PDB rendering based on 1dfv.
|Symbols||LCN2 (; 24p3; MSFI; NGAL)|
|External IDs||ChEMBL: GeneCards:|
|RNA expression pattern|
Lipocalin-2 (LCN2), also known as oncogene 24p3 or neutrophil gelatinase-associated lipocalin (NGAL), is a protein that in humans is encoded by the LCN2 gene. NGAL is involved in innate immunity by sequestrating iron that in turn limits bacterial growth. It is expressed in neutrophils and in low levels in the kidney, prostate, and epithelia of the respiratory and alimentary tracts. NGAL is used as a biomarker of kidney injury.
The binding of NGAL to bacterial siderophores is important in the innate immune response to bacterial infection. Upon encountering invading bacteria the toll-like receptors on immune cells stimulate the synthesis and secretion of NGAL. Secreted NGAL then limits bacterial growth by sequestering iron-containing siderophores. Lipocalin-2 also functions as a growth factor.
Originally, NGAL was isolated from a supernatant of activated human neutrophils. However, NGAL levels have also been shown to increase in patients with a low number of neutrophils due to leukemia, which indicates that increases in NGAL levels are not exclusively associated with neutrophils.
In the case of acute kidney injury (AKI), NGAL is secreted in high levels into the blood and urine within 2 hours of injury. Because NGAL is protease resistant and small, the protein is easily excreted and detected in the urine. NGAL levels in patients with AKI have been associated with the severity of their prognosis and can be used as a biomarker for AKI NGAL can also be used as an early diagnosis for procedures such as chronic kidney disease, contrast induced nephropathy, and kidney transplant.
Kidney health is most frequently measured by serum creatinine. Serum creatinine is a marker of kidney function, whereas NGAL is a marker of kidney injury. NGAL levels are a more precise and sensitive marker for diagnosing AKI than serum creatinine levels. Therefore, monitoring NGAL levels reduces delayed AKI diagnosis and treatment. Using a more sensitive and specific marker allows for earlier diagnosis, correct responses to AKI, and reduced risk of morbidity and mortality.
The NGAL level measured in an individual is proportional to the severity of the AKI. Individuals positive for NGAL tend to have higher incidence of renal replacement therapy and have higher rates of in-hospital mortality, both in the presence and the absence of serum creatinine. Therefore, an individual may have AKI without the presence of serum creatinine.
The ability to diagnose AKI before acute kidney failure is financially beneficial and favorable for preventative health measures. More than 10% of people in the United States will develop some kind of chronic kidney disease (CKD), with higher incidences for individuals that suffer from obesity, elevated cholesterol, and a family history of CKD. There is no point of return once there is a significant injury to the kidney; therefore, early diagnosis of kidney injury is important for preventing AKI. Using NGAL as a biomarker can lower hospital costs because less patients will reach a critical stage in kidney injury. Ultimately, diagnosis of AKI with NGAL can reduced the time a patient stays in a hospital. For example, the early diagnosis of AKI with NGAL as a biomarker can help a patient avoid kidney dialysis.
NGAL can be used as a biomarker for percutaneous coronary interventions (PCI), cardiopulmonary bypass, and critically ill patients (heart failure, sepsis, multi-organ failure). Acute kidney injury is common after these surgical procedures, especially if the individual suffers of high systolic blood pressure, renal dysfunction, or obesity. The use of NGAL in these situations is more efficient than serum creatinine at diagnosing AKI.
NGAL has also been shown to play a role in cancer. NFAT3 (NFATc4) inhibits breast carcinoma cell motility by blocking the expression of NGAL, and NFAT1 modulates the axis to potentiate breast carcinoma motility by increasing the expression of NGAL. Like NFAT1, NFAT5 modulates the expression of the NGAL and increases breast carcinoma migration. NGAL has also been shown to be highly expressed in tumor cells. Complexes such as NGAL-MMP-9 in the urine may have relevance as a biomarker for breast cancer.
Other studies indicate NGAL as a player in bone turnover, it can enable osteoclast differentiation and inhibit osteoblast matrix deposition and maturation. Hence mice who overexpress NGAL are dwarfs. This is due to the ability of osteoblasts to secrete LCN2 since first stages of development.
