Urinary kidney injury molecule-1: a sensitive quantitative biomarker for early detection of kidney tubular injury

A basic science view of acute kidney injury biomarkers

Over the last decade, significant progress has been made in the identification and validation of novel biomarkers as well as refinements in the use of serum creatinine as a marker of kidney function. These advances have taken advantage of laboratory investigations, which have identified these novel molecules that serve important biological functions in the pathogenesis of acute kidney injury (AKI). As we advance and validate these markers for clinical studies in AKI, we recognize that they serve not only to improve our understanding of AKI, but they could also serve as potential targets for the treatment of AKI. This review will underscore the biological basis of specific biomarkers that will contribute to the advancement in the treatment and outcomes of AKI.

Renal cortical pyruvate depletion during AKI

Pyruvate is a key intermediary in energy metabolism and can exert antioxidant and anti-inflammatory effects. However, the fate of pyruvate during AKI remains unknown. Here, we assessed renal cortical pyruvate and its major determinants (glycolysis, gluconeogenesis, pyruvate dehydrogenase [PDH], and H2O2 levels) in mice subjected to unilateral ischemia (15-60 minutes; 0-18 hours of vascular reflow) or glycerol-induced ARF. The fate of postischemic lactate, which can be converted back to pyruvate by lactate dehydrogenase, was also addressed. Ischemia and glycerol each induced persistent pyruvate depletion. During ischemia, decreasing pyruvate levels correlated with increasing lactate levels. During early reperfusion, pyruvate levels remained depressed, but lactate levels fell below control levels, likely as a result of rapid renal lactate efflux. During late reperfusion and glycerol-induced AKI, pyruvate depletion corresponded with increased gluconeogenesis (pyruvate consumption). This finding was underscored by observations that pyruvate injection increased renal cortical glucose content in AKI but not normal kidneys. AKI decreased PDH levels, potentially limiting pyruvate to acetyl CoA conversion. Notably, pyruvate therapy mitigated the severity of AKI. This renoprotection corresponded with increases in cytoprotective heme oxygenase 1 and IL-10 mRNAs, selective reductions in proinflammatory mRNAs (e.g., MCP-1 and TNF-α), and improved tissue ATP levels. Paradoxically, pyruvate increased cortical H2O2 levels. We conclude that AKI induces a profound and persistent depletion of renal cortical pyruvate, which may induce additional injury.

Urinary neutrophil gelatinase-associated lipocalin predicts graft loss after acute kidney injury in kidney transplant

OBJECTIVE

Establish the prognostic value for graft loss of urinary neutrophil gelatinase-associated lipocalin (uNGAL), kidney injury molecule-1 (uKIM-1), interleukin-18 (uIL-18), and heat shock protein 72 (uHsp72) in kidney transplant recipients (KTR) with acute kidney injury (AKI).

METHODS

Biomarkers were measured in 67 KTR with AKI caused by different entities.

RESULTS

After 1 year, 11 KTR with graft loss had higher uNGAL compared to KTR without loss (p < 0.001). There were no differences for uKIM-1, uIL-18 and uHsp-72. uNGAL >200 ng/mL had 84% sensitivity and 86% specificity for graft loss (ROC AUC: 0.89, 95% CI: 0.81-0.97). uNGAL may be useful to predict graft loss after AKI.

Impaired renal function and development in Belgrade rats

Belgrade rats carry a disabling mutation in the iron transporter divalent metal transporter 1 (DMT1). Although DMT1 plays a major role in intestinal iron absorption, the transporter is also highly expressed in the kidney, where its function remains unknown. The goal of this study was to characterize renal physiology of Belgrade rats. Male Belgrade rats died prematurely with ∼50% survival at 20 wk of age. Necropsy results indicated marked glomerular nephritis and chronic end-stage renal disease. By 15 wk of age, Belgrade rats displayed altered renal morphology associated with sclerosis and fibrosis. Creatinine clearance was significantly lower compared with heterozygote littermates. Urinary biomarkers of kidney injury, including albumin, fibrinogen, and kidney injury molecule-1, were significantly elevated. Pilot morphological studies suggest that nephrogenesis is delayed in Belgrade rat pups due to their low iron status and fetal growth restriction. Such defects in renal development most likely underlie the compromised renal metabolism observed in adult b/b rats. Belgrade rat kidney nonheme iron levels were not different from controls but urinary iron and transferrin levels were higher. These results further implicate an important role for the transporter in kidney function not only in iron reabsorption but also in glomerular filtration of the serum protein.

Antioxidant signal and kidney injury molecule-1 levels in shockwave lithotripsy induced kidney injury

PURPOSE

Shockwave lithotripsy (SWL) induces acute kidney injury (AKI) that extends from the papilla to the outer cortex by causing ischemia and the production of nephrotoxic agents. Direct ischemic damage and the generation of free radicals cause injury to the proximal tubular cells. Kidney injury molecule-1 (KIM-1) is a transmembrane glycoprotein that is upregulated in proximal tubular cells after ischemic or nephrotoxic injury and is not expressed in healthy kidneys. We evaluated the extent of free radical production in response to SWL by measuring urinary total antioxidant capacity (TAC) and total oxidant status (TOS). Furthermore, we investigated the severity of SWL-induced kidney injury by measuring KIM-1 expression levels.

PATIENTS AND METHODS

The study population comprised 30 patients who were carefully selected and 30 age and sex matched control subjects. All patients received the same SWL procedure. Midstream urine samples were collected from patients before SWL and at 120 minutes after SWL. Urine KIM-1 levels were measured by enzyme-linked immunosorbent assay, and TAC and TOS were measured via spectrophotometry.

RESULTS

Mean levels of TAC (2.88±0.56 mmolTxEq/L),TOS (8.27±1.57 μmolH2O2Eq/L), and KIM-1 (0.55±0.08 ng/mL) before SWL were not significantly different from mean TAC, TOS, and KIM-1 levels measured from the control group at 2.81±0.42 mmolTxEq/L, 10.73±1.4 μmolH2O2Eq/L, and 0.51±0.07 ng/mL, respectively. Two hours after SWL, mean urine TAC levels (2.81±0.85 mmolTxEq/L, P=0.02) were decreased and mean KIM-1 expression (0.85±0.11 ng/mL, P=0.01) was significantly increased, but there was no significant difference in mean TOS levels (11.24±1.9 μmolH2O2Eq/L, P=0.627) compared with the control group.

