Ligand preference inferred from the structure of neutrophil gelatinase associated lipocalin

Holistic in silico developability assessment of novel classes of small proteins using publicly available sequence-based predictors

The development of novel therapeutic proteins is a lengthy and costly process, with an average attrition rate of 91% (Thomas et al. Clinical Development Success Rates and Contributing Factors 2011-2020, 2021). To increase the probability of success and ensure robust drug supply beyond approval, it is essential to assess the developability profile of new potential drug candidates as early and broadly as possible in development (Jain et al. MAbs, 2023. https://doi.org/10.1016/j.copbio.2011.06.002 ). Predicting these properties in silico is expected to be the next leap in innovation as it would enable significantly reduced development timelines combined with broader screens at lower costs. However, developing predictive algorithms typically requires substantial datasets generated under very defined conditions, a limiting factor especially for new classes of therapeutic proteins that hold immense clinical promise. Here we describe a strategy for assessing the developability of a novel class of small therapeutic Anticalin® proteins using machine learning in conjunction with a knowledge-driven approach. The knowledge-driven approach considers developability attributes such as aggregation propensity, charge variants, immunogenicity, specificity, thermal stability, hydrophobicity, and potential post-translational modifications, to calculate a holistic developability score. Based on sequence-derived descriptors as input parameters we established novel statistical models designed to predict the developability scores for Anticalin proteins. The best models yielded low root mean square errors across the entire dataset and were further validated by removing input data from individual screening campaigns and predicting developability scores for those drug candidates. The adoption of the described workflow will enable significantly streamlined preclinical development of Anticalin drug candidates and could potentially be applied to other therapeutic protein scaffolds.

Lipocalin-2 promotes breast cancer brain metastasis by enhancing tumor invasion and modulating brain microenvironment

Breast cancer is the leading cancer diagnosed in women globally, with brain metastasis emerging as a major cause of death, particularly in human epidermal growth factor receptor 2 positive and triple-negative breast cancer subtypes. Comprehensive understanding of the molecular foundations of central nervous system metastases is imperative for the evolution of efficacious treatment strategies. Lipocalin-2 (LCN2), a secreted iron transport protein with multiple functions, has been linked to the progression of breast cancer brain metastasis (BCBM). In primary tumors, LCN2 promotes the proliferation and angiogenesis of breast cancer cells, triggers the epithelial-mesenchymal transition, interacts with matrix metalloproteinase-9, thereby facilitating the reorganization of the extracellular matrix and enhancing cancer cell invasion and migration. In brain microenvironment, LCN2 undermines the blood-brain barrier and facilitates tumor seeding in the brain by modulating the behavior of key cellular components. In summary, this review meticulously examines the fuel role of LCN2 in BCBM cascade, and investigates the potential mechanisms involved. It highlights the potential of LCN2 as both a therapeutic target and biomarker, indicating that interventions targeting LCN2 may offer improved outcomes for patients afflicted with BCBM.

Backbone chemical shift and secondary structure assignments for mouse siderocalin

The lipocalin protein family is a structurally conserved group of proteins with a variety of biological functions defined by their ability to bind small molecule ligands and interact with partner proteins. One member of this family is siderocalin, a protein found in mammals. Its role is discussed in inflammatory processes, iron trafficking, protection against bacterial infections and oxidative stress, cell migration, induction of apoptosis, and cancer. Though it seems to be involved in numerous essential pathways, the exact mechanisms are often not fully understood. The NMR backbone assignments for the human siderocalin and its rat ortholog have been published before. In this work we describe the backbone NMR assignments of siderocalin for another important model organism, the mouse - data that might become important for structure-based drug discovery. Secondary structure elements were predicted based on the assigned backbone chemical shifts using TALOS-N and CSI 3.0, revealing a high content of beta strands and one prominent alpha helical region. Our findings correlate well with the known crystal structure and the overall conserved fold of the lipocalin family.

Lipocalin-2: a therapeutic target to overcome neurodegenerative diseases by regulating reactive astrogliosis

Glial cell activation precedes neuronal cell death during brain aging and the progression of neurodegenerative diseases. Under neuroinflammatory stress conditions, lipocalin-2 (LCN2), also known as neutrophil gelatinase-associated lipocalin or 24p3, is produced and secreted by activated microglia and reactive astrocytes. Lcn2 expression levels are known to be increased in various cells, including reactive astrocytes, through the activation of the NF-κB signaling pathway. In the central nervous system, as LCN2 exerts neurotoxicity when secreted from reactive astrocytes, many researchers have attempted to identify various strategies to inhibit LCN2 production, secretion, and function to minimize neuroinflammation and neuronal cell death. These strategies include regulation at the transcriptional, posttranscriptional, and posttranslational levels, as well as blocking its functions using neutralizing antibodies or antagonists of its receptor. The suppression of NF-κB signaling is a strategy to inhibit LCN2 production, but it may also affect other cellular activities, raising questions about its effectiveness and feasibility. Recently, LCN2 was found to be a target of the autophagy‒lysosome pathway. Therefore, autophagy activation may be a promising therapeutic strategy to reduce the levels of secreted LCN2 and overcome neurodegenerative diseases. In this review, we focused on research progress on astrocyte-derived LCN2 in the central nervous system.

Reduced secretion of LCN2 (lipocalin 2) from reactive astrocytes through autophagic and proteasomal regulation alleviates inflammatory stress and neuronal damage

LCN2/neutrophil gelatinase-associated lipocalin/24p3 (lipocalin 2) is a secretory protein that acts as a mammalian bacteriostatic molecule. Under neuroinflammatory stress conditions, LCN2 is produced and secreted by activated microglia and reactive astrocytes, resulting in neuronal apoptosis. However, it remains largely unknown whether inflammatory stress and neuronal loss can be minimized by modulating LCN2 production and secretion. Here, we first demonstrated that LCN2 was secreted from reactive astrocytes, which were stimulated by treatment with lipopolysaccharide (LPS) as an inflammatory stressor. Notably, we found two effective conditions that led to the reduction of induced LCN2 levels in reactive astrocytes: proteasome inhibition and macroautophagic/autophagic flux activation. Mechanistically, proteasome inhibition suppresses NFKB/NF-κB activation through NFKBIA/IκBα stabilization in primary astrocytes, even under inflammatory stress conditions, resulting in the downregulation of Lcn2 expression. In contrast, autophagic flux activation via MTOR inhibition reduced the intracellular levels of LCN2 through its pre-secretory degradation. In addition, we demonstrated that the N-terminal signal peptide of LCN2 is critical for its secretion and degradation, suggesting that these two pathways may be mechanistically coupled. Finally, we observed that LPS-induced and secreted LCN2 levels were reduced in the astrocyte-cultured medium under the above-mentioned conditions, resulting in increased neuronal viability, even under inflammatory stress.Abbreviations: ACM, astrocyte-conditioned medium; ALP, autophagy-lysosome pathway; BAF, bafilomycin A1; BTZ, bortezomib; CHX, cycloheximide; CNS, central nervous system; ER, endoplasmic reticulum; GFAP, glial fibrillary acidic protein; GFP, green fluorescent protein; JAK, Janus kinase; KD, knockdown; LCN2, lipocalin 2; LPS, lipopolysaccharide; MACS, magnetic-activated cell sorting; MAP1LC3/LC3, microtubule-associated protein 1 light chain 3; MTOR, mechanistic target of rapamycin kinase; NFKB/NF-κB, nuclear factor of kappa light polypeptide gene enhancer in B cells 1, p105; NFKBIA/IκBα, nuclear factor of kappa light polypeptide gene enhancer in B cells inhibitor, alpha; OVEX, overexpression; SLC22A17, solute carrier family 22 member 17; SP, signal peptide; SQSTM1, sequestosome 1; STAT3, signal transducer and activator of transcription 3; TNF/TNF-α, tumor necrosis factor; TUBA, tubulin, alpha; TUBB3/β3-TUB, tubulin, beta 3 class III; UB, ubiquitin; UPS, ubiquitin-proteasome system.

