Neutrophil gelatinase-associated lipocalin, a siderophore-binding eukaryotic protein

Levels of neutrophil gelatinase-associated lipocalin in 2 patients with crush syndrome after a mudslide

Neutrophil gelatinase-associated lipocalin is one of the most promising biomarkers for the diagnosis of acute kidney injury. An increase in the level of neutrophil gelatinase-associated lipocalin is a good predictor of acute kidney injury and is associated with an increase in the serum level of creatinine. Two victims of a mudslide in Messina, Italy, initially had crush syndrome followed by development of acute kidney injury. The development of acute kidney injury is the second most common cause of death after large earthquakes and other natural disasters, but at the same time, crush-related acute kidney injury is one of the few life-threatening complications of crush injuries that can be reversed if diagnosed early and treated. In this case, measuring the level of neutrophil gelatinase-associated lipocalin enabled early diagnosis of acute kidney injury and anticipation of the changes in levels of conventional markers such as creatinine.

Neutrophil gelatinase-associated lipocalin in gastric carcinoma cells and its induction by TPA are controlled by C/EBPβ

Neutrophil gelatinase-associated lipocalin (NGAL) expression has been found to be upregulated in a variety of tumors, but the mechanism of NGAL elevation in gastric carcinoma remains unknown. Here, immunohistochemistry was applied to analyze NGAL expression in gastric carcinoma patients. Reverse transcription PCR, Western blot, and enzyme-linked immunosorbent assay (ELISA) were performed to evaluate NGAL mRNA and protein levels before and after 12-O-tetradecanoylphorbol-13-acetate (TPA) induction. Luciferase reporter assay was carried out to identify the core cis element in NGAL promoter. The binding ability and specificity of transcription factors were analyzed by electrophoretic mobility-shift assay (EMSA) and chromatin immunoprecipitation (ChIP), respectively. Results showed that NGAL was overexpressed in gastric tumor tissues. Gastric cancer cells treated with TPA resulted in the transactivation of NGAL promoter and the upregulation of its mRNA and protein levels. We identified the -110 to -79 sequence segment upstream from the transcription initiation site of NGAL as a TPA responsive element (TRE) and confirmed that C/EBPβ was able to bind to the -87 to -79 segment. Forced expression of C/EBPβ significantly increased the promoter activity of NGAL as well as its mRNA level. These results suggest that NGAL is overexpressed in gastric cancer, the binding of C/EBPβ to the TRE of its gene promoter mediates its TPA-induced overexpression in gastric carcinoma cells.

Induction of lipocalin-2 expression in acute and chronic experimental liver injury moderated by pro-inflammatory cytokines interleukin-1β through nuclear factor-κB activation

BACKGROUND

Lipocalin-2 (LCN2) belongs to the lipocalin superfamily, sharing a barrel-shaped tertiary structure with a hydrophobic pocket and an ability to bind lipophilic molecules. LCN2 has recently emerged as an important modulator of cellular homeostasis in several organs, i.e. heart, lung and kidney, but little is known about the expression of LCN2 in acute and chronic liver injury.

AIMS

In this study, we wanted to analyse the expression and regulation of LCN2 in models of acute and chronic experimental liver injury.

MATERIALS AND METHODS

We analysed LCN2 expression in livers of rats subjected to bile duct ligation or repeated doses of carbon tetrachloride and tested the impact of various pro-inflammatory cytokines in cultured primary liver cells.

RESULTS

By using primary cultures of hepatic stellate cells and hepatocytes isolated from normal and injured rat livers, we found a significant LCN2 expression in early hepatic stellate cell cultures, a lower expression in fully transdifferentiated myofibroblasts and no expression in freshly isolated hepatocytes. However, LCN2 expression and secretion in hepatocytes increased dramatically during culturing. In addition, chronic in vivo liver injury resulting from both bile duct ligation and repeated application of carbon tetrachloride resulted in rapid and well-sustained induction of LCN2 expression. Immunohistochemistry and primary liver cell isolation identified injured hepatocytes as the main source of LCN2 production. LCN2 is strongly induced in both primary hepatocytes and immortalized hepatocellular carcinoma cell line HepG2 by the pro-inflammatory cytokine interleukin-1β via nuclear factor-κB activation, but not by the profibrotic cytokines platelet-derived growth factor and transforming growth factor-β.

