment, now it can be controlled with a daily pill, and ongoing research is pushing treatment even further and controls the virus with longer-acting treatment. A cure is no longer impossible for HIV and other viral infections such as hepatitis B and C and many malignancies, but so far there is no cure for CKD.

SUMMARY

Billions of dollars have been spent on kidney disease research in the past decades, with no tangible progress in clinical practice. The challenges of improving the quantity and quality of trials in nephrology are enormous. The number of randomized controlled trials (RCTs) published in nephrology is lower than that in other medical subspecialties, and most of the big RCTs in nephrology yield negative results. Nephrology studies evaluating hard clinical endpoints or surrogate endpoints are scarce.

KEY MESSAGE

Herein we discuss the slow progress in nephrology research that has impacted clinical practice over the last couple of decades and highlight the major obstacles, challenges, and potential solutions.

Kidney Injury Biomarkers in an Academic Hospital Setting: Where Are We Now?

Acute kidney injury (AKI) is a frequent complication in hospitalised patients and is diagnosed by urinary output and serum creatinine. Serum creatinine is an indirect marker for renal glomerular filtration, but lacks specificity for damage to kidney tissue and the relatively late response to injury precludes early recognition of AKI. Timely diagnosis of kidney injury using biomarkers that provide information about the aetiology of kidney injury is an unmet clinical need. To overcome the suboptimal performance of serum creatinine, injury biomarkers have been proposed that predict AKI in diverse clinical settings. The clinical performance of these markers is considered moderate due to the lack of specificity for kidney tissue or the underlying injury mechanisms, poor test specificity and confounding by interventions or comorbidities. Hence, it is not unequivocally beneficial to implement current kidney injury biomarkers in the clinical laboratory for diagnostic purposes. In this article we review biomarkers that might fulfil AKI-related unmet clinical needs in the academic hospital setting.

Fiend and friend in the renin angiotensin system: An insight on acute kidney injury

Besides assisting the maintenance of blood pressure and sodium homeostasis, the renin-angiotensin system (RAS) plays a pivotal role in pathogenesis of acute kidney injury (AKI). The RAS is equipped with two arms i) the pressor arm composed of Angiotensin II (Ang II)/Angiotensin converting enzyme (ACE)/Angiotensin II type 1 receptor (AT1R) also called conventional RAS, and ii) the depressor arm consisting of Angiotensin (1-7) (Ang 1-7)/Angiotensin converting enzyme 2 (ACE2)/MasR known as non-conventional RAS. Activation of conventional RAS triggers oxidative stress, inflammatory, hypertrophic, apoptotic, and pro-fibrotic signaling cascades which promote AKI. The preclinical and clinical studies have reported beneficial as well as deleterious effects of RAS blockage either by angiotensin receptor blocker or ACE inhibitor in AKI. On the contrary, the depressor arm opposes the conventional RAS, has beneficial effects on the kidney but has been less explored in pathogenesis of AKI. This review focuses on significance of RAS in pathogenesis of AKI and provides better understanding of novel and possible therapeutic approaches to combat AKI.

[New Sepsis-3 definition : Do we have to treat sepsis before we can diagnose it from now on?]

The Third International Consensus Definitions for Sepsis and Septic Shock (Sepsis-3) have been available since the beginning of 2016. SEPSIS-3 completely replaces the old SIRS criteria in the definition of sepsis and defines sepsis from now on as "life-threatening organ dysfunction caused by a dysregulated host response to infection". However, it seems questionable whether in clinical practice the new definition is really superior to the old one. The most important question is the following: Is it helpful to have a definition that first recognizes a patient once organ dysfunction has occurred and the patient already needs intensive care?

Lack of impact of iodinated contrast media on kidney cell-cycle arrest biomarkers in critically ill patients

Background

Iodinated contrast media may contribute to acute kidney injury. However, several recent works suggest that this toxicity is minimal in the clinical setting. Recently, urinary G1 cell-cycle arrest proteins tissue inhibitor of metalloproteinase 2 (TIMP-2) and insulin like growth factor binding protein 7 (IGFBP-7) were identified as highly sensitive and specific biomarkers for early detection of kidney aggression. The impact of contrast administration on those biomarkers has not been specifically evaluated but could provide clues about the toxicity of contrast media. This study aimed at measuring changes in TIMP-2 and IGFBP-7 urinary concentrations before and after a contrast-enhanced computed tomography in critically ill patients.

Methods

77 patients were included in a prospective observational cohort study. Urinary [TIMP -2]·[IGFBP-7] was measured before, 6 and 24 h after contrast infusion. Urine output and serum creatinine were followed 3 days.