The Review of Current Knowledge on Neutrophil Gelatinase-Associated Lipocalin (NGAL)

Neutrophil gelatinase-associated lipocalin (NGAL) is a 25-kDa protein that is secreted mostly by immune cells such as neutrophils, macrophages, and dendritic cells. Its production is stimulated in response to inflammation. The concentrations of NGAL can be measured in plasma, urine, and biological fluids such as peritoneal effluent. NGAL is known mainly as a biomarker of acute kidney injury and is released after tubular damage and during renal regeneration processes. NGAL is also elevated in chronic kidney disease and dialysis patients. It may play a role as a predictor of the progression of renal function decreases with complications and mortality due to kidney failure. NGAL is also useful in the diagnostic processes of cardiovascular diseases. It is highly expressed in injured heart tissue and atherosclerostic plaque; its serum concentrations correlate with the severity of heart failure and coronary artery disease. NGAL increases inflammatory states and its levels rise in arterial hypertension, obesity, diabetes, and metabolic complications such as insulin resistance, and is also involved in carcinogenesis. In this review, we present the current knowledge on NGAL and its involvement in different pathologies, especially its role in renal and cardiovascular diseases.

The role of lipocalin 2 in brain injury and recovery after ischemic and hemorrhagic stroke

Ischemic and hemorrhagic stroke (including intracerebral hemorrhage, intraventricular hemorrhage, and subarachnoid hemorrhage) is the dominating cause of disability and death worldwide. Neuroinflammation, blood–brain barrier (BBB) disruption, neuronal death are the main pathological progress, which eventually causes brain injury. Increasing evidence indicated that lipocalin 2 (LCN2), a 25k-Da acute phase protein from the lipocalin superfamily, significantly increased immediately after the stroke and played a vital role in these events. Meanwhile, there exists a close relationship between LCN2 levels and the worse clinical outcome of patients with stroke. Further research revealed that LCN2 elimination is associated with reduced immune infiltrates, infarct volume, brain edema, BBB leakage, neuronal death, and neurological deficits. However, some studies revealed that LCN2 might also act as a beneficial factor in ischemic stroke. Nevertheless, the specific mechanism of LCN2 and its primary receptors (24p3R and megalin) involving in brain injury remains unclear. Therefore, it is necessary to investigate the mechanism of LCN2 induced brain damage after stroke. This review focuses on the role of LCN2 and its receptors in brain injury and aiming to find out possible therapeutic targets to reduce brain damage following stroke.

Lipocalin-2: a novel link between the injured kidney and the bone

PURPOSE OF REVIEW

Fibroblast growth factor 23 (FGF23) excess is associated with left ventricular hypertrophy (LVH) and early mortality in patients with chronic kidney disease (CKD) and in animal models. Elevated Lipocalin-2 (LCN2), produced by the injured kidneys, contributes to CKD progression and might aggravate cardiovascular outcomes. The current review aims to highlight the role of LCN2 in CKD, particularly its interactions with FGF23.

RECENT FINDINGS

Inflammation, disordered iron homeostasis and altered metabolic activity are common complications of CKD, and are associated with elevated levels of kidney-produced LCN2 and bone-secreted FGF23. A recent study shows that elevated LCN2 increases FGF23 production, and contributes to cardiac injury in patients and animals with CKD, whereas LCN2 reduction in mice with CKD reduces FGF23, improves cardiovascular outcomes and prolongs lifespan.

SUMMARY

In this manuscript, we discuss the potential pathophysiological functions of LCN2 as a major kidney-bone crosstalk molecule, linking the progressive decline in kidney function to excessive bone FGF23 production. We also review associations of LCN2 with kidney, cardiovascular and bone and mineral alterations. We conclude that the presented data support the design of novel therapeutic approaches to improve outcomes in CKD.

Mass Spectrometry-Based Structural Proteomics for Metal Ion/Protein Binding Studies

Metal ions are critical for the biological and physiological functions of many proteins. Mass spectrometry (MS)-based structural proteomics is an ever-growing field that has been adopted to study protein and metal ion interactions. Native MS offers information on metal binding and its stoichiometry. Footprinting approaches coupled with MS, including hydrogen/deuterium exchange (HDX), "fast photochemical oxidation of proteins" (FPOP) and targeted amino-acid labeling, identify binding sites and regions undergoing conformational changes. MS-based titration methods, including "protein-ligand interactions by mass spectrometry, titration and HD exchange" (PLIMSTEX) and "ligand titration, fast photochemical oxidation of proteins and mass spectrometry" (LITPOMS), afford binding stoichiometry, binding affinity, and binding order. These MS-based structural proteomics approaches, their applications to answer questions regarding metal ion protein interactions, their limitations, and recent and potential improvements are discussed here. This review serves as a demonstration of the capabilities of these tools and as an introduction to wider applications to solve other questions.

Lipocalin-2 (LCN2) Deficiency Leads to Cellular Changes in Highly Metastatic Human Prostate Cancer Cell Line PC-3

The transporter protein lipocalin-2 (LCN2) also termed neutrophil-gelatinase-associated lipocalin (NGAL) has pleiotropic effects in tumorigenesis in various cancers. Since the precise role of LCN2 in prostate cancer (PCa) is poorly understood, we aimed to elucidate its functions in PCa in vitro. For this purpose, LCN2 was transiently suppressed or permanently depleted in human PC-3 cells using siRNA or CRISPR/Cas9-mediated knockout. Effects of LCN2 suppression on expression of different tumorigenic markers were investigated by Western blot analysis and RT-qPCR. LCN2 knockout cells were analyzed for cellular changes and their ability to cope endoplasmic stress compared to parenteral PC-3 cells. Reduced LCN2 was accompanied by decreased expression of IL-1β and Cx43. In PC-3 cells, LCN2 deficiency leads to reduced proliferation, diminished expression of pro-inflammatory cytokines, lower adhesion, and disrupted F-actin distribution. In addition, IL-1β expression strongly correlated with LCN2 levels. LCN2 knockout cells showed enhanced and sustained activation of unfolded protein response proteins when treated with tunicamycin or cultured under glucose deprivation. Interestingly, an inverse correlation between phosphorylation of eukaryotic initiation factor 2 α subunit (p-eIF2α) and LCN2 expression was observed suggesting that LCN2 triggers protein synthesis under stress conditions. The finding that LCN2 depletion leads to significant phenotypic and cellular changes in PC-3 cells adds LCN2 as a valuable target for the treatment of PCa.

