Mass Spectrometry–Based Proteomic Analysis of Urine in Acute Kidney Injury Following Cardiopulmonary Bypass: A Nested Case-Control Study

doi:10.1053/j.ajkd.2008.10.037

American Journal of Kidney Diseases

Volume 53, Issue 4, April 2009, Pages 584-595

https://doi.org/10.1053/j.ajkd.2008.10.037 Get rights and content

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.

Study Design

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.

Outcomes

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

Measurements

Serum creatinine, urine protein-creatinine ratio, neutrophil gelatinase-associated lipocalin (NGAL), α₁-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-1β, 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 β₂-microglobulinuria. Non-AKI proteomes returned toward baseline postoperatively. In contrast, AKI proteomes showed a second phase of tubular injury/stress with the reappearance of β₂-microglobulin and multiple unidentified peaks (3 to 5 and 6 to 8 kDa) and the appearance of established tubular injury markers: urinary protein, α₁-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-1β, and IL-10). Of these, IP-10 was upregulated in patients with versus without AKI postoperatively.

Limitations

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.

Section snippets

Methods

The study protocol was approved by the University of Manitoba Research Ethics Board. All adult patients undergoing elective cardiac surgery (CABG or valvular surgery, nonpulsatile CPB perfusion) from December 2005 to May 2007 at St Boniface General Hospital, Winnipeg, Manitoba, Canada, were considered for the study. Informed consent was obtained from 250 patients who agreed to participate.

Clinical Outcomes

Thirty of 250 patients (12%) developed AKI (increase in serum creatinine > 50%), and 6 of those patients required dialysis (2.4%). Eight of the 30 patients with AKI were excluded because of a baseline estimated glomerular filtration rate less than 60 mL/min/1.73 m², and none was excluded for baseline proteinuria, leaving 22 patients with AKI (4 requiring hemodialysis) for proteomic analysis. Patients without AKI (n = 22; increase in serum creatinine < 10%) were randomly selected as controls

Discussion

Ischemic AKI in animal models is characterized by alteration in microvascular hemodynamics followed by tubular epithelial injury.6, 7 An important role of inflammation is suggested with activation and recruitment of leukocytes, which augments renal injury.¹² Human correlates of these events have been proposed, but have been less well studied. We tracked intraoperative and postoperative urine proteomic changes in cardiac surgery patients, affording unique insight into the evolution of human

Acknowledgements

The authors thank Dr John Wilkins, Jennifer Bestland, and Patricia Sauder for assistance in the laboratory and Christine Smilski for data collection.

Support: Dr Ho is funded by a Bristol Myers Squibb Cardiovascular Research Fellowship; Dr Nickerson is funded by the Canadian Institutes of Health Research; and Drs Reslerova and Rigatto are funded by the Norman S. Coplan Extramural Satellite Health Research Grant and the Department of Medicine, University of Manitoba.

Financial Disclosure: None.

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: Originally published online as doi:10.1053/j.ajkd.2008.10.037 on December 15, 2008.

: J.H. and M.L. contributed equally to this manuscript.

View full text

Original InvestigationPathogenesis and Treatment of Kidney DiseaseMass Spectrometry–Based Proteomic Analysis of Urine in Acute Kidney Injury Following Cardiopulmonary Bypass: A Nested Case-Control Study

Background

Study Design

Outcomes

Measurements

Results

Limitations

Conclusions

Section snippets

Methods

Clinical Outcomes

Discussion

Acknowledgements

Mol Genet Metab

Ann Thorac Surg

Ann Thorac Surg

Ann Thorac Surg

Kidney Int

Am J Transplant

Blood Cells Mol Dis

Kidney Int

Clin Chim Acta

Cytokine

Am J Pathol

Lancet

FEBS Lett

Preoperative renal risk stratification

Circulation

A clinical score to predict acute renal failure after cardiac surgery

J Am Soc Nephrol

Renal dysfunction after myocardial revascularization: Risk factors, adverse outcomes, and hospital resource utilization

Ann Intern Med

Immediate postoperative renal function deterioration in cardiac surgical patients predicts in-hospital mortality and long-term survival

J Am Soc Nephrol

Biomarkers of acute renal injury and renal failure

Shock

Recent advances in the pathophysiology of ischemic acute renal failure

J Am Soc Nephrol

Acute kidney injury associated with cardiac surgery

Clin J Am Soc Nephrol

Original Investigation
Pathogenesis and Treatment of Kidney Disease
Mass Spectrometry–Based Proteomic Analysis of Urine in Acute Kidney Injury Following Cardiopulmonary Bypass: A Nested Case-Control Study