Urinary neprilysin in the critically ill patient

Background

Critically ill patients in intensive care face hazardous conditions. Among these, acute kidney injury (AKI) is frequently seen as a result of sepsis. Early diagnosis of kidney injury is of the utmost importance in the guidance of interventions or avoidance of treatment-induced kidney injury. On these grounds, we searched for markers that could indicate proximal tubular cell injury.

Methods

Urine samples of 90 patients admitted to the intensive or intermediate care unit were collected over 2 to 5 days. The biomarker neprilysin (NEP) was investigated in urine using several methods such as dot blot, ELISA and immunofluorescence of urinary casts. Fifty-five healthy donors acted as controls.

Results

NEP was highly significantly elevated in the urine of patients who suffered AKI according to the KDIGO criteria in comparison to healthy controls. It was also found to be elevated in ICU patients without overt signs of AKI according to serum creatinine changes, however they were suffering from potential nephrotoxic insults. According to our findings, urinary NEP is indicative of epithelial cell alterations at the proximal tubule. This was elaborated in ICU patients when ghost fragments and NEP⁺ microvesicles were observed in urinary sediment cytopreparations. Furthermore, NEP⁺ immunofluorescence of healthy kidney tissue showed staining at the proximal tubules.

Conclusions

NEP, a potential marker for proximal tubular epithelia, can be measured in urine. This does not originate from leakage of elevated serum levels, but indicates proximal tubular cell alterations such as brush border severing, which can heal in most cases.

High expression of neutrophil gelatinase-associated lipocalin (NGAL) in the kidney proximal tubules of diabetic rats

PURPOSE

Recent evidence suggests that neutrophil gelatinase-associated lipocalin (NGAL) plays important roles in many physiological and pathological processes including diabetic nephropathy (DN), in which a markedly increasing in NGAL levels in patient's serum and urine has been reported. This study investigated the expression of NGAL in the kidney of diabetic rats.

MATERIALS/METHODS

Sixty-four Sprague Dawley rats were randomly divided into 2 groups: non-diabetic control groups and diabetic groups. Diabetes was induced by intraperitoneal injection of streptozotocin. Relevant indicators were separately evaluated 2, 4, 8 and 12 weeks after induction of diabetes.

RESULTS

In the diabetic groups, urinary NGAL values were markedly increased even before the appearance of pathological albuminuria. Moreover, diabetic rats showed significant upregulation of NGAL mRNA expression starting at week 2 (1.0±0.03 vs. 3.09±0.40, NGAL/β-actin, P<0.05), while the increase of NGAL protein expression appeared subsequently (0.58±0.03 vs. 0.65±0.01, NGAL/β-actin, P<0.05). At the end of week 12, kidney NGAL mRNA and protein levels were increased to 5.95-fold and 1.24-fold of the control groups, respectively. Observable ultrastructural alterations of renal tubules were not detected until week 4, while pathological changes gradually became apparent in the course of the study. Strong positive immunohistochemical staining of NGAL was visualized in the proximal tubular cells of diabetic rats at week 12.

CONCLUSIONS

High expression of NGAL in the kidney is associated with diabetic kidney injury in STZ rats, suggesting NGAL may play a role in tubular injury of DN.