Comprehensive review of lipocalin 2-mediated effects in lung inflammation

Lipocalin-2 (LCN2) is an inflammatory mediator best known for its role as an innate acute-phase protein. LCN2 mediates the innate immune response to pathogens by sequestering iron, thereby inhibiting pathogen growth. Although LCN2 and its bacteriostatic properties are well studied, other LCN2 functions in the immune response to inflammatory stimuli are less well understood, such as its role as a chemoattractant and involvement in the regulation of cell migration and apoptosis. In the lungs, most studies thus far investigating the role of LCN2 in the immune response have looked at pathogenic inflammatory stimuli. Here, we compile data that explore the role of LCN2 in the immune response to various inflammatory stimuli in an effort to differentiate between protective versus detrimental roles of LCN2.

Lipocalin-2: Structure, function, distribution and role in metabolic disorders

Lipocalin-2 (LCN-2) is a novel, 198 amino acid adipocytokine also referred to as neutrophil gelatinase-associated lipocalin (NGAL). LCN-2 is a circulatory protein responsible for the transportation of small and hydrophobic molecules (steroid, free fatty acids, prostaglandins and hormones) to target organs after binding to megalin/glycoprotein and GP330 SLC22A17 or 24p3R LCN-2 receptors. LCN-2 has been used as a biomarker for acute and chronic renal injury. It is present in a large variety of cells including neutrophil, hepatocytes, lung, bone marrow, adipose tissue, macrophages, thymus, non-neoplastic breast duct, prostate, and renal cells. Different functions have been associated with LCN-2. These functions include antibacterial, anti-inflammatory, and protection against cell and tissue stress. Moreover, LCN-2 can increase the pool of matrix metalloproteinase 9 in human neutrophil granulocytes. Other reported functions of LCN-2 include its ability to destroy the extracellular matrix, which could enable cancer progression and spread of metastasis. Recent reports show that the tissue level of LCN-2 is increased in metabolic disorders such as obesity and type 2 diabetes, suggesting an association between LCN-2 and insulin sensitivity and glucose homeostasis. The precise role of LCN-2 in the modulation of insulin sensitivity, glucose and lipid metabolism is still unclear. This review explores the structure of LCN-2, tissue distribution, and its interaction with important metabolic pathways.

Lipocalin 2 as a link between ageing, risk factor conditions and age-related brain diseases

Chronic (neuro)inflammation plays an important role in many age-related central nervous system (CNS) diseases, including Alzheimer's disease, Parkinson's disease and vascular dementia. Inflammation also characterizes many conditions that form a risk factor for these CNS disorders, such as physical inactivity, obesity and cardiovascular disease. Lipocalin 2 (Lcn2) is an inflammatory protein shown to be involved in different age-related CNS diseases, as well as risk factor conditions thereof. Lcn2 expression is increased in the periphery and the brain in different age-related CNS diseases and also their risk factor conditions. Experimental studies indicate that Lcn2 contributes to various neuropathophysiological processes of age-related CNS diseases, including exacerbated neuroinflammation, cell death and iron dysregulation, which may negatively impact cognitive function. We hypothesize that increased Lcn2 levels as a result of age-related risk factor conditions may sensitize the brain and increase the risk to develop age-related CNS diseases. In this review we first provide a comprehensive overview of the known functions of Lcn2, and its effects in the CNS. Subsequently, this review explores Lcn2 as a potential (neuro)inflammatory link between different risk factor conditions and the development of age-related CNS disorders. Altogether, evidence convincingly indicates Lcn2 as a key constituent in ageing and age-related brain diseases.

Lipid transport proteins in malaria, from Plasmodium parasites to their hosts

Eukaryotic unicellular pathogens from the genus Plasmodium are the etiological agents of malaria, a disease that persists over a wide range of vertebrate species, including humans. During its dynamic lifecycle, survival in the different hosts depends on the parasite's ability to establish a suitable environmental milieu. To achieve this, specific host processes are exploited to support optimal growth, including extensive modifications to the infected host cell. These modifications include the formation of novel membranous structures, which are induced by the parasite. Consequently, to maintain a finely tuned and dynamic lipid environment, the organisation and distribution of lipids to different cell sites likely requires specialised lipid transfer proteins (LTPs). Indeed, several parasite and host-derived LTPs have been identified and shown to be essential at specific stages. Here we describe the roles of LTPs in parasite development and adaptation to its host including how the latest studies are profiting from the improved genetic, lipidomic and imaging toolkits available to study Plasmodium parasites. Lastly, a list of predicted Plasmodium LTPs is provided to encourage research in this field.

Interaction between matrix metalloproteinase-9 (MMP-9) and neutrophil gelatinase-associated lipocalin (NGAL): A recent evolutionary event in primates

Matrix metalloproteases are known to represent an early step in the evolution of the immune system. Similarly, neutrophil gelatinase-associated lipocalin is known to be a key effector in immune response. MMP-9 interacts with NGAL, but their interaction mechanisms remain unclear. Functional interaction between proteins is ensured by coevolution. Protein coevolution was inferred by calculating the linear correlation coefficients between inter-protein distance matrices using MirrorTree. Among examined mammal species, we found a robust signal of MMP-9/NGAL coevolution exclusively within Primates (R = 0.96, p < 1e-06). Owing to the high conservation of these proteins among Mammals, we chose to utilize a recent version of Blocks in Sequences (BIS2) algorithm implemented in BIS2Analyzer webserver. Coevolution clusters between the two proteins were identified in MMP-9 fibronectin and hemopexin domains. Our results suggest that MMP-9/NGAL interaction is a recent evolutionary acquisition in Primates. Furthermore, MMP-9 hemopexin domain would represent a promising target for drug design against these molecules.

Role of neutrophil gelatinase-associated lipocalin in renal cell carcinoma

Human neutrophil gelatinase-associated lipocalin (NGAL) is a glycoprotein present in a wide variety of tissues and cell types. It exists as a monomer of 25 kDa, a homodimer of 45 kDa or a heterodimer of 135 kDa (disulfide bound to latent matrix metalloproteinase-9). NGAL is considered the biochemical gold standard for the early diagnosis of acute kidney injury and has attracted much attention as a diagnostic biomarker. NGAL has controversial (i.e. both beneficial and detrimental) effects on cellular processes associated with tumor development, such as cell proliferation, survival, migration, invasion and drug resistance. Therefore, the present review aimed at clarifying the role of NGAL in renal cell carcinoma (RCC). Relevant studies of NGAL and RCC were searched in PubMed and relevant information about the structure, expression, function and mechanism of NGAL in RCC were summarized. Finally, the following conclusions could be drawn from the literature: i) NGAL can be detected in cancer tissues, serum and urine of patients with RCC; ii) NGAL is not a suitable diagnostic marker for early screening of RCC; iii) NGAL expression may be used to predict the prognosis of patients with RCC; and iv) Further research on NGAL may be helpful to decrease sunitinib resistance and find new treatment strategies for RCC.

Molecular docking analysis of docetaxel analogues as duel lipocalin 2 inhibitors

Lipocalin 2 (Lcn2, also called as neutrophil gelatinase-associated lipocalin) is a member of the lipocalin family and a known target for breast cancer. Therefore, it is of interest to use Docetaxel as a scaffold to design molecules with improved efficiency from naturally derived phytochemicals. We document 10 analogues (4Deacetyltaxol, 7Acetyltaxol, Cabazitaxel, Cephalomannine, Docetaxal, Deacetyltaxol, Docetaxeltrihydrate, Ortataxel, Paclitaxel, Taxoline) having optimal binding with Lipocalin 2 in comparison with Docetaxel. This data is highly useful for consideration in the design and development of drugs for breast cancer.