CONCLUSION

LCN2 expression shows clear correlation to liver damage and resulting inflammatory responses, rather than to the degree of liver fibrosis, which in fact may imply a distinct diagnostic value as an early biomarker of liver inflammation.

Increased plasma levels of lipocalin 2 in mild cognitive impairment

BACKGROUND

Alzheimer's disease (AD) is a progressive neurodegenerative disorder characterized by an irreversible cognitive decline and neuronal loss associated with neurofibrillary tangles and senile plaques. Mild cognitive impairment (MCI) is a prodromal stage of AD and is associated with memory loss and a high risk of developing AD. Lipocalin 2 (LCN2) is an acute phase protein. Our previous studies have shown that exposure to inflammatory stimuli resulted in elevated LCN2 levels in brain microglia and astrocytes implicating LCN2 in brain inflammation. Therefore, we hypothesize that there may be a significant change in the plasma LCN2 levels in patients with MCI and AD when compared to healthy control subjects.

METHODS

Forty-one patients with MCI, 62 patients with AD and 38 healthy elderly control subjects were recruited for this study. They were given a comprehensive battery of neuropsychological tests including a mini-mental status examination (MMSE) and clinical dementia rating (CDR). A variety of clinical information was collected from the semi-structured questionnaire administered. The LCN2 levels were measured using a specific enzyme-linked immunosorbent assay in the plasma, which had been collected early in the morning after overnight fasting.

RESULTS

The LCN2 levels were significantly higher in MCI patients compared to the healthy control subjects and AD patients [control vs. MCI (p=0.005); MCI vs. AD (p=0.009)]. There was a significant negative correlation between the LCN2 levels and CDR scores (r=-0.245, p=0.014), and there was a positive correlation between the LCN2 levels and MMSE scores (r=0.317, p=0.001) among all of the MCI and AD patients.

CONCLUSION

MCI represents a prodromal stage of AD, and inflammation occurs as one of the earliest pathological events in AD. Thus, increased plasma LCN2 levels during MCI could be helpful in predicting the progression from MCI to AD.

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.

Lipocalin 2 is essential for chronic kidney disease progression in mice and humans

Mechanisms of progression of chronic kidney disease (CKD), a major health care burden, are poorly understood. EGFR stimulates CKD progression, but the molecular networks that mediate its biological effects remain unknown. We recently showed that the severity of renal lesions after nephron reduction varied substantially among mouse strains and required activation of EGFR. Here, we utilized two mouse strains that react differently to nephron reduction--FVB/N mice, which develop severe renal lesions, and B6D2F1 mice, which are resistant to early deterioration--coupled with genome-wide expression to elucidate the molecular nature of CKD progression. Our results showed that lipocalin 2 (Lcn2, also known as neutrophil gelatinase-associated lipocalin [NGAL]), the most highly upregulated gene in the FVB/N strain, was not simply a marker of renal lesions, but an active player in disease progression. In fact, the severity of renal lesions was dramatically reduced in Lcn2-/- mice. We discovered that Lcn2 expression increased upon EGFR activation and that Lcn2 mediated its mitogenic effect during renal deterioration. EGFR inhibition prevented Lcn2 upregulation and lesion development in mice expressing a dominant negative EGFR isoform, and hypoxia-inducible factor 1α (Hif-1α) was crucially required for EGFR-induced Lcn2 overexpression. Consistent with this, cell proliferation was dramatically reduced in Lcn2-/- mice. These data are relevant to human CKD, as we found that LCN2 was increased particularly in patients who rapidly progressed to end-stage renal failure. Together our results uncover what we believe to be a novel function for Lcn2 and a critical pathway leading to progressive renal failure and cystogenesis.

Iron metabolism gene expression in human skeletal muscle

Little is known about iron metabolism in skeletal muscle while hepatic iron metabolism is well understood. The aim of this study is to compare the iron metabolism gene expression profile in skeletal muscle and the liver in humans. Muscle and hepatic biopsies from six normal individuals were acquired. Twelve genes involved in iron metabolism( import, storage, export) were selected to be studied. Reverse transcriptase polymerase chain reaction (RT-PCR) was performed in order to determine the expression profile in skeletal muscle and compare it to the one from the liver. Semi-quantification of the gene expression in the studied tissues was performed by densitometric analysis (DA). The results were expressed relative to the percentage of the β-actin gene. Fine analysis was performed by real-time PCR (q-PCR) quantification for the genes that their expression presented a difference of more than 20% in the 2 tissues in the first applied densitometric analysis. Most of the studied genes, HJV, TFR1, HFE, DMT1, DMT1nonIRE, NGAL, HEPH, IREG1, FTH1 were well expressed (>70% of β-actin) in skeletal muscle . HAMP, CP, and TFR2 were absent or minimally expressed (<10% of β-actin) in skeletal muscle while they were well expressed in liver. HJV and Heph were found to have higher expression in skeletal muscle (SM) compared to liver (L) (SM/L=2.65 ± 1.1(p<0.05) and SM/L=1.5 ± 0.06(p<0.05 respectively in q-PCR). The relative expressions of the studied genes in both tissues and their relative contribution in iron homeostasis in different pathways are discussed.

