Mark Mitsnefes

Neutrophil gelatinase-associated lipocalin (NGAL) as a biomarker for acute renal injury after cardiac surgery

BACKGROUND The scarcity of early biomarkers for acute renal failure has hindered our ability to launch preventive and therapeutic measures for this disorder in a timely manner. We tested the hypothesis that neutrophil gelatinase-associated lipocalin (NGAL) is an early biomarker for ischaemic renal injury after cardiopulmonary bypass. METHODS We studied 71 children undergoing cardiopulmonary bypass. Serial urine and blood samples were analysed by western blots and ELISA for NGAL expression. The primary outcome measure was acute renal injury, defined as a 50% increase in serum creatinine from baseline. FINDINGS 20 children (28%) developed acute renal injury, but diagnosis with serum creatinine was only possible 1-3 days after cardiopulmonary bypass. By contrast, urine concentrations of NGAL rose from a mean of 1.6 microg/L (SE 0.3) at baseline to 147 microg/L (23) 2 h after cardiopulmonary bypass, and the amount in serum increased from a mean of 3.2 microg/L (SE 0.5) at baseline to 61 microg/L (10) 2 h after the procedure. Univariate analysis showed a significant correlation between acute renal injury and the following: urine and serum concentrations of NGAL at 2 h, and cardiopulmonary bypass time. By multivariate analysis, the amount of NGAL in urine at 2 h after cardiopulmonary bypass was the most powerful independent predictor of acute renal injury. For concentration in urine of NGAL at 2 h, the area under the receiver-operating characteristic curve was 0.998, sensitivity was 1.00, and specificity was 0.98 for a cutoff value of 50 microg/L. INTERPRETATION Concentrations in urine and serum of NGAL represent sensitive, specific, and highly predictive early biomarkers for acute renal injury after cardiac surgery.

Identification of Neutrophil Gelatinase-Associated Lipocalin as a Novel Early Urinary Biomarker for Ischemic Renal Injury

Acute renal failure (ARF) secondary to ischemic injury remains a common and potentially devastating problem. A transcriptome-wide interrogation strategy was used to identify renal genes that are induced very early after renal ischemia, whose protein products might serve as novel biomarkers for ARF. Seven genes that are upregulated >10-fold were identified, one of which (Cyr61) has recently been reported to be induced after renal ischemia. Unexpectedly, the induction of the other six transcripts was novel to the ARF field. In this study, one of these previously unrecognized genes was further characterized, namely neutrophil gelatinase-associated lipocalin (NGAL), because it is a small secreted polypeptide that is protease resistant and consequently might be readily detected in the urine. The marked upregulation of NGAL mRNA and protein levels in the early postischemic mouse kidney was confirmed. NGAL protein expression was detected predominantly in proliferating cell nuclear antigen-positive proximal tubule cells, in a punctate cytoplasmic distribution that co-localized with markers of late endosomes. NGAL was easily detected in the urine in the very first urine output after ischemia in both mouse and rat models of ARF. The appearance of NGAL in the urine was related to the dose and duration of renal ischemia and preceded the appearance of other urinary markers such as N-acetyl-beta-D-glucosaminidase and beta2-microglobulin. The origin of NGAL from tubule cells was confirmed in cultured human proximal tubule cells subjected to in vitro ischemic injury, where NGAL mRNA was rapidly induced in the cells and NGAL protein was readily detectable in the culture medium within 1 h of mild ATP depletion. NGAL was also easily detectable in the urine of mice with cisplatin-induced nephrotoxicity, again preceding the appearance of N-acetyl-beta-D-glucosaminidase and beta2-microglobulin. The results indicate that NGAL may represent an early, sensitive, noninvasive urinary biomarker for ischemic and nephrotoxic renal injury.

