Mass spectrometry-based proteomic analysis of urine in acute kidney injury following cardiopulmonary bypass: a nested case-control study.
BACKGROUND
The early evolution of acute kidney injury (AKI) in humans is difficult to study noninvasively. We hypothesized that urine proteomics could provide insight into the early pathophysiology of human AKI.


METHODS
A prospective nested case-control study (n = 250) compared serial urinary proteomes of 22 patients with AKI and 22 patients without AKI before, during, and after cardiopulmonary bypass surgery.


RESULTS
AKI was defined as a greater than 50% increase in serum creatinine level, and non-AKI, as less than 10% increase from baseline.


METHODS
Serum creatinine, urine protein-creatinine ratio, neutrophil gelatinase-associated lipocalin (NGAL), alpha1-microglobulin, interferon-inducible protein-10 (IP-10), monokine induced by interferon gamma (Mig), interferon-inducible T cell alpha chemoatractant (I-TAC), interleukin 6 (IL-6), IL-1beta, and IL-10. Urine protein profiling by means of surface-enhanced laser desorption/ionization time-of-flight mass spectrometry (SELDI-TOF-MS).


RESULTS
SELDI-TOF-MS showed intraoperative tubular stress in both groups on arrival to the intensive care unit, evidenced by beta2-microglobulinuria. Non-AKI proteomes returned toward baseline postoperatively. In contrast, AKI proteomes showed a second phase of tubular injury/stress with the reappearance of beta2-microglobulin and multiple unidentified peaks (3 to 5 and 6 to 8 kDa) and the appearance of established tubular injury markers: urinary protein, alpha1-microglobulin, and NGAL. Furthermore, 2 novel peaks (2.43 and 2.78 kDa) were found to be dominant in postoperative non-AKI urine samples. The 2.78-kDa protein was identified as the active 25-amino acid form of hepcidin (hepcidin-25), a key regulator of iron homeostasis. Finally, an inflammatory component of reperfusion injury was evaluated by means of enzyme-linked immunosorbent assay analysis of candidate chemokines (IP-10, I-TAC, and Mig) and cytokines (IL-6, IL-1beta, and IL-10). Of these, IP-10 was upregulated in patients with versus without AKI postoperatively.


CONCLUSIONS
This is an observational study. SELDI-TOF-MS is a semiquantitative technique.


CONCLUSIONS
Evaluation of human AKI revealed early intraoperative tubular stress in all patients. A second phase of injury observed in patients with AKI may involve IP-10 recruitment of inflammatory cells. The enhancement of hepcidin-25 in patients without AKI may suggest a novel role for iron sequestration in modulating AKI.
Ho
Julie
J
Section of Nephrology, University of Manitoba, Winnipeg, Manitoba, Canada.
Lucy
Malcolm
M
Krokhin
Oleg
O
Hayglass
Kent
K
Pascoe
Edward
E
Darroch
Gayle
G
Rush
David
D
Nickerson
Peter
P
Rigatto
Claudio
C
Reslerova
Martina
M
D058186:Acute Kidney Injury / Q000209:etiology* / Q000652:urine*; D000209:Acute-Phase Proteins / Q000652:urine; D000368:Aged; D000510:Alpha-Globulins / Q000652:urine; D023181:Antimicrobial Cationic Peptides / Q000652:urine; D015415:Biomarkers / Q000097:blood / Q000652:urine; D002315:Cardiopulmonary Bypass / Q000009:adverse effects*; D016022:Case-Control Studies; D054357:Chemokine CXCL10; D003404:Creatinine / Q000097:blood / Q000652:urine; D018450:Disease Progression; D005260:Female; D005919:Glomerular Filtration Rate / Q000502:physiology; D064451:Hepcidins; D006801:Humans; D016753:Interleukin-10 / Q000652:urine; D015850:Interleukin-6 / Q000652:urine; D000071068:Lipocalin-2; D054834:Lipocalins / Q000652:urine; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D040901:Proteomics / Q000379:methods*; D011518:Proto-Oncogene Proteins / Q000652:urine; D015427:Reperfusion Injury / Q000209:etiology* / Q000652:urine*; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D001613:beta 2-Microglobulin / Q000652:urine
D000209:Acute-Phase Proteins; D000510:Alpha-Globulins; D023181:Antimicrobial Cationic Peptides; D015415:Biomarkers; C114753:CXCL10 protein, human; D054357:Chemokine CXCL10; C578702:HAMP protein, human; D064451:Hepcidins; D015850:Interleukin-6; C489506:LCN2 protein, human; D000071068:Lipocalin-2; D054834:Lipocalins; D011518:Proto-Oncogene Proteins; D001613:beta 2-Microglobulin; D016753:Interleukin-10; D003404:Creatinine