Role of lung iron in determining the bacterial and host struggle in cystic fibrosis

Cystic fibrosis (CF) is the most common lethal genetic disorder in Caucasian populations. It is a multiorgan system disease that affects the lungs, gastrointestinal tract, liver, and pancreas. The majority of morbidity and mortality in CF relates to chronic airway infection with a variety of bacterial species, commencing in very early infancy, which results in lung destruction and ultimately organ failure ( 41 , 43 ). This review focuses on iron homeostasis in the CF lung and its role in determining the success and chronicity of Pseudomonas aeruginosa infection. There have been previous excellent reviews regarding iron metabolism in the lower respiratory tract and mechanisms of P. aeruginosa iron acquisition, and we direct readers to these articles for further background reading ( 31 , 53 , 58 , 77 , 96 ). In this review, we have brought the “two sides of the coin” together to provide a holistic overview of the relationship between host and bacterial iron homeostasis and put this information into the context of current understanding on infection in the CF lung.

Corticosteroid effects on blood gene expression in Duchenne muscular dystrophy

Though Deflazacort and prednisone improve clinical endpoints in Duchenne muscular dystrophy (DMD) patients, Deflazacort produces fewer side effects. As mechanisms of improvement and side effect differences remain unknown, we evaluated effects of corticosteroid administration on gene expression in blood of DMD patients. Whole blood was obtained from 14 children and adolescents with DMD treated with corticosteroids (DMD-STEROID) and 20 DMD children and adolescents naïve to corticosteroids (DMD). The DMD-STEROID group was further subdivided into Deflazacort and prednisone groups. Affymetrix U133 Plus 2.0 expression microarrays were used to evaluate mRNA expression. Expression of 524 probes changed with corticosteroids, including genes in iron trafficking and the chondroitin sulfate biosynthesis pathway. Deflazacort compared with prednisone yielded 508 regulated probes, including many involved in adipose metabolism. These genes and pathways help explain mechanisms of efficacy and side effects of corticosteroids, and could provide new treatment targets for DMD and other neuromuscular disorders.

Up-regulation of neutrophil gelatinase-associated lipocalin in cholesteatoma

CONCLUSION

Neutrophil gelatinase-associated lipocalin (NGAL) and Ki-67 expression were up-regulated in cholesteatoma and the expression pattern of NGAL in the epithelial layer was inversely related to the expression of Ki-67. Therefore, NGAL may be related to dysregulated differentiation in the keratinocytes during the development of a cholesteatoma.

OBJECTIVES

We investigated the differential expression and localization of NGAL in middle ear cholesteatoma and compared the results to normal external auditory canal (EAC) skin. We also compared the expression and localization of NGAL with the expression and localization of Ki-67 in middle ear cholesteatoma.

SUBJECTS AND METHODS

Tissue samples from middle ear cholesteatomas and normal EAC skin were obtained from 20 patients undergoing middle ear surgery. NGAL mRNA expression was determined by the reverse transcriptase-polymerase chain reaction (RT-PCR). The expression of NGAL protein was analyzed by Western blot. NGAL and Ki-67 were localized by immunohistochemical staining.

RESULTS

A significantly greater expression of the NGAL mRNA was observed in cholesteatoma epithelium than in normal EAC skin (p < 0.05). NGAL was detected in the granular layer of cholesteatoma. However, NGAL was scarcely expressed in normal EAC skin. Ki-67 was detected predominantly in the basal and parabasal layers of cholesteatoma epithelium.

