Bootcongres

Background: Neutrophil gelatinase-associated lipocalin (NGAL) and Kidney injury molecule-1 (KIM-1) are promising tubular injury markers in the context of various forms of acute kidney injury, including delayed graft function and transplantation. Upon injury, both markers are expressed by renal tubular epithelial cells. Recently, we demonstrated a crucial role for Mannan-binding lectin (MBL) in the pathogenesis of renal ischemia/reperfusion injury (IRI). Here, we assessed the kinetics and tissue distribution of NGAL and KIM-1 in a rat model of renal IRI and explored the consequence of protective anti-MBL treatment on these markers. Methods: Rats were subjected to 45 min of unilateral renal ischemia. Serum was collected and kidneys were harvested at consecutive time points after reperfusion and analyzed for NGAL and KIM-1 mRNA and protein expression. Additionally, as a protective therapy rats were treated with anti-MBL or a control antibody prior to induction of ischemia. Results: I/R induced an extensive mRNA expression of both NGAL and KIM-1 which peaked at 48h and 72h after reperfusion, respectively. Interestingly, immunostaining revealed that KIM-1 protein was mainly present in the injured cortico-medullary region, while NGAL protein was predominantly stained in the non-injured cortex of the kidney. No colocalization between NGAL and KIM-1 could be found, suggesting differences in function and regulation of expression. Therapeutic inhibition of MBL protected against tubular injury and significantly reduced mRNA and protein expression of KIM-1 compared to control treated animals. In contrast, there was no difference in NGAL mRNA expression, while cortical NGAL protein staining was even 7-fold higher at 24h in anti-MBL-treated animals. Measurement of plasma NGAL revealed a 6-fold increase at 24h in both treatment groups. In view of the molecular size of NGAL (~25 kD), presence of NGAL in tubular cells after reperfusion could potentially be derived from circulation as a result of filtration and reabsorption by viable tubular cells. Conclusion: Our results indicate that NGAL and KIM-1 are present in distinct regions of the reperfused kidney and therefore might be involved in different processes. Based on differences in mRNA and protein levels, we propose that cortical NGAL does not perse imply local production, but might also be derived from circulation. These findings shed new light on the role of NGAL as biomarker and its potential protective function.