Results

Median [TIMP-2]·[IGFBP-7] was 0.06 [interquartile range 0.04;0.26], 0.07 [0.03;0.34] and 0.10 [0.04;0.37] (ng/mL)²/1000 respectively before, 6 and 24 h after contrast infusion. Individual changes from baseline were − 0.01 [− 0.11;0.11] and 0.00 [− 0.10;0.09] (ng/ml)²/1000 at 6 and 24 h. These changes were not higher among the patients increasing their Kidney Disease Improving Global Outcome (KDIGO) classification within 3 days after contrast infusion (n = 14 [18%] based on creatinine criterion only, n = 42 [55%] based on creatinine and urine output).

Conclusions

Changes in [TIMP-2]·[IGFBP-7] urinary concentration after contrast-enhanced computed tomography were insignificant, suggesting minimal kidney aggression by modern iodinated contrast media.

The Accuracy of Urinary TIMP-2 and IGFBP7 for the Diagnosis of Cardiac Surgery-Associated Acute Kidney Injury: A Systematic Review and Meta-Analysis

Background:

Tissue inhibitor of metalloproteinase 2 (TIMP-2) and insulin-like growth factor binding protein 7 (IGFBP7) are recent promising markers for identification of cardiac surgery-associated acute kidney injury (CSA-AKI). The aim of this study was systematically and quantitatively to evaluate the accuracy of urinary TIMP-2 and IGFBP7 for the diagnosis of CSA-AKI.

Methods:

Three databases including PubMed, ISI web of knowledge, and Embase were systematically searched from inception to March 2018. Two investigators conducted the processes of literature search study selection, data extraction, and quality evaluation independently. Meta-DiSc and STATA were used for all statistical analyses.

Results:

A total of 8 studies comprising 552 patients were included in this meta-analysis. Pooled sensitivity and specificity with corresponding 95% confidence intervals (CIs) were 0.79 (95% CI, 0.71-0.86, I 2 = 74.2%) and 0.76 (95% CI, 0.72-0.80, I 2 = 80.8%), respectively. Pooled positive likelihood ratio (LR), negative LR, and diagnostic odds ratio were 3.49 (95% CI, 2.44-5.00, I 2 = 61.5%), 0.31(95% CI, 0.19-0.51, I 2 = 51.8%), and 14.89 (95% CI, 7.31-30.32, I 2 = 27.9%), respectively. The area under curve estimated by summary receiver operating characteristic was 0.868 (standard error [SE] 0.032) with a Q* value of 0.799 (SE 0.032). Sensitivity analysis demonstrated that one study notably affected the stability of pooled results. One of the subgroups investigated—AKI threshold—could account for partial heterogeneity.

Conclusion:

Urinary TIMP-2 and IGFBP7 is a helpful biomarker for early diagnosis of CSA-AKI. And, the potential of this biomarker with a broader spectrum of clinical settings may be the focus of future studies.

Intraoperative prediction of cardiac surgery-associated acute kidney injury using urinary biomarkers of cell cycle arrest

OBJECTIVE

Tissue inhibitor of metalloproteinases 2 (TIMP-2) and insulin-like growth factor-binding protein 7 (IGFBP7) are postoperative urinary biomarkers of renal stress and acute kidney injury (AKI). We conducted this study to test the hypothesis that intraoperative concentrations of urinary [TIMP-2]·[IGFBP7] are associated with postoperative AKI.

METHODS

We measured urinary [TIMP-2]·[IGFBP7] at 8 perioperative timepoints in 400 patients who participated in a randomized controlled trial of atorvastatin for AKI in cardiac surgery. We compared [TIMP-2]·[IGFBP7] between subjects who did and did not develop KDIGO stage 2 or 3 AKI within 48 hours of surgery, adjusted for AKI risk factors.

RESULTS

Fourteen patients (3.5%) met the primary endpoint of stage 2 or 3 AKI within 48 hours of surgery, and an additional 77 patients (19.3%) developed stage 1 AKI. Patients who developed stage 2 or 3 AKI displayed bimodal elevations of [TIMP-2]·[IGFBP7], with a first elevation (median, 0.45 [ng/mL]²/1000) intraoperatively and a second elevation (1.45 [ng/mL]²/1000) 6 hours postoperatively. Patients who did not develop AKI did not have any elevations in [TIMP-2]·[IGFBP7]. Each 10-fold increase in intraoperative [TIMP-2]·[IGFBP7] was independently associated with a 290% increase in the odds of stage 2 or 3 AKI (P = .01), and each 10-fold increase in the 6 hours postoperative [TIMP-2]·[IGFBP7] was independently associated with a 650% increase in the odds of stage 2 or 3 AKI (P < .001). The maximum [TIMP-2]·[IGFBP7] between these 2 timepoints provided an area under the receiver operating characteristic curve of 0.82 (95% confidence interval [CI], 0.73-0.90), 100% sensitivity, and 100% negative predictive value using the >0.3 cutoff to predict stage 2 or 3 AKI.