Altered iron metabolism is part of the choroid plexus response to peripheral inflammation

Iron is essential for normal cellular homeostasis but in excess promotes free radical formation and is detrimental. Therefore, iron metabolism is tightly regulated. Here, we show that mechanisms regulating systemic iron metabolism may also control iron release into the brain at the blood-choroid plexus-cerebrospinal fluid (CSF) barrier. Intraperitoneal administration of lipopolysaccharide (LPS) in mice triggers a transient transcription of the gene encoding for hepcidin, a key regulator of iron homeostasis, in the choroid plexus, which correlated with increased detection of pro-hepcidin in the CSF. Similarly, the expression of several other iron-related genes is influenced in the choroid plexus by the inflammatory stimulus. Using primary cultures of rat choroid plexus epithelial cells, we show that this response is triggered not only directly by LPS but also by molecules whose expression increases in the blood in response to inflammation, such as IL-6. Intracellular conveyors of these signaling molecules include signal transducer and activator of transcription 3, which becomes phosphorylated, and SMAD family member 4, whose mRNA levels increase soon after LPS administration. This novel role for the choroid plexus-CSF barrier in regulating iron metabolism may be particularly relevant to restrict iron availability for microorganism growth, and in neurodegenerative diseases in which an inflammatory underlying component has been reported.

A general map of iron metabolism and tissue-specific subnetworks

Iron is required for survival of mammalian cells. Recently, understanding of iron metabolism and trafficking has increased dramatically, revealing a complex, interacting network largely unknown just a few years ago. This provides an excellent model for systems biology development and analysis. The first step in such an analysis is the construction of a structural network of iron metabolism, which we present here. This network was created using CellDesigner version 3.5.2 and includes reactions occurring in mammalian cells of numerous tissue types. The iron metabolic network contains 151 chemical species and 107 reactions and transport steps. Starting from this general model, we construct iron networks for specific tissues and cells that are fundamental to maintaining body iron homeostasis. We include subnetworks for cells of the intestine and liver, tissues important in iron uptake and storage, respectively, as well as the reticulocyte and macrophage, key cells in iron utilization and recycling. The addition of kinetic information to our structural network will permit the simulation of iron metabolism in different tissues as well as in health and disease.

Lipocalin-2 is an autocrine mediator of reactive astrocytosis

Astrocytes, the most abundant glial cell type in the brain, provide metabolic and trophic support to neurons and modulate synaptic activity. In response to a brain injury, astrocytes proliferate and become hypertrophic with an increased expression of intermediate filament proteins. This process is collectively referred to as reactive astrocytosis. Lipocalin 2 (lcn2) is a member of the lipocalin family that binds to small hydrophobic molecules. We propose that lcn2 is an autocrine mediator of reactive astrocytosis based on the multiple roles of lcn2 in the regulation of cell death, morphology, and migration of astrocytes. lcn2 expression and secretion increased after inflammatory stimulation in cultured astrocytes. Forced expression of lcn2 or treatment with LCN2 protein increased the sensitivity of astrocytes to cytotoxic stimuli. Iron and BIM (Bcl-2-interacting mediator of cell death) proteins were involved in the cytotoxic sensitization process. LCN2 protein induced upregulation of glial fibrillary acidic protein (GFAP), cell migration, and morphological changes similar to characteristic phenotypic changes termed reactive astrocytosis. The lcn2-induced phenotypic changes of astrocytes occurred through a Rho-ROCK (Rho kinase)-GFAP pathway, which was positively regulated by nitric oxide and cGMP. In zebrafishes, forced expression of rat lcn2 gene increased the number and thickness of cellular processes in GFAP-expressing radial glia cells, suggesting that lcn2 expression in glia cells plays an important role in vivo. Our results suggest that lcn2 acts in an autocrine manner to induce cell death sensitization and morphological changes in astrocytes under inflammatory conditions and that these phenotypic changes may be the basis of reactive astrocytosis in vivo.

Effect of exercise training on A-FABP, lipocalin-2 and RBP4 levels in obese women

OBJECTIVE

Lipocalin family proteins, including adipocyte fatty acid-binding protein (A-FABP), lipocalin-2 and retinol-binding protein 4 (RBP4), have recently been identified as novel adipokines associated with obesity, type 2 diabetes and the metabolic syndrome. We have evaluated the effect of exercise training on lipocalin family proteins and inflammatory markers.

STUDY SUBJECTS

Thirty obese Korean women and 15 age-matched nonobese control subjects were studied.

DESIGN

Concentrations of the lipocalin family proteins were compared between obese and nonobese women and were evaluated before and 3 months after an exercise programme consisting of aerobic exercise (45 min/session, 300 kcal/day) and muscle strength training (20 min/session, 100 kcal/day) five times a week.

