Urinary kidney injury-1 (Kim-1) outperforms serum creatinine, blood urea nitrogen and urinary N-acetyl-β-D-glucosaminidase in detecting kidney damage induced in rats by a range of nephrotoxicants. Earlier detection of renal injury, enabled by monitoring levels of urinary Kim-1, should enable elimination of nephrotoxic candidates sooner in the drug development pipeline. Kidney toxicity accounts both for the failure of many drug candidates as well as considerable patient morbidity. Whereas histopathology remains the gold standard for nephrotoxicity in animal systems, serum creatinine (SCr) and blood urea nitrogen (BUN) are the primary options for monitoring kidney dysfunction in humans. The transmembrane tubular protein kidney injury molecule-1 (Kim-1) was previously reported to be markedly induced in response to renal injury. Owing to the poor sensitivity and specificity of SCr and BUN, we used rat toxicology studies to compare the diagnostic performance of urinary Kim-1 to BUN, SCr and urinary N-acetyl-β-D-glucosaminidase (NAG) as predictors of kidney tubular damage scored by histopathology. Kim-1 outperforms SCr, BUN and urinary NAG in multiple rat models of kidney injury. Urinary Kim-1 measurements may facilitate sensitive, specific and accurate prediction of human nephrotoxicity in preclinical drug screens. This should enable early identification and elimination of compounds that are potentially nephrotoxic.

Sensitive and specific biomarkers are needed to detect early kidney injury. The objective of the present work was to develop a sensitive quantitative urinary test to identify renal injury in the rodent to facilitate early assessment of pathophysiological influences and drug toxicity. Two mouse monoclonal antibodies were made against the purified ectodomain of kidney injury molecule-1 (Kim-1), and these were used to construct a sandwich Kim-1 ELISA. The assay range of this ELISA was 50 pg/ml to 5 ng/ml, with inter- and intra-assay variability of <10%. Urine samples were collected from rats treated with one of three doses of cisplatin (2.5, 5, or 7.5 mg/kg). At one day after each of the doses, there was an approximately three- to fivefold increase in the urine Kim-1 ectodomain, whereas other routinely used biomarkers measured in this study [plasma creatinine, blood urea nitrogen (BUN), urinary N-acetyl-β-glucosaminidase (NAG), glycosuria, proteinuria] lacked the sensitivity to show any sign of renal damage at this time point. When rats were subjected to increasing periods (10, 20, 30, or 45 min) of bilateral ischemia, there was an increasing amount of urinary Kim-1 detected. After only 10 min of bilateral ischemia, Kim-1 levels on day 1 were 10-fold higher (5 ng/ml) than control levels, whereas plasma creatinine and BUN were not increased and there was no glycosuria, increased proteinuria, or increased urinary NAG levels. Thus urinary Kim-1 levels serve as a noninvasive, rapid, sensitive, reproducible, and potentially high-throughput method to detect early kidney injury in pathophysiological studies and in preclinical drug development studies for risk-benefit profiling of pharmaceutical agents.

MicroRNAs (miRNAs) are endogenous noncoding RNA molecules that are involved in post-transcriptional gene silencing. Using global miRNA expression profiling, we found miR-21, -155, and 18a to be highly upregulated in rat kidneys following tubular injury induced by ischemia/reperfusion (I/R) or gentamicin administration. Mir-21 and -155 also showed decreased expression patterns in blood and urinary supernatants in both models of kidney injury. Furthermore, urinary levels of miR-21 increased 1.2-fold in patients with clinical diagnosis of acute kidney injury (AKI) (n = 22) as compared with healthy volunteers (n = 25) (p < 0.05), and miR-155 decreased 1.5-fold in patients with AKI (p < 0.01). We identified 29 messenger RNA core targets of these 3 miRNAs using the context likelihood of relatedness algorithm and found these predicted gene targets to be highly enriched for genes associated with apoptosis or cell proliferation. Taken together, these results suggest that miRNA-21 and -155 could potentially serve as translational biomarkers for detection of AKI and may play a critical role in the pathogenesis of kidney injury and tissue repair process.

Kidney injury molecule-1 (Kim-1) has been qualified by the Food and Drug Administration and European Medicines Agency as a highly sensitive and specific urinary biomarker to monitor drug-induced kidney injury in preclinical studies and on a case-by-case basis in clinical trials. Here we report the development and evaluation of a rapid direct immunochromatographic lateral flow 15-min assay for detection of urinary Kim-1 (rat) or KIM-1 (human). The urinary Kim-1 band intensity using the rat Kim-1 dipstick significantly correlated with levels of Kim-1 as measured by a microbead-based assay, histopathological damage, and immunohistochemical assessment of renal Kim-1 in a dose- and time-dependent manner. Kim-1 was detected following kidney injury induced in rats by cadmium, gentamicin, or bilateral renal ischemia/reperfusion. In humans, the urinary KIM-1 band intensity was significantly greater in urine from patients with acute kidney injury than in urine from healthy volunteers. The KIM-1 dipstick also enabled temporal evaluation of kidney injury and recovery in two patients who developed postoperative acute kidney injury following cytoreductive surgery for malignant mesothelioma with intraoperative local cisplatin administration. We hope that future, more extensive studies will confirm the utility of these results, which show that the Kim-1/KIM-1 dipsticks can provide a sensitive and accurate detection of Kim-1/KIM-1, thereby providing a rapid diagnostic assay for kidney damage and facilitating the rapid and early detection of kidney injury in preclinical and clinical studies.

Renal ischemia and reperfusion (I/R) injury is the major cause of acute renal failure and may also be involved in the development and progression of some forms of chronic kidney disease. We previously showed that a mineralocorticoid receptor (MR) blockade prevents renal vasoconstriction induced by cyclosporine that leads to acute and chronic renal failure (Feria I, Pichardo I, Juarez P, Ramirez V, Gonzalez MA, Uribe N, Garcia-Torres R, Lopez-Casillas F, Gamba G, Bobadilla NA. Kidney Int 63: 43–52, 2003; Perez-Rojas JM, Derive S, Blanco JA, Cruz C, Martinez de la Maza L, Gamba G, Bobadilla NA. Am J Physiol Renal Physiol 289: F1020–F1030, 2005). Thus we investigated whether spironolactone administration prevents the functional and structural damage induced by renal ischemia-reperfusion (I/R). Five groups were studied: sham-operated animals, rats that underwent 20 min of ischemia and 24 h of reperfusion, and three groups that received spironolactone 1, 2, or 3 days before I/R, respectively. Renal I/R produced significant renal dysfunction and tubular damage. Spironolactone administration completely prevented a decrease in renal blood flow, the development of acute renal failure, and tubular apoptosis. The protection conferred by spironolactone was characterized by decreasing oxidative stress, as evidenced by a reduction in kidney lipoperoxidation, increasing expression of antioxidant enzymes, and restoration of urinary NO₂/NO₃ excretion. Endothelial nitric oxide synthase expression was upregulated by a mineralocorticoid receptor blockade in I/R groups; in addition, an increase in activating phosphorylation of this enzyme at residue S1177 and a decrease in inactivating phosphorylation at T497 were observed. In conclusion, our study shows that spironolactone administration prevents the renal injury induced by I/R, suggesting that aldosterone plays a central role in this model of renal injury.