CONCLUSIONS

The increased burden of free radical oxidants in the setting of decreasing antioxidant capacity may be one of the initial indicators of AKI after SWL. Moreover, KIM-1 demonstrates great potential as an early and noninvasive biomarker of SWL-induced kidney injury.

Urinary expression of novel tissue markers of kidney injury after ureteroscopy, shockwave lithotripsy, and in normal healthy controls

BACKGROUND AND PURPOSE

Shockwave lithotripsy (SWL) and ureteroscopy (URS) are minimally invasive treatment alternatives for kidney stones. Although less invasive, SWL subjects the renal parenchyma to a high level of energy and the potential to cause renal injury. The ability to detect renal injury post-SWL in a reliable and noninvasive way would be clinically beneficial. Kidney injury molecule 1 (KIM-1) and N-acetyl-β-D-glucosaminidase (NAG) are two proteins secreted by the kidney into the urine and have been found to be sensitive markers of acute kidney injury in transplant patients. The aim of this work was to measure urinary levels of KIM-1 and NAG in patients with kidney stone who were treated by SWL or URS and in nonstone volunteers.

PATIENTS AND METHODS

Patients with kidney stones who were treated by SWL (n = 50) or URS (n = 10) were recruited. Voided urine samples were collected before and 2 to 3 hours after URS and SWL. In addition, further urinary specimens were collected 2 days and 2 weeks post-SWL treatment. Voided urine samples from healthy volunteers were also collected.

RESULTS

Mean KIM-1 values were increased in patients with kidney stones when compared with volunteers. KIM-1 and NAG levels significantly increased post-SWL and returned to baseline within 2 weeks post-SWL. Poor kidney function was significantly associated with increased biomarker activity both in baseline and post-SWL measurements. There was no significant change in urinary KIM-1 and NAG concentrations before and after URS.

CONCLUSIONS

Kim-1 and NAG levels significantly increased post-SWL treatment suggesting a potential role for these urinary markers in identifying patients at higher risk of tissue injury.

The current status of biomarkers for predicting toxicity

INTRODUCTION

There are significant rates of attrition in drug development. A number of compounds fail to progress past preclinical development due to limited tools that accurately monitor toxicity in preclinical studies and in the clinic. Research has focused on improving tools for the detection of organ-specific toxicity through the identification and characterization of biomarkers of toxicity.

AREAS COVERED

This article reviews what we know about emerging biomarkers in toxicology, with a focus on the 2012 Northeast Society of Toxicology meeting titled 'Translational Biomarkers in Toxicology.' The areas covered in this meeting are summarized and include biomarkers of testicular injury and dysfunction, emerging biomarkers of kidney injury and translation of emerging biomarkers from preclinical species to human populations. The authors also provide a discussion about the biomarker qualification process and possible improvements to this process.

EXPERT OPINION

There is currently a gap between the scientific work in the development and qualification of novel biomarkers for nonclinical drug safety assessment and how these biomarkers are actually used in drug safety assessment. A clear and efficient path to regulatory acceptance is needed so that breakthroughs in the biomarker toolkit for nonclinical drug safety assessment can be utilized to aid in the drug development process.

Biomarkers in the assessment of acute and chronic kidney diseases in the dog and cat

In both human and veterinary medicine, diagnosing and staging renal disease can be difficult. Measurement of glomerular filtration rate is considered the gold standard for assessing renal function but methods for its assessment can be technically challenging and impractical. The main parameters used to diagnose acute and chronic kidney disease include circulating creatinine and urea concentrations, and urine-specific gravity. However, these parameters can be insensitive. Therefore, there is a need for better methods to diagnose and monitor patients with renal disease. The use of renal biomarkers is increasing in human and veterinary medicine for the diagnosis and monitoring of acute and chronic kidney diseases. An ideal biomarker would identify site and severity of injury, and correlate with renal function, among other qualities. This article will review the advantages and limitations of renal biomarkers that have been used in dogs and cats, as well as some markers used in humans that may be adapted for veterinary use. In the future, measuring a combination of biomarkers will likely be a useful approach in the diagnosis of kidney disorders.

Effects of rebamipide on nephrotoxicity associated with selected NSAIDs in rats

Use of nonsteroidal anti-inflammatory drugs (NSAIDs) is primarily limited by renal and gastrointestinal adverse effects. Rebamipide suppresses gastric mucosal injury when administered with NSAIDs. This study aimed to determine rebamipide's influence upon renal effects following concomitant use with celecoxib or diclofenac. On day 0, rats were randomly divided into 6 groups (n≥6). On days 1 and 2, three groups received placebo and three groups were administered rebamipide (30 mg/kg) twice daily. On day 3, the rats treated with placebo received another dose of placebo and ten minutes later a single dose of celecoxib (40 mg/kg), diclofenac (10mg/kg), or placebo, respectively. The rats treated with rebamipide received one more dose of rebamipide and ten minutes later one single dose of celecoxib, diclofenac, or placebo, respectively. Urine and blood samples were collected on days 0, 2, and 3. Sodium and potassium excretion rates decreased significantly in the rats treated with celecoxib, diclofenac, rebamipide plus celecoxib, or rebamipide plus diclofenac on day 3. Blood urea nitrogen (BUN) levels significantly increased in placebo plus diclofenac and rebamipide plus diclofenac groups on day 3. Comparing the two groups, the levels of BUN was significantly higher in the rebamipide plus diclofenac group compared to that of placebo plus diclofenac group. Concomitant administration of rebamipide with either NSAID caused a rise in concentrations of urinary kidney injury molecule-1. Histopathological evaluations revealed an intensified NSAID-induced tubular necrosis by rebamipide. Based upon the results obtained, concomitant administration of rebamipide with NSAIDs enhances the effect of NSAIDs on tubular injury.