Plasma neutrophil gelatinase-associated lipocalin predicts acute kidney injury, morbidity and mortality after pediatric cardiac surgery: a prospective uncontrolled cohort study

IntroductionAcute kidney injury (AKI) is a frequent complication of cardiopulmonary bypass (CPB). The lack of early biomarkers has impaired our ability to intervene in a timely manner. We previously showed in a small cohort of patients that plasma neutrophil gelatinase-associated lipocalin (NGAL), measured using a research enzyme-linked immunosorbent assay, is an early predictive biomarker of AKI after CPB. In this study we tested whether a point-of-care NGAL device can predict AKI after CPB in a larger cohort.MethodsFirst, in a cross-sectional pilot study including 40 plasma samples (NGAL range 60 to 730 ng/ml) and 12 calibration standards (NGAL range 0 to 1,925 ng/ml), NGAL measurements by enzyme-linked immunosorbent assay and by Triage® NGAL Device (Biosite Inc., San Diego, CA, USA) were highly correlated (r = 0.94). Second, in a subsequent prospective uncontrolled cohort study, 120 children undergoing CPB were enrolled. Plasma was collected at baseline and at frequent intervals for 24 hours after CPB, and analyzed for NGAL using the Triage® NGAL device. The primary outcome was AKI, which was defined as a 50% or greater increase in serum creatinine.ResultsAKI developed in 45 patients (37%), but the diagnosis using serum creatinine was delayed by 2 to 3 days after CPB. In contrast, mean plasma NGAL levels increased threefold within 2 hours of CPB and remained significantly elevated for the duration of the study. By multivariate analysis, plasma NGAL at 2 hours after CPB was the most powerful independent predictor of AKI (β = 0.004, P < 0.0001). For the 2-hour plasma NGAL measurement, the area under the curve was 0.96, sensitivity was 0.84, and specificity was 0.94 for prediction of AKI using a cut-off value of 150 ng/ml. The 2 hour postoperative plasma NGAL levels strongly correlated with change in creatinine (r = 0.46, P < 0.001), duration of AKI (r = 0.57, P < 0.001), and length of hospital stay (r = 0.44, P < 0.001). The 12-hour plasma NGAL strongly correlated with mortality (r = 0.48, P = 0.004) and all measures of morbidity mentioned above.ConclusionAccurate measurements of plasma NGAL are obtained using the point-of-care Triage® NGAL device. Plasma NGAL is an early predictive biomarker of AKI, morbidity, and mortality after pediatric CPB.

Amelioration of Ischemic Acute Renal Injury by Neutrophil Gelatinase-Associated Lipocalin

Acute renal failure secondary to ischemic injury remains a common problem, with limited and unsatisfactory therapeutic options. Neutrophil gelatinase-associated lipocalin (NGAL) was recently shown to be one of the maximally induced genes early in the postischemic kidney. In this study, the role of NGAL in ischemic renal injury was explored. Intravenous administration of purified recombinant NGAL in mice resulted in a rapid uptake of the protein predominantly by proximal tubule cells. In an established murine model of renal ischemia-reperfusion injury, intravenous NGAL administered before, during, or after ischemia resulted in marked amelioration of the morphologic and functional consequences, as evidenced by a significant decrease in the histopathologic damage to tubules and in serum creatinine measurements. NGAL-treated animals also displayed a reduction in the number of apoptotic tubule cells and an increase in proliferating proximal tubule cells after ischemic injury. The results indicate that NGAL may represent a novel therapeutic intervention in ischemic acute renal failure, based at least in part on its ability to tilt the balance of tubule cell fate toward survival.

Kidney NGAL is a novel early marker of acute injury following transplantation

Acute kidney injury secondary to ischemia–reperfusion in renal allografts often results in delayed graft function. We tested the hypothesis that expression of neutrophil gelatinase-associated lipocalin (NGAL) is an early marker of acute kidney injury following transplantation. Sections from paraffin-embedded protocol biopsy specimens obtained at approximately one hour of reperfusion after transplantation of 13 cadaveric (CAD) and 12 living-related (LRD) renal allografts were examined by immunohistochemistry for expression of NGAL. The staining intensity was correlated with cold ischemia time, peak post-operative serum creatinine, and dialysis requirement. There were no differences between the LRD and CAD groups in age, gender or preoperative serum creatinine. Using a scoring system of 0 (no staining) to 3 (most intense staining), NGAL expression was significantly increased in CAD specimens (2.3±0.8 versus 0.8±0.7 in LRD, p<0.001). There was a strong correlation between NGAL staining intensity and cold ischemia time (R=0.87, p<0.001). Importantly, NGAL staining in these early CAD biopsies was strongly correlated with peak postoperative serum creatinine, which occurred days later (R=0.86, p<0.001). Four patients developed delayed graft function requiring dialysis during the first week posttransplantation; all of these patients displayed the most intense NGAL staining in their first protocol biopsies. We conclude that NGAL staining intensity in early protocol biopsies represents a novel predictive biomarker of acute kidney injury following transplantation.