CONCLUSIONS

Intraoperative elevations of [TIMP-2]·[IGFBP7] can predict moderate or severe AKI and could provide an opportunity to alter postoperative management to prevent kidney injury.

Epidemiology, outcomes, and management of acute kidney injury in the vascular surgery patient

OBJECTIVE

Conventional clinical wisdom has often been nihilistic regarding the prevention and management of acute kidney injury (AKI), despite its being a frequent and morbid complication associated with both increased mortality and cost. Recent developments have shown that AKI is not inevitable and that changes in management of patients can reduce both the incidence and morbidity of perioperative AKI. The purpose of this narrative review was to review the epidemiology and outcomes of AKI in patients undergoing vascular surgery using current consensus definitions, to discuss some of the novel emerging risk stratification and prevention techniques relevant to the vascular surgery patient, and to describe a standardized perioperative pathway for the prevention of AKI after vascular surgery.

METHODS

We performed a critical review of the literature on AKI in the vascular surgery patient using the PubMed and MEDLINE databases and Google Scholar through September 2017 using web-based search engines. We also searched the guidelines and publications available online from the organizations Kidney Disease: Improving Global Outcomes and the Acute Dialysis Quality Initiative. The search terms used included acute kidney injury, AKI, epidemiology, outcomes, prevention, therapy, and treatment.

RESULTS

The reported epidemiology and outcomes associated with AKI have been evolving since the publication of consensus criteria that allow accurate identification of mild and moderate AKI. The incidence of AKI after major vascular surgery using current criteria is as high as 49%, although there are significant differences, depending on the type of procedure performed. Many tools have become available to assess and to stratify the risk for AKI and to use that information to prevent AKI in the surgical patient. We describe a standardized clinical assessment and management pathway for vascular surgery patients, incorporating current risk assessment and preventive strategies to prevent AKI and to decrease its complications. Patients without any risk factors can be managed in a perioperative fast-track pathway. Those patients with positive risk factors are tested for kidney stress using the urinary biomarker TIMP-2•IGFBP7, and care is then stratified according to the result. Management follows current Kidney Disease: Improving Global Outcomes guidelines.

CONCLUSIONS

AKI is a common postoperative complication among vascular surgery patients and has a significant impact on morbidity, mortality, and cost. Preoperative risk assessment and optimal perioperative management guided by that risk assessment can minimize the consequences associated with postoperative AKI. Adherence to a standardized perioperative pathway designed to reduce risk of AKI after major vascular surgery offers a promising clinical approach to mitigate the incidence and severity of this challenging clinical problem.

Epidemiology of acute kidney injury and the role of urinary [TIMP-2]·[IGFBP7]: a prospective cohort study in critically ill obstetric patients

BACKGROUND

There are few data regarding acute kidney injury in critically-ill obstetric patients. A combination of urinary cell cycle arrest markers, tissue inhibitor of metalloproteinase-2 (TIMP-2) and insulin-like growth factor binding protein7 (IGFBP7), is validated for the early prediction of acute kidney injury in non-obstetric patients.

METHODS

We evaluated the epidemiology of acute kidney injury in critically-ill obstetric patients and the role of the biomarker combination in predicting acute kidney injury and mortality. Acute kidney injury, its severity and risk factors, were assessed using Kidney Disease: Improving Global Outcomes (KDIGO) guidelines during the intensive care unit stay. An ELISA technique measured TIMP-2 and IGFBP7 in urine samples collected at the time of admission there.

RESULTS

Results for 66 patients showed an overall incidence of acute kidney injury of 40/66 (61%), with 50%, 10% and 40% being in stage 1, 2 and 3 respectively. Patients with acute kidney injury showed significantly greater sepsis and shock; longer stay and higher mortality during intensive care (33% vs 0%) and in hospital (38% vs 0%) compared to those without (P <0.05). The area-under-the receiver operating characteristics curve was <0.5 for urinary [TIMP-2]·[IGFBP7] as a predictor of kidney injury and mortality (P >0.05).

CONCLUSIONS

Acute kidney injury is common in critically-ill obstetric patients, increasing mortality and duration of hospitalization. It was significantly more common in patients with septic shock. Previously validated results of urinary [TIMP-2]·[IGFBP7] that successfully predict early acute kidney injury or mortality are not applicable to obstetric patients.

Urinary neutrophil gelatinase-associated lipocalin-guided risk assessment for major adverse kidney events after open-heart surgery

AIM

To assess weather doctors' clinical risk-assessment for major adverse kidney events (MAKE) and acute kidney injury (AKI) after open-heart surgery would improve when being informed about neutrophil gelatinase-associated lipocalin (NGAL) test result at ICU admission.