Site-Specific Siderocalin Binding to Ferric and Ferric-Free Enterobactin As Revealed by Mass Spectrometry

Both host and pathogen competitively manipulate coordination environments during bacterial infections. Human cells release the innate immune protein siderocalin (Scn, also known as lipocalin-2/Lcn2, neutrophil gelatinase-associated lipocalin/NGAL) that can inhibit bacterial growth by sequestering iron in a ferric complex with enterobactin (Ent), the ubiquitous Escherichia coli siderophore. Pathogenic E. coli use the virulence-associated esterase IroE to linearize the Ent cyclic trilactone to linear enterobactin (lin-Ent). We characterized lin-Ent interactions with Scn by using native mass spectrometry (MS) with hydrogen-deuterium exchange (HDX) and Lys/Arg specific covalent footprinting. These approaches support 1:1 binding of both Fe(III)-lin-Ent to Scn and iron-free lin-Ent to Scn. Both ferric and nonferric lin-Ent localize to all three pockets of the Scn calyx, consistent with Scn capture of lin-Ent both before and after Fe(III) chelation. These findings raise the possibility that Scn neutralizes both siderophores and siderophore-bound iron during infections. This integrated, MS-based approach circumvents the limitations that frustrate traditional structural approaches to examining Scn interactions with enterobactin-based ligands.

A Unique Conformational Distortion Mechanism Drives Lipocalin 2 Binding to Bacterial Siderophores

Lcn2 is a host defense protein induced via the innate immune response to sequester iron-loaded bacterial siderophores. However, excess or prolonged elevation of Lcn2 levels can induce adverse cellular effects, including oxidative stress and inflammation. In this work, we use Hydrogen-Deuterium eXchange (HDX) and Isothermal Titration Calorimetry (ITC) to characterize the binding interaction between Lcn2 and siderophores enterobactin and 2,3-DHBA, in the presence and absence of iron. Our results indicate a rare "Type II" interaction in which binding of siderophores drives the protein conformational equilibrium toward an unfolded state. Linking our molecular model to cellular assays, we demonstrate that this "distorted binding mode" facilitates a deleterious cellular accumulation of reactive oxygen species that could represent the molecular origin of Lcn2 pathology. These results add important insights into mechanisms of Lcn2 action and have implications in Lcn2-mediated effects including inflammation.

Interaction of Alt a 1 with SLC22A17 in the airway mucosa

BACKGROUND

Despite all the efforts made up to now, the reasons that facilitate a protein becoming an allergen have not been elucidated yet. Alt a 1 protein is the major fungal allergen responsible for chronic asthma, but little is known about its immunological activity. Our main purpose was to investigate the ligand-dependent interactions of Alt a 1 in the human airway epithelium.

METHODS

Alt a 1 with and without its ligand (holo- and apo- forms) was incubated with the pulmonary epithelial monolayer model, Calu-3 cells. Allergen transport and cytokine production were measured. Pull-down and immunofluorescence assays were employed to identify the receptor of Alt a 1 using the epithelial cell model and mouse tissues. Receptor-allergen-ligand interactions were analyzed by computational modeling.

RESULTS

The holo-form could activate human monocytes, PBMCs, and polarized airway epithelial (Calu-3) cell lines. The allergen was also transported through the monolayer, without any alteration of the epithelial integrity (TEER). Alt a 1 also induced the production of proinflammatory IL8 and specific epithelial cytokines (IL33 and IL25) by Calu-3 cells. The interaction between epithelial cells and holo-Alt a 1 was found to be mediated by the SLC22A17 receptor, and its recognition of Alt a 1 was explained in structural terms.

CONCLUSIONS

Our findings identified the Alt a 1 ligand as a central player in the interaction of the allergen with airway mucosa, shedding light into its potential role in the immunological response, while unveiling its potential as a new target for therapy intervention.

Lipocalin-2-The myth of its expression and function

Lipocalin-2 is a functional biomarker for acute and chronic kidney diseases, heart failure and obesity-related medical complications. It is rapidly induced in epithelial cells under stress conditions, but constitutively produced from pre-adipocytes and mature adipocytes. Measuring the lipocalin-2 levels represents an effective approach for risk prediction, patient stratification and disease management. Nevertheless, due to ligand-binding, post-translational modification and protein-protein interaction, lipocalin-2 exists as multiple variants that elicit different pathophysiological functions. To characterize the specific structure-functional relationships of lipocalin-2 variants is critical for the development of biomarker assays with sufficient precision and reliability. Moreover, identifying the pathological forms of lipocalin-2 will provide new therapeutic targets and treatment approaches for obesity-related complications.

Postpartum human breast milk levels of neutrophil gelatinase-associated lipocalin (NGAL) and matrix metalloproteinase-9 (MMP-9)/NGAL complex in normal and pregnancies complicated with insulin-dependent gestational diabetes mellitus. A prospective pilot case-control study

Neutrophil gelatinase-associated lipocalin (NGAL) and its complex with matrix metalloproteinase-9 (MMP-9) are present in a variety of human tissues and extracellular fluids. The aim of this pilot prospective case-control study was to detect NGAL and MMP-9/NGAL complex in human breast milk postpartum in women with normal and pregnancies that developed insulin-depended gestational diabetes mellitus (iGDM). We detected both biomarkers in human breast milk and concentrations were determined at the first day of colostrum secretion and two days after, in 22 normal pregnancies and 13 pregnancies with iGDM. Mean NGAL concentration decreased significantly from the first to the second sample, in both groups. Mean MMP-9/NGAL complex concentration decreased also significantly from the first to the second sample in normal pregnancies. Mean complex concentration was significantly higher in diabetic pregnancies compared to normal ones in the second sample.IMPACT STATEMENTWhat is already known on this subject? There is limited information on the presence of Neutrophil gelatinase-associated lipocalin (NGAL) in human milk and its physiological role.What the results of this study add? It is the first time that MMP-9/NGAL complex is detected in human milk in both normal and pregnancies complicated with insulin-depended gestational diabetes mellitus (iGDM). We confirm the presence of NGAL in colostrum of normal pregnancies and for the first time we detected NGAL in milk of pregnancies with iGDM. Concentrations of NGAL and MMP-9/NGAL complex tend to lessen postpartum in both groups. Pregnancies with iGDM compared to normal ones showed significantly higher concentration of MMP-9/NGAL complex two days after the beginning of lactation.What the implications are of these findings for clinical practice and/or further research? Further studies are necessary to determine the levels of NGAL and MMP-9/NGAL complex in human milk postpartum in normal and pathological pregnancies. Taking into consideration the well-established NGAL's ability to act as a bacteriostatic agent and its mucosal healing activity in gastrointestinal track, early breastfeeding of neonates is a logical recommendation. Finally, new studies on the actual physiological role of milk NGAL in neonates are necessary.

Urinary neutrophil gelatinase-associated lipocalin for diagnosis of spontaneous bacterial peritonitis

Cirrhotic patients with ascites are at high risk of developing spontaneous bacterial peritonitis (SBP). After exclusion of patients with acute kidney injury (AKI) or other infections, urinary neutrophil gelatinase-associated lipocalin (NGAL) levels were compared between two matched groups of Egyptian cirrhotic patients with ascites, mostly secondary to hepatitis C infection (98%). Group 1 had SBP (n = 41) and group 2 did not (n = 45). By univariate analysis, urinary-NGAL, high total bilirubin, serum creatinine, international normalised ratio and the Model of End-Stage Liver Disease (MELD) score and low platelet count were all significantly correlated with the presence of SBP, but only urinary-NGAL could independently predict development of SBP (P = 0.001). Urinary-NGAL at a cut-off value of 1225 pg/mL, showed a sensitivity of 95% and a specificity of 76%, and is therefore a most useful tool.

