Abstract
Background and Aims
Neonatal kidney damage is a wide spread pathology, especially among preterm infants. Acute kidney injury (AKI) in newborns remains one of the most important problems because the features of neonatal nephrogenesis and physiology. The current clinical criteria for the diagnosis of AKI, including pediatric scales pRIFLE and nRIFLE, rely on glomerulal filtration rate (GFR), blood urea nitrogen (BUN), and serum creatinine (SCr), which are the late biomarkers detectable only within days or weeks after kidney damage occurred, and therefore have limitations when used within the first days after birth. Therefore, sensitive and specific tests for early diagnostics of kidney injury are extremely needed in neonatology. Urine biomarkers appear to be promising for early diagnosis of AKI. Quite often renal pathologies result in markedly increased (or decreased) urinary excretion of a number of protein biomarkers, indicating subclinical tubular injury while conventional AKI signs are not manifested yet.
The aim of this study was to determine clinical value of urine molecular biomarkers for the prediction of acute kidney injury in newborns.
Method
Urine samples from newborns with congenital malformation were collected on the 1st day after born, and then once a week until the 21th postnatal day. Urine samples were centrifuged, aliquoted and stored at –80°С until testing. The next urinary biomarkers were analyzed: calbindin 1, clusterin, IL-18, KIM-1, GST-π, MCP-1 and NGAL. Quantitative determination was performed with immunoassay kit Bio-Plex Pro™ RBM Human Kidney Toxicity Panel 1 (Bio-Rad Inc., USA) and Human NGAL ELISA kit (Invitrogen, Germany). Control group included five age-matched healthy infants.
Results
8 of 20 patients showed a direct correlation of increased NGAL levels in urine (50-fold compared to control group) with high levels of C-reactive protein in the blood (3-10-fold rise above the reference level). NGAL is the most sensitive marker for assessing AKI or tubular damage. These 8 patients were further investigated for other urine biomarkers.
The IL-18 level in urine was slightly increased in 4 patients. IL-18 is proposed to be a predictor for AKI severity and mortality in children with critical illness.
KIM-1 has low basal expression in the normal kidney but its appearance is highly specific and sensitive sign for nephrotoxicity in proximal tubules. We observed the increase of KIM-1 urinary excretion for 7 patients. However, we discover the equal occurrence of decrease or increase of urine MCP-1 through studied patients. Elevated levels of urine MCP-1 were earlier observed in experimental maleate induced azotemia, LPS injection and in model of unilateral ureteral obstruction (UUO). An increase of KIM-1 and/or MCP-1 urinary excretion is known to be associated with some risk of AKI development.
We found 3-fold growth of urine clusterin in 7 children. It is noticed, that clusterin increased in damaged tubular cells during polycystic kidney disease and renal carcinoma.
Additionally, we revealed 7-fold decrease of calbindin 1 in urine of 7 patients. Сalbindin 1 exclusively localized in the kidney distal nephron segment, and its decrease was discribed for models of UUO, glomerulonephritis and cisplatin nephropathy.
GST-π protein is found in cells lining the lumen of the distal tubules and is elevated in the urine of patients with sepsis, independently of accompanied AKI. We also observed 10- to 20-fold rising of urine GST-π for all 8 NGAL-positive newborns.
Conclusion
The specificity, rate of increase, and non-invasive detection of urine markers studied in this work, make them indispensable in clinical practice. However, their use in neonatology is still experimental. We showed potential applicability of wide biomarker panel for early detection and prediction of AKI in newborns.
Urine biomarkers for gentamicin-induced acute kidney injury in the neonatal ICU