KIM-1 and NGAL: new markers of obstructive nephropathy

Urinary biomarker detection of melamine- and cyanuric acid-induced kidney injury in rats

Oral coexposure of rats to melamine (MEL) and cyanuric acid (CYA) results in a dose-dependent increase in the formation of MEL-CYA crystals in the kidney. The aim of this study was to determine if urinary biomarkers of acute kidney injury could be used to noninvasively detect renal damage associated with crystal formation in the kidneys of MEL- and CYA-exposed rats. Urine was obtained on days 0 (predose), 2, 4, 14, and 28 from male and female Fischer 344 rats fed a diet supplemented with 0, 120, 180, or 240 ppm each of MEL and CYA. A number of urinary protein biomarkers (kidney injury molecule-1, neutrophil gelatinase-associated lipocalin, osteopontin, albumin, alpha-GST, GST-Yb1, renal papillary antigen 1 [RPA-1], and clusterin) were measured using a multiplex assay system. The results showed that RPA-1 (distal tubule and collecting duct injury biomarker) was elevated on day 28 at the 120 ppm dose and higher in male rats and at the 180 ppm dose and higher in female rats; however, other urinary protein biomarkers were significantly elevated only at the 240 ppm dose. Significant elevation in blood urea nitrogen and serum creatinine levels, and severe renal damage evidenced by histopathology, were observed after 28 days of exposure to the highest dose, despite the fact that MEL-CYA crystals were observable at the 120 and 180 ppm doses. These data indicate that RPA-1 may serve as a noninvasive urinary biomarker for the detection and monitoring of obstructive nephropathy associated with MEL-CYA exposure.

Structural equation modeling highlights the potential of Kim-1 as a biomarker for chronic kidney disease

BACKGROUND

Chronic kidney disease (CKD) is a major public health problem, and despite continued research in the field, there is still a need to identify both biomarkers of risk and progression, as well as potential therapeutic targets. Structural equation modeling (SEM) is a family of statistical techniques that has been utilized in the fields of sociology and psychology for many years; however, its utilization in the biological sciences is relatively novel. SEM's ability to investigate complex relationships in an efficient, single model could be utilized to understand the progression of CKD, as well as to develop a predictive model to assess kidney status in the patient.

METHODS

Fischer 344 rats were fed either an ad libitum diet or a calorically restricted diet, and a time-course study of kidney structure and function was performed. EQS, a SEM software package, was utilized to generate five CKD models of the Fisher 344 rat and identify relationships between measured variables and estimates of kidney damage and kidney function.

RESULTS

All models identified strong relationships between a biomarker for CKD, kidney injury molecule-1 (Kim-1) and kidney damage, in the Fischer 344 rat CKD model. Models also indicate a strong relationship between age and renal damage and dysfunction.

CONCLUSION

SEM can be used to model CKD and could be useful to examine biomarkers in CKD patients.

Urine neutrophil gelatinase-associated lipocalin identifies unilateral and bilateral urinary tract obstruction

BACKGROUND

Urinary tract obstruction (UTO) is a common problem that can lead to permanent loss of kidney function. Unilateral UTO may be difficult to diagnose. Urinary neutrophil gelatinase-associated Lipocalin (uNGAL) may identify unilateral and bilateral UTO.

METHODS

Retrospective case-control study of patients undergoing hospital admission at three sites. UTO was determined by review of medical records and cases were matched to control patients. uNGAL was measured by immunoblot.

RESULTS

Twenty-four unilateral UTO and 15 bilateral UTO cases were identified. Admission serum creatinine (sCr) (milligram per decilitre) was significantly higher in bilateral UTO, 2.0 (1.1-5.3), but not unilateral UTO, 1.1 (0.8-1.5), compared to controls, 0.9 (0.8-1.2). uNGAL (nanogram per millilitre) was significantly higher both in patients with bilateral UTO, 140 (40-450), and unilateral UTO, 50 (20-100), compared to controls, 20 (10-45).

DISCUSSION

uNGAL identifies kidney injury in unilateral and bilateral UTO even in the absence of an elevated sCr.