Parsing the functional specificity of Siderocalin/Lipocalin 2/NGAL for siderophores and related small-molecule ligands

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Ligand recognition by antibacterial Siderocalin controls the competition for iron during infection.

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We determined nine crystal structures of Siderocalin mutants with ligands.

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We determined three candidate ligands did not bind.

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We determined the crystal structure of SBP YfiY.

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Multiplexed specificity of Siderocalin was determined.

Siderocalin/Lipocalin 2/Neutrophil Gelatinase Associated Lipocalin/24p3 is an innate immune system protein with bacteriostatic activity, acting by tightly binding and sequestering diverse catecholate and mixed-type ferric siderophores from enteric bacteria and mycobacteria. Bacterial virulence achieved through siderophore modifications, or utilization of alternate siderophores, can be explained by evasion of Siderocalin binding. Siderocalin has also been implicated in a wide variety of disease processes, though often in seemingly contradictory ways, and has been proposed to bind to a broader array of ligands beyond siderophores. Using structural, directed mutational, and binding studies, we have sought to rigorously test, and fully elucidate, the Siderocalin recognition mechanism. Several proposed ligands fail to meet rigorous binding criteria, including the bacterial siderophore pyochelin, the iron-chelating catecholamine hormone norepinephrine, and the bacterial second messenger cyclic diguanylate monophosphate. While possessing a remarkably rigid structure, in principle simplifying analyses of ligand recognition, understanding Scn recognition is complicated by the observed conformational and stoichiometric plasticity, and instability, of its bona fide siderophore ligands. Since the role of Siderocalin at the early host/pathogen interface is to compete for bacterial ferric siderophores, we also analyzed how bacterial siderophore binding proteins and enzymes alternately recognize siderophores that efficiently bind to, or evade, Siderocalin sequestration – including determining the crystal structure of Bacillus cereus YfiY bound to schizokinen. These studies combine to refine the potential physiological functions of Siderocalin by defining its multiplexed recognition mechanism.

The anti-bacterial iron-restriction defence mechanisms of egg white; the potential role of three lipocalin-like proteins in resistance against Salmonella

Salmonella enterica serovar Enteritidis (SE) is the most frequently-detected Salmonella in foodborne outbreaks in the European Union. Among such outbreaks, egg and egg products were identified as the most common vehicles of infection. Possibly, the major antibacterial property of egg white is iron restriction, which results from the presence of the iron-binding protein, ovotransferrin. To circumvent iron restriction, SE synthesise catecholate siderophores (i.e. enterobactin and salmochelin) that can chelate iron from host iron-binding proteins. Here, we highlight the role of lipocalin-like proteins found in egg white that could enhance egg-white iron restriction through sequestration of certain siderophores, including enterobactin. Indeed, it is now apparent that the egg-white lipocalin, Ex-FABP, can inhibit bacterial growth via its siderophore-binding capacity in vitro. However, it remains unclear whether Ex-FABP performs such a function in egg white or during bird infection. Regarding the two other lipocalins of egg white (Cal-γ and α-1-glycoprotein), there is currently no evidence to indicate that they sequester siderophores.

Response to different furosemide doses predicts AKI progression in ICU patients with elevated plasma NGAL levels

BACKGROUND

Furosemide responsiveness (FR) is determined by urine output after furosemide administration and has recently been evaluated as a furosemide stress test (FST) for predicting severe acute kidney injury (AKI) progression. Although a standardized furosemide dose is required for FST, variable dosing is typically employed based on illness severity, including renal dysfunction in the clinical setting. This study aimed to evaluate whether FR with different furosemide doses can predict AKI progression. We further evaluated the combination of an AKI biomarker, plasma neutrophil gelatinase-associated lipocalin (NGAL), and FR for predicting AKI progression.

RESULTS

We retrospectively analyzed 95 patients who were treated with bolus furosemide in our medical-surgical intensive care unit. Patients who had already developed AKI stage 3 were excluded. A total of 18 patients developed AKI stage 3 within 1 week. Receiver operating curve analysis revealed that the area under the curve (AUC) values of FR and plasma NGAL were 0.87 (0.73-0.94) and 0.80 (0.67-0.88) for AKI progression, respectively. When plasma NGAL level was < 142 ng/mL, only one patient developed stage 3 AKI, indicating that plasma NGAL measurements were sufficient to predict AKI progression. We further evaluated the performance of FR in 51 patients with plasma NGAL levels > 142 ng/mL. FR was associated with AUC of 0.84 (0.67-0.94) for AKI progression in this population with high NGAL levels.

CONCLUSIONS

Although different variable doses of furosemide were administered, FR revealed favorable efficacy for predicting AKI progression even in patients with high plasma NGAL levels. This suggests that a combination of FR and biomarkers can stratify the risk of AKI progression in a clinical setting.

Neutrophil Gelatinase-Associated Lipocalin as a Biomarker of Allograft Function After Renal Transplantation: Evaluation of the Current Status and Future Insights

Neutrophil gelatinase‐associated lipocalin (NGAL), a protein belonging to the lipocalin superfamily initially found in activated neutrophils, is expressed by several cell types, including kidney tubule. The increase in NGAL production and release from tubular cells in response to various insults has been proven to predict acute kidney injury (AKI). For this reason, it has emerged as a valuable noninvasive biomarker of AKI in clinical nephrology. Also in the renal transplant setting, different studies have indicated NGAL as a valuable tool, especially in the early postoperative period, since the currently available clinical and laboratory parameters remain poorly sensitive to monitor immediate posttransplant graft function. This is an analysis of the recent literature to assess the utility of plasma and urinary NGAL, exosomal mRNA for NGAL, and NGAL levels in the perfusate of machine‐perfused kidneys for the prediction of graft function recovery in the early postsurgery phase after renal transplantation. We found that NGAL appears as a promising troponin‐like biomarker to detect short‐term impairment of graft function after renal transplant, but there are still some limitations in its clinical application, essentially related to its low specificity. Moreover, comparing NGAL assayed in serum, urine, machine‐perfusate, or as exosomal mRNA, each one has shown limitations and benefits in terms of predictive performance for DGF, according to various existing studies, feasibly due to different cut‐off levels, designs and patient sample sizes.

Overcoming antibiotic resistance: Is siderophore Trojan horse conjugation an answer to evolving resistance in microbial pathogens?

Comparative study of siderophore biosynthesis pathway in pathogens provides potential targets for antibiotics and host drug delivery as a part of computationally feasible microbial therapy. Iron acquisition using siderophore models is an essential and well established model in all microorganisms and microbial infections a known to cause great havoc to both plant and animal. Rapid development of antibiotic resistance in bacterial as well as fungal pathogens has drawn us at a verge where one has to get rid of the traditional way of obstructing pathogen using single or multiple antibiotic/chemical inhibitors or drugs. 'Trojan horse' strategy is an answer to this imperative call where antibiotic are by far sneaked into the pathogenic cell via the siderophore receptors at cell and outer membrane. This antibiotic once gets inside, generates a 'black hole' scenario within the opportunistic pathogens via iron scarcity. For pathogens whose siderophore are not compatible to smuggle drug due to their complex conformation and stiff valence bonds, there is another approach. By means of the siderophore biosynthesis pathways, potential targets for inhibition of these siderophores in pathogenic bacteria could be achieved and thus control pathogenic virulence. Method to design artificial exogenous siderophores for pathogens that would compete and succeed the battle of intake is also covered with this review. These manipulated siderophore would enter pathogenic cell like any other siderophore but will not disperse iron due to which iron inadequacy and hence pathogens control be accomplished. The aim of this review is to offer strategies to overcome the microbial infections/pathogens using siderophore.