RESULTS

Obese women exhibited higher A-FABP levels compared to nonobese women (21.4 +/- 6.4 microg/l vs. 13.6 +/- 4.4 microg/l, P < 0.001). However, neither lipocalin-2 nor RBP4 levels were significantly different between the two groups, although the difference in lipocalin-2 was marginally significant (P = 0.054). Circulating A-FABP levels were significantly associated with body mass index (BMI), waist circumference, triglyceride, alanine aminotransferase (ALT), lipocalin-2 and high-sensitivity C-reactive protein (hsCRP) levels. After 3 months of the exercise training programme, serum A-FABP levels decreased significantly from 21.4 +/- 6.4 microg/l to 19.3 +/- 6.8 microg/l (P = 0.038), along with a reduction in weight, BMI, waist circumference, fasting glucose and total cholesterol levels. There was no significant change in the lipocalin-2 and RBP4 levels, although IL-6 levels increased after the exercise programme.

CONCLUSION

Exercise training with weight loss induced a significant reduction in circulating A-FABP levels in obese Korean women.

Induction of a chemoattractant transcriptional response by a Campylobacter jejuni boiled cell extract in colonocytes

BACKGROUND

Campylobacter jejuni, the commonest cause of bacterial diarrhoea worldwide, can also induce colonic inflammation. To understand how a previously identified heat stable component contributes to pro-inflammatory responses we used microarray and real-time quantitative PCR to investigate the transcriptional response to a boiled cell extract of Campylobacter jejuni NCTC 11168.

RESULTS

RNA was extracted from the human colonocyte line HCA-7 (clone 29) after incubation for 6 hours with Campylobacter jejuni boiled cell extract and was used to probe the Affymetrix Human Genome U133A array. Genes differentially affected by Campylobacter jejuni boiled cell extract were identified using the Significance Score algorithm of the Bioconductor software suite and further analyzed using the Ingenuity Pathway Analysis program. The chemokines CCL20, CXCL3, CXCL2, Interleukin 8, CXCL1 and CXCL6 comprised 6 of the 10 most highly up-regulated genes, all with Significance Scores > or = 10. Members of the Tumor Necrosis Factor alpha/Nuclear Factor-kappaB super-family were also significantly up-regulated and involved in the most significantly regulated signalling pathways (Death receptor, Interleukin 6, Interleukin 10, Toll like receptor, Peroxisome Proliferator Activated Receptor-gamma and apoptosis). Ingenuity Pathway Analysis also identified the most affected functional gene networks such as cell movement, gene expression and cell death. In contrast, down-regulated genes were predominantly concerned with structural and metabolic functions.

CONCLUSION

A boiled cell extract of Campylobacter jejuni has components that can directly switch the phenotype of colonic epithelial cells from one of resting metabolism to a pro-inflammatory one, particularly characterized by increased expression of genes for leukocyte chemoattractant molecules.

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.

Lipocalin-2-induced renal regeneration depends on cytokines

This study investigated whether the renal regeneration occurring in the recovery phase of kidney ischemia-reperfusion (I/R) is mediated by endogenously generated lipocalin-2 (Lcn2). A second objective was to examine whether Lcn2-mediated cell effects could be regulated by the inflammatory cytokines in the environment through their action on Lcn2 receptors (Lcn2R and megalin). Male Swiss mice were subjected to 30 min of renal ischemia with a reperfusion period of 24 h (early reperfusion, expected time for maximum inflammation) and 96 h (late reperfusion, expected time for maximum regeneration). Different experimental groups underwent I/R, I/R with iv anti-mouse Lcn2 monoclonal antibody injected during the early/inflammatory or late/recovery phase, and I/R with proinflammatory cytokine cocktail administration (recombinant mouse IL-1β, TNF-α, and IFN-γ). Compared with control nonischemic mice, the expression of three proliferation markers (stathmin, PCNA, and Ki-67, analyzed by quantitative RT-PCR) increased significantly in the I/R-treated animals. Blockade of Lcn2 by addition of anti-Lcn2 antibody significantly decreased the expression of these three proliferation markers when administered in the late/reparative phase, but had the opposite effect when administered in the early/inflammatory phase. Proinflammatory cytokine cocktail administration reduced the proliferative effects of Lcn2, and repressed Lcn2R and megalin expression. In conclusion, endogenously generated Lcn2 induces renal cell regeneration depending on the inflammatory cytokines in kidney I/R.