PATIENTS & METHODS

Clinical risk-assessment for MAKE and AKI were performed with and without providing NGAL test result and compared in an exploratory- and a validation-cohort using reclassification metrics, exemplary category-free net reclassification improvement (cfNRI).

RESULTS

Exploratory cohort: doctors' prediction of MAKE (cfNRI = 0.750 [0.130-1.370]; p = 0.018) and AKI (cfNRI = 0.565 [0.001-1.129]; p = 0.049) improved being provided with NGAL test information. This finding was confirmed in the validation-cohort (MAKE cfNRI = 0.930 [0.188-1.672]; p = 0.014) and the combined-cohort (MAKE: cfNRI = 0.847 [0.371-1.323], p < 0.001); AKI: cfNRI = 0.468 [0.099-0.836; p = 0.013]). Improvements mostly generated from correctly reclassifying patients who not developed events (p < 0.001).

CONCLUSION

Biomarker informed risk-assessment is superior in predicting MAKE and AKI after open-heart surgery.

Prevention of Acute Kidney Injury in Children Undergoing Cardiac Surgery: A Narrative Review

Children undergoing cardiac surgery are at risk of developing acute kidney injury (AKI). Preventing cardiac surgery-associated AKI (CS-AKI) is important as it is associated with increased early- and long-term mortality and morbidity. Targeting modifiable risk factors (eg, avoiding poor renal perfusion, nephrotoxic drugs, and fluid overload) reduces the risk of CS-AKI. There is currently no strong evidence for the routine use of pharmacological approaches (eg, aminophylline, dexmedetomidine, fenoldopam, and steroids) to prevent CS-AKI. There is robust evidence to support the role of early peritoneal dialysis as a nonpharmacologic approach to prevent CS-AKI.

Plasma and urinary p21: potential biomarkers of AKI and renal aging

p21 is upregulated in renal tubules in response to acute kidney injury ( AKI). and localizes in the nucleus, where it induces cell cycle arrest (CCA). These events can mitigate early injury but can also facilitate the onset of the degenerative cell senescence/"aging" process. Hence, we asked the following: 1) can AKI-induced p21 upregulation be gauged by plasma and/or urinary p21 assay; 2) might p21 serve as an AKI/CCA biomarker; and 3) does p21 accumulate during normal renal aging, and might plasma p21 reflect this process? Mice were subjected to either ischemia-reperfusion (I/R) or nephotoxic (maleate) AKI. Renal cortical p21 expression (protein, mRNA) was assessed 2-18 h later and contrasted with plasma/urine p21 concentrations (ELISA). p21 mRNA/protein levels were also measured in aging mice (2, 12, 24 mo). AKI induced marked, progressive, increases in renal cortical p21 mRNA and protein levels. These changes were marked by acute (within 2-4 h) and profound increases (up to 200×) in both plasma and urine p21 concentrations. Renal I/R also activated p21 gene expression in extrarenal organs (heart, brain), consistent with so-called "organ cross talk". p21 efflux from damaged cells was confirmed with studies of hypoxia-injured, isolated proximal tubules. Aging was associated with progressive renal cortical p21 expression, which correlated ( r, 0.83) with rising plasma p21 concentrations. We concluded that 1) during AKI, renal p21 increases can be gauged by either plasma or urine p21 assay, serving as potentially useful AKI/CCA biomarkers; 2) AKI can activate p21 in extrarenal organs; and 3) plasma p21 levels may provide an index of the renal/systemic aging process.

Predictive value of cell cycle arrest biomarkers for cardiac surgery-associated acute kidney injury: a meta-analysis

BACKGROUND

A biomarker test based on a combination of urine tissue inhibitor of metalloproteinases 2 (TIMP-2) and insulin-like growth factor binding protein 7 (IGFBP7) has been used as a potential biomarker of acute kidney injury (AKI). This meta-analysis aimed to evaluate the predictive value of this biomarker for cardiac surgery-associated acute kidney injury (CSA-AKI).

METHODS

We searched MEDLINE, PubMed, Cochrane, and EMBASE for studies. We evaluated the methodological quality of each included study using the Quality Assessment of Diagnostic Accuracy Studies 2 criteria. Meta-DiSc and STATA were used for statistical analyses.

RESULTS

A total of 10 studies (747 patients) were included in this meta-analysis. Pooled sensitivity and specificity with corresponding 95% confidence intervals (CI) were 0.77 (95% CI: 0.70-0.83, I2=40.7%) and 0.76 (95% CI: 0.72-0.79, I2=69.1%), respectively. Pooled positive likelihood ratio (LR), negative LR, and diagnostic odds ratio were 3.26 (95% CI: 2.51-4.23, I2=50.7%), 0.32 (95% CI: 0.24-0.41, I2=6.7%), and 10.08 (95% CI: 6.85-14.84, I2=6.7%), respectively. The area under the curve estimated by summary receiver operating characteristics was 0.83 [standard error (SE) 0.023] with a Q* value of 0.759 (se 0.021). There was no heterogeneity amongst the 10 studies from both threshold and non-threshold effects. Subgroup analysis showed that the diagnostic value was related to the severity of AKI and time measurement.