A bioinformatics approach identifies signal transducer and activator of transcription-3 and checkpoint kinase 1 as upstream regulators of kidney injury molecule-1 after kidney injury

Kidney injury molecule-1 (KIM-1)/T cell Ig and mucin domain-containing protein-1 (TIM-1) is upregulated more than other proteins after AKI, and it is highly expressed in renal damage of various etiologies. In this capacity, KIM-1/TIM-1 acts as a phosphatidylserine receptor on the surface of injured proximal tubular epithelial cells, mediating phagocytosis of apoptotic cells, and it may also act as a costimulatory molecule for immune cells. Despite recognition of KIM-1 as an important therapeutic target for kidney disease, the regulators of KIM-1 transcription in the kidney remain unknown. Using a bioinformatics approach, we identified upstream regulators of KIM-1 after AKI. In response to tubular injury in rat and human kidneys or oxidant stress in human proximal tubular epithelial cells (HPTECs), KIM-1 expression increased significantly in a manner that corresponded temporally and regionally with increased phosphorylation of checkpoint kinase 1 (Chk1) and STAT3. Both ischemic and oxidant stress resulted in a dramatic increase in reactive oxygen species that phosphorylated and activated Chk1, which subsequently bound to STAT3, phosphorylating it at S727. Furthermore, STAT3 bound to the KIM-1 promoter after ischemic and oxidant stress, and pharmacological or genetic induction of STAT3 in HPTECs increased KIM-1 mRNA and protein levels. Conversely, inhibition of STAT3 using siRNAs or dominant negative mutants reduced KIM-1 expression in a kidney cancer cell line (769-P) that expresses high basal levels of KIM-1. These observations highlight Chk1 and STAT3 as critical upstream regulators of KIM-1 expression after AKI and may suggest novel approaches for therapeutic intervention.

Acute kidney injuries induced by various irrigation pressures in rat models of mild and severe hydronephrosis

OBJECTIVE

To clarify whether tolerance to irrigation pressure could be modified over varying degrees of kidney obstruction during the endoscopic treatment of kidney stones in a rat model.

METHODS

A total of 126 rats were randomly allocated into 2 experimental groups and a control group. The experimental groups underwent a surgical procedure to induce mild (group M, n = 60) or severe (group S, n = 60) hydronephrosis. In each group, the rats were then randomly allocated into 4 subgroups (M0 to M3 and S0 to S3) of respectively 6, 18, 18, and 18 rats. Groups 0 to 3 were respectively perfused with 0 (no irrigation), 20, 60, and 100 mm Hg pressure fluid. The control group underwent no surgical procedures and was only perfused with 100 mm Hg pressure fluid. Acute kidney injuries were assessed by analyzing the kidney microstructure, tubular cell apoptosis, kidney injury molecule-1, and cysteine-rich 61 (Cyr61/CCN1) expression using immunohistochemistry.

RESULTS

No abnormalities were observed for the control group, groups 0, or 1. In group 2, abnormalities were observed only in the S group, whereas all kidneys in group 3 suffered acute kidneys injuries, along with occurrence of tubular cells necrosis, increased apoptosis, and increased expression of kidney injury molecule-1 and Cyr61.

CONCLUSION

Rats with severely obstructed kidneys were more likely to suffer acute kidney injuries than those with less obstructed kidneys when exposed to higher kidney irrigation pressures. This suggests that the pressure should be controlled and reduced when performing endourologic procedures in the context of kidney obstruction.

Use of the kidney injury molecule-1 as a biomarker for early detection of renal tubular dysfunction in a population chronically exposed to cadmium in the environment

Cadmium (Cd) has been found as an environmental pollutant in Mae Sot district, Tak province, Thailand. Prolong exposure to high levels of Cd of the resident increases high risk of Cd toxicity especially to kidney which is the primary target of Cd. In order to investigate the early effect of Cd induced renal dysfunction, a kidney injury molecule-1 (KIM-1), a novel biomarker of renal tubular dysfunction, was measured using an enzyme linked immunosorbent assay (ELISA). The method was validated and used to quantify the KIM-1 concentrations in the urine of 700 subjects (260 men, 440 women) who lived in the Cd contaminated area. The KIM-1 concentrations were compared to the concentrations of two conventional renal tubular dysfunction biomarkers, N-acetyl-β-D-glucosaminidase (NAG) and β₂-microglobulin (β₂-MG). Urinary KIM-1 was correlated with urinary and blood Cd as well as NAG. After adjustment of age and smoking, urinary KIM-1 was correlated with blood Cd more than urinary NAG did. Clear dose response relationships of urinary KIM-1 with urinary Cd were shown in both men and women. These results indicate that the urinary KIM-1 might be more sensitive biomarker than urinary NAG and β₂-MG for an early detection of renal tubular dysfunction. It is useful as a tool to detect renal effect of toxicity due to chronic Cd exposure at high level.

Organic anion transporter 5 renal expression and urinary excretion in rats with vascular calcification

It has been described renal damage in rats with vascular calcification. The organic anion transporter 5 (Oat5) is only expressed in kidney, and its urinary excretion was proposed as potential early biomarker of renal injury. The aim of this study was to evaluate the Oat5 renal expression and its urinary excretion in an experimental model of vascular calcification in comparison with traditional markers of renal injury. Vascular calcification was obtained by the administration of an overdose of vitamin D₃ (300,000 IU/kg, b.w., i.m.) to male Wistar rats. Oat5 urinary abundance was evaluated by Western blotting. Traditional markers of renal injury, such as creatinine and urea plasma levels, urinary protein levels, and urinary alkaline phosphatase (AP) activity, were determined using commercial kits. Histology was assessed by hematoxylin/eosin staining. Oat5 renal expression was evaluated by Western blotting and by immunohistochemistry. An increased expression of Oat5 in renal homogenates, in apical membranes, and in its urinary excretion was observed in rats with vascular calcification. The traditional parameters used to evaluate renal function were not modified, with the exception of histology. It is possible to postulate the urinary excretion of Oat5 as a potential noninvasive biomarker of renal injury associated with vascular calcification.

Urine kidney injury molecule-1: a potential non-invasive biomarker for patients with renal cell carcinoma

BACKGROUND

KIM-1 staining is upregulated in proximal tubule-derived renal cell carcinoma (RCC) including clear renal cell carcinoma and papillary renal cell carcinoma, but not in chromophobe RCC (distal tubular tumor). This study was designed to prospectively examine urine KIM-1 level before and 1 month after removal of renal tumors.