Age-Specific Reference Intervals for Indexed Left Ventricular Mass in Children

BACKGROUND In older children, one of the standards for indexing left ventricular mass (LVM) is height raised to an exponential power of 2.7. The purpose of this study was to establish a normal value for the pediatric age group and to determine how, if at all, LVM/height(2.7) varies in children. METHODS M-mode echocardiography was performed in 2,273 nonobese, healthy children (1,267 boys, 1,006 girls; age range 0-18 years). Curves were constructed for the 5th, 10th, 25th, 50th, 75th, 90th, and 95th quantiles of LVM/height(2.7). RESULTS In children aged > 9 years, median LVM/height(2.7) ranged from 27 to 32 g/m(2.7) and had little variation with age. However, in those aged < 9 years, LVM/height(2.7) varied significantly, and percentiles for newborns and infants were approximately double the levels for older children and adolescents: the 95th percentile ranged from 80 g/m(2.7) for newborns to 40 g/m(2.7) for 11-year-olds. CONCLUSION For patients aged > 9 years, quantiles of LVM/height(2.7) vary little, and values > 40 g/m(2.7) in girls and > 45 g/m(2.7) in boys can be considered abnormal (ie, > 95th percentile). However, for patients aged < 9 years, the index varies with age, and therefore, measured LVM/height(2.7) must be compared with percentile curves, which are provided. This variation in LVM/height(2.7) in younger children indicates that a better indexing method is needed for this age group. Nevertheless, these data are valuable in that they provide normal values with which patient data can be compared.

Update: Ambulatory Blood Pressure Monitoring in Children and Adolescents: A Scientific Statement From the American Heart Association

Ambulatory blood pressure monitoring (ABPM) has established roles in the evaluation and management of hypertension in adults but has only been applied to children and adolescents more recently.1 In 2008, the American Heart Association (AHA) issued the first set of consensus recommendations for performance and interpretation of ABPM in pediatrics. Since then, ABPM has found increasing use in children and adolescents, as recently summarized.2 The present document updates the 2008 AHA statement on the use of ABPM in the pediatric population3 with additional data published since the release of that report and also presents a revised interpretation schema. Because no outcome studies are yet available relating ABPM levels in children to outcomes such as myocardial infarction or stroke, these guidelines are largely driven by expert opinion, although they are also informed by available pediatric data on ABPM and surrogate markers of cardiovascular disease. ### Epidemiology of Hypertension High blood pressure (BP) is the leading risk factor–related cause of death throughout the world, accounting for 12.8% of all deaths, including 51% of stroke deaths and 45% of coronary heart disease deaths.4 In the United States, 33.0% of adults >20 years of age have hypertension.5 As our population continues to age, this will only increase, because 90% of people with normal BP at age 55 years will go on to develop hypertension in their lifetimes.6 The prevalence of hypertension in youths is also on the rise. US National Health and Nutrition Examination Survey (NHANES) data from 1963 to 2002 showed a 2.3% increase in prehypertension and a 1% increase in hypertension from 1988 to 1999, with higher rates in non-Hispanic blacks and Mexican Americans.7 In fact, the entire distribution of childhood BP has shifted upward in the United States by 1.4 mm Hg for systolic BP (SBP) and 3.3 …

Severe left ventricular hypertrophy in pediatric dialysis: prevalence and predictors.