Iron Acquisition Strategies of Bacterial Pathogens

Iron is an essential micronutrient for both microbes and humans alike. For well over half a century we have known that this element, in particular, plays a pivotal role in health and disease and, most especially, in shaping host-pathogen interactions. Intracellular iron concentrations serve as a critical signal in regulating the expression not only of high-affinity iron acquisition systems in bacteria, but also of toxins and other noted virulence factors produced by some major human pathogens. While we now are aware of many strategies that the host has devised to sequester iron from invading microbes, there are as many if not more sophisticated mechanisms by which successful pathogens overcome nutritional immunity imposed by the host. This review discusses some of the essential components of iron sequestration and scavenging mechanisms of the host, as well as representative Gram-negative and Gram-positive pathogens, and highlights recent advances in the field. Last, we address how the iron acquisition strategies of pathogenic bacteria may be exploited for the development of novel prophylactics or antimicrobials.

Estimating the prevalence of elevated plasma neutrophil gelatinase associated lipocalin level in patients with acute coronary syndromes and its association with outcomes

Objectives

The principal objective of this study was to estimate the plasma levels of neutrophil gelatinase associated lipocalin (NGAL) in a cohort of patients with acute coronary syndromes (ACS) across their entire spectrum, and to correlate them with outcomes.

Methods

87 patients with acute coronary syndromes were included in the study. Apart from the routine work up and management, all patients underwent determination of plasma NGAL and serum high sensitivity C reactive protein (HSCRP) levels at admission. The patients were followed up through the hospital stay as well as for one month after discharge for clinical outcomes, and echocardiographic parameters of left ventricular function. Plasma NGAL was studied for its predictive power for various defined outcomes.

Results

Plasma NGAL levels were detectably elevated in 67% of patients with ACS without any significant proportion with renal dysfunction, sepsis or overt infection. Plasma NGAL was the strongest independent predictor of all cause hospital mortality in Cox regression multivariate analysis with an odds ratio of 8.353, p = 0.0237. Plasma NGAL did not correlate with HSCRP, or severity of coronary artery disease (CAD).

Conclusion

This is a small study that shows that plasma NGAL in patients admitted with ACS can predict hospital mortality and forms the basis for consideration of this molecule as a possible new risk marker in ACS meriting further and more extensive investigation.

Neutrophil gelatinase-associated lipocalin levels are U-shaped in the Ludwigshafen Risk and Cardiovascular Health (LURIC) study-Impact for mortality

INTRODUCTION

Neutrophil gelatinase-associated lipocalin (NGAL) is a glycoprotein released by damaged renal tubular cells and mature neutrophils. It is elevated in kidney injury, but also in patients with coronary artery disease (CAD) and myocardial infarction. We investigated the prognostic value of NGAL for total and cardiovascular mortality in patients undergoing coronary angiography without history of renal insufficiency at inclusion into the study.

PARTICIPANTS

The LURIC study is an ongoing prospective cohort study of patients referred for coronary angiography and is designed to evaluate determinants of cardiovascular health.

RESULTS

NGAL was determined in plasma of 2997 persons (mean age: 62.7 years; 69.7% men) with a follow up for 10 years. 2358 patients suffered from CAD and 638 did not-these patients served as controls. Stable CAD was found in 1408 and unstable CAD in 950 patients. Death rate from cardiovascular events and all causes was highest in patients within the 4th quartile of NGAL (≥56 ng/ml, p<0.001 vs third quartile), even after adjustment for age and gender. According to multivariable-adjusted Cox analysis adjusting for well-known cardiovascular risk factors, as well as lipid lowering therapy, angiographic CAD, and C-reactive protein we found patients in the highest NGAL quartile being at increased risk for cardiovascular (hazard ratio (HR) 1.33, 95%CI 1.05-1.67, p = 0.016) and all cause mortality (HR 1.29 95%CI 1.07-1.55, p = 0.007) compared to those in the third quartile. The lowest risk was seen in the third quartile of NGAL (41-56 ng/ml) suggesting a U-shaped relationship between NGAL and mortality. Further adjustment for creatinine abrogated the predictive effect of NGAL. However, the 3rd and 4th quartiles of NGAL were significantly associated with higher neutrophil counts, which were associated with CAD, non-ST elevation and ST-elevation myocardial infarction (p<0.05).

CONCLUSIONS

Plasma NGAL concentrations are mainly derived from neutrophils and do not predict mortality independent of renal function.

Plasma neutrophil gelatinase-associated lipocalin levels are positively associated with diabetic retinopathy in patients with Type 2 diabetes

AIM

To assess the relationship between plasma neutrophil gelatinase-associated lipocalin (NGAL) levels and diabetic retinopathy in patients with Type 2 diabetes.

METHODS

In total, 204 patients with Type 2 diabetes were investigated in this cross-sectional study. They were classified as having no diabetic retinopathy, non-proliferative diabetic retinopathy (NPDR) or proliferative retinopathy (PDR), according to the degree of diabetic retinopathy. Thus, diabetic retinopathy in the patients in this study was either NPDR or PDR.

RESULTS

Plasma NGAL concentrations were significantly higher in patients with diabetic retinopathy than in those without. The mean plasma NGAL levels differed significantly according to the severity of diabetic retinopathy (no diabetic retinopathy, 120.8 ng/ml; NPDR, 217.8 ng/ml; PDR, 372.4 ng/ml; P for trend = 0.002) after adjustment for other covariates. In multivariable analysis, plasma NGAL levels were significantly associated with diabetic retinopathy (odds ratio for each standard deviation increase in the logarithmic value, 7.75; 95% confidence interval, 2.04-29.41, P = 0.003).

CONCLUSION

Plasma NGAL levels were positively associated with diabetic retinopathy in patients with Type 2 diabetes.

Lipocalin 2 (LCN2) Expression in Hepatic Malfunction and Therapy

Lipocalin 2 (LCN2) is a secreted protein that belongs to the Lipocalins, a group of transporters of small lipophilic molecules such as steroids, lipopolysaccharides, iron, and fatty acids in circulation. Two decades after its discovery and after a high variety of published findings, LCN2's altered expression has been assigned to critical roles in several pathological organ conditions, including liver injury and steatosis, renal damage, brain injury, cardiomyopathies, muscle-skeletal disorders, lung infection, and cancer in several organs. The significance of this 25-kDa lipocalin molecule has been impressively increased during the last years. Data from several studies indicate the role of LCN2 in physiological conditions as well as in response to cellular stress and injury. LCN2 in the liver shows a protective role in acute and chronic injury models where its expression is highly elevated. Moreover, LCN2 expression is being considered as a potential strong biomarker for pathological conditions, including rheumatic diseases, cancer in human organs, hepatic steatosis, hepatic damage, and inflammation. In this review, we summarize experimental and clinical findings linking LCN2 to the pathogenesis of liver disease.