PATIENTS AND DESIGN

A total of 19 patients were eventually enrolled in the study based on pre-operative imaging studies. Pre-operative and follow-up (1 month) urine KIM-1 levels were measured. The urine KIM-1 levels (uKIM-1) were then normalized to urine creatinine levels (uCr). Renal tumors were also stained for KIM-1 using immunohistochemical techniques.

RESULTS

The KIM-1-negative staining group included 7 cases, and the KIM-1-positive group consisted of 12 cases. The percentage of KIM-1-positive staining RCC cells ranged from 10 to 100 %, and the staining intensity ranged from 1+ to 3+. In both groups, serum creatinine levels were both significantly elevated after nephrectomy. In the KIM-1-negative group, uKIM-1/uCr remained at a similar level before (0.37 ± 0.1 ng/mg Cr) and after nephrectomy (0.32 ± 0.01 ng/mg Cr). However, in the KIM-1-positive group, elevated uKIM-1/uCr at 1.20 ± 0.31 ng/mg Cr was significantly reduced to 0.36 ± 0.1 ng/mg Cr, which was similar to the pre-operative uKIM-1/uCr (0.37 ± 0.1 ng/mg Cr) in the KIM-1-negative group.

CONCLUSION

Our small but prospective study showed significant reduction in uKIM-1/uCr after nephrectomy in the KIM-1 positive group, suggesting that urine KIM-1 may serve as a surrogate biomarker for kidney cancer and a non-invasive pre-operative measure to evaluate the malignant potential of renal masses.

Clinical utility of biomarkers in chronic kidney disease and chronic heart failure

Biomarkers have an increasingly important clinical role in managing patients with heart failure as well as those with kidney disease, both common conditions with generally poor prognostic outcomes and huge impacts on healthcare economics. For patients with chronic heart failure, biomarkers have become centre place in streamlining diagnostic pathways as well as identifying those with worse prognosis. There is much interest in the role for biomarkers in identifying patients at risk of acute kidney injury, although a number of these currently remain as research tools or are in the early stages of evaluation in clinical practice. Patients with cardiorenal syndrome represent a particular challenge to the clinician, and recent studies have suggested a valuable clinical role for certain biomarkers in this setting, either on their own or in combination. This paper will focus on biomarkers with a current clinical role in patients with cardiorenal disease (natriuretic peptides and neutrophil gelatinase-associated lipocalin), although brief reference will be made to other biomarkers with potential future application.

Deficiency in mitochondrial complex I activity due to Ndufs6 gene trap insertion induces renal disease

AIMS

Defects in the activity of enzyme complexes of the mitochondrial respiratory chain are thought to be responsible for several disorders, including renal impairment. Gene mutations that result in complex I deficiency are the most common oxidative phosphorylation disorders in humans. To determine whether an abnormality in mitochondrial complex I per se is associated with development of renal disease, mice with a knockdown of the complex I gene, Ndufs6 were studied.

RESULTS

Ndufs6 mice had a partial renal cortical complex I deficiency; Ndufs6gt/gt, 32% activity and Ndufs6gt/+, 83% activity compared with wild-type mice. Both Ndufs6gt/+ and Ndufs6gt/gt mice exhibited hallmarks of renal disease, including albuminuria, urinary excretion of kidney injury molecule-1 (Kim-1), renal fibrosis, and changes in glomerular volume, with decreased capacity to generate mitochondrial ATP and superoxide from substrates oxidized via complex I. However, more advanced renal defects in Ndufs6gt/gt mice were observed in the context of a disruption in the inner mitochondrial electrochemical potential, 3-nitrotyrosine-modified mitochondrial proteins, increased urinary excretion of 15-isoprostane F2t, and up-regulation of antioxidant defence. Juvenile Ndufs6gt/gt mice also exhibited signs of early renal impairment with increased urinary Kim-1 excretion and elevated circulating cystatin C.

INNOVATION

We have identified renal impairment in a mouse model of partial complex I deficiency, suggesting that even modest deficits in mitochondrial respiratory chain function may act as risk factors for chronic kidney disease.

CONCLUSION

These studies identify for the first time that complex I deficiency as the result of interruption of Ndufs6 is an independent cause of renal impairment.

Effect of treatment on urinary kidney injury molecule-1 in IgA nephropathy

Background

Kidney injury molecule-1 (KIM-1) is a biomarker useful for detecting early tubular damage and has been recently reported as a useful marker for evaluating kidney injury in IgA nephropathy (IgAN). We therefore investigated whether treatment decreases urinary KIM-1 excretion in IgAN.

Methods

We prospectively enrolled 37 patients with biopsy-proven IgAN. Urinary KIM-1 was assessed before and after treatment, which included low salt diet, blood pressure control, pharmacotherapy with angiotensin receptor blockers and/or angiotensin converting enzyme inhibitors, and immunosuppressive agents as necessary. The median treatment duration was 24 months.

Results

Urinary KIM-1/creatinine (Cr) was significantly decreased in patients with IgAN after treatment compared to baseline (P < 0.0001, 1.16 [0.51-1.83] vs 0.26 [0.12-0.65] ng/mg). There was a decrease in the amount of proteinuria after treatment, but it was not statistically significant (P = 0.052, 748.1 [405-1569.7] vs 569.2 [252.2-1114] g/d). Estimated glomerular filtration rate (eGFR) did not change with treatment (P = 0.599, 79.28 ± 30.56 vs 80.98 ± 32.37 ml/min/1.73 m²). Urinary KIM-1 was not correlated with proteinuria baseline or follow up (pre-: R = - 0.100, P = 0.577, post-: R = 0.001, P = 0.993). In patients with higher baseline urinary KIM-1, both urinary KIM-1 level and proteinuria were significantly decreased following treatment.

Conclusions

Treatment decreases urinary KIM-1/Cr in patients with IgAN. It also reduces proteinuria in patients with higher baseline urinary KIM-1. These results suggest a potential role for urinary KIM-1 as a biomarker for predicting treatment response in IgAN, however, further study is needed to verify this.

