Neutrophil gelatinase-associated lipocalin does not originate from the kidney during reperfusion in clinical renal transplantation

Arie Passov,Sture Andersson,Kethe Hermunen,Markku Heikinheimo,Villemikko Kailari,Eero Pesonen,Marjut Pihlajoki,Marko Lempinen,Minna Ilmakunnas,Ilkka Helanterä

doi:10.1186/s40635-021-00422-7

Abstract

BackgroundAcute Kidney Injury (AKI) is a common clinical complication. Plasma/serum neutrophil gelatinase-associated lipocalin (NGAL) has been proposed as a rapid marker of AKI. However, NGAL is not kidney-specific. It exists in three isoforms (monomeric, homo-dimeric and hetero-dimeric). Only the monomeric isoform is produced by renal tubular cells and plasma NGAL levels are confounded by the release of all NGAL isoforms from neutrophils. Our aim was to investigate whether NGAL is released into blood from injured renal tubules.MethodsKidney transplantation (n = 28) served as a clinical model of renal ischaemic injury. We used ELISA to measure NGAL concentrations at 2 minutes after kidney graft reperfusion in simultaneously taken samples of renal arterial and renal venous blood. Trans-renal gradients (venous–arterial) of NGAL were calculated. We performed Western blotting to distinguish between renal and non-renal NGAL isoforms. Liver-type fatty acid binding protein (LFABP) and heart-type fatty acid binding protein (HFABP) served as positive controls of proximal and distal tubular damage.ResultsSignificant renal release of LFABP [trans-renal gradient 8.4 (1.7–30.0) ng/ml, p = 0.005] and HFABP [trans-renal gradient 3.7 (1.1–5.0) ng/ml, p = 0.003] at 2 minutes after renal graft reperfusion indicated proximal and distal tubular damage. NGAL concentrations were comparable in renal venous and renal arterial blood. Thus, there was no trans-renal gradient of NGAL. Western blotting revealed that the renal NGAL isoform represented only 6% of the total NGAL in renal venous blood.ConclusionsIschaemic proximal and distal tubular damage occurs in kidney transplantation without concomitant NGAL washout from the kidney graft into blood. Plasma/serum NGAL levels are confounded by the release of NGAL from neutrophils. Present results do not support the interpretation that increase in plasma NGAL is caused by release from the renal tubules.

Highlights

Acute Kidney Injury (AKI) is a common clinical complication
In conclusion, proximal and distal tubular damage occurs in kidney transplantation without concomitant neutrophil gelatinase-associated lipocalin (NGAL) washout into renal venous blood after cold and warm ischaemia
Circulating NGAL both preoperatively and at early reperfusion is confounded by neutrophils

Summary

Introduction

Plasma/ serum neutrophil gelatinase-associated lipocalin (NGAL) has been proposed as a rapid marker of AKI. The monomeric isoform is produced by renal tubular cells and plasma NGAL levels are confounded by the release of all NGAL isoforms from neutrophils. Neutrophil gelatinase-associated lipocalin (NGAL) has been proposed as early marker of renal injury [3, 4]. Experimental ischaemic kidney injury causes upregulation of NGAL gene expression and protein synthesis, which predominantly seems to occur in renal distal tubular epithelial cells [5,6,7]. Some reports suggest that tubular NGAL upregulation does not seem to translate into NGAL release into renal venous blood in experimental ischemic kidney injury [10, 11]. Evidence of NGAL back-leak from renal tubular cells into circulating blood remains elusive [11, 12]

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