Cytokine-mediated regulation of antimicrobial proteins

Antimicrobial proteins constitute a phylogenetically ancient form of innate immunity that provides host defence at skin and mucosal surfaces. Although some components of this system are constitutively expressed, new evidence reviewed in this Progress article shows that the production of certain antimicrobial proteins by epithelial cells can also be regulated by cytokines of the innate and adaptive immune systems. In particular, the effector cytokines interleukin-17 and interleukin-22, which are produced by the T-helper-17-cell subset, are emerging as crucial regulators of antimicrobial-peptide production in the gut and the lungs. This suggests that this T-cell lineage and its cytokines have important roles in skin and mucosal immunity.

The siderocalin/enterobactin interaction: a link between mammalian immunity and bacterial iron transport

The siderophore enterobactin (Ent) is produced by enteric bacteria to mediate iron uptake. Ent scavenges iron and is taken up by the bacteria as the highly stable ferric complex [Fe (III)(Ent)] (3-). This complex is also a specific target of the mammalian innate immune system protein, Siderocalin (Scn), which acts as an antibacterial agent by specifically sequestering siderophores and their ferric complexes during infection. Recent literature suggesting that Scn may also be involved in cellular iron transport has increased the importance of understanding the mechanism of siderophore interception and clearance by Scn; Scn is observed to release iron in acidic endosomes and [Fe (III)(Ent)] (3-) is known to undergo a change from catecholate to salicylate coordination in acidic conditions, which is predicted to be sterically incompatible with the Scn binding pocket (also referred to as the calyx). To investigate the interactions between the ferric Ent complex and Scn at different pH values, two recombinant forms of Scn with mutations in three residues lining the calyx were prepared: Scn-W79A/R81A and Scn-Y106F. Binding studies and crystal structures of the Scn-W79A/R81A:[Fe (III)(Ent)] (3-) and Scn-Y106F:[Fe (III)(Ent)] (3-) complexes confirm that such mutations do not affect the overall conformation of the protein but do weaken significantly its affinity for [Fe (III)(Ent)] (3-). Fluorescence, UV-vis, and EXAFS spectroscopies were used to determine Scn/siderophore dissociation constants and to characterize the coordination mode of iron over a wide pH range, in the presence of both mutant proteins and synthetic salicylate analogues of Ent. While Scn binding hinders salicylate coordination transformation, strong acidification results in the release of iron and degraded siderophore. Iron release may therefore result from a combination of Ent degradation and coordination change.

Neutrophil gelatinase-associated lipocalin: a novel suppressor of invasion and angiogenesis in pancreatic cancer

Neutrophil gelatinase-associated lipocalin (NGAL) is a 25-kDa secreted acute phase protein, which is also up-regulated in multiple cancers, including breast, lung, and pancreas. Recently, NGAL has been proposed as an early biomarker in pancreatic cancer (PaCa). However, its biological role in PaCa is unknown. In this study, we examined in vitro and in vivo the functional role of NGAL in PaCa. Well- to moderately differentiated PaCa cells (AsPC-1, BxPC-3, and Capan-2) expressed high levels of NGAL but moderately to poorly differentiated PaCa cells (PANC-1 and MIAPaCa-2) expressed undetectable NGAL levels. Immunohistochemistry of untreated tissue microarray showed specific NGAL staining in resected PaCa specimens (P = 0.0167). Stable NGAL overexpression (MIAPaCa-2 and PANC-1) significantly blocked PaCa cell adhesion and invasion in vitro and vice versa with stable PaCa clones (BxPC-3 and AsPC-1). Moreover, NGAL overexpression reduced focal adhesion kinase (FAK) tyrosine-397 phosphorylation in PaCa cells. Furthermore, NGAL overexpression potently decreased angiogenesis in vitro partly through reduced vascular endothelial growth factor (VEGF) production and vice versa. Stable NGAL overexpression or underexpression had no effect on PaCa cell survival, viability, and response to chemotherapeutic drugs. Finally, MIAPaCa-2 cells overexpressing NGAL reduced tumor volume (P = 0.012), local and distant metastasis (P = 0.002), and angiogenesis (P = 0.05) with no effect on K-67 proliferation index (P > 0.1) in an orthotopic nude mouse PaCa model. Collectively, our results suggest that NGAL reduces adhesion/invasion partly by suppressing FAK activation and inhibits angiogenesis partly by blocking VEGF production in PaCa cells. Thus, NGAL is a potential suppressor of invasion and angiogenesis in advanced PaCa.