CONCLUSIONS

Urinary [TIMP-2]·[IGFBP7] is an effective predictive test for cardiac surgery associated acute kidney injury with good diagnostic accuracy within 24 h. Studies examining use of biomarker-guided care bundles are indicated.

Acute Kidney Injury Before and After Liver Transplant

The development of acute kidney injury in the setting of liver disease is a significant event both before and after liver transplant. Whether acute kidney injury is the cause of or merely associated with worse outcomes, the development of renal failure is significant from a prognostic as well as from a diagnostic and therapeutic standpoint. Although not every etiology is reversible, there are number of etiologies that are correctable, to include hypovolemia, nephrotoxic medications, and acute tubular necrosis. In the post-liver transplant period, renal failure is associated with graft failure as well as worse outcomes overall. Prompt recognition, workup, and intervention can significantly impact outcomes and survival both before and after liver transplant.

RNA-seq analyses the effect of high-salt diet in hypertension

OBJECTIVES

High-salt diet is one of the major risk factors in the development of hypertension. Previous studies have observed a relationship between high-salt induced blood pressure levels and cardiac-cerebral disease. However, the molecular mechanism of high-salt diet induced hypertension and the serious complications in cardiovascular system still remain unknown.

MATERIALS AND METHODS

We built high-salt diet induced hypertension rat models, and investigated the transcriptomic alteration in four hypertension affected tissues, i.e. ventricle and atrium in heart as well as cortex and medulla in kidney. Differential expression gene (DEG) analysis and further functional annotation including Ingenuity Pathway Analysis (IPA) was performed to reveal the molecular mechanism of high-salt induced hypertension and organ injury.

RESULTS

We observed that several genes associated with cardiovascular development and organ injury were significantly dysregulated rat fed with high-salt diet, such as Mmp-15, Igfbp7, Rgs18 and Hras. We demonstrated that differential expressed genes were functionally related to the increased levels of alkaline phosphatase (ALP).

CONCLUSION

Our study provided new insight about molecular mechanism of high-salt induced hypertension and heart and kidney damage.

Biomarkers in acute kidney injury (AKI)

Acute kidney injury is common in critically ill patients and portends a significant impact on mortality, progressive chronic kidney disease, and cardiovascular disease and mortality. Though most physicians alter therapy depending on changes in serum creatinine, this often represents delayed intervention. Various AKI biomarkers have been discovered and validated to improve timely detection, differentiation and stratification into risk groups for progressive renal decline, need for renal replacement therapy or death. This chapter will review AKI biomarkers validated over the past decade. We also describe the clinical performance of the biomarkers. We suggest that using AKI biomarkers to complement serum creatinine (or cystatin C) and urine output will better integrate patient care through earlier recognition and clinical outcome prediction after AKI.

Innovative Use of Novel Biomarkers to Improve the Safety of Renally Eliminated and Nephrotoxic Medications

Over the last decade, the discovery of novel renal biomarkers and research on their use to improve medication effectiveness and safety has expanded considerably. Pharmacists are uniquely positioned to leverage this new technology for renal assessment to improve medication dosing and monitoring. Serum cystatin C is a relatively new, inexpensive, functional renal biomarker that responds more quickly to changing renal function than creatinine and is not meaningfully affected by age, sex, skeletal muscle mass, dietary intake, or deconditioning. Cystatin C has been proposed as an adjunct or alternative to creatinine for glomerular filtration rate assessment and estimation of drug clearance. Tissue inhibitor of metalloproteinase-2·insulin-like growth factor-binding protein 7 ([TIMP-2]·[IGFBP7]) is a composite of two damage biomarkers released into the urine at a checkpoint in mitosis when renal cells undergo stress or sense a future risk of damage. Concentrations of [TIMP-2]·[IGFBP7] increase before a rise in serum creatinine is evident, thus providing insightful information for evaluation in the context of other patient data to predict the risk for impending kidney injury. This article provides a brief overview of novel renal biomarkers being used as a mechanism to improve medication safety including a discussion of cystatin C, as part of drug-dosing algorithms and specifically for vancomycin dosing, and the use of [TIMP-2]·[IGFBP7] for risk prediction in acute kidney injury and drug-induced kidney disease. Select cases of clinical experience with novel renal biomarkers are outlined, and lessons learned and future applications are described.

Ventilator-Induced Kidney Injury: Are Novel Biomarkers the Key to Prevention?