Early detection of diabetic kidney disease: Present limitations and future perspectives

Diabetic kidney disease (DKD) is one of the most common diabetic complications, as well as the leading cause of chronic kidney disease and end-stage renal disease around the world. To prevent the dreadful consequence, development of new assays for diagnostic of DKD has always been the priority in the research field of diabetic complications. At present, urinary albumin-to-creatinine ratio and estimated glomerular filtration rate (eGFR) are the standard methods for assessing glomerular damage and renal function changes in clinical practice. However, due to diverse tissue involvement in different individuals, the so-called “non-albuminuric renal impairment” is not uncommon, especially in patients with type 2 diabetes. On the other hand, the precision of creatinine-based GFR estimates is limited in hyperfiltration status. These facts make albuminuria and eGFR less reliable indicators for early-stage DKD. In recent years, considerable progress has been made in the understanding of the pathogenesis of DKD, along with the elucidation of its genetic profiles and phenotypic expression of different molecules. With the help of ever-evolving technologies, it has gradually become plausible to apply the thriving information in clinical practice. The strength and weakness of several novel biomarkers, genomic, proteomic and metabolomic signatures in assisting the early diagnosis of DKD will be discussed in this article.

Evidence for participation of neutrophil gelatinase-associated lipocalin/matrix metalloproteinase-9 (NGAL•MMP-9) complex in the inflammatory response to infection in pregnancies complicated by preterm birth

PROBLEM

Neutrophil gelatinase-associated lipocalin (NGAL) is expressed in neutrophils and involved in innate immunity by sequestering iron. NGAL's ability to complex with matrix metalloproteinase-9 (MMP-9) and extend its gelatinolytic activity led us to investigate its role in pregnancies complicated by preterm birth (PTB) and intra-amniotic infection/inflammation (IAI).

METHOD OF STUDY

We assayed the amniotic fluid (AF) levels of NGAL and MMP-9 in 308 women that had a clinically indicated amniocentesis and a normal pregnancy outcome or PTB. qRT-PCR was employed to determine NGAL mRNA expression of placental villous trophoblast and amniochorion. Immunohistochemistry was used for cellular localization.

RESULTS

AF NGAL levels were gestational age-regulated. Women with IAI and PTB had significantly higher levels of NGAL, MMP-9 and NGAL•MMP-9 complex.

CONCLUSION

The amniochorion is a source of NGAL and similarly to other inflammatory conditions, this protein may augment the collagenolytic effect of MMP-9 and modulate host-microbe interactions in pregnancies complicated by IAI.

Help-me signaling: Non-cell autonomous mechanisms of neuroprotection and neurorecovery

Self-preservation is required for life. At the cellular level, this fundamental principle is expressed in the form of molecular mechanisms for preconditioning and tolerance. When the cell is threatened, internal cascades of survival signaling become triggered to protect against cell death and defend against future insults. Recently, however, emerging findings suggest that this principle of self-preservation may involve not only intracellular signals; the release of extracellular signals may provide a way to recruit adjacent cells into an amplified protective program. In the central nervous system where multiple cell types co-exist, this mechanism would allow threatened neurons to "ask for help" from glial and vascular compartments. In this review, we describe this new concept of help-me signaling, wherein damaged or diseased neurons release signals that may shift glial and vascular cells into potentially beneficial phenotypes, and help remodel the neurovascular unit. Understanding and dissecting these non-cell autonomous mechanisms of self-preservation in the CNS may lead to novel opportunities for neuroprotection and neurorecovery.

Plasma Neutrophil Gelatinase-Associated Lipocalin Reflects Both Inflammation and Kidney Function in Patients with Myocardial Infarction

BACKGROUND/AIMS

Neutrophil gelatinase-associated lipocalin (NGAL) has emerged as a marker for acute kidney injury and cardiovascular outcome. However, the relative importance of inflammation versus kidney function on plasma NGAL levels is uncertain, making the interpretation of plasma NGAL unclear. Accordingly, we investigated the relationship between plasma NGAL, inflammation and kidney function in patients with myocardial infarction (MI).

METHODS

We prospectively included 584 patients with acute ST-segment elevation MI (STEMI) treated with primary percutaneous coronary intervention (PCI) from 2006 to 2008. Blood samples were drawn immediately before PCI. Additionally, we included 42 patients who had 4 blood samples drawn before and after PCI. Plasma NGAL was measured using a time-resolved immunofluorometric assay. Cross-sectional analyses were performed in these two single-center, prospective study cohorts.

RESULTS

Estimated glomerular filtration rate (eGFR) was associated significantly more strongly with plasma NGAL when eGFR was abnormal compared to normal eGFR: a decrease in eGFR of 10 ml/min was associated with an increase in NGAL of 27% (18-36%) versus 4% (1-7%), respectively (p < 0.001). Leukocyte count and C-reactive protein were the main determinants of plasma NGAL in patients with normal eGFR, whereas eGFR was the main determinant at reduced kidney function.

CONCLUSIONS

eGFR determines the association of NGAL with either inflammation or kidney function; in patients with normal eGFR, plasma NGAL reflects inflammation but when eGFR is reduced, plasma NGAL reflects kidney function, highlighting the dual perception of plasma NGAL. From a clinical perspective, eGFR may be used to guide the interpretation of elevated NGAL levels in patients with STEMI.

The Ligands of Neutrophil Gelatinase-Associated Lipocalin

Neutrophil gelatinase associated lipocalin (NGAL), was originally identified in neutrophil granules as a heterodimer complex with gelatinase B (matrix metalloproteinase 9, MMP9), but more recently has been found to be secreted by damaged epithelial cells. Ngal is a member of the lipocalin family and subsequently named as lipocalin 2 on the basis of structural similarity with other members of the lipocalin family and its potential association with hydrophobic retinol and cholesterol oleate more strongly than their hydrophilic counterparts. In 2002, a landmark paper suggested that Ngal is a bacteriostatic agent which blocks iron acquisition by interacting with a number of bacterial siderophores, especially enterobactin. Since then, more siderophore-carrying functions have been reported than the possibility of hydrophobic ligand transport. In this setting, Ngal was renamed Siderocalin. Functions of siderocalin include not only bacteriostatic activity but potentially as a mediator of cell growth and differentiation; some of these functions appear to be referable to the holo siderocalin:siderophore:iron complex and recent work suggests that metabolic products may act as mammalian siderophores bound by Ngal. While still speculative, it may be that the mammalian siderophores can establish the missing link between Ngal and a number of its functions in vivo. This review provides an overview of the discoveries of the different ligands of Ngal and consequently related functions. Hydrophobic ligands, bacterial siderophores as well as their modified structures (synthetic siderophores), and mammalian siderophores are summarized.

Biomarkers of drug-induced acute kidney injury in the adult

INTRODUCTION

This article addresses general biomarkers of drug-induced acute kidney injury (AKI) and their application in development and progression of AKI in the adult. It also highlights some clinical benefits, but also uncertainties, of biomarker use.

AREAS COVERED

Drug-induced AKI is traditionally diagnosed by monitoring serum creatinine (SCr), blood urea nitrogen and albuminuria. The sensitivity of these measures is, however, limited to well-established AKI. Application of selected biomarkers for early diagnosis of drug-induced AKI may inform on progression of AKI and alert clinicians to adopt renoprotective strategies at the earliest times. Novel biomarkers, accepted for early detection of drug-induced AKI (kidney injury molecule-1, neutrophil gelatinase-associated lipocalin and N-acetyl-β-d-glucosaminidase), may be useful additions in panels of biomarkers. Clinical biomarkers of cell cycle arrest, tissue inhibitor of metalloproteinase-2 and insulin-like growth factor binding protein 7 show promise but need further validation in clinical trials.