Dexamethasone-induced expression of the glucocorticoid response gene lipocalin 2 in chondrocytes

Glucocorticoids (GC) are commonly used anti-inflammatory drugs, but long-term use can result in marked growth retardation in children due to their actions on growth plate chondrocytes. To gain an insight into the mechanisms involved in GC-induced growth retardation, we performed Affymetrix microarray analysis of the murine chondrogenic cell line ATDC5, incubated with 10(-6) M dexamethasone (Dex) for 24 h. Downregulated genes included secreted frizzled-related protein and IGF-I, and upregulated genes included serum/GC-regulated kinase, connective-tissue growth factor, and lipocalin 2. Lipocalin 2 expression increased 40-fold after 24-h Dex treatment. Expression increased further after 48-h (75-fold) and 96-h (84-fold) Dex treatment, and this response was Dex concentration dependent. Lipocalin 2 was immunolocalized to both proliferating and hypertrophic growth plate zones, and its expression was increased by Dex in primary chondrocytes at 6 h (3-fold, P < 0.05). The lipocalin 2 response was blocked by the GC-receptor antagonist RU-486 and was increased further by the protein synthesis blocker cycloheximide. Proliferation in lipocalin 2-overexpressing cells was less than in control cells (49%, P < 0.05), and overexpression caused an increase in collagen type X expression (4-fold, P < 0.05). The effects of lipocalin 2 overexpression on chondrocyte proliferation (64%, P < 0.05) and collagen type X expression (8-fold, P < 0.05) were further exacerbated with the addition of 10(-6) M Dex. This synergistic effect may be explained by a further increase in lipocalin 2 expression with Dex treatment of transfected cells (45%, P < 0.05). These results suggest that lipocalin 2 may mediate Dex effects on chondrocytes and provides a potential novel mechanism for GC-induced growth retardation.

New challenges in studying nutrition-disease interactions in the developing world

Latest estimates indicate that nutritional deficiencies account for 3 million child deaths each year in less-developed countries. Targeted nutritional interventions could therefore save millions of lives. However, such interventions require careful optimization to maximize benefit and avoid harm. Progress toward designing effective life-saving interventions is currently hampered by some serious gaps in our understanding of nutrient metabolism in humans. In this Personal Perspective, we highlight some of these gaps and make some proposals as to how improved research methods and technologies can be brought to bear on the problems of undernourished children in the developing world.

Increased incidence of acute kidney injury with aprotinin use during cardiac surgery detected with urinary NGAL

BACKGROUND

Use of aprotinin has been associated with acute kidney injury after cardiac surgery. Neutrophil gelatinase-associated lipocalin (NGAL) is a novel, very sensitive marker for renal injury. Urinary NGAL may be able to detect renal injury caused by aprotinin. This study determined if the use of aprotinin is associated with an increased incidence of acute kidney injury and increased levels of urinary NGAL.

METHODS

In this prospective, observational study 369 patients undergoing cardiac surgery were enrolled. 205 patients received aprotinin and 164 received epsilon amino-caproic acid intraoperatively. Urinary NGAL was measured before and immediately after cardiac surgery and 3, 18 and 24 h later. The association of aprotinin use with the incidence of acute kidney injury (increase of serum creatinine >0.5 mg/dl) and NGAL levels was determined using logistic and linear regression models.

RESULTS

51 of 205 patients (25%) who received aprotinin developed acute kidney injury compared to 19 of 164 patients (12%) who received epsilon amino-caproic acid (p = 0.0013). Aprotinin use was associated with a two-fold higher risk of acute kidney injury when adjusted for potential confounders (age, Parsonnet score, preoperative serum creatinine, cardiopulmonary bypass and cross-clamp times; multiple logistic regression: OR = 2.164; CI (95%) = 1.102 to 4.249; p = 0.0249. Urinary NGAL was 19 times higher immediately after cardiopulmonary bypass and 18 times higher 3 h later in patients who had received aprotinin (postoperative: 19.23; CI (95%) = 12.60 to 29.33; p < 0.0001; 3 h post-cardiopulmonary bypass 18.67; CI (95%) = 11.45 to 30.43; p < 0.0001).