Renal expression of NGAL increases in the kidneys after injury for a variety of reasons. The level of NGAL in the urine and plasma increases within 2 hours of kidney injury. It is possible to measure NGAL in serum or urine in the range of 25 to 5,000 ng/mL by current laboratory tests. Low levels for NGAL have been considered to be 20 ng/mL, medium levels 200 ng/mL, and high levels 1200 ng/mL.
A study on children with pediatric cardiopulmonary bypass operations showed that urinary NGAL concentrations above 50 ng/mL 2 hours after surgery is indicative of serum creatinine levels 50% over basal values. Normally, children tend to have almost undetectable levels of NGAL. Therefore, studies that include children are considered to be “pure.” Adult patients presenting for cardiopulmonary bypass surgery are not considered to be “pure” in NGAL studies because adults often have other disorders such as inflammatory conditions, which can cause slight increases in NGAL.
AKI studies investigating the use of NGAL as a biomarker often compare serum creatinine and NGAL production. Unfortunately, serum creatinine production is variable; therefore, the comparison is not always reliable. In addition, NGAL levels are relative to each person, and a study on specific numbers and their accurate predicted outcomes is yet to be done.
Although NGAL is generally a precise biomarker of AKI, there are limitations to the use of the biomarker. Studies have proven that NGAL is not only present when there is chance for AKI. There are many other ways to have elevated NGAL levels such as taking certain kinds of antibiotics and other endogenous substances. Creatinine, for example, can elevate NGAL levels and create a false positive for an AKI. There are also some medical conditions that may interfere with NGAL levels including Epstein-Barr Virus, Hepatitis A Virus, Herpes Simplex Virus, Myeloma, and Rubella Virus.
Particle-enhanced turbidimetric immunoassay (PETIA)
PETIA is a turbidimetry test which runs on clinical chemistry analyzers with open channels. PETIA can be used to measure NGAL in the urine, heparin, and plasma in quantities of 25 to 5,000 ng/mL. For an in vitro test, NGAL concentration can be determined with ELISA using urine, plasma, serum, tissue extracts or culture media.
Point-of-Care NGAL test
The point-of-care NGAL test is an in-vitro test that uses a fluorescence immunoassay to measure NGAL levels in anticoagulated blood or plasma samples during triage. The test is initiated by adding a several drops of an EDTA anti-coagulated blood sample or plasma specimen to the test device, which filters out the blood cells from the plasma. The specimen reacts with fluorescent antibody conjugates and flows through the device to a discrete zone specific to the analyte. The amount of fluorescence expressed by the specimen is analyzed. The concentration of NGAL in the sample correlates directly to the amount of fluorescence.
An immunoassay is an in-vitro test that uses a chemiluminescent microparticle immunoassay (CMIA) to give a quantitative measurement of NGAL levels in a sample of urine. It utilizes microparticles coated with monoclonal antibodies, which set off a reaction that indicates how much NGAL is present in the sample.
The test is initiated by diluting the sample with wash buffer and adding anti-NGAL coated paramagnetic microparticles. The NGAL in the urine binds to the microparticles and the reaction mixture is washed before adding an anti-NGAL acridinium-labeled conjugate. After another wash cycle, pre-trigger and trigger solutions are added to induce the chemiluminescent reaction. This reaction is measured in Relative Light Units (RLUs),which are proportional to the concentration of NGAL in the sample.
In 2004, the US FDA announced that there is a need for increased product development involving biomarkers and surrogate markers. In particular, there has been intense research regarding the use of the NGAL biomarker.
The first study conducted to determine if NGAL is effective as a biomarker was published in July 2011. The study found that the treatment with fenoldopam decreases urinary NGAL significantly after cardiac surgery. This suggests that fenoldopam has nephroprotective effects. This study was important in defining NGALs role in AKI.
In the Philippines, the first guideline implementation of NGAL as a diagnostic biomarker occurred in 2010 for the detection of AKI in leptospirosis management.
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