EXPERT OPINION

Traditional parameters, such as SCr, provide some guidance for functional decline in drug-induced AKI but early, more sensitive, affordable, clinically acceptable, biomarkers of kidney dysfunction are needed. Basic biological understanding of AKI will improve with high-throughput methodologies such as proteomics and metabolomics, and this should lead to identification and usage of novel biomarkers. Ultimately, a combination of biomarkers indicating kidney dysfunction and damage is likely to be required.

A systematic analysis of human lipocalin family and its expression in esophageal carcinoma

The lipocalin proteins (lipocalins) are a large family of small proteins characterized by low sequence similarity and highly conserved crystal structures. Lipocalins have been found to play important roles in many human diseases. For this reason, a systemic analysis of the molecular properties of human lipocalins is essential. In this study, human lipocalins were found to contain four structurally conserved regions (SCRs) and could be divided into two subgroups. A human lipocalin protein-protein interaction network (PPIN) was constructed and integrated with their expression data in esophageal carcinoma. Many lipocalins showed obvious co-expression patterns in esophageal carcinoma. Their subcellular distributions also suggested these lipocalins may transfer signals from the extracellular space to the nucleus using the pathway-like paths. These analyses also expanded our knowledge about this human ancient protein family in the background of esophageal carcinoma.

Novel biomarkers in heart failure with preserved ejection fraction

Heart failure with preserved ejection fraction (HFPEF) is a common subtype of heart failure with morbidity and mortality similar to that of heart failure with systolic dysfunction. This article discusses the numerous biomarkers that promise to play a substantial role in terms of our ability to understand the mechanisms of HFPEF and discern possible phenotypes that respond to targeted therapies: natriuretic peptides, high-sensitivity troponins, galectin-3, soluble ST2, neutrophil gelatinase-associated lipocalin, and cystatin C.

Neutrophil gelatinase-associated lipocalin as a marker of acute renal disease

PURPOSE OF REVIEW

Acute renal disease has major prognostic impact in hospitalized patients. Early diagnosis using renal function markers such as serum creatinine or urinary output and effective treatment are currently not possible. This review focuses on recent studies examining the biological characteristics and the diagnostic and prognostic value of a novel biomarker, neutrophil gelatinase-associated lipocalin (NGAL), in patients at risk for acute renal disease.

RECENT FINDINGS

NGAL levels increase early and proportional to the degree of renal injury in the urine and plasma. Here, we report the results of clinical studies where NGAL was measured in 325 patients with autoimmune and infectious diseases, those with cisplatin-associated nephrotoxicity, and more than 4000 patients at risk of acute kidney injury due to sepsis, cardiac surgery, exposure to contrast media, or after renal transplantation. Whenever renal damage occurred, as evidenced by histopathology or subsequent increase in serum creatinine levels, NGAL levels were higher than in patients without acute renal disease. An increase in NGAL substantially preceded clinical diagnosis of acute renal disease.

SUMMARY

NGAL fulfills many characteristics of an appropriate 'real-time' renal biomarker. The data on NGAL could justify re-assessment of the concept and definition of acute kidney injury.

Clinical and prognostic implications of plasma NGAL and NT-proBNP in adult patients with congenital heart disease

BACKGROUND

Prognostic value of NT-proBNP is well established in patients with congenital heart disease. Growing evidence suggests that plasma NGAL is elevated in heart failure but data is limited in congenital heart disease. This study investigates the combined prognostic value of plasma NGAL with plasma NT-proBNP in adult patients with congenital heart disease.

METHODS

Plasma levels of NT-proBNP and NGAL were measured in 76 consecutive adult patients (33 men, mean age 31.7 ± 14 yrs) with congenital heart disease and normal values of serum creatinine. Patients were divided in three groups: A: simple cardiac lesions, B: complex cardiac lesions and C: cyanotic lesions. Patients were also monitored for long-term major cardiovascular events: death, hospitalization, NYHA class worsening, new onset of arrhythmias, surgical or percutaneous intervention.

RESULTS

NGAL value was significantly different between groups: In group A median NGAL value was 64.5 ± 36.7 ng/ml, in group B median NGAL value was 88.77 ± 36.17 ng/ml and in group C median NGAL value was 121 ± 40 ng/ml (group A vs. group B: p = 0.048, group B vs. group C: p = 0.037, group A vs. group C: p = 0.003). Plasma NT-proBNP predicted all events (HR = 1.001, CI = 1.001-1.002, p = 0.0006) as well as cardiovascular death alone (HR = 1.001, CI = 1.001-1.002, p = 0.0004); plasma NGAL was the only predictor of cardiovascular death (HR = 1.017, CI = 1.001-1.033, p = 0.037).

CONCLUSION

Plasma NGAL levels were lower in patients with simple congenital disease compared to patients with complex congenital heart disease and cyanotic congenital heart disease. Plasma NGAL levels correlated with NT-proBNP and could predict cardiovascular death in this small cohort of patients.

Functional analysis of the mRNA profile of neutrophil gelatinase‑associated lipocalin overexpression in esophageal squamous cell carcinoma using multiple bioinformatic tools

Neutrophil gelatinase-associated lipocalin (NGAL) is a member of the lipocalin superfamily; dysregulated expression of NGAL has been observed in several benign and malignant diseases. In the present study, differentially expressed genes, in comparison with those of control cells, in the mRNA expression profile of EC109 esophageal squamous cell carcinoma (ESCC) cells following NGAL overexpression were analyzed by multiple bioinformatic tools for a comprehensive understanding. A total of 29 gene ontology (GO) terms associated with immune function, chromatin structure and gene transcription were identified among the differentially expressed genes (DEGs) in NGAL overexpressing cells. In addition to the detected GO categories, the results from the functional annotation chart revealed that the differentially expressed genes were also associated with 101 functional annotation category terms. A total of 59 subpathways associated locally with the differentially expressed genes were identified by subpathway analysis, a markedly greater total that detected by traditional pathway enrichment analysis only. Promoter analysis indicated that the potential transcription factors Snail, deltaEF1, Mycn, Arnt, MNB1A, PBF, E74A, Ubx, SPI1 and GATA2 were unique to the downregulated DEG promoters, while bZIP910, ZNF42 and SOX9 were unique for the upregulated DEG promoters. In conclusion, the understanding of the role of NGAL overexpression in ESCC has been improved through the present bioinformatic analysis.

Mechanism and clinical evidence of lipocalin-2 and adipocyte fatty acid-binding protein linking obesity and atherosclerosis

Obesity is considered to be a chronic inflammatory state in which the dysfunction of adipose tissue plays a central role. The adipokines, which are cytokines secreted by adipose tissue, are key links between obesity and related diseases such as metabolic syndrome and atherosclerosis. LCN2 and A-FABP, both of which are major adipokines predominantly produced in adipose tissue, have recently been shown to be pivotal modulators of vascular function. However, different adipokines modulate the development of atherosclerosis in distinctive manners, which are partly attributable to their unique regulatory mechanisms and functions. This review highlights recent advances in the understanding of the role of two adipokines in mediating chronic inflammation and the pathogenesis of atherosclerosis.