CONCLUSIONS

Postoperative urinary NGAL - a novel marker for renal injury - is increased in cardiac surgical patients receiving aprotinin compared to patients receiving epsilon amino-caproic acid. These results further support the hypothesis that aprotinin may cause renal injury. The substantial rise of urinary NGAL associated with aprotinin use may in part be due to aprotinin blocking the uptake of NGAL by megalin/gp330 receptors in the proximal tubules.

Decreased serum lipocalin-2 levels in human immunodeficiency virus-infected patients: increase during highly active anti-retroviral therapy

Although neutrophil gelatinase-associated lipocalin (NGAL) may play a pivotal role in the innate immune response, there are currently no data on NGAL levels in human immunodeficiency virus (HIV)-infected patients. In this study we aimed to examine the regulation of NGAL in HIV infection. The regulation of NGAL in HIV infection was examined by different experimental approaches, including studies in peripheral blood and mononuclear cells (MNC) from bone marrow aspirates before and during highly active anti-retroviral therapy (HAART). We found that: before initiating HAART, HIV-infected patients (n = 37) had significantly decreased serum NGAL levels compared with healthy controls (n = 26); (ii) during HAART, there was a gradual and significant increase in NGAL concentrations reaching levels comparable to those in healthy controls after 12 months; (iii) this increase was seen primarily in virological responders to HAART (HIV RNA level <200 copies/ml after 24 months); (iv) phytohaemagglutinin-stimulated NGAL release in MNC cells from bone marrow aspirates was decreased in untreated HIV-infected patients compared with healthy controls, but increased after 26 weeks on HAART; and (v) there was a significant positive correlation between neutrophil counts and NGAL levels at all time-points during HAART. We have shown decreased NGAL levels in HIV-infected patients, potentially reflecting decreased number and function of neutrophils as well as impaired bone marrow myelopoiesis. These abnormalities were reversed by successful HAART. Our findings underscore further the involvement of neutrophils and innate immunity in HIV-related immunodeficiency.

Iron homeostasis and erythropoiesis

Erythrocytes require iron to perform their duty as oxygen carriers. Mammals have evolved a mechanism to maintain systemic iron within an optimal range that fosters erythroid development and function while satisfying other body iron needs. This chapter reviews erythroid iron uptake and utilization as well as systemic factors that influence iron availability. One of these factors is hepcidin, a circulating peptide hormone that maintains iron homeostasis. Elevated levels of hepcidin in the bloodstream effectively shut off iron absorption by disabling the iron exporter ferroportin. Conversely, low levels of circulating hepcidin allow ferroportin to export iron into the bloodstream. Aberrations in hepcidin expression or responsiveness to hepcidin result in disorders of iron deficiency and iron overload. It is clear that erythroid precursors communicate their iron needs to the liver to influence the production of hepcidin and thus the amount of iron available for use. However, the mechanism by which erythroid cells accomplish this remains unclear and is an area of active investigation.

A dual role of lipocalin 2 in the apoptosis and deramification of activated microglia

Activated microglia are thought to undergo apoptosis as a self-regulatory mechanism. To better understand molecular mechanisms of the microglial apoptosis, apoptosis-resistant variants of microglial cells were selected and characterized. The expression of lipocalin 2 (lcn2) was significantly down-regulated in the microglial cells that were resistant to NO-induced apoptosis. lcn2 expression was increased by inflammatory stimuli in microglia. The stable expression of lcn2 as well as the addition of rLCN2 protein augmented the sensitivity of microglia to the NO-induced apoptosis, while knockdown of lcn2 expression using short hairpin RNA attenuated the cell death. Microglial cells with increased lcn2 expression were more sensitive to other cytotoxic agents as well. Thus, inflammatory activation of microglia may lead to up-regulation of lcn2 expression, which sensitizes microglia to the self-regulatory apoptosis. Additionally, the stable expression of lcn2 in BV-2 microglia cells induced a morphological change of the cells into the round shape with a loss of processes. Treatment of primary microglia cultures with the rLCN2 protein also induced the deramification of microglia. The deramification of microglia was closely related with the apoptosis-prone phenotype, because other deramification-inducing agents such as cAMP-elevating agent forskolin, ATP, and calcium ionophore also rendered microglia more sensitive to cell death. Taken together, our results suggest that activated microglia may secrete LCN2 protein, which act in an autocrine manner to sensitize microglia to the self-regulatory apoptosis and to endow microglia with an amoeboid form, a canonical morphology of activated microglia in vivo.