Mechanical ventilation is associated with significant increases in the risk of acute kidney injury (AKI). The rate of AKI due to mechanical ventilation and the associated mortality remain unacceptably high. Preventative and therapeutic strategies are clearly lacking. Ventilator-induced kidney injury is believed to occur due to changes in hemodynamics that impair renal perfusion, neurohumoral-mediated alterations in intra-renal blood flow, and systemic inflammatory mediators generated by ventilator-induced lung injury. The risk of injury to the kidney by these mechanisms may be modified by open lung protective ventilation with low tidal volumes and high positive end expiratory pressure. However, these strategies may also increase the risk of injury in some settings, and clinicians have limited means to identify the optimal ventilator strategy for each specific patient. Novel urinary biomarkers have demonstrated the ability to predict AKI prior to classic clinical signs such as decreased urine output and increased creatinine. These biomarkers may serve as an early indication to intensivists of an injurious ventilator strategy and failure of traditional management.

Mechanisms Underlying Increased TIMP2 and IGFBP7 Urinary Excretion in Experimental AKI

BACKGROUND

Recent clinical data support the utility/superiority of a new AKI biomarker ("NephroCheck"), the arithmetic product of urinary TIMP × IGFBP7 concentrations. However, the pathophysiologic basis for its utility remains ill defined.

METHODS

To clarify this issue, CD-1 mice were subjected to either nephrotoxic (glycerol, maleate) or ischemic AKI. Urinary TIMP2/IGFBP7 concentrations were determined at 4 and 18 hours postinjury and compared with urinary albumin levels. Gene transcription was assessed by measuring renal cortical and/or medullary TIMP2/IGFBP7 mRNAs (4 and 18 hours after AKI induction). For comparison, the mRNAs of three renal "stress" biomarkers (NGAL, heme oxygenase 1, and p21) were assessed. Renal cortical TIMP2/IGFBP7 protein was gauged by ELISA. Proximal tubule-specific TIMP2/IGFBP7 was assessed by immunohistochemistry.

RESULTS

Each AKI model induced prompt (4 hours) and marked urinary TIMP2/IGFBP7 increases without an increase in renal cortical concentrations. Furthermore, TIMP2/IGFBP7 mRNAs remained at normal levels. Endotoxemia also failed to increase TIMP2/IGFBP7 mRNAs. In contrast, each AKI model provoked massive NGAL, HO-1, and p21 mRNA increases, confirming that a renal "stress response" had occurred. Urinary albumin rose up to 100-fold and strongly correlated (r=0.87-0.91) with urinary TIMP2/IGFBP7 concentrations. Immunohistochemistry showed progressive TIMP2/IGFBP7 losses from injured proximal tubule cells. Competitive inhibition of endocytic protein reabsorption in normal mice tripled urinary TIMP2/IGFBP7 levels, confirming this pathway's role in determining urinary excretion.

CONCLUSIONS

AKI-induced urinary TIMP2/IGFBP7 elevations are not due to stress-induced gene transcription. Rather, increased filtration, decreased tubule reabsorption, and proximal tubule cell TIMP2/IGFBP7 urinary leakage seem to be the most likely mechanisms.

Postoperative cellular stress in the kidney is associated with an early systemic γδ T-cell immune cell response

Background

Basic science data suggest that acute kidney injury (AKI) induced by ischemia-reperfusion injury (IRI) is an inflammatory process involving the adaptive immune response. Little is known about the T-cell contribution in the very early phase, so we investigated if tubular cellular stress expressed by elevated cell cycle biomarkers is associated with early changes in circulating T-cell subsets, applying a bedside-to-bench approach.

Methods

Our observational pilot study included 20 consecutive patients undergoing endovascular aortic repair for aortic aneurysms affecting the renal arteries, thereby requiring brief kidney hypoperfusion and reperfusion. Clinical-grade flow cytometry-based immune monitoring of peripheral immune cell populations was conducted perioperatively and linked to tubular cell stress biomarkers ([TIMP-2]•[IGFBP7]) immediately after surgery. To confirm clinical results and prove T-cell infiltration in the kidney, we simulated tubular cellular injury in an established mouse model of mild renal IRI.

Results

A significant correlation between tubular cell injury and a peripheral decline of γδ T cells, but no other T-cell subpopulation, was discovered within the first 24 hours (r = 0.53; p = 0.022). Turning to a mouse model of kidney warm IRI, a similar decrease in circulating γδ T cells was found and concomitantly was associated with a 6.65-fold increase in γδ T cells (p = 0.002) in the kidney tissue without alterations in other T-cell subsets, consistent with our human data. In search of a mechanistic driver of IRI, we found that the damage-associated molecule high-mobility group box 1 protein HMGB1 was significantly elevated in the peripheral blood of clinical study subjects after tubular cell injury (p = 0.019). Correspondingly, HMGB1 RNA content was significantly elevated in the murine kidney.

