Neutrophil gelatinase-associated lipocalin (NGAL): a new marker of kidney disease

Increased urinary excretion of albumin, hemopexin, transferrin and VDBP correlates with chronic sensitization to gentamicin nephrotoxicity in rats

Drug nephrotoxicity is a serious health and economic problem worldwide. Rats can be acutely sensitized to acute kidney injury (AKI) by subnephrotoxic treatments with potentially nephrotoxic drugs. Acquired sensitization to AKI poses a silent risk impossible to diagnose pre-emptively with the technology available at the clinical level. Herein, we hypothesized whether a chronic, subnephrotoxic insult to the kidneys might result in chronically acquired sensitization to AKI, and whether chronic sensitization might be detected through specific urinary markers. To this end, rats were treated with a subtoxic dosage of the experimental nephrotoxin uranyl nitrate (UN) in the drinking water for 21 weeks, or plain water (as control), and then with low-dose gentamicin for 7 days. Renal function and renal tissue damage were evaluated through the experiment. The mild renal damage caused by gentamicin was markedly magnified in rats having received UN chronically, which was evident both at the functional and histological level. Four proteins, namely albumin, hemopexin, transferrin and vitamin D binding protein were increased in the urine in temporal association with the appearance of chronic predisposition. Although further studies are necessary, our results suggest that these proteins might be potentially used as markers of hidden, chronic predisposition to gentamicin nephrotoxicity, in order to appropriately and pre-emptively stratify and handle individuals according to their specific risk in the long term, and to conveniently optimize their life conditions or additional clinical procedures or treatments that might trigger the disease. This might reduce AKI incidence and severity and the associated costs.

Global trends, potential mechanisms and early detection of organ damage in SLE

Increased longevity of patients with systemic lupus erythematosus (SLE) leads to chronic organ damage accrual, which reduces the possibility of further survival improvement in patients with the disease. Observations from lupus centres worldwide revealed that the prevalence of damage occurring in the cardiovascular system in patients with SLE has increased over the past four decades. The results of a meta-analysis involving over 70 observational studies demonstrated that lupus-related organ damage involving the neuropsychiatric and renal systems also remains a major factor that limits survival improvement in patients with this disease. While efforts to halt acute lupus-related injury are continuing, through early diagnosis and effective use of immunosuppressive agents, a concomitant strategy to improve survival of patients with SLE would be early detection and timely treatment of lupus-related organ damage with meticulous monitoring. This Review discusses the pattern and trend of organ damage in patients with SLE worldwide, the potential serological and genetic mechanisms of organ damage, and the advances in research on potential tools for early detection of lupus-related organ damage, such as functional brain imaging techniques, measurement of endothelial function, identification of biomarkers from body fluids, and development of risk calculation models.

New biomarkers for the quick detection of acute kidney injury

Acute kidney injury (AKI) is a common and strong problem in the diagnosis of which based on measurement of BUN and serum creatinine. These traditional methods are not sensitive and specific for the diagnosis of AKI. AKI is associated with increased morbidity and mortality in critically ill patients and a quick detection is impossible with BUN and serum creatinine. A number of serum and urinary proteins have been identified that may messenger AKI prior to a rise in BUN and serum creatinine. New biomarkers of AKI, including NGAL, KIM-1, cystatin-C, IL-18, and L-FABP, are more favourable tests than creatinine which have been identified and studied in several experimental and clinical training. This paper will discuss some of these new biomarkers and their potential as useful signs of AKI. We searched the literature using PubMed and MEDLINE with acute kidney injury, urine, and serum new biomarkers and the articles were selected only from publication types in English.

Cardiorenal biomarkers in acute heart failure

Managing patients with heart failure (HF) is a challenging task within itself, but the presence of associated worsening renal function can greatly increase mortality and morbidity. Early diagnosis and treatment is the key to prevent re-hospitalizations and reduce healthcare costs. Biomarkers have long been established as highly sensitive and specific tools in diagnosing and prognosticating patients with HF. Reflecting distinct pathophysiological events and ongoing cellular insult, biomarkers have been proven superior to conventional laboratory tests. Availability of better assays and rapid analysis has allowed the use of biomarkers as point-of-care tests in the emergency department and at the patient's bed-side. Acute HF patients often go on to develop worsening renal function, termed as acute cardiorenal syndrome. The growing breadth of studies has shown the implications of combining multiple biomarkers to better chart outcomes and produce desirable results in such patients.

Systemic and urinary neutrophil gelatinase-associated lipocalins are poor predictors of acute kidney injury in unselected critically ill patients

Background. Neutrophil gelatinase-associated lipocalin (NGAL) in serum and urine have been suggested as potential early predictive biological markers of acute kidney injury (AKI) in selected critically ill patients. Methods. We performed a secondary analysis of a multicenter prospective observational cohort study of unselected critically ill patients. Results. The analysis included 140 patients, including 57 patients who did not develop AKI, 31 patients who developed AKI, and 52 patients with AKI on admission to the ICU. Levels of sNGAL and uNGAL on non-AKI days were significantly lower compared to levels of sNGAL on RIFLE_RISK days, RIFLE_INJURY days, and RIFLE_FAILURE days. The AUC of sNGAL for predicting AKI was low: 0.45 (95% confidence interval (CI) 0.27–0.63) and 0.53 (CI 0.38–0.67), 2 days and 1 day before development of AKI, respectively. The AUC of uNGAL for predicting AKI was also low: 0.48 (CI 0.33–0.62) and 0.48 (CI 0.33–0.62), 2 days and 1 day before development of AKI, respectively. AUC of sNGAL and uNGAL for the prediction of renal replacement therapy requirement was 0.47 (CI 0.37–0.58) and 0.26 (CI 0.03–0.50). Conclusions. In unselected critically ill patients, sNGAL and uNGAL are poor predictors of AKI or RRT.