Abstract Left ventricular hypertrophy (LVH) has been recognized as an independent risk factor for cardiovascular morbidity and mortality in adults with end-stage renal disease. However, the prevalence and severity of LVH in children on chronic dialysis therapy is not well established. Retrospectively, 64 chronic dialysis patients, aged 20 months to 22 years, on chronic dialysis had echocardiographic evaluation of LV mass (LVM) and geometry. Forty-eight (75%) children had LVH, including 22 of 26 (85%) on hemodialysis (HD) and 26 of 38 (68%) on peritoneal dialysis (PD). The prevalence of LVH in patients on HD was significantly higher than those on PD (P=0.02). Abnormal LV geometry was found in 51 of 64 (80%) patients: 25 patients (39%) had eccentric hypertrophy, 3 (5%) had concentric remodelling, and 23 (36%) had concentric LVH. Twenty-six children (41%) had severe LVH, defined as LVM index greater than 51 g/m2.7, which is associated with a fourfold greater risk for development of cardiovascular disease in adults. Patients with severe LVH had a significantly lower hemoglobin level (P=0.027) and longer duration of renal disease prior to the start of dialysis therapy (P=0.003) than patients without LVH. Multiple logistic regression analysis revealed HD as opposed to PD as a significant independent predictor for severe LVH (P=0.036). Higher systolic blood pressure remained in the final model as an independent predictor with a borderline level of significance (P=0.065). The results indicate that severe LVH and abnormal left ventricular geometry are common in young dialysis patients. Better control of blood pressure, anemia, and hypervolemia may be important in prevention or improving LVH.

Blood Pressure in Children with Chronic Kidney Disease: A Report from the Chronic Kidney Disease in Children Study

To characterize the distribution of blood pressure (BP), prevalence, and risk factors for hypertension in pediatric chronic kidney disease, we conducted a cross-sectional analysis of baseline BPs in 432 children (mean age 11 years; 60% male; mean glomerular filtration rate 44 mL/min per 1.73 m2) enrolled in the Chronic Kidney Disease in Children cohort study. BPs were obtained using an aneroid sphygmomanometer. Glomerular filtration rate was measured by iohexol disappearance. Elevated BP was defined as BP ≥90th percentile for age, gender, and height. Hypertension was defined as BP ≥95th percentile or as self-reported hypertension plus current treatment with antihypertensive medications. For systolic BP, 14% were hypertensive and 11% were prehypertensive (BP 90th to 95th percentile); 68% of subjects with elevated systolic BP were taking antihypertensive medications. For diastolic BP, 14% were hypertensive and 9% were prehypertensive; 53% of subjects with elevated diastolic BP were taking antihypertensive medications. Fifty-four percent of subjects had either systolic or diastolic BP ≥95th percentile or a history of hypertension plus current antihypertensive use. Characteristics associated with elevated BP included black race, shorter duration of chronic kidney disease, absence of antihypertensive medication use, and elevated serum potassium. Among subjects receiving antihypertensive treatment, uncontrolled BP was associated with male sex, shorter chronic kidney disease duration, and absence of angiotensin-converting enzyme inhibitor or angiotensin receptor blocker use. Thirty-seven percent of children with chronic kidney disease had either elevated systolic or diastolic BP, and 39% of these were not receiving antihypertensives, indicating that hypertension in pediatric chronic kidney disease may be frequently under- or even untreated. Treatment with angiotensin-converting enzyme inhibitors or angiotensin receptor blockers may improve BP control in these patients.

Masked Hypertension Associates with Left Ventricular Hypertrophy in Children with CKD

Left ventricular hypertrophy (LVH) associates with increased risk for cardiovascular disease. Hypertension leads to LVH in adults, but its role in the pathogenesis of LVH in children is not as well established. To examine left ventricular mass and evaluate factors associated with LVH in children with stages 2 through 4 chronic kidney disease (CKD), we analyzed cross-sectional data from children who had baseline echocardiography (n = 366) and underwent ambulatory BP monitoring (n = 226) as a part of the observational Chronic Kidney Disease in Children (CKiD) cohort study. At baseline, 17% of children had LVH (11% eccentric and 6% concentric) and 9% had concentric remodeling of the left ventricle. On the basis of a combination of ambulatory and casual BP assessment (n = 198), 38% of children had masked hypertension (normal casual but elevated ambulatory BP) and 18% had confirmed hypertension (both elevated casual and ambulatory BP). There was no significant association between LVH and kidney function. LVH was more common in children with either confirmed (34%) or masked (20%) hypertension compared with children with normal casual and ambulatory BP (8%). In multivariable analysis, masked (odds ratio 4.1) and confirmed (odds ratio 4.3) hypertension were the strongest independent predictors of LVH. In conclusion, casual BP measurements alone are insufficient to predict the presence of LVH in children with CKD. The high prevalence of masked hypertension and its association with LVH supports early echocardiography and ambulatory BP monitoring to evaluate cardiovascular risk in children with CKD.