Conclusions

Our investigation supports a hypothesis that γδ T cells are important in the very early phase of human AKI and should be considered when designing clinical trials aimed at preventing kidney damage.

Trial registration

ClinicalTrials.gov, NCT01915446. Registered on 5 Aug 2013.

Electronic supplementary material

The online version of this article (10.1186/s13054-018-2094-x) contains supplementary material, which is available to authorized users.

Prognostic value of cell cycle arrest biomarkers in patients at high risk for acute kidney injury: A systematic review and meta-analysis

Urinary tissue inhibitor of metalloproteinase-2 (TIMP-2) and insulin-like growth factor binding protein 7 (IGFBP7) are G1 cell cycle arrest biomarkers. This systematic review aimed to evaluate the prognostic value of urinary [TIMP-2]·[IGFBP7] in patients at high risk for AKI. The MEDLINE (via PubMed), Ovid, EMBASE and Cochrane Library databases were systematically searched from inception to December 25, 2016. Original clinical studies which met the eligibility criteria were included in this study. The prognostic accuracy of urinary [TIMP-2]·[IGFBP7] for assessing the need for renal replacement therapy (RRT) and mortality was evaluated by pooled sensitivity, specificity, diagnostic odds ratio, and summary receiver operating characteristic curves. A total of four prospective cohort studies evaluating 277 patients were included. The estimated area under the receiver operating characteristic curve (AUC) of urinary [TIMP-2]·[IGFBP7] for predicting the need for RRT in patients at high risk for AKI was 0.915 (standard error [SE] = 0.040). Pooled sensitivity and specificity with corresponding 95% confidence intervals (CI) were 0.69 (95% CI 0.53-0.82) and 0.81 (95% CI 0.75-0.86), respectively. Urinary [TIMP-2]·[IGFBP7] for mortality prediction in patients at high risk for AKI was assessed by qualitative description. Based on the above data, urinary [TIMP-2]·[IGFBP7] performs well in predicting the need for RRT and mortality in patients at high risk for AKI. However, further meta-analyses are warranted as more data become available.

Clinical Relevance and Predictive Value of Damage Biomarkers of Drug-Induced Kidney Injury

Nephrotoxin exposure accounts for up to one-fourth of acute kidney injury episodes in hospitalized patients, and the associated consequences are as severe as acute kidney injury due to other etiologies. As the use of nephrotoxic agents represents one of the few modifiable risk factors for acute kidney injury, clinicians must be able to identify patients at high risk for drug-induced kidney injury rapidly. Recently, significant advancements have been made in the field of biomarker utilization for the prediction and detection of acute kidney injury. Such biomarkers may have a role both for detection of drug-induced kidney disease and implementation of preventative and therapeutic strategies designed to mitigate injury. In this article, basic principles of renal biomarker use in practice are summarized, and the existing evidence for six markers specifically used to detect drug-induced kidney injury are outlined, including liver-type fatty acid binding protein, neutrophil gelatinase-associated lipocalin, tissue inhibitor of metalloproteinase-2 times insulin-like growth factor-binding protein 7 ([TIMP-2]·[IGFBP7]), kidney injury molecule-1 and N-acetyl-β-D-glucosaminidase. The results of the literature search for these six kidney damage biomarkers identified 29 unique articles with none detected for liver-type fatty acid binding protein and [TIMP-2]·[IGFBP7]. For three biomarkers, kidney injury molecule-1, neutrophil gelatinase-associated lipocalin and N-acetyl-β-D-glucosaminidase, the majority of the studies suggest utility in clinical practice. While many questions need to be answered to clearly articulate the use of biomarkers to predict drug-induced kidney disease, current data are promising.

Phase 2a Clinical Trial of Mitochondrial Protection (Elamipretide) During Stent Revascularization in Patients With Atherosclerotic Renal Artery Stenosis

BACKGROUND

Atherosclerotic renal artery stenosis reduces renal blood flow (RBF) and amplifies stenotic kidney hypoxia. Revascularization with percutaneous transluminal renal angioplasty (PTRA) and stenting often fails to recover renal function, possibly because of ischemia/reperfusion injury developing after PTRA. Elamipretide is a mitochondrial-targeted peptide that binds to cardiolipin and stabilizes mitochondrial function. We tested the hypothesis that elamipretide plus PTRA would improve renal function, oxygenation, and RBF in patients with atherosclerotic renal artery stenosis undergoing PTRA.

METHODS AND RESULTS

Inpatient studies were performed in patients with severe atherosclerotic renal artery stenosis scheduled for PTRA. Patients were treated before and during PTRA with elamipretide (0.05 mg/kg per hour intravenous infusion, n=6) or placebo (n=8). Stenotic kidney cortical/medullary perfusion and RBF were measured using contrast-enhanced multidetector CT, and renal oxygenation by 3-T blood oxygen level-dependent magnetic resonance imaging before and 3 months after PTRA. Age and basal glomerular filtration rate did not differ between groups. Blood oxygen level-dependent imaging demonstrated increased fractional hypoxia 24 hours after angiography and stenting in placebo (+47%) versus elamipretide (-6%). These were reverted to baseline 3 months later. Stenotic kidney RBF rose (202±29-262±115 mL/min; P=0.04) 3 months after PTRA in the elamipretide-treated group only. Over 3 months, systolic blood pressure decreased, and estimated glomerular filtration rate increased (P=0.003) more in the elamipretide group than in the placebo group (P=0.11).

CONCLUSIONS

Adjunctive elamipretide during PTRA was associated with attenuated postprocedural hypoxia, increased RBF, and improved kidney function in this pilot trial. These data support a role for targeted mitochondrial protection to minimize procedure-associated ischemic injury and to improve outcomes of revascularization for human atherosclerotic renal artery stenosis.

CLINICAL TRIAL REGISTRATION

URL: https://www.clinicaltrials.gov. Unique identifier: NCT01755858.

TIMP-2/IGFBP7 predicts acute kidney injury in out-of-hospital cardiac arrest survivors

Background

Acute kidney injury (AKI) is a common complication after cardiopulmonary resuscitation (CPR) and predicts in-hospital mortality. To which extent post-resuscitation disease or the initial event of cardiac arrest and the duration of insufficient cardiac output triggers AKI is challenging to discriminate. Knowledge on molecular mediators of AKI is scarce. Early identification of patients at high risk of AKI is hampered by the low sensitivity of the established tests in clinical routine practice. The present study aimed to determine the diagnostic utility of the novel urine biomarkers tissue inhibitor of metalloproteinases-2 (TIMP-2) and insulin-like growth factor-binding protein 7 (IGFBP7) for the early recognition of AKI in patients with non-traumatic shock.

Methods

The performance of [TIMP-2]·[IGFBP7] was prospectively analysed in 48 patients with shock following out-of-hospital cardiac arrest (OHCA). All patients were treated with target temperature management (TTM) for 24 h. Urinary [TIMP-2]·[IGFBP7] samples were collected at 3 and 24 h after determination of OHCA.

Results

Patients (n = 31 (65%)) developed AKI after an average of 26 ± 12 h. Patients who developed AKI had significantly higher [TIMP-2]·[IGFBP7] compared to individuals that did not develop AKI (1.52 ± 0.13 vs. 0.13 ± 0.14; p < 0.05) as early as 3 h after determination of OHCA,. For urine [TIMP-2]*[IGFBP7], the area under the curve (AUC) for the development of AKI was 0.97 (CI 0.90–1.00) at 3 h after OHCA. The optimal [TIMP-2]·[IGFBP7] cut-off value for the prediction of AKI was 0.24. The sensitivity was 96.8% and specificity was 94.1%.

Conclusions

Urinary [TIMP-2]•[IGFBP7] reliably predicts AKI in high-risk patients only 3 h after determination of OHCA with a cut-off at 0.24. This novel test may help to identify patients at high risk of AKI to enrol into clinical studies to further elucidate the pathophysiology of AKI and devise targeted interventions in the future.

Electronic supplementary material

The online version of this article (10.1186/s13054-018-2042-9) contains supplementary material, which is available to authorized users.

Sepsis-induced acute kidney injury

PURPOSE OF REVIEW

Sepsis is a common and frequently fatal condition in which mortality has been consistently linked to increasing organ dysfunction. For example, acute kidney injury (AKI) occurs in 40-50% of septic patients and increases mortality six to eight-fold. However, the mechanisms by which sepsis causes organ dysfunction are not well understood and hence current therapy remains reactive and nonspecific.

RECENT FINDINGS

Recent studies have challenged the previous notion that organ dysfunction is solely secondary to hypoperfusion, by showing, for example, that AKI occurs in the setting of normal or increased renal blood flow; and that it is characterized not by acute tubular necrosis or apoptosis, but rather by heterogeneous areas of colocalized sluggish peritubular blood flow and tubular epithelial cell oxidative stress. Evidence has also shown that microvascular dysfunction, inflammation, and the metabolic response to inflammatory injury are fundamental pathophysiologic mechanisms that may explain the development of sepsis-induced AKI.

SUMMARY

The implications of these findings are significant because in the context of decades of negative clinical trials in the field, the recognition that other mechanisms are at play opens the possibility to better understand the processes of injury and repair, and provides an invaluable opportunity to design mechanism-targeted therapeutic interventions.