Urinary neutrophil gelatinase-associated lipocalin (uNGAL) levels in patients with nonalcoholic fatty liver disease

Background/Aims

Nonalcoholic fatty liver disease (NAFLD), one of the most common forms of chronic liver disease, is closely associated with obesity and insulin resistance (IR). Adipokines secreted by adipose tissue have recently been implicated in initiating and perpetuating the chronic inflammatory state observed in obesity and NAFLD. Recent studies suggest neutrophil gelatinase-associated lipocalin (NGAL) plays a key role in the pathogenesis of IR. The aims of this study were to determine urinary NGAL levels in patients with ultrasonography proven NAFLD and to correlate these levels with the metabolic profile and fibrosis grade in this population.

Methodology

Our cohort consisted of 65 consecutive patients undergoing abdominal ultrasonography for clinical suspicion of NAFLD. Patients were subsequently divided into two groups: no steatosis (n=20) and steatosis (n=45). The stage of fibrosis was measured using a four-point scale. Urinary NGAL was measured by a specific microparticle enzyme immunoassay. The degree of insulin resistance was determined by the homeostatic model assessment (HOMA). Glucose, insulin, lipid profile, and transaminases were also measured.

Results

Urinary NGAL levels correlated with body mass index, HOMA, fasting glucose, and insulin levels in patients with steatosis. Moreover, uNGAL levels were higher in patients with steatosis compared to those with no steatosis (49.8 ng/mL and 22.7 ng/mL, respectively) with a statistically significant difference (p<0.001). A stepwise increase in uNGAL levels from patients without fibrosis (21.7 ng/mL) to patients with cirrhosis (47.4 ng/mL) was noted (p<0.001).

Conclusions

Our study demonstrates that in adult patients with NAFLD, uNGAL levels correlate with BMI, insulin resistance, and lipid profiles, and identifies a novel association between uNGAL levels and hepatocellular injury in these patients.

Mechanism-based urinary biomarkers to identify the potential for aminoglycoside-induced nephrotoxicity in premature neonates: a proof-of-concept study

Premature infants are frequently exposed to aminoglycoside antibiotics. Novel urinary biomarkers may provide a non-invasive means for the early identification of aminoglycoside-related proximal tubule renal toxicity, to enable adjustment of treatment and identification of infants at risk of long-term renal impairment. In this proof-of-concept study, urine samples were collected from 41 premature neonates (≤32 weeks gestation) at least once per week, and daily during courses of gentamicin, and for 3 days afterwards. Significant increases were observed in the three urinary biomarkers measured (Kidney Injury Molecule-1 (KIM-1), Neutrophil Gelatinase-associated Lipocalin (NGAL), and N-acetyl-β-D-glucosaminidase (NAG)) during treatment with multiple courses of gentamicin. When adjusted for potential confounders, the treatment effect of gentamicin remained significant only for KIM-1 (mean difference from not treated, 1.35 ng/mg urinary creatinine; 95% CI 0.05–2.65). Our study shows that (a) it is possible to collect serial urine samples from premature neonates, and that (b) proximal tubule specific urinary biomarkers can act as indicators of aminoglycoside-associated nephrotoxicity in this age group. Further studies to investigate the clinical utility of novel urinary biomarkers in comparison to serum creatinine need to be undertaken.

Combination of renal biomarkers predicts acute kidney injury in critically ill adults

OBJECTIVE

Most studies so far have focused on the performance of individual biomarkers to detect early acute kidney injury (AKI) in the adult intensive care unit (ICU) patients; however, they have not determined the predictive ability of their combinations. The aim of this study was to compare the predictive abilities of plasma neutrophil gelatinase-associated lipocalin (pNGAL), urine neutrophil gelatinase-associated lipocalin (uNGAL), plasma cystatin C (pCysC), serum creatinine (sCr), and their combinations in detecting AKI in an adult general ICU population.

METHODS

A total of 100 consecutive ICU patients were included in the analysis. AKI was defined according to RIFLE criteria. Biomarker predictive abilities were evaluated by area under the curve (AUC), net reclassification improvement (NRI), and integrated discrimination improvement (IDI).

RESULTS

AKI occurred in 36% of patients 7 days post-admission. All three novel biomarkers as well as sCr had moderate predictive abilities for AKI occurrence. The most efficient combinations (pNGAL + sCr and pNGAL + uNGAL + sCr) were selected to participate in the subsequent analyses. Both combinations, when added to a reference clinical model, increased its AUC significantly (0.858, p = 0.04). Their NRI (0.78, p = 0.0002) was equal to that of pNGAL, but higher than that of the other three biomarkers, whereas their IDI was higher than that of any individual biomarker (0.23, p = 0.0001). Both combinations had better specificities, positive likelihood ratios, and positive predictive values than those of any individual biomarker.

CONCLUSION

The biomarker combinations had better predictive characteristics compared with those of each biomarker alone.

The ratio of plasma neutrophil gelatinase-associated lipocalin predicts acute kidney injury in patients undergoing liver transplantation

BACKGROUND

Postoperative acute kidney injury (AKI) is associated with high morbidity and mortality after liver transplantation (OLT). Previous studies have shown the value of plasma neutrophil gelatinase-associated lipocalin (NGAL) taken 2 hours after reperfusion of the liver graft as an early marker predicting AKI. The study was performed to determine whether plasma NGAL concentrations obtained as early as 1 hour after reperfusion was predictive of AKI and whether the NGAL ratio was an early predictor for AKI in the first 48 hours after OLT.

METHODS

Twenty-six liver transplant recipients donated plasma samples for NGAL determinations at induction (T1), at graft reperfusion (T3) as well as after 1 (T4) and hours 2 (T5), and at the end of the surgery (T7). AKI was defined at 48 hours after liver transplantation according to the acute kidney injury network criteria. Predictive ability was assessed using areas under the curve of receiver operator characteristic analyses.

RESULTS

The area under the curve of the receiver operator characteristics curve of (plasma NGAL concentration at T4)/(plasma NGAL concentration at T1) to predict AKI was 0.717 at T5, 0.765 at T7, 0.714 at T8 (24 hours post-OLT), and 0.781 at T9 (48 hours post-OLT).

CONCLUSION

The plasma NGAL concentrations taken 1 hour after reperfusion of the liver graft seem to be predictive of AKI; the NGAL changing ratio may be an early predictor for AKI in the first 48 hours after OLT.

Plasma neutrophil gelatinase-associated lipocalin as an early biomarker for prediction of acute kidney injury after cardio-pulmonary bypass in pediatric cardiac surgery

INTRODUCTION

Cardiopulmonary bypass (CPB) surgery is considered one of the most frequent surgical procedures in which acute kidney injury (AKI) represents a frequent and serious complication. The aim of the present study was to evaluate the efficiency of neutrophil gelatinase-associated lipocalin (NGAL) as an early AKI biomarker after CPB in pediatric cardiac surgery.

MATERIAL AND METHODS

The study included forty children aged 2 to 78 months undergoing CPB. They were divided into group I: patients who suffered AKI grades II and III; and group II: patients who did not develop AKI or at risk. Peripheral venous blood was withdrawn pre- and post-operatively for serial measurements of NGAL and creatinine. Statistical analysis was performed using Statistical Package for Social Sciences version 14.

RESULTS

Mean plasma NGAL levels showed highly significant elevations in group I patients at 2, 12, and 24 h after surgery (p < 0.0001) compared to group II. Significant correlations were found between NGAL and creatinine at different time intervals. Highly significant correlations (p < 0.0001) were found between plasma NGAL and AKI at 2, 12 and 24 h after surgery. A cut-off level of 100 ng/ml at 2 h, and 125 ng/ml at 12 h post-operatively both recorded the highest accuracy, being 95% accurate, with sensitivity of 100% and 89.5% respectively, and specificity of 90.5% and 100% respectively.

CONCLUSIONS

This study showed that plasma NGAL could be used as an early biomarker for detection of AKI following CPB. We recommend further studies on a wider scale to validate the current study results.

Cardio-renal syndrome: new perspective in diagnostics

Chronic heart failure and chronic renal failure are at epidemic proportions. These patients have significantly altered cardiac, renal, and all-cause outcomes. Much of the current research has focused on treating these individual organs in isolation. Although there are positive data on outcomes with neurohormonal modulation, they, however, remain underused. At present, data lacks for novel treatment options, while evidence continues to point at significantly worsened prognosis. Current diagnostic tools that detect acute changes in renal function or renal injury appear retrospective, which often hinder meaningful diagnostic and therapeutic decisions. This review is aimed at exploring the importance of accurate assessment of renal function for the heart failure patient by providing a synopsis on cardio-renal physiology and establishing the possibility of novel approaches in bridging the divide.

Acute kidney injury biomarkers: renal angina and the need for a renal troponin I

Acute kidney injury (AKI) in hospitalized patients is independently associated with increased morbidity and mortality in pediatric and adult populations. Continued reliance on serum creatinine and urine output to diagnose AKI has resulted in our inability to provide successful therapeutic and supportive interventions to prevent and mitigate AKI and its effects. Research efforts over the last decade have focused on the discovery and validation of novel urinary biomarkers to detect AKI prior to a change in kidney function and to aid in the differential diagnosis of AKI. The aim of this article is to review the AKI biomarker literature with a focus on the context in which they should serve to add to the clinical context facing physicians caring for patients with, or at-risk for, AKI. The optimal and appropriate utilization of AKI biomarkers will only be realized by understanding their characteristics and placing reasonable expectations on their performance in the clinical arena.

Neutrophil gelatinase-associated lipocalin in dehydrated patients: a preliminary report

Background

Acute kidney injury has been recognized as a major contributor to end stage renal disease. Although neutrophil gelatinase-associated lipocalin (Ngal) has been reported as a promising biomarker for early detection of acute kidney injury, no study has yet examined its potential clinical impact in patients with normal renal function. The purpose of current study is to investigate possible difference in serum Ngal levels between dehydrated and control patients.

Findings

A total of twelve patients presented with symptoms of mild dehydration defined by history of diarrheas or vomiting and orthostatic (postural) hypotension and an age and sex matched group of twelve control patients were included. The two groups of patients did not seem to differ in basic clinical and laboratory parameters. Serum Ngal was higher in dehydrated patients when compared to control group (Ngal = 129.4 ± 25.7 ng/mL vs 60.6 ± 0.4 ng/mL, p = 0.02). Ngal was not correlated with age, hemoglobin, white blood cell count, red blood cell count, urea or creatinine.

Conclusions

The presence of elevated Ngal levels in dehydrated patients may suggest its role as a very sensitive biomarker in even minimal and "silent" prerenal kidney dysfunction

Sensitivity and specificity of urinary neutrophil gelatinase-associated lipocalin and kidney injury molecule-1 for the diagnosis of renal cell carcinoma

BACKGROUND/AIMS

Neutrophil gelatinase-associated lipocalin (NGAL) and kidney injury molecule-1 (KIM-1) are urinary biomarkers of diagnostic relevance in a wide variety of acute and chronic kidney diseases. Their diagnostic sensitivity and specificity for kidney cancer are largely unknown and therefore the subject of this investigation.

METHODS

A prospective cohort study was performed to evaluate urine biomarkers for clear-cell and papillary subtypes of renal cancer (67 patients undergoing nephrectomy) and 55 control patients undergoing non-kidney surgery. Urinary KIM-1 and NGAL concentrations were determined by sensitive and specific ELISAs.

RESULTS

In renal cancer patients, median NGAL excretion was 0.52 (1st to 3rd quartiles: 0.28-0.82) ng/mg urinary creatinine (U(Cr)) before nephrectomy compared to 0.15 (0.04-0.31) ng/mg U(Cr) in controls (p < 0.001), and there was a modest decrease of 30% after nephrectomy (p < 0.008). NGAL was not correlated to tumor size (r = 0.19, p = 0.27) or stage. Before nephrectomy, KIM-1 excretion was 0.68 (0.40-1.12) ng/mg U(Cr) compared to 0.03 (0.01-0.06) in controls (p < 0.001). There was a linear correlation between KIM-1 excretion before nephrectomy and tumor size (Spearman's r = 0.66, p < 0.001), tumor stage, and a 50% decrease in median KIM-1 concentration 1 month following tumor excision (p < 0.01). Biomarker concentration ranges for renal cancer patients and controls overlapped substantially for NGAL but not KIM-1.

CONCLUSION

NGAL is not a sensitive or specific urinary biomarker of kidney cancer. Although KIM-1 had diagnostic sensitivity for kidney cancer, it is well known to reflect many types of kidney injuries, thus limiting its specificity as a diagnostic biomarker for renal cancer.

Baseline values of candidate urine acute kidney injury biomarkers vary by gestational age in premature infants

Acute kidney injury (AKI) is common in premature infants and is associated with poor outcomes. Novel biomarkers can detect AKI promptly. Because premature infants are born with underdeveloped kidneys, baseline biomarker values may differ. We describe baseline values of urinary neutrophil gelatinase-associated lipocalin (NGAL), IL-18, kidney injury molecule-1 (KIM-1), osteopontin (OPN), beta-2 microglobulin (B2mG), and Cystatin-C (Cys-C). Next, we test the hypothesis that these biomarkers are inversely related to GA. Candidate markers were compared according to GA categories in 123 infants. Mixed linear regression models were performed to determine the independent association between demographics/interventions and baseline biomarker values. We found that urine NGAL, KIM-1, Cys-C, and B2mG decreased with increasing GA. With correction for urine creatinine (cr), these markers and OPN/cr decreased with increasing GA. IL-18 (with or without correction for urine creatinine) did not differ across GA categories. Controlling for other potential clinical and demographic confounders with regression analysis shows that NGAL/cr, OPN/cr, and B2mG/cr are independently associated with GA. We conclude that urine values of candidate AKI biomarkers are higher in the most premature infants. These findings should be considered when designing and analyzing biomarker studies in newborn with AKI.

Biomarker strategies to predict need for renal replacement therapy in acute kidney injury

The early detection and diagnosis of acute kidney injury (AKI) with the standardization of novel kidney-injury-specific biomarkers is one of the highest research priorities in nephrology. Accordingly, the majority of studies of novel AKI biomarkers have focused on the early diagnosis of AKI using serum creatinine-based definitions as the gold standard. However, another potential application of kidney-injury-specific biomarkers is for guiding decisions on when to initiate renal replacement therapy (RRT). The purpose of this review is to summarize recent findings concerning some of the more promising AKI biomarkers on their capacity, either alone or integrated with traditional surrogate measures of kidney injury, for early prediction of whether patients will develop severe AKI requiring RRT. Some studies that have examined neutrophil gelatinase-associated lipocalin, cystatin-C, N-acetyl-β-d-glucosaminidase, kidney injury molecule-1, and α(1)-microglobulin, among others, have suggested that these novel biomarkers have the potential to distinguish patients in whom RRT will be needed. This would imply that these biomarkers may be integrated into clinical decision algorithms and could synergistically improve our current ability to predict worsening AKI and need for RRT. However, published studies have many recognized limitations, which preclude our ability to adapt their findings into clinical practice today. While currently available data are not sufficient to conclude that biomarkers should be used routinely for clinical decision making for RRT initiation, additional data may in the future significantly modify the clinical variability for initiation of RRT, and potentially translate into improved outcomes and cost-effectiveness. Finally, we propose a potential approach to future biomarker strategies for RRT initiation, integrating these biomarkers with "traditional" clinical factors.

Early fluid resuscitation in patients with rhabdomyolysis

Extensive rhabdomyolysis is often lethal unless treated immediately. Early mortality arises from hypovolemic shock, hyperkalemia, acidosis and myoglobinuric acute kidney injury (AKI). Many individuals with rhabdomyolysis could be saved, and myoglobinuric AKI prevented, by early vigorous fluid resuscitation with ≥12 l daily intravenous infusion of alkaline solution started at the scene of injury. This regimen stabilizes the circulation and mobilizes edema fluids sequestered in the injured muscles into the circulation, corrects hyperkalemia and acidosis, and protects against the nephrotoxic effects of myoglobinemia and hyperuricosuria. This regime results in a large positive fluid balance, which is well tolerated in young, carefully monitored individuals. In patients with rhabdomyolysis caused by muscle crush syndrome, mortality has been reduced from nearly 100% to <20% over the past 70 years through utilization of this intervention. This Perspectives discusses the lifesaving and limb-saving potential of early vigorous fluid resuscitation in patients with extensive traumatic and nontraumatic rhabdomyolysis.

Biomarker discovery and development in pediatric critical care medicine

OBJECTIVES

To frame the general process of biomarker discovery and development; and to describe a proposal for the development of a multibiomarker-based risk model for pediatric septic shock.

DATA SOURCE

Narrative literature review and author-generated data.

DATA SELECTION

Biomarkers can be grouped into four broad classes, based on the intended function: diagnostic, monitoring, surrogate, and stratification.

DATA EXTRACTION AND SYNTHESIS

Biomarker discovery and development requires a rigorous process, which is frequently not well followed in the critical care medicine literature. Very few biomarkers have successfully transitioned from the candidate stage to the true biomarker stage. There is great interest in developing diagnostic and stratification biomarkers for sepsis. Procalcitonin is currently the most promising diagnostic biomarker for sepsis. Recent evidence suggested that interleukin-8 can be used to stratify children with septic shock having a high likelihood of survival with standard care. Currently, there is a multi-institutional effort to develop a multibiomarker-based sepsis risk model intended to predict outcome and illness severity for individual children with septic shock.

CONCLUSIONS

Biomarker discovery and development are an important portion of the pediatric critical care medicine translational research agenda. This effort will require collaboration across multiple institutions and investigators. Rigorous conduct of biomarker-focused research holds the promise of transforming our ability to care for individual patients and our ability to conduct clinical trials in a more effective manner.

Acute kidney injury: current perspectives

Acute kidney injury (AKI) increases morbidity and mortality, particularly for the critically ill. Recent definitions standardizing AKI to reflect graded changes in serum creatinine and urine output (per the Risk, Injury, Failure, Loss, and End-stage renal failure [RIFLE] and Acute Kidney Injury Network [AKIN] criteria) with severity of renal injury and developments in AKI pathobiology are being utilized to identify biomarkers of early kidney injury. These developments may be useful in the early intervention of preventing AKI. Although there has been progress in the management of AKI, therapeutic challenges include appropriate prophylaxis prior to contrast administration, use of diuretics, vasopressors, and the type and dose of renal replacement therapy. Future use of bioartificial dialyzers, plasma therapies, and the possibility of stem cell regeneration of injured kidney tissue are being actively investigated to provide alternative treatment options for AKI. This review aims to provide an overview of current practices, available therapies, and continued research in AKI therapy.

Low renal oximetry correlates with acute kidney injury after infant cardiac surgery

Acute kidney injury (AKI) is a frequent complication after cardiopulmonary bypass surgery during infancy. Standard methods for evaluating renal function are not particularly sensitive nor are proximate indicators of renal dysfunction that allow intervention in real time. Near-infrared spectroscopy (NIRS) is a newer noninvasive technology that continuously evaluates regional oximetry and may correlate with renal injury and adverse outcomes after cardiac surgery in infants. This prospective observational study enrolled 40 infants (age, <12 months) undergoing biventricular repair. Continuous renal oximetry data were collected for the first 48 postoperative hours and correlated with postoperative course, standard laboratory data, and the occurrence of acute renal injury. Subjects with low renal oximetry (below 50% for >2 h) had significantly higher postoperative peak creatinine levels by 48 h (0.8 ± 0.4 vs. 0.52 ± 0.2; p = 0.003) and a higher incidence of AKI (50 vs. 3.1%; p = 0.003) than those with normal renal oximetry. These subjects also required more ventilator days and greater vasoactive support, and they had elevated lactate levels. Prolonged low renal near-infrared oximetry appears to correlate with renal dysfunction, decreased systemic oxygen delivery, and the overall postoperative course in infants with congenital heart disease undergoing biventricular repair.

Acute kidney injury: novel biomarkers and potential utility for patient care in urology

Urologists are integrally involved in the management of acute kidney injury (AKI), which is common after renal surgery or secondary to postrenal (obstructive) etiologies. The measurement of serum creatinine is a suboptimal indicator of AKI because it lags behind acute changes in renal function. Recent advances indicate that serum/urine biomarkers will prove useful for early detection of AKI, analogous to the use of cardiac enzymes for acute myocardial infarction. These serum/urine markers may guide future therapy, facilitate research efforts to reduce the severity of AKI, such as after partial nephrectomy, and allow for more accurate prognostication for patients with AKI.

Clinical implication of plasma neutrophil gelatinase-associated lipocalin (NGAL) concentrations in patients with advanced carotid atherosclerosis

BACKGROUND

Neutrophil gelatinase-associated lipocalin (NGAL) is well established as an early and specific biomarker of kidney disease. Recent evidence further suggests that NGAL may play a crucial role in vascular remodeling and plaque instability during the development of atherosclerosis.

METHODS

Plasma NGAL concentrations measured using a solid-phase enzyme-linked immunosorbent assay (ELISA) were correlated with medical history, risk factors and medication intake in 141 patients with advanced carotid atherosclerotic lesions who underwent carotid endarterectomy for vascular repair.

RESULTS

Plasma NGAL concentrations were associated with patient age (R(s)=0.2055, p=0.0144), plasma homocysteine (R(s)=0.4274, p<0.00001) and serum creatinine (R(s)=0.4640, p<0.00001) concentrations and estimated glomerular filtration rate (eGFR) (R(s)=-0.4911, p<0.00001). Hypertensive patients, as well as those receiving therapy with angiotensin converting enzyme (ACE) inhibitors, presented with significantly enhanced plasma NGAL concentrations when compared to normotensive (p=0.0341) patients and those not treated (p=0.0004). Enhanced NGAL concentrations did not meet statistical significance for patients with advanced stenosis grade (p=0.0971) or a history of peripheral artery disease (p=0.0827). Multiple regression analysis identified homocysteine, creatinine, eGFR and treatment with ACE inhibitors (p=0.0019, <0.00001, 0.0005 and 0.0219, respectively) as independent predictors of NGAL concentration.

CONCLUSIONS

Plasma NGAL concentrations were associated with patient age, hypertension, eGFR, creatinine and homocysteine concentrations and therapy with ACE inhibitors. The role of NGAL in the development of atherosclerosis needs to be further explored taking into consideration the uncontrolled effect of renal disease in atherosclerotic patients with multiple risk factors.

Klotho deficiency is an early biomarker of renal ischemia-reperfusion injury and its replacement is protective

Klotho is an antiaging substance with pleiotropic actions including regulation of mineral metabolism. It is highly expressed in the kidney and is present in the circulation and urine but its role in acute kidney injury (AKI) is unknown. We found that ischemia-reperfusion injury (IRI) in rodents reduced Klotho in the kidneys, urine, and blood, all of which were restored upon recovery. Reduction in kidney and plasma Klotho levels were earlier than that of neutrophil gelatinase-associated lipocalin (NGAL), a known biomarker of kidney injury. Patients with AKI were found to have drastic reductions in urinary Klotho. To examine whether Klotho has a pathogenic role, we induced IRI in mice with different endogenous Klotho levels ranging from heterozygous Klotho haploinsufficient, to wild-type (WT), to transgenic mice overexpressing Klotho. Klotho levels in AKI were lower in haploinsufficient and higher in transgenic compared with WT mice. The haploinsufficient mice had more extensive functional and histological alterations compared with WT mice, whereas these changes were milder in overexpressing transgenic mice, implying that Klotho is renoprotective. Rats with AKI given recombinant Klotho had higher Klotho protein, less kidney damage, and lower NGAL than rats with AKI given vehicle. Hence, AKI is a state of acute reversible Klotho deficiency, low Klotho exacerbates kidney injury and its restoration attenuates renal damage and promotes recovery from AKI. Thus, endogenous Klotho not only serves as an early biomarker for AKI but also functions as a renoprotective factor with therapeutic potential.

Molecular biomarker candidates of acute kidney injury in zero-hour renal transplant needle biopsies

The aim of this study was to assess gene expression levels of four biomarker candidates [lipocalin 2 (LCN2), the kidney injury molecule 1 (HAVCR1), netrin 1, and the cysteine-rich, angiogenic inducer, 61] in the tubulointerstitial and the glomerular compartment of zero-hour kidney biopsies in order to predict developing delayed graft function (DGF). Thirty-four needle kidney biopsy samples of deceased donors were manually microdissected. Relative gene expression levels were determined by real-time RT-PCR. For the validation of the biomarker candidates, we calculated a mixed model comparing kidneys with DGF, primary function and control samples from the healthy parts of tumor nephrectomies. Significant biomarker candidates were analyzed together with donor age in multivariable regression models to determine the prognostic value. Expression levels of LCN2 and HAVCR1 in the tubulointerstitium were significantly upregulated in the DGF group (LCN2: fold change = 3.78, P = 0.031 and HAVCR1: fold change = 3.44, P = 0.010). Odds ratios of both genes could not reach significance in the multivariable model together with donor age. The area under the curve of the receiver operating characteristic ranges between 0.75 and 0.83. LCN2 and HAVCR1 gene expression levels in zero-hour biopsies show potential to act as early biomarkers for DGF.

Elevated serum neutrophil gelatinase-associated lipocalin is an early predictor of severity and outcome in acute pancreatitis

OBJECTIVES

About 210,000 new cases of acute pancreatitis (AP) involving reversible inflammation of the pancreas are reported in the United States every year. About one-fourth of all patients with AP go on to develop severe acute pancreatitis (SAP), which, unlike uncomplicated or mild acute pancreatitis (MAP, usually a self-limiting disease), constitutes a life-threatening condition with systemic complications, chiefly multiorgan dysfunction. An early prediction of the severity and outcome of patients with acute pancreatitis (AP) can lead to better treatment regimens for patients with SAP. There is currently no established biomarker for the early diagnosis of SAP. In this study, we investigated the potential of serum neutrophil gelatinase-associated lipocalin (NGAL) as an early marker to distinguish severe (SAP) from MAP and examine its ability to predict the prognosis of patients with SAP.

METHODS

To check the time kinetics of rise in NGAL during AP, we quantified NGAL levels in sera from mice with MAP or SAP at various time points (6, 12, 24 and 48 h) using sandwich enzyme-linked immunosorbent assay. NGAL levels were also quantified in serum from 28 MAP and 16 SAP cases and compared with 28 chronic pancreatitis and 30 healthy control samples. Samples collected within 5 days from onset of symptoms were included. The relationship of NGAL levels with survival and multiorgan failure (MOF) in SAP was also examined.

RESULTS

Although NGAL levels were significantly higher in mice with both MAP and SAP 6 h after induction (compared to control animals), only mice with SAP exhibited a significant increase in NGAL levels at 24 h (P=0.003). NGAL levels declined at 48 h after induction in animals with both MAP and SAP but did not reach baseline levels. Among patients, mean (+/-s.e.) serum NGAL level was significantly higher in SAP (634+/-139 ng/ml) compared to MAP (84.7+/-7 ng/ml, P=0.0001). On subanalysis, the difference between MAP and SAP cases was significant in the first 48 h but not at 72, 96, or 120 h. NGAL was 100%, 96%, 97%, and 84% specific and 100%, 87.5%, 92%, and 94% sensitive in distinguishing SAP from MAP at 48, 72, 96, and 120 h, respectively, after the onset of symptoms. NGAL levels were significantly higher in SAP cases complicated by MOF (P=0.004), and high NGAL levels in SAP appeared to correlate with a fatal outcome.

CONCLUSIONS

Our data provide the first evidence for the potential of serum NGAL as an early marker to distinguish MAP from SAP. Further, high NGAL levels predict MOF and fatal outcome in patients with SAP. This study provides sufficient evidence for multi-institutional randomized trials for estimating the potential of NGAL as early biomarker for SAP.

Sub-nephrotoxic doses of gentamicin predispose animals to developing acute kidney injury and to excrete ganglioside M2 activator protein

We studied whether nephrotoxic drug administration sensitizes to acute renal failure (ARF) by administering a sub-nephrotoxic dose of gentamicin. This pre-treatment sensitized animals with no sign of renal injury to develop ARF when exposed to a second potential nephrotoxic drug, also given at sub-nephrotoxic doses that would be otherwise harmless to non-sensitized animals. We identified urinary ganglioside M2 activator protein (GM2AP) as a biomarker of an enhanced sensitivity to suffer ARF following sub-nephrotoxic treatment with gentamicin. Sub-nephrotoxic gentamicin did not alter renal GM2AP gene expression or protein levels, determined by reverse transcriptase-PCR, western blot, and immunostaining, nor was its serum level modified. The origin of increased GM2AP in the urine is thought to be a defective tubular handling of this protein as a consequence of gentamicin action. Hence, markers of acquired sensitivity may improve the prevention of ARF by enhancing our capacity to monitor for this condition, in a preemptive manner.

Aqueous humor neutrophil gelatinase-associated lipocalin levels in patients with idiopathic acute anterior uveitis

PURPOSE

The purpose of this study was to evaluate the levels of neutrophil gelatinase-associated lipocalin (NGAL) in the aqueous humor in eyes with idiopathic acute anterior uveitis (AAU).

METHODS

A comparative control study. Aqueous humor was collected from 20 eyes of 20 patients with idiopathic AAU. The control group included 20 aqueous samples from 20 patients about to undergo cataract surgery and without any other ocular or systemic diseases. The level of NGAL was determined with a commercially available ELISA kit.

RESULTS

The concentration of NGAL in aqueous humor was markedly higher in patients with idiopathic AAU than in control subjects (Mann-Whitney U test, p<0.001). The level of NGAL was 139,197.38+/-183,426.36 (mean+/-SD) pg/ml in eyes with AAU and 3,169.96+/-1,595.78 pg/ml in the eyes of the control group.

CONCLUSIONS

The aqueous humor NGAL level is increased in eyes with idiopathic AAU. These results imply that NGAL is associated with the regulation of inflammation in patients with AAU and could be used as a biomarker of ocular inflammation and immunomodulatory treatment response.

Renal CD14 expression correlates with the progression of cystic kidney disease

Monocyte and macrophage markers are among the most highly overexpressed genes in cpk mouse kidneys with severely progressive renal cystic disease. We show here that one of these markers, CD14, is abnormally transcribed, activated and shed in cystic kidneys. However, these abnormalities were not associated with an increased number of interstitial CD14-positive mononuclear cells. Instead, we found that most non-cystic and cystic renal tubular epithelia were CD14-positive; even distal nephron-derived principal cells. Cd14 was significantly overexpressed in the kidneys of 5-day-old cpk mice and further increased as the disease progressed. In the cpk model with variable rates of cystic kidney enlargement (due to an intercross of two distinct genetic backgrounds), Cd14 expression positively correlated with kidney volume, exceeding the correlation with MCP-1, an established marker of autosomal-dominant polycystic kidney disease (ADPKD). In 16 patients with ADPKD, the baseline urinary CD14 level showed some tendency to correlate with the 2-year change in total kidney volume; however, the tendency was not statistically significant. But the association was significant when the analysis was confined to males. Clearly more studies need to be done to evaluate the utility of CD14 as a marker for outcomes in ADPKD.

Neutrophil gelatinase-associated lipocalin: a promising biomarker for human acute kidney injury

Acute kidney injury (AKI) is a common and serious condition, the diagnosis of which depends on serum creatinine measurements. Unfortunately, creatinine is a delayed and unreliable indicator of AKI. The lack of early biomarkers has crippled our ability to translate promising experimental therapies to human AKI. Fortunately, understanding the early stress response of the kidney to acute injuries has revealed a number of potential biomarkers. The discovery, translation and validation of neutrophil gelatinase-associated lipocalin, arguably the most promising novel AKI biomarker, are reviewed in this article. Neutrophil gelatinase-associated lipocalin is emerging as an excellent standalone troponin-like biomarker in the plasma and urine for the prediction of AKI, monitoring clinical trials in AKI and for the prognosis of AKI in several common clinical scenarios.

Disease and gender-specific dysregulation of NGAL and MMP-9 in type 1 diabetes mellitus

Neutrophil gelatinase-associated lipocalin (NGAL), a biomarker of renal injury, can bind matrix metalloproteinase-9 (MMP-9) and inhibit its degradation, thereby sustaining MMP-9 proteolytic activity. MMP-9 is produced by renal podocytes, and podocyte MMP production can be modified by high ambient glucose levels. Moreover, dysregulation of MMP-9 activity, gene expression, or urine concentrations has been demonstrated in T2DM-associated nephropathy and in non-diabetic proteinuric renal diseases. Our objective was to determine whether NGAL/MMP-9 dysregulation might contribute to or serve as a biomarker of diabetic nephropathy in type 1 DM (T1DM). Plasma MMP-9, and urine NGAL and MMP-9 concentrations were measured in 121 T1DM and 55 control subjects and examined relative to indicators of glycemia, renal function, and degree of albuminuria. T1DM was associated with a significant increase in urinary excretion of both NGAL and MMP-9, and urine NGAL:Cr (NGAL corrected to urine creatinine) and urine MMP-9:Cr concentrations were highly correlated with each other. Both were also positively correlated with measurements of glycemic control and with albuminuria. Plasma MMP-9, urine MMP-9, and urine NGAL concentrations were significantly higher in females compared to males, and urine MMP-9:Cr concentrations displayed a menstrual cycle specific pattern. Increased urinary excretion of NGAL and MMP-9 supports a role for NGAL/MMP-9 dysregulation in renal dysfunction; moreover, gender-specific differences could support a gender contribution to pathological mechanisms or susceptibility for the development of renal complications in diabetes mellitus.

The impact of crystalloid and colloid infusion on the kidney in rodent sepsis

PURPOSE

Volume replacement remains one of the pillars of sepsis therapy. The effect of different volume solutions on kidney function in sepsis still remains unclear. We therefore determined the impact of crystalloid and colloid solutions on kidney function in a rodent model of abdominal sepsis induced by cecal ligation and puncture (CLP).

METHODS

Anesthetized rats underwent the CLP procedure, whereas control animals were sham operated. Septic animals were treated with crystalloid and colloid solutions. Hemodynamic variables and blood gases were measured. After 24 h animals were re-anesthetized, the kidneys were harvested, and creatinine (crea), urea, cystatin C and neutrophil gelatinase-associated lipocalin (NGAL) were investigated.

RESULTS

Septic animals exhibited a mortality rate of 19% after 24 h. Gelatin-treated animals showed significantly increased levels of crea and urea. Colloids [gelatin 4% (Gel) or hydroxyethyl starch 6% 130/0.4 (HES)] as volume replacement resulted in elevated levels of NGAL. The histopathological observations revealed that Gel- and HES-treated animals showed vesicles within epithelial cells of the tubulus system and an overall increased injury. In contrast, total injury scores in groups treated with crystalloids [0.9% NaCl (NaCl) and Sterofundin ISO (SteroIso)] were not significantly different compared to sham-treated animals.

CONCLUSION

None of the examined volume solution was inert to the kidney. In a CLP rodent sepsis model, animals infused with balanced crystalloid SteroIso exhibited the least effects on kidney function. Both hydroxyethyl starch 6% 130/0.4 and gelatin 4% derogated the kidney, whereas gelatin was more harmful when compared with hydroxyethyl starch.

Cardiorenal syndrome: biomarkers linking kidney damage with heart failure

All the vital organs of the body share information by virtue of various biological mediators. Primary pathology of a major organ can lead to dysfunction of the other. Cardiorenal syndrome is an important example of such organ crosstalk. Primary dysfunction of the heart or kidney can lead to injury of the other organ. As molecular injury occurs prior to clinical dysfunction, effective interventions can be planned if one can detect this organ dysfunction at an earlier stage by virtue of some biological markers. Such biomarkers can be substances in urine, serum, imaging maneuvers or any other quantifiable parameters. Some currently available biomarkers are not sensitive enough to provide timely diagnosis of the disorder. An important research priority is the development of newer biomarkers or a panel of biomarkers for the early diagnosis of organ dysfunction, as well as nature of injury, guidance for therapeutic interventions and prognosis. Many newer biomarkers have been studied for both heart and kidney dysfunction. This article focuses on newer biomarkers for the cardiorenal syndrome.

NGAL: a biomarker of acute kidney injury and other systemic conditions

Neutrophil gelatinase-associated lipocalin (NGAL) is a 25 kDa protein belonging to the lipocalin superfamily. It was initially found in activated neutrophils, however, many other cells, like kidney tubular cells, may produce NGAL in response to various insults. Recently, it has been found to have a role in iron metabolism by virtue of its binding with siderophores. It has also been found to have a role in kidney development and tubular regeneration after injury. In experimental studies, it was found to be highly expressed in response to tubular injury. In subsequent clinical studies, urine NGAL has been found to be an early predictor for acute kidney injury (AKI). Newer devices for early bedside detection of NGAL are now available. Since serum creatinine is known to be an inadequate and late marker of AKI, NGAL might soon emerge as a troponin-like early marker for AKI. Recent evidence also suggests its role as a biomarker in a variety of other renal and non-renal conditions.

Iron behaving badly: inappropriate iron chelation as a major contributor to the aetiology of vascular and other progressive inflammatory and degenerative diseases

BACKGROUND

The production of peroxide and superoxide is an inevitable consequence of aerobic metabolism, and while these particular 'reactive oxygen species' (ROSs) can exhibit a number of biological effects, they are not of themselves excessively reactive and thus they are not especially damaging at physiological concentrations. However, their reactions with poorly liganded iron species can lead to the catalytic production of the very reactive and dangerous hydroxyl radical, which is exceptionally damaging, and a major cause of chronic inflammation.

REVIEW

We review the considerable and wide-ranging evidence for the involvement of this combination of (su)peroxide and poorly liganded iron in a large number of physiological and indeed pathological processes and inflammatory disorders, especially those involving the progressive degradation of cellular and organismal performance. These diseases share a great many similarities and thus might be considered to have a common cause (i.e. iron-catalysed free radical and especially hydroxyl radical generation).The studies reviewed include those focused on a series of cardiovascular, metabolic and neurological diseases, where iron can be found at the sites of plaques and lesions, as well as studies showing the significance of iron to aging and longevity. The effective chelation of iron by natural or synthetic ligands is thus of major physiological (and potentially therapeutic) importance. As systems properties, we need to recognise that physiological observables have multiple molecular causes, and studying them in isolation leads to inconsistent patterns of apparent causality when it is the simultaneous combination of multiple factors that is responsible.This explains, for instance, the decidedly mixed effects of antioxidants that have been observed, since in some circumstances (especially the presence of poorly liganded iron) molecules that are nominally antioxidants can actually act as pro-oxidants. The reduction of redox stress thus requires suitable levels of both antioxidants and effective iron chelators. Some polyphenolic antioxidants may serve both roles.Understanding the exact speciation and liganding of iron in all its states is thus crucial to separating its various pro- and anti-inflammatory activities. Redox stress, innate immunity and pro- (and some anti-)inflammatory cytokines are linked in particular via signalling pathways involving NF-kappaB and p38, with the oxidative roles of iron here seemingly involved upstream of the IkappaB kinase (IKK) reaction. In a number of cases it is possible to identify mechanisms by which ROSs and poorly liganded iron act synergistically and autocatalytically, leading to 'runaway' reactions that are hard to control unless one tackles multiple sites of action simultaneously. Some molecules such as statins and erythropoietin, not traditionally associated with anti-inflammatory activity, do indeed have 'pleiotropic' anti-inflammatory effects that may be of benefit here.

CONCLUSION

Overall we argue, by synthesising a widely dispersed literature, that the role of poorly liganded iron has been rather underappreciated in the past, and that in combination with peroxide and superoxide its activity underpins the behaviour of a great many physiological processes that degrade over time. Understanding these requires an integrative, systems-level approach that may lead to novel therapeutic targets.