Protective effects of naringenin on carbon tetrachloride-induced acute nephrotoxicity in mouse kidney

The ability of naringenin (NGN) to protect the kidney against CCl4-induced renal toxicity in male Swiss mice was investigated. The flavonoid was given orally to mice for 7days and then on the 8th day, these were intraperitoneally injected with 10mmol/kg CCl4. When the toxicant was administrated alone, an increase of malondialdehyde (MDA) concentration was observed and a significant decrease in superoxide dismutase (SOD), catalase (CAT) glutathione-peroxidase (GPx) specific activities as well as glutathione (GSH) levels was detected after 24h. These were accompanied by glomerular and tubular degenerations, vascular congestion, necrosis and fatty changes. Marked collagen deposition and strong TGF-β1 expression were observed mainly in the mesangial cells of the glomeruli and tubulointerstitial areas. Ultrastructural investigations showed proximal and distal tubular epithelial cells alterations including numerous lysosomes and dense granular bodies, altered mitochondria, appearance of "myeloid bodies" and basal enfolding dilatation. Pre-treatment with NGN resulted in the return of biochemical markers to control values. Histopathological and electron-microscopic examinations confirmed the biochemical results. In conclusion, NGN showed antioxidant and renal protective effects against injuries induced by CCl4.

Acute kidney injury and critical cardiac disease

The field of cardiac intensive care continues to advance in tandem with congenital heart surgery. The survival of patients with critical congenital heart disease is seldom in question. Consequently, the focus has now shifted to that of morbidity reduction and eventual elimination. Acute kidney injury (AKI) after cardiac surgery is associated with adverse outcomes, including prolonged intensive care and hospital stays, diminished quality of life, and increased long-term mortality. Acute kidney injury occurs frequently, complicating 30% to 40% of adult and pediatric cardiac surgeries. Patients who require dialysis are at high risk of mortality, but even minor degrees of postoperative AKI portend a significant increase in mortality and morbidity.

Performance of kidney injury molecule-1 and liver fatty acid-binding protein and combined biomarkers of AKI after cardiac surgery

BACKGROUND AND OBJECTIVES

AKI is common and novel biomarkers may help provide earlier diagnosis and prognosis of AKI in the postoperative period.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

This was a prospective, multicenter cohort study involving 1219 adults and 311 children consecutively enrolled at eight academic medical centers. Performance of two urine biomarkers, kidney injury molecule-1 (KIM-1) and liver fatty acid-binding protein (L-FABP), alone or in combination with other injury biomarkers during the perioperative period was evaluated. AKI was defined as doubling of serum creatinine or need for acute dialysis.

RESULTS

KIM-1 peaked 2 days after surgery in adults and 1 day after surgery in children, whereas L-FABP peaked within 6 hours after surgery in both age groups. In multivariable analyses, the highest quintile of the first postoperative KIM-1 level was associated with AKI compared with the lowest quintile in adults, whereas the first postoperative L-FABP was not associated with AKI. Both KIM-1 and L-FABP were not significantly associated with AKI in adults or children after adjusting for other kidney injury biomarkers (neutrophil gelatinase-associated lipocalin and IL-18). The highest area under the curves achievable for discrimination for AKI were 0.78 in adults using urine KIM-1 from 6 to 12 hours, urine IL-18 from day 2, and plasma neutrophil gelatinase-associated lipocalin from day 2 and 0.78 in children using urine IL-18 from 0 to 6 hours and urine L-FABP from day 2.

CONCLUSIONS

Postoperative elevations of KIM-1 associate with AKI and adverse outcmes in adults but were not independent of other AKI biomarkers. A panel of multiple biomarkers provided moderate discrimination for AKI.

Changes in mRNA and protein expression in the renal cortex of male and female F344 rats treated with bromate

Bromate (BrO3(-)), a by-product of ozonation of drinking water, induces nephrotoxicity in male rats at much lower doses than in female rats. This difference appears to be related to the development of α-2u-globulin nephropathy in males. To determine sex-dependent changes in mRNA and protein expression in the renal cortex attributable to α-2u-globulin nephropathy, we performed microarray and immunohistochemical analyses in proximal renal tubules of male and female F344 rats treated with KBrO3 for 28 days. Particular attention was paid to molecular biomarkers of renal tubular injury. Microarray analysis of male and female rats treated with BrO3(-) at low doses (125 mg/L KBrO3) displayed marked sex-dependent changes in renal gene expression. The greatest differences were seen in genes encoding for cellular differentiation, apoptosis, ion transport, and cell proliferation. Differences by sex were especially prominent for the cell cycle checkpoint gene p21, the renal injury protein Kim-1, and the kidney injury and cancer biomarker protein osteopontin. Dose-related nephrotoxicity, assessed by hematoxylin and eosin staining, was greater in males compared to female rats, as was cellular proliferation, assessed by bromodeoxyuridine staining. The fraction of proximal renal cells with elevated 8-oxodeoxyguanosine (8-OH-dG) was only increased at the high dose and did not differ by sex. Dose-dependent increases in the expression of osteopontin were detected immunohistochemically only in male rats and were localized in proximal tubule cells. Similarly, BrO3(-) treatment increased clusterin and Kim-1 staining in the proximal tubules; however, staining for these proteins did not differ appreciably between males and females. These data demonstrate both qualitative and quantitative differences in the response of male versus female kidneys to BrO3(-)-treatment. These sex-dependent effects likely contribute to renal carcinogenesis of BrO3(-) in the male rat.

Kidney injury molecule-1: more than just an injury marker of tubular epithelial cells?

Regardless of the original causes and etiology, the progression to renal function declines follows a final common pathway associated with tubulointerstitial injury, in which the proximal tubular epithelial cells (PTEC) are instrumental. Kidney injury molecule-1 (KIM-1) is an emerging biomarker, and its expression and release are induced in PTEC upon injury. KIM-1 plays the role as a double-edged sword and implicates in the process of kidney injury and healing. Expression of KIM-1 is also associated with tubulointerstitial inflammation and fibrosis. More importantly, KIM-1 expressing PTEC play the role as the residential phagocytes, contribute to the removal of apoptotic cells and facilitate the regeneration of injured tubules. The precise mechanism of KIM-1 and its sheded ectodomain on restoration of tubular integrity after injury is not fully understood. Other than PTEC, macrophages (Mø) also implicate in tubular repair. Understanding the crosstalk between Mø and the injured PTEC is essential for designing appropriate methods for controlling the sophisticated machinery in tubular regeneration and healing. This article will review the current findings of KIM-1, beginning with its basic structure, utility as a biomarker, and possible functions, with focus on the role of KIM-1 in regeneration and healing of injured PTEC.

urinary biomarkers in relapsing antineutrophil cytoplasmic antibody-associated vasculitis

OBJECTIVE

Glomerulonephritis (GN) is common in antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV), but tools for early detection of renal involvement are imperfect. We investigated 4 urinary proteins as markers of active renal AAV: alpha-1 acid glycoprotein (AGP), kidney injury molecule-1 (KIM-1), monocyte chemoattractant protein-1 (MCP-1), and neutrophil gelatinase-associated lipocalin (NGAL).

METHODS

Patients with active renal AAV (n = 20), active nonrenal AAV (n = 16), and AAV in longterm remission (n = 14) were identified within a longitudinal cohort. Urinary biomarker concentrations (by ELISA) were normalized for urine creatinine. Marker levels during active AAV were compared to baseline remission levels (from 1-4 visits) for each patient. Areas under receiver-operating characteristic curves (AUC), sensitivities, specificities, and likelihood ratios (LR) comparing disease states were calculated.

RESULTS

Baseline biomarker levels varied among patients. All 4 markers increased during renal flares (p < 0.05). MCP-1 discriminated best between active renal disease and remission: a 1.3-fold increase in MCP-1 had 94% sensitivity and 89% specificity for active renal disease (AUC = 0.93, positive LR 8.5, negative LR 0.07). Increased MCP-1 also characterized 50% of apparently nonrenal flares. Change in AGP, KIM-1, or NGAL showed more modest ability to distinguish active renal disease from remission (AUC 0.71-0.75). Hematuria was noted in 83% of active renal episodes, but also 43% of nonrenal flares and 25% of remission samples.

CONCLUSION

Either urinary MCP-1 is not specific for GN in AAV, or it identifies early GN not detected by standard assessment and thus has potential to improve care. A followup study with kidney biopsy as the gold standard is needed.

Renal dysfunction in acute heart failure: epidemiology, mechanisms and assessment

Renal dysfunction is often present and/or worsens in patients with heart failure and this is associated with increased costs of care, complications and mortality. The cardiorenal syndrome can be defined as the presence or development of renal dysfunction in patients with heart failure. Its mechanisms are likely related to low cardiac output, increased venous congestion and renal venous pressure, neurohormonal and inflammatory activation and local changes, such as adenosine release. Many drugs, including loop diuretics, may contribute to worsening renal function through the activation of some of these mechanisms. Renal damage is conventionally defined by the increase in creatinine and blood urea nitrogen blood levels. However, these changes may be not related with renal injury or prognosis. New biomarkers of renal injury seem promising but still need to be validated. Thus, despite the epidemiological evidence, we are still lacking of satisfactory tools to assess renal injury and function and its prognostic significance.

Current and novel renal biomarkers in heart failure

Renal function is the most important predictor of clinical outcome in heart failure (HF). It is therefore essential to have accurate and reliable measurement of renal function and early specific markers of renal impairment in patients with HF. Several renal functional entities exist, including glomerular filtration (GFR), glomerular permeability, tubulointerstitial damage, and endocrine function. Different markers have been studied that can be used to determine changes and the effect of treatment in these entities. In the present review, we summarize current and novel markers that give an assessment of renal function and prognosis in the setting of acute and chronic HF.

Novel biomarkers for early diagnosis of acute kidney injury

BACKGROUND

Acute kidney injury (AKI) is a common and serious problem in critically ill patients. Tests currently used to detect AKI (i.e., serum creatinine, serum urea and various urinary indices) often result in serious delays in detection of clinically relevant injury. This delayed detection translates into a potential missed opportunity for therapeutic interventions at a time when kidney damage may be limitable or reversible. This is also recognized as a potential reason for the poor clinical outcomes often associated with AKI.

OBJECTIVES

To appraise the recent literature characterizing several novel serum and urinary biomarkers, including neutrophil gelatinase-associated lipocalin, IL-18 and kidney injury molecule-1, which are capable of detecting AKI at an earlier phase of injury. Also to discuss the pitfalls of current conventional testing in kidney injury.

METHOD

Narrative literature review.

CONCLUSIONS

These novel biomarkers can detect injury when damage may still be reversible, allow for early risk stratification and/or prognostication, and are associated in early clinical studies with important outcomes such as severity of AKI, need for renal replacement therapy and survival. There is optimism that these novel biomarkers will discriminate the underlying pathophysiology of AKI (i.e., ischemia, sepsis, toxins or multifactorial), discriminate AKI from other renal disease (i.e., chronic kidney disease) and aid in localizing the site of acute injury in the kidney. As such, the future may entail development of an 'AKI biomarker panel' (i.e., analogous to a cardiac or liver enzyme panel) for use in clinical practice.

In vitro evaluation of biomarkers for cisplatin-induced nephrotoxicity using HK-2 human kidney epithelial cells

The non-animal in vitro test methods, especially for assessment of kidney toxicity, have become invaluable tools due to the target organ-selective nature of many nephrotoxic xenobiotics. In vitro evaluation of biomarkers for nephrotoxicity assessment using human cell lines, which can provide more reliable information for toxicological risk evaluation in humans than animal cells, has not been well established to date. The present study investigated the potential use of biomarkers for cisplatin-induced nephrotoxicity assessment in vitro using HK-2 cells derived from human kidney proximal tubule epithelial cells. Cisplatin induced apoptosis of HK-2 cells in which down-regulation of Bcl-2 and activation of caspase-3 were possibly involved. We investigated the effect of cisplatin on the protein levels of kidney injury molecule (KIM)-1, clusterin, calbindin, tissue inhibitor of metalloproteinase (TIMP)-1, cystatin C (CysC), β₂-microglobulin (β₂-M) and neutrophil gelatinase associated lipocalin (NGAL), which have been recently identified as in vivo biomarkers of nephrotoxicity. The protein levels of KIM-1, calbindin and TIMP-1 were significantly increased in the conditioned media of HK-2 cells treated with cisplatin, while β₂-M, CysC, NGAL and clusterin were not affected by cisplatin treatment. The mRNA levels of KIM-1, calbindin and TIMP-1 were increased by cisplatin, indicating that cisplatin-induced up-regulation involves transcriptional activation. The levels of KIM-1, calbindin and TIMP-1 were significantly increased in urine of cisplatin-treated rats, providing in vivo validation of the in vitro results. Taken together, our results clearly demonstrate that among the known in vivo nephrotoxic biomarkers, KIM-1, calbindin and TIMP-1 can be effectively used as in vitro biomarkers for cisplatin-induced nephrotoxicity using a HK-2 human kidney cell system.

Noninvasive analyses of kidney injury molecule-1 messenger RNA in kidney transplant recipients with graft dysfunction

BACKGROUND

Kidney graft fibrosis is a major factor related to chronic loss of kidney function. At present, the finding of fibrosis depends on the analysis of tissue in the renal biopsy, which has important limitations. In this study, we evaluated the messenger mRNA transcription and gene expression of kidney injury molecule-1 (KIM-1) in kidney tissue and in urinary sediment cells of kidney transplant patients with graft dysfunction aiming at the development of techniques that may allow the noninvasive diagnosis of interstitral fibrosis/tubular atrophy (IF/TA).

PATIENTS AND METHODS

RNA extracted from cells in tissue and urine of 77 renal transplant patients whose biopsies were classified according to the Banff scheme-2007. Four diagnostic groups were established: (1) acute tubular necrosis (n = 9); (2) acute rejection (n = 49); (3) acute calcineurin inhibitors nephrotoxicity (n = 10); and (4) interstitial fibrosis and tubular atrophy (IFTA, n = 29). Tissue and urine cell RNA was amplified and quantification were made by real-time polymerase chain reactron. Data from the quantification of gene expression are presented as median and 25th to 75th percentiles.

RESULTS

Messenger RNA levels of the KIM-1 gene were higher in the biopsies (26.17; 3.38-294.53) and urinary sediment cells (0.09; 0-5.81) of the patients classified as having IF/TA as compared with all others groups. A significant correlation between gene expression in samples of urine and tissue cells was found (P < .01).

CONCLUSION

These initial data suggests that KIM-1 gene mRNA quantification can be used as a noninvasive biomarker of IF/TA.

Biomarkers of acute kidney injury in neonatal encephalopathy

Acute kidney injury (AKI) is a common complication of neonatal encephalopathy (NE). The accurate diagnosis of neonatal AKI, irrespective of the cause, relies on suboptimal methods such as identification of rising serum creatinine, decreased urinary output and glomerular filtration rate. Studies of AKI biomarkers in adults and children have shown that biomarkers can improve the early diagnosis of AKI. Hypoxia-ischaemia is the proposed aetiological basis of AKI in both NE and cardiopulmonary bypass (CPB). However, there is a paucity of studies examining the role of AKI biomarkers specifically in NE. Urinary cystatin C (CysC), neutrophil gelatinase-associated lipocalin (NGAL), interleukin-18, kidney injury molecule-1, liver-type fatty acid-binding protein, serum CysC and serum NGAL all show good ability to predict early AKI in a heterogeneous critically ill neonatal population including infants post-CPB. Moreover, serum and urinary NGAL and urinary CysC are early predictors of AKI secondary to NE. These findings are promising and open up the possibility of biomarkers playing a significant role in the early diagnosis and treatment of NE-related AKI. There is an urgent need to explore the role of AKI biomarkers in infants with NE as establishing the diagnosis of AKI earlier may allow more timely intervention with potential for improving long-term outcome.

Role of new biomarkers: functional and structural damage

Traditional diagnosis of acute kidney injury (AKI) depends on detection of oliguria and rise of serum creatinine level, which is an unreliable and delayed marker of kidney damage. Delayed diagnosis of AKI in the critically ill patient is related to increased morbidity and mortality, prolonged length of stay, and cost escalation. The discovery of a reliable biomarker for early diagnosis of AKI would be very helpful in facilitating early intervention, evaluating the effectiveness of therapy, and eventually reducing cost and improving outcome. Innovative technologies such as genomics and proteomics have contributed to the discovery of new biomarkers, such as neutrophil gelatinase-associated lipocalin (NGAL), cystatin C (Cys C), kidney injury molecule-1 (KIM-1), interleukin-18 (IL-18), and liver-type fatty acid binding protein (L-FABP). The current status of the most promising of these novel AKI biomarkers, including NGAL, Cys C, KIM-1, L-FABP, and IL-18, is reviewed.

Urinary chemokine (C-C motif) ligand 2 (monocyte chemotactic protein-1) as a tubular injury marker for early detection of cisplatin-induced nephrotoxicity

Because of the difficulty in detecting segment-specific response in the kidney, we investigated the molecular events underlying acute kidney injury in the proximal tubules of rats with cisplatin (cis-diamminedichloroplatinum II)-induced nephrotoxicity. Microarray analysis revealed that mRNA levels of several cytokines and chemokines, such as interleukin-1beta, chemokine (C-C motif) ligand (CCL) 2, CCL20, chemokine (C-X-C motif) ligand (CXCL) 1, and CXCL10 were significantly increased after cisplatin treatment in both isolated proximal tubules and whole kidney. Interestingly, tubular CCL2 mRNA levels increased soon after cisplatin administration, whereas CCL2 mRNA levels in whole kidney first decreased and then increased. Levels of both CCL2 and kidney injury molecule-1 (KIM-1) in the whole kidney increased after cisplatin administration. Immunofluorescence analysis revealed CCL2 changes in the proximal tubular cells initially and then in the medullary interstitium. Urinary CCL2 excretion significantly increased approximately 3-fold compared with controls the day after cisplatin administration (5mg/kg), when no changes were observed plasma creatinine and blood urea nitrogen levels. Urinary levels of KIM-1 also increased 3-fold after cisplatin administration. In addition, urinary CCL2 rather than KIM-1 increased in chronic renal failure rats after administration of low-dose cisplatin (2mg/kg), suggesting that urinary CCL2 was selective for cisplatin-induced nephrotoxicity in renal impairment. These results indicated that the increase in cytokine and chemokine expression in renal epithelial cells might be responsible for kidney deterioration in cisplatin-induced nephrotoxicity, and that urinary CCL2 is associated with tubular injury and serves as a sensitive and noninvasive marker for the early detection of cisplatin-induced tubular injury.

Urine NGAL and KIM-1 in children and adolescents with hyperuricemia

BACKGROUND

The aim of this study was to test the hypothesis that urine levels of neutrophil gelatinase-associated lipocalin (NGAL) and kidney injury molecule-1 (KIM-1) are enhanced in pediatric patients with hyperuricemia.

METHODS

The study included 88 children and adolescents (60 males, 28 females) with a median age of 16 (range 11-18.5) years who had been referred to our department to rule out or confirm hypertension. The subjects were divided into two groups: the hyperuricemic (HU) group comprising 59 subjects with hyperuricemia (defined as serum uric acid >4.8 and >5.5 mg/dl in girls and boys, respectively) and the reference group comprising 29 patients with normouricemia. Urine NGAL and KIM-1 levels were evaluated using a commercially available kit.

RESULTS

Concentrations of the examined biomarkers [urine NGAL, NGAL/creatinine (cr.) ratio, urine KIM-1, KIM-1/cr. ratio] were increased in the HU group compared with the reference group (p < 0.01). There were positive correlations between the serum uric acid and urine NGAL/cr. ratio (R = 0.67, p < 0.001) and the urine KIM-1/cr. ratio (R = 0.36, p < 0.001). In the multiple regression models, serum uric acid, systolic blood pressure and cholesterol accounted for more than 49 % of the variation in the NGAL/cr. ratio (R = 0.702, p < 0.001). In the second model, serum uric acid, gender, age and systolic blood pressure accounted for more than 36 % of the variation in the KIM-1/cr. ratio (R = 0.604, p < 0.001).

CONCLUSION

We demonstrated that male, obese, hypertensive adolescents with hyperuricemia have higher urine NGAL and KIM-1 levels relative to a reference group with normouricemia.

Glomerulopathy in the KK.Cg-A(y) /J mouse reflects the pathology of diabetic nephropathy

The KK.Cg-A (y) /J (KK-A (y) ) mouse strain is a previously described model of type 2 diabetes with renal impairment. In the present study, female KK-A (y) mice received an elevated fat content diet (24% of calories), and a cohort was uninephrectomized (Unx) to drive renal disease severity. Compared to KK-a/a controls, 26-week-old KK-A (y) mice had elevated HbA1c, insulin, leptin, triglycerides, and cholesterol, and Unx further elevated these markers of metabolic dysregulation. Unx KK-A (y) mice also exhibited elevated serum BUN and reduced glomerular filtration, indicating that reduction in renal mass leads to more severe impairment in renal function. Glomerular hypertrophy and hypercellularity, mesangial matrix expansion, podocyte effacement, and basement membrane thickening were present in both binephric and uninephrectomized cohorts. Glomerular size was increased in both groups, but podocyte density was reduced only in the Unx animals. Consistent with functional and histological evidence of increased injury, fibrotic (fibronectin 1, MMP9, and TGF β 1) and inflammatory (IL-6, CD68) genes were markedly upregulated in Unx KK-A (y) mice, while podocyte markers (nephrin and podocin) were significantly decreased. These data suggest podocyte injury developing into glomerulopathy in KK-A (y) mice. The addition of uninephrectomy enhances renal injury in this model, resulting in a disease which more closely resembles human diabetic nephropathy.

New biomarkers for the quick detection of acute kidney injury

Acute kidney injury (AKI) is a common and strong problem in the diagnosis of which based on measurement of BUN and serum creatinine. These traditional methods are not sensitive and specific for the diagnosis of AKI. AKI is associated with increased morbidity and mortality in critically ill patients and a quick detection is impossible with BUN and serum creatinine. A number of serum and urinary proteins have been identified that may messenger AKI prior to a rise in BUN and serum creatinine. New biomarkers of AKI, including NGAL, KIM-1, cystatin-C, IL-18, and L-FABP, are more favourable tests than creatinine which have been identified and studied in several experimental and clinical training. This paper will discuss some of these new biomarkers and their potential as useful signs of AKI. We searched the literature using PubMed and MEDLINE with acute kidney injury, urine, and serum new biomarkers and the articles were selected only from publication types in English.

Role of biomarkers in the diagnosis and prognosis of acute kidney injury in patients with cardiorenal syndrome

Cardiac and renal disease frequently coexist but have long been difficult to diagnose in a timely manner and treat effectively. Noninvasive and cost-effective biomarkers are needed to help identify cardiac patients who are at risk of acute kidney injury early in the course of disease. Biomarkers can provide insights into underlying mechanisms and lead to a better understanding of complex disease states such as the cardiorenal syndrome, which can lead to better therapies and, ultimately, to improved patient outcomes. The natriuretic peptides are established biomarkers in heart failure and have set the standard for how a well-validated biomarker can be useful for diagnosis/prognosis, monitoring response to therapy and chronic disease management. For patients with acute kidney injury in the setting of cardiac disease, new biomarkers such as neutrophil gelatinase-associated lipocalin, cystatin C, kidney injury molecule-1 and IL-18 are emerging as early signals of renal dysfunction prior to any elevations in serum creatinine. Other promising candidate biomarkers for the early diagnosis of acute kidney injury include osteopontin, N-acetyl-b-d-glucosaminidase, stromal cell-derived factor-1 and exosomes. More research with all of these novel biomarkers is needed; however, the early results are very promising.

Novel assays for detection of urinary KIM-1 in mouse models of kidney injury

Kidney injury molecule-1 (KIM-1) has been qualified by the Food and Drug Administration and European Medicines Agency as a urinary biomarker to monitor preclinical nephrotoxicity in rats and on a case-by-case basis for the translation of potentially nephrotoxic drugