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

Neutrophil Gelatinase-Associated Lipocalin: A New Marker of Renal Function in C-Related End Stage Liver Disease

Background/Aims. Renal impairment is a common complication of cirrhosis. Serum creatinine is less sensitive in these patients. Measurement of the glomerular filtration rate (GFR) is the gold standard but time consuming. The aim is to validate plasma NGAL (pNGAL) and urinary NGAL (uNGAL) as markers of renal function in patients with HCV related cirrhosis.Patient and Methods. One hundred HCV related end stage liver cirrhosis patients were randomized into two groups: Group I (n=35), patients with GFR < 60 mL/m measured by isotope scanning of the kidney (Renogram), and Group II (n=65), patients with GFR ≥ 60 mL/m. The pNGAL and uNGAL were measured within 2 days of the Renogram.Results. Both groups were matched with age, sex, and Child Pugh score. There was statistically significant difference between both groups regarding serum creatinine (1.98 ± 1.04 versus 1.38 ± 0.88 mg/dL;p=0.003) and pNGAL level (5.79 ± 2.06 versus 7.25 ± 3.30 ng/dL;p=0.019). Both groups were comparable (p>0.05) for the uNGAL (6.00 ± 0.78 versus 6.03 ± 0.96 ng/mL). Unlike uNGAL, the pNGAL positively correlated with total GFR by Renogram (r=0.3;p=0.001). With a cutoff ≥4 ng/mL, pNGAL had 94.3% sensitivity and 1.5% specificity and PPV = 34, NPV = 33.3, LR+ = −175.1, and LR− = −60.6.Conclusion. The pNGAL is a promising marker of the renal function in patients with cirrhosis.

Determination of early urinary renal injury markers in obese children

BACKGROUND

Obesity is an important health issue, the prevalence of which is increasing in childhood. The aim of this study was to examine urinary renal injury markers in order to determine the renal effect of obesity and its comorbidities in a pediatric population.

METHODS

Eighty-four obese children and 64 healthy control subjects were enrolled in the study. We checked their urine using N-acetyl-beta-D-glucosaminidase (NAG), neutrophil gelatinase-associated lipocalin (NGAL), kidney injury molecule-1 (KIM-1), and microalbumin as renal injury markers. Associations of renal damage markers with hypertension, an impaired glucose tolerance test, and insulin resistance were assessed.

RESULTS

Obese individuals had higher urinary NAG and KIM-1 values compared to those of healthy controls (p = 0.027, p = 0.026). There was no difference in urinary NGAL between obese and lean subjects (p = 0.885). Urinary renal injury markers were not statistically different in the obese group when checked for impaired glucose tolerance, insulin resistance, and hypertension (p > 0.05).

CONCLUSIONS

This study shows that urinary NAG and KIM-1 could be used as a screening method for detection of early renal damage in obese children.

Lipocalin2 as a plasma marker for tumors with hypoxic regions

Hypoxic tumors have been identified as appropriate indicators of tumor malignancy. However, no convenient plasma marker for hypoxic tumors has been described. Therefore, to identify a novel, convenient plasma marker for hypoxic tumors, we used microarray analysis to compare gene expression profiles of normoxic and hypoxic tumor tissues of mice bearing melanomas. Among the upregulated genes detected in hypoxic tumors, we chose to study the secretory protein lipocalin2 (LCN2) as a marker for hypoxic tumors. LCN2 protein levels in the plasma of mice bearing hypoxic tumors were significantly increased compared with those in mice bearing normoxic tumors. Interestingly, LCN2 mRNA levels were 17-fold higher in HIF-1α-positive hypoxic tumors than in HIF-1α-negative normoxic tumors. Furthermore, LCN2 mRNA levels were significantly higher in the B16-F1 cells and various human tumor cells cultured under hypoxic conditions than in cells cultured under normoxic conditions, while no changes in mRNA expression were observed in nontumor NIH-3T3 cells, even under hypoxic conditions. In cultured cells, the expression pattern of LCN2 was mostly consistent with that of HIF-1α, whereas that of a conventional hypoxic marker, carbonic anhydrase IX, was not. Collectively, our data suggested that LCN2 was a useful plasma marker for hypoxic tumors.

The clinical utility window for acute kidney injury biomarkers in the critically ill

INTRODUCTION

Acute Kidney Injury (AKI) biomarker utility depends on sample timing after the onset of renal injury. We compared biomarker performance on arrival in the emergency department (ED) with subsequent performance in the intensive care unit (ICU).

METHODS

Urinary and plasma Neutrophil Gelatinase-Associated Lipocalin (NGAL), and urinary Cystatin C (CysC), alkaline phosphatase, γ-Glutamyl Transpeptidase (GGT), α- and π-Glutathione S-Transferase (GST), and albumin were measured on ED presentation, and at 0, 4, 8, and 16 hours, and days 2, 4 and 7 in the ICU in patients after cardiac arrest, sustained or profound hypotension or ruptured abdominal aortic aneurysm. AKI was defined as plasma creatinine increase ≥ 26.5 μmol/l within 48 hours or ≥ 50% within 7 days.

RESULTS

In total, 45 of 77 patients developed AKI. Most AKI patients had elevated urinary NGAL, and plasma NGAL and CysC in the period 6 to 24 hours post presentation. Biomarker performance in the ICU was similar or better than when measured earlier in the ED. Plasma NGAL diagnosed AKI at all sampling times, urinary NGAL, plasma and urinary CysC up to 48 hours, GGT 4 to 12 hours, and π-GST 8 to 12 hours post insult. Thirty-one patients died or required dialysis. Peak 24-hour urinary NGAL and albumin independently predicted 30-day mortality and dialysis; odds ratios 2.87 (1.32 to 6.26), and 2.72 (1.14 to 6.48), respectively. Urinary NGAL improved risk prediction by 11% (IDI event of 0.06 (0.002 to 0.19) and IDI non-event of 0.04 (0.002 to 0.12)).

CONCLUSION

Early measurement in the ED has utility, but not better AKI diagnostic performance than later ICU measurement. Plasma NGAL diagnosed AKI at all time points. Urinary NGAL best predicted mortality or dialysis compared to other biomarkers.

TRIAL REGISTRATION

Australian and New Zealand Clinical Trials Registry ACTRN12610001012066. Registered 12 February 2010.

Hypertension and hyperglycemia synergize to cause incipient renal tubular alterations resulting in increased NGAL urinary excretion in rats

Background

Hypertension and diabetes are the two leading causes of chronic kidney disease (CKD) eventually leading to end stage renal disease (ESRD) and the need of renal replacement therapy. Mortality among CKD and ESRD patients is high, mostly due to cardiovascular events. New early markers of risk are necessary to better anticipate the course of the disease, to detect the renal affection of additive risk factors, and to appropriately handle patients in a pre-emptive and personalized manner.

Methods

Renal function and NGAL urinary excretion was monitored in rats with spontaneous (SHR) or L-NAME induced hypertension rendered hyperglycemic (or not as controls).

Results

Combination of hypertension and hyperglycemia (but not each of these factors independently) causes an increased urinary excretion of neutrophil gelatinase-associated lipocalin (NGAL) in the rat, in the absence of signs of renal damage. Increased NGAL excretion is observed in diabetic animals with two independent models of hypertension. Elevated urinary NGAL results from a specific alteration in its tubular handling, rather than from an increase in its renal expression. In fact, when kidneys of hyperglycaemic-hypertensive rats are perfused in situ with Krebs-dextran solution containing exogenous NGAL, they excrete more NGAL in the urine than hypertensive rats. We also show that albuminuria is not capable of detecting the additive effect posed by the coexistence of these two risk factors.

Conclusions

Our results suggest that accumulation of hypertension and hyperglycemia induces an incipient and quite specific alteration in the tubular handling of NGAL resulting in its increased urinary excretion.

Diagnostic and prognostic significance of neutrophil gelatinase-associated lipocalin in disseminated intravascular coagulation

BACKGROUND

Neutrophil gelatinase-associated lipocalin (NGAL) exists as monomers, homodimers, and NGAL/matrix metalloproteinase-9 (MMP-9) complexes. Circulating neutrophils are activated in ongoing disseminated intravascular coagulation (DIC); therefore, plasma NGAL levels are likely to be increased in DIC. We investigated the diagnostic performance of the plasma NGAL level in predicting acute kidney injury (AKI) in patients with DIC and determined the prognostic value of NGAL.

METHODS

A total of 126 patients with suspected DIC were enrolled. The plasma free NGAL was analyzed with a point-of-care immunoassay. Plasma total NGAL and NGAL/MMP-9 complex levels were measured using commercial kits.

RESULTS

Median free and total NGAL levels were markedly higher in patients with AKI than those without AKI. However, no significant difference in the NGAL/MMP-9 complex level was found between the groups. In patients without AKI, the plasma free and total NGAL levels were significantly higher in those with overt-DIC than in those without overt-DIC. Of note, the free NGAL level showed a significant prognostic value in DIC.

CONCLUSION

Plasma free and total NGAL proved to be powerful markers for AKI in DIC patients and plasma free NGAL also has a prognostic relevance in DIC patients without AKI.

Neutrophil gelatinase-associated lipocalin: a novel inflammatory marker associated with late-life depression

OBJECTIVE

Systemic low graded inflammation has been identified as a possible biological pathway in late-life depression. Identification of inflammatory markers and their association with characteristics of depression is essential with the aim to improve diagnosis and therapeutic approaches. This study examines the determinants of plasma Neutrophil Gelatinase-Associated Lipocalin (NGAL), which is selectively triggered by TNFα receptor 1 signaling within the central nervous system, and its association with late-life depressive disorder.

METHODS

Baseline data were obtained from a well-characterized prospective cohort study of 350 depressed and 129 non-depressed older persons (≥60years). Past 6month diagnosis of major depressive disorder (MDD) according to DSM-IV-TR criteria was assessed with the Composite International Diagnostic Interview (CIDI 2.0). Potential determinants of plasma NGAL included sociodemographic characteristics, lifestyle and psychiatric and physical comorbidity.

RESULTS

Plasma NGAL concentrations were significantly associated with age, male gender, smoking and waist circumference. Adjusted for these determinants, depressed patients had significantly higher NGAL plasma levels compared to non-depressed comparison group. Depressed patients who did not meet full criteria for MDD in the month before sampling (partially remitted) had lower plasma NGAL levels compared with those who did. Subjects with a recurrent depression had higher plasma NGAL levels compared to those with a first episode. NGAL levels were neither related with specific symptom profiles of depression nor with antidepressant drug use.

CONCLUSION

Adjusted for confounders, NGAL plasma levels are increased in depressed older persons, without any effect of antidepressant medication and age of onset.

Biomarkers in the assessment of acute and chronic kidney diseases in the dog and cat

In both human and veterinary medicine, diagnosing and staging renal disease can be difficult. Measurement of glomerular filtration rate is considered the gold standard for assessing renal function but methods for its assessment can be technically challenging and impractical. The main parameters used to diagnose acute and chronic kidney disease include circulating creatinine and urea concentrations, and urine-specific gravity. However, these parameters can be insensitive. Therefore, there is a need for better methods to diagnose and monitor patients with renal disease. The use of renal biomarkers is increasing in human and veterinary medicine for the diagnosis and monitoring of acute and chronic kidney diseases. An ideal biomarker would identify site and severity of injury, and correlate with renal function, among other qualities. This article will review the advantages and limitations of renal biomarkers that have been used in dogs and cats, as well as some markers used in humans that may be adapted for veterinary use. In the future, measuring a combination of biomarkers will likely be a useful approach in the diagnosis of kidney disorders.

Evaluation of neutrophil gelatinase-associated lipocalin in pediatric patients with acute rotavirus gastroenteritis and dehydration

Background

Dehydration caused by acute rotavirus gastroenteritis is a frequent finding in pediatric patients. The most important treatment modality in these patients is recognising and treating dehydration, electrolyte imbalance and acute kidney injury. Neutrophil gelatinase-asssociated lipocalin (NGAL) is used widely as a biomarker for the diagnosis of acute or chronic renal injury in numerous clinical studies. It is recognized as an early marker of acute renal failure before the elevation of routine biochemical tests such as creatinine. The aim of this study is to investigate the plasma and urine NGAL concentrations in mildly or moderately dehydrated patients with acute rotavirus gastroenteritis.

Material and methods

A total of 30 patients (13 girls, mean age 62.5 ± 46.2 months) with diarrhea and mild/moderate dehydration and 35 healthy controls (17 girls, mean age 81.1 ± 41.8 months) were enrolled in the study. Plasma and urine NGAL levels of the two groups were compared.

Results

The mean age, gender and serum creatinine levels of the patients and healthy controls were similar. The mean plasma and urine NGAL levels of the patients were significantly higher than controls (plasma: 118.6 ± 81.2 vs. 66.5 ± 11.3, p = 0.001 and urine: 17.7 ± 17.5 vs. 10.6 ± 7.9, p = 0.035, respectively).

Conclusion

Mildly or moderately dehydrated children have higher plasma and urine NGAL levels compared to control subjects. Plasma and/or urine NGAL levels can be used for the early prediction of renal impairment in children with mild or moderate dehydration.

Copious urinary excretion of a male Syrian hamster (Mesocricetus auratus) salivary gland protein after its endocrine-like release upon β-adrenergic stimulation

Salivary glands, although widely considered as typically exocrine, may also release specific proteins in an endocrine manner. However, endocrine release of salivary gland proteins is not generally acknowledged since the evidences are not easily demonstrable. Submandibular salivary glands (SMG) of male Syrian hamsters express male-specific secretory proteins (MSP; which are lipocalins) visible in SDS-PAGE of SMG extracts, as major bands and also detectable in immunoblots of whole-saliva and urine as low MSP crossreactions. We report here that MSP is localized in acinar cells of SMG and acute treatment with isoproterenol (IPR; non-specific β1/β2-adrenergic agonist) results in considerable release of MSP in SMG-saliva. Moreover, acute IPR treatment markedly depletes SMG-MSP in a dose- and time-dependent manner. However, MSP depleted from SMG, far exceeds that recovered in SMG-saliva. Blood, submandibular lymph nodes and kidney of IPR-treated males showed MSP crossreactions and SDS-PAGE of their urine revealed profuse MSP excretion; this was undetectable in IPR-treated-SMG-ablated males, confirming that a substantial amount of MSP depleted from SMG after IPR treatment enters circulation and is excreted in urine. Treatments with specific β1- or β2-adrenergic agonists also reduced SMG-MSP levels and resulted in copious urinary excretion of MSP. Co-treatments with specific β1/β2-blockers indicated that above effects of IPR, β1- and even β2-agonists are very likely mediated by β1-adrenoceptors. MSP's detection by SDS-PAGE in urine after β-agonist treatment is a compelling and easily demonstrable evidence of release into circulation of a salivary gland protein. The possible means (endocrine-like or otherwise) of MSP's release into circulation and significance of its presence in saliva, blood and urine of male hamsters are discussed.

Current developments in early diagnosis of acute kidney injury

Acute kidney injury (AKI) is a very frequent and serious clinical problem, accounting for overall high morbidity and mortality. Up to date, mortality due to AKI is virtually unchanged over the past 50 years. This may partly be explained due to a delay in initiating renal protective and appropriate therapeutic measures since until now there are no reliable early-detecting biomarkers. The gold standard, serum creatinine, displays poor specificity and sensitivity with regard to identification of the incipient phase of AKI, and this is also true for cystatin C. We aimed to review novel biomarkers of AKI in urine and serum which have now progressed to the clinical phase. The main focus refers to their diagnostic and prognostic value. For this purpose, a web-based literature search using PubMed was performed comprising the following terms: renal failure, acute kidney injury and biomarkers. New molecules such as neutrophil gelatinase-associated lipocalin (NGAL), kidney injury molecule-1 (KIM-1), N-acetyl-β-D-glucosaminidase (NAG), monocyte chemotactic peptide (MCP-1), Il-18, liver-type fatty acid-binding protein (L-FABP) and Netrin-1 are available and represent promising new markers that, however, need to be further evaluated in the clinical setting for suitability. In clinical settings with incipient AKI, not only the development and the implementation of more sensitive, practicable and accurate biomarkers are required for well-timed treatment initiation. Just as important is a substantial improvement of refined and applicable prophylactic therapeutic options in these situations. Before full adoption in clinical practice can be accomplished, adequately powered clinical trials testing a row of biomarkers are strongly warranted.

Plasma FGF23 levels increase rapidly after acute kidney injury

Emerging evidence suggests that fibroblast growth factor 23 (FGF23) levels are elevated in patients with acute kidney injury (AKI). In order to determine how early this increase occurs we used a murine folic acid nephropathy model and found that plasma FGF23 levels increased significantly from baseline already after 1 hour of AKI, with an 18-fold increase at 24 hours. Similar elevations of FGF23 levels were found when AKI was induced in mice with osteocyte-specific parathyroid hormone receptor ablation or the global deletion of parathyroid hormone or vitamin D receptor, indicating that the increase in FGF23 was independent of parathyroid hormone and vitamin D signaling. Furthermore, FGF23 levels increased to a similar extent in wild-type mice maintained on normal or phosphate-depleted diets prior to induction of AKI, indicating that the marked FGF23 elevation is at least partially independent of dietary phosphate. Bone production of FGF23 was significantly increased in AKI. The half-life of intravenously administered recombinant FGF23 was only modestly increased. Consistent with the mouse data, plasma FGF23 levels rose 15.9-fold by 24 hours following cardiac surgery in patients who developed AKI. The levels were significantly higher than in those without postoperative AKI. Thus, circulating FGF23 levels rise rapidly during AKI in rodents and humans. In mice this increase is independent of established modulators of FGF23 secretion.

Creatine pretreatment prevents birth asphyxia-induced injury of the newborn spiny mouse kidney

BACKGROUND

Acute kidney injury (AKI) is a major complication for infants following an asphyxic insult at birth. We aimed to determine if kidney structure and function were affected in an animal model of birth asphyxia and if maternal dietary creatine supplementation could provide an energy reserve to the fetal kidney, maintaining cellular respiration during asphyxia and preventing AKI.

METHODS

Pregnant spiny mice were maintained on normal chow or chow supplemented with creatine from day 20 gestation. On day 38 (term ~39 d), pups were delivered by cesarean section (c-section) or subjected to intrauterine asphyxia. Twenty-four hours after insult, kidneys were collected for histological or molecular analysis. Urine and plasma were also collected for biochemical analysis.

RESULTS

AKI was evident at 24 h after birth asphyxia, with a higher incidence of shrunken glomeruli (P < 0.02), disturbance to tubular arrangement, tubular dilatation, a twofold increase (P < 0.02) in expression of Ngal (early marker of kidney injury), and decreased expression of the podocyte differentiation marker nephrin. Maternal creatine supplementation prevented the glomerular and tubular abnormalities observed in the kidney at 24 h and the increased expression of Ngal.

CONCLUSION

Maternal creatine supplementation may prove useful in ameliorating kidney injury associated with birth asphyxia.

Effects of high-dose cholecalciferol on serum markers of inflammation and immunity in patients with early chronic kidney disease

BACKGROUND/OBJECTIVES

Vitamin D has anti-inflammatory and immune-regulating properties. We aimed to determine if high-dose cholecalciferol supplementation for 1 year in subjects with early chronic kidney disease (CKD) improved circulating markers of inflammation and immunity.

SUBJECTS/METHODS

In this double-blind, randomized, placebo-controlled trial, 46 subjects with early CKD (stages 2 and 3) were supplemented with oral cholecalciferol (50 000 IU weekly for 12 weeks followed by 50 000 IU every other week for 40 weeks) or a matching placebo for 1 year. Serum tumor necrosis factor-α, interleukin-6, monocyte chemoattractant protein-1 (MCP-1), interferon gamma-induced protein-10 and neutrophil gelatinase-associated lipocalin were measured at baseline, 12 weeks and 1 year. Serum cathelicidin (LL-37) was measured at baseline and 12 weeks. An in vitro experiment was performed to investigate the effect of 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) treatment on MCP-1 secretion in THP-1 monocytes activated with lipopolysaccharide (LPS) and Pseudomonas aeruginosa.

RESULTS

By 12 weeks, serum MCP-1 decreased in the cholecalciferol group (66.2±2.5 to 60.8±2.6 pg/ml, group-by-time interaction P=0.02) but was not different from baseline at 1 year. Other markers of inflammation and immunity did not change. In vitro, LPS- and Pseudomonas-activated monocytes treated with 1,25(OH)2D3 had significantly less MCP-1 secretion compared with untreated cells.

CONCLUSIONS

High-dose cholecalciferol decreased serum MCP-1 concentrations by 12 weeks in patients with early CKD, although the decrease was not maintained for the remainder of the year. In vitro results confirm an MCP-1-lowering effect of vitamin D. Future studies should determine if vitamin D-mediated reductions in MCP-1 concentrations reflect improved clinical outcomes.

Neutrophil gelatinase-associated lipocalin as a biomarker of cardiovascular disease: a systematic review

BACKGROUND

Neutrophil gelatinase-associated lipocalin (NGAL) is a biomarker of acute kidney injury (AKI). Recently, elevated NGAL levels have also been reported in heart failure, coronary heart disease, and stroke. Other studies demonstrate that NGAL is upregulated in failing myocardium and in atherosclerotic plaque. Our aim was to synthesize the current evidence on NGAL and cardiovascular disease (CVD), and to clarify the prognostic significance of systemic NGAL levels in CVD.

METHODS

We performed a systematic review to identify experimental and human studies on NGAL and CVD. We excluded articles which specifically dealt with AKI or renal endpoints.

RESULTS

We identified 22 studies, including both animal and human data. NGAL is highly expressed in the heart, both in failing myocardium and myocarditis, and is also expressed in atherosclerotic plaques. Areas of co-localization of NGAL and matrix metalloproteinase (MMP)-9 exhibited increased MMP-9 proteolytic activity. Systemic NGAL levels correlated with renal function and severity of CVD in several, but not all, studies. An association between elevated systemic NGAL levels and clinical outcomes (e.g., death, hospital readmissions) were reported in six CVD studies, but these had limited adjustment for potential confounders.

CONCLUSIONS

There is ample literature to support a putative role of NGAL in the pathophysiology of CVD, but at present there is insufficient data regarding the clinical utility of systemic NGAL levels in the management of CVD. Available evidence regarding NGAL as a predictor of outcomes in CVD is very limited.

Cardiac biomarkers: new tools for heart failure management

The last decade has seen exciting advances in the field of biomarkers used in managing patients with heart failure (HF). Biomarker research has broadened our knowledge base, shedding more light on the underlying pathophysiological mechanisms occurring in patients with both acute and chronic HF. The criterion required by an ideal cardiovascular biomarker has been progressively changing to an era of sensitive assays that can be used to guide treatment. Recent technological advances have made it possible to rapidly measure even minute amounts of these proteins by means of higher sensitivity assays. With a high prevalence of comorbidities associated with HF, an integrated approach utilizing multiple biomarkers have shown promise in predicting mortality, better risk stratification and reducing re-hospitalizations, thus lowering health-care costs. This review provides a brief insight into recent advances in the field of biomarkers currently used in the diagnosis and prognosis of patients with acute and chronic HF.

Biomarkers in acute heart failure--state of the art

The role of biomarkers in the management of patients with acute heart failure (HF) has evolved rapidly in the past several years. Representing a major burden on health systems, acute HF has increased the need for earlier diagnosis, better risk stratification, and cost-effective treatment to reduce rates of hospitalization. Biomarker-guided diagnosis and treatment have become essential, especially in the acute setting to which the majority of the patients with acute HF initially present. Studies clearly demonstrate the complexity of these patients, who commonly have multiple comorbidities necessitating an integrative approach. Several groundbreaking studies conducted in the past decade have demonstrated how biomarkers, individually or in combination, can outperform conventional laboratory tests used in the emergency department as well as in hospitalized patients with acute HF. In this Review, we will provide an update on biomarkers considered state of the art in the diagnosis and management of patients with acute HF.

Marking renal injury: can we move beyond serum creatinine?

Acute kidney injury (AKI) is a prevalent and devastating condition associated with significant morbidity and mortality. Despite marked improvements in clinical care, the outcomes for subjects with AKI have shown limited improvement in the past 50 years. A major factor inhibiting clinical progress in this field has been the inability to accurately predict and diagnose early kidney dysfunction. The current gold standard clinical and biochemical criteria for diagnosis of AKI, Risk Injury Failure Loss End-stage renal disease, and its modification, Acute Kidney Injury Network criteria, rely on urine output and serum creatinine, which are insensitive, nonspecific, and late markers of disease. The recent development of a variety of analytic mass spectrometry-based platforms have enabled separation, characterization, detection, and quantification of proteins (proteomics) and metabolites (metabolomics). These high-throughput platforms have raised hopes of identifying novel protein and metabolite markers, and recent efforts have led to several promising novel markers of AKI. However, substantial challenges remain, including the need to systematically evaluate incremental performance of these markers over and beyond current clinical and biochemical criteria for AKI. We discuss the basic issues surrounding AKI biomarker development, highlight the most promising markers currently under development, and discuss the barriers toward widespread clinical implementation of these markers.

Preclinical perspective of urinary biomarkers for the detection of nephrotoxicity: what we know and what we need to know

The assessment of kidney damage is a challenge and must incorporate assessment of the functional capacity of the kidney, as well as a comprehensive understanding of the kidney's role. Multiple parameters have been used for many years to measure renal functionality to assess renal damage. It is astonishing that, beside histopathology, the most common traditional parameters are serum based. However, urine is also used to obtain additional information regarding the health status of the kidneys. Since 2008, several novel urinary protein biomarkers have been qualified by the US FDA and the European Medicines Agency in conjunction with the Predictive Safety Testing Consortium in a specially developed qualification process. Subsequently, the Pharmaceuticals and Medical Devices Agency accepted the qualification of these seven urinary biomarkers. This review will give an overview of the state-of-the-art detection based on urinary biomarkers, which will enhance toxicological research in the future. In addition, the qualification process that leads to acceptance of these biomarkers will be described because of its uniqueness and importance for the field of biomarker research.

Bactericidal antibiotics temporarily increase inflammation and worsen acute kidney injury in experimental sepsis

OBJECTIVE

To explore the relationships among bactericidal antimicrobial treatment of sepsis, inflammatory response, severity of acute kidney injury, and outcomes.

DESIGN

Controlled laboratory experiment.

SETTING

University laboratory.

INTERVENTIONS

Sepsis was induced by cecal ligation and puncture in 52 rats and was treated with either bactericidal antibiotics (ampicillin/sulbactam) or placebo (saline). Serial blood specimens were obtained after cecal ligation and puncture for serum creatinine, interleukin-6, and neutrophil gelatinase-associated lipocalin concentrations. RIFLE (Risk, Injury, Failure, Loss, End-stage kidney disease) criteria were used to assess severity of acute kidney injury. All animals were observed for survival up to 1 wk. In a separate experiment, six healthy animals were given antibiotics and renal function was assessed. Another 12 animals were euthanized 2 days after laparotomy for kidney histology.

MEASUREMENTS AND MAIN RESULTS

Survival in the placebo group was 50% compared with 81.8% in the antibiotic group (p < .05). Most animals (93%) without antibiotics developed acute kidney injury, of which 39% exhibited greater than a threefold rise in serum creatinine (RIFLE-F). Furthermore, survival decreased as acute kidney injury severity increased. Surprisingly, all antibiotic-treated animals developed acute kidney injury, of which 68.6% reached RIFLE-F. However, renal dysfunction was less persistent in these animals. Patterns of plasma interleukin-6 were similar to creatinine with higher concentrations seen earlier in antibiotic-treated animals but with faster resolution. Interleukin-6 concentration at 24 hrs was independently associated with the development of RIFLE-F. Histologic findings were consistent with functional parameters showing that antibiotics worsened acute kidney injury.

CONCLUSION

In polymicrobial sepsis, bactericidal antibiotics resulted in more inflammation and more severe acute kidney injury. However, resolution of inflammation and acute kidney injury was faster with antibiotics and correlated best with survival. These results suggest that transient worsening of renal function may be an expected consequence of sepsis therapy. These findings also question the value of peak severity of acute kidney injury as a primary end point and suggest that resolution of acute kidney injury may be more appropriate.

A Potential Biomarker for Acute Kidney Injury in Preterm Infants from Metabolic Profiling

BACKGROUND

Currently used biomarkers for acute kidney injury (AKI), namely Ngal, SCr, and BUN, are inadequate for timely detection of AKI in preterm infants.

METHODS

Nuclear magnetic resonance (NMR) spectroscopy-based metabolic profiling was conducted on urines from 20 preterm infants to determine if novel metabolic biomarkers could be identified for early detection of AKI. Urines were collected from every patient each day for the first 14 days of life. NMR spectra were measured for all urines and metabolic profiling analysis conducted.

RESULTS

One metabolite, carnitine, increased significantly in urines of three extremely low birth weight (ELBW) infants starting on day five of life. The three affected infants either received prolonged antibiotic treatment, extended treatment with indomethacin, or both. One ELBW patient who received both treatments and reached the highest urinary carnitine level died on day 10 of life due to localized gut perforation complicated by suspected AKI.

CONCLUSIONS

It was concluded that carnitine increased in the three neonates in part due to antibiotic- and/or indomethacin-induced AKI. It is hypothesized that combined antibiotic and indomethacin treatment promoted AKI resulting in reduced proximal renal tubule reabsorption of carnitine and that β-lactam antibiotics blocked renal carnitine uptake by human organic cation transporter, hOCTN2.

Laboratory parameters of cardiac and kidney dysfunction in cardio-renal syndromes

"Cardio-Renal Syndromes" (CRS) are disorders of the heart and kidneys in which acute or chronic dysfunction in one organ may induce acute or chronic dysfunction of the other. The pathophysiology of CRS is complex, and there is accumulating evidence that various novel biomarkers are useful for diagnosis, prognostication, and risk stratification in patients with heart failure and chronic kidney disease (CRS). When both the heart failure (HF) and CKD occur together, it is important to have biomarkers that are able to risk stratify patients by looking at both their heart and kidney aspects. There are some promising newer renal biomarkers that may contribute to a better evaluation and prediction of prognosis in CRS patients. Most of the renal biomarkers studies in CRS have been performed in the setting of cardiac surgery, acute coronary syndrome (ACS), HF or after exposure to radiocontrast media in diagnostic and/or therapeutic percutaneous coronary procedures. Natriuretic peptides (NPs) have been validated as an important cardiac biomarker for risk stratification and prognostication in HF patients with or without CKD. However, the best cutoff values for each stage of CKD, including those on renal replacement therapy, are yet to be ascertained. In this context, it is likely that panels of multiple biomarkers will be needed for optimal evaluation, risk stratification, timely treatment initiation, and follow-up of patients with CRS.

Insights on urinary NGAL obtained in a primary care setting

BACKGROUND

A majority of patients developing acute kidney injury (AKI) receive medical care from their primary care physicians prior to the occurrence of conditions that predispose them to this complication.

METHODS

To characterize the uNGAL concentrations in primary care patients and to assess these concentrations with regard to different reference intervals, we conducted a multicenter, cross-sectional study with random selection of general practitioners (GP) from all GP offices in seven Swiss cantons. 1000 adults (566 females; mean age 57±17 years) were included.

RESULTS

The median absolute uNGAL was 21 ng/L. Elevated uNGAL (>100 ng/L) together with normal kidney test results (eGFR and albuminuria) were found in 6.5% of all patients. Females had a significantly higher uNGAL than did males. Among a multitude of different clinical and laboratory variables, only age, gender, liver function parameters, WBC and CRP were significantly associated with uNGAL levels in a multivariate analysis. When examining the proposed KDIGO classification of chronic kidney disease, the uNGAL levels at the given eGFR stages changed with increasing albuminuria stages and vice versa.

CONCLUSIONS

Age, gender, markers of inflammation and liver function, exert influences on uNGAL concentrations. A substantial proportion of patients exhibited normal kidney testing together with elevated uNGAL, potentially identifying patients with increased renal stress and at increased risk for the development of AKI.

In situ assembly, regeneration and plasmonic immunosensing of a Au nanorod monolayer in a closed-surface flow channel

Herein, a simple and effective approach is reported for the in situ generation and regeneration of a Au nanorod (AuNR) monolayer inside a glass/silica-based, closed-surface flow channel. The density of the AuNR monolayer in the flow channel can be easily modified by varying the concentration of the AuNR and the cetyltrimethylammonium bromide as well as the incubation time. The fabricated AuNR monolayer in the flow channels was stable under harsh conditions, such as in extreme pH, organic solvents and at a fast flow rate. In addition, the flow channel could be reused by removing the immobilized AuNRs via the injection of diluted aqua regia or potassium iodide; the AuNR monolayer can subsequently be regenerated. The AuNRs in the closed flow channel were further exploited as a label-free detection method for a clinical biomarker, neutrophil gelatinase-associated lipocalin (NGAL), based on single-nanoparticle plasmonic assay. The corresponding limit of detection for NGAL was measured to be 8.5 ng mL(-1) (~340 pM) based on a signal-to-noise ratio of 3. The estimated recovery of NGAL in human serum and urine was higher than 80%, which indicates that this technique could potentially be used for the diagnosis of acute kidney injury.

New biomarkers for acute renal injury

Incidence of acute kidney injury (AKI) is increasing rapidly to epidemic proportions. Development of AKI, especially in intensive care settings, is associated with increased morbidity, mortality and hospitalization costs. Currently available diagnostic tools are mostly insensitive for early diagnosis, however prompt diagnosis and risk stratification are necessary for guiding therapy and preventing progression of disease. Finding an early, reliable, suitable, easily reproducible, economical and accurate biomarker for AKI is a top research priority. In recent years, many urinary and serum proteins have been investigated as possible early markers of AKI and some of them have shown great promise. This topic reviews some of the emerging biomarkers of AKI.

Intra-amniotic infection upregulates neutrophil gelatinase-associated lipocalin (NGAL) expression at the maternal-fetal interface at term: implications for infection-related preterm birth

OBJECTIVE

Neutrophil gelatinase-associated lipocalin (NGAL) is a ubiquitous lipocalin that serves as a critical component of innate immunity and a transport shuttle for numerous substances (retinoids, arachidonic acid, prostaglandins, fatty acids, steroids, iron, and MMPs). Despite the well-documented association between intra-amniotic infection/inflammation (IAI) and preterm birth, NGAL expression in the uterus has not previously been examined. This study investigates NGAL expression at the maternal-fetal interface in vivo and in vitro.

METHODS

Neutrophil gelatinase-associated lipocalin expression in term placenta with/without IAI was examined by immunohistochemistry. Trophoblast and decidual stromal cells were retrieved from elective cesarean, purified, and depleted of leukocytes. On days 1 (cytotrophoblast cells) and 4 (syncytiotrophoblast), cells were stimulated with/without interleukin 1β (IL-1β; 1 ng/mL), tumor necrosis factor α (TNF-α; 1 ng/mL), or lipopolysaccharide (LPS; 1 μg/mL). Neutrophil gelatinase-associated lipocalin messenger RNA (mRNA) and protein expression were measured by immunocytochemistry/Western blot and RT-qPCR, respectively.

RESULTS

Under basal conditions, NGAL is expressed in trophoblast, but not decidua. Trophoblast NGAL is significantly upregulated in tissues with evidence of IAI vs controls. NGAL expression was increased after stimulation with all 3 pro-inflammatory mediators in day 1 (cytotrophoblast) but not day 4 cells (syncytiotrophoblast). IL-1β and TNF-α (not LPS) upregulated NGAL gene expression in cytotrophoblast (not syncytiotrophoblast) cells.

CONCLUSIONS

Intra-amniotic infection/inflammation is associated with increased expression of NGAL in trophoblast tissues in vivo. IL-1β, TNF-α, and LPS stimulated NGAL in cytotrophoblast cells (not syncytiotrophoblast and decidua) in vitro. These data suggest that, in keeping with its role as a mediator of innate immunity, NGAL may have a central role to play in IAI-induced preterm birth.

Acute kidney injury in critically ill infants: the role of urine Neutrophil Gelatinase-Associated Lipocalin (NGAL)

Acute kidney injury (AKI) has emerged as an important health problem in the intensive care units, especially among infants delivered prematurely. Recent efforts to define and characterize AKI have led to studies of early AKI detection and will ultimately contribute to improvements in AKI outcomes. The discovery of biomarkers for AKI that might enable early recognition and clinical intervention to limit renal injury is therefore of intense contemporary interest. Neutrophil gelatinase-associated lipocalin (NGAL) is the most promising among all emerging markers for AKI; specifically, urine NGAL (uNGAL) predicts renal failure much earlier than serum creatinine. The recent availability of an automated immunoassay for measuring uNGAL in the clinical practice permits to introduce the test in emergency, having a turn around time (TAT) closely comparable with that of serum creatinine. On the basis of data reported in the literature, it is reasonable to forecast an increasing clinical use of uNGAL capable to change our approach to the diagnosis and leading to better preventative and therapeutic interventions which will improve outcomes of critically ill infants with acute kidney disease.

Defining a relationship between dietary fatty acids and the cytochrome P450 system in a mouse model of fatty liver disease

Liver-specific ablation of cytochrome P450 reductase in mice (LCN) results in hepatic steatosis that can progress to steatohepatitis characterized by inflammation and fibrosis. The specific cause of the fatty liver phenotype is poorly understood but is hypothesized to result from elevated expression of genes encoding fatty acid synthetic genes. Since expression of these genes is known to be suppressed by polyunsaturated fatty acids, we performed physiological and genomics studies to evaluate the effects of dietary linoleic and linolenic fatty acids (PUFA) or arachidonic and decosahexaenoic acids (HUFA) on the hepatic phenotypes of control and LCN mice by comparison with a diet enriched in saturated fatty acids. The dietary interventions with HUFA reduced the fatty liver phenotype in livers of LCN mice and altered the gene expression patterns in these livers to more closely resemble those of control mice. Importantly, the expression of genes encoding lipid pathway enzymes were not different between controls and LCN livers, indicating a strong influence of diet over POR genotype. These analyses highlighted the impact of POR ablation on expression of genes encoding P450 enzymes and proteins involved in stress and inflammation. We also found that livers from animals of both genotypes fed diets enriched in PUFA had gene expression patterns more closely resembling those fed diets enriched in saturated fatty acids. These results strongly suggest only HUFA supplied from an exogenous source can suppress hepatic lipogenesis.

Neutrophil gelatinase-associated lipocalin (NGAL): a new marker of cyclosporine nephrotoxicity?

The aim of work was to investigate whether serum and urinary neutrophil gelatinase-associated lipocalin(sNGAL and uNGAL, respectively) are potential biomarkers of early cyclosporine A (CsA) nephrotoxicity in steroid-dependent nephrotic children (SDNS). The study group (I) consisted of 19 children with SDNS aged 9.46+/-5.52 years treated with CsA. The children were examined four times: at proteinuria relapse, prior to CsA treatment,then after 3, 6, and 12 months of CsA treatment. The control group (II) consisted of 18 healthy children aged 3-15 years. A commercial enzyme-linked immunosorbent assay method was used to measure NGAL concentration.The sNGAL level in SDNS children prior to the administration of CsA was similar to that in the healthy controls (p>0.05), but it increased significantly during the course of treatment (p<0.01). The uNGAL/creatinine (cr) ratio in SDNS patients was higher before the withdrawal of CsA therapy (p<0.05), and was also increased at the consecutive examinations (p<0.01). There was a positive correlation between both sNGAL and uNGAL levels and CsA serum level. However, based on the serum and urinary NGAL/cr receiver operating characteristic curve and area under the curve (AUC) analysis, it remains uncertain whether uNGAL is a good predictor of cyclosporine nephropathy. Both sNGAL and uNGAL concentrations increased during the course of CsA treatment. Further studies in larger groups of patients are therefore necessary to confirm our experimental data that increased NGAL levels may be a non-invasive marker for the early detection of tubulointerstitial damage in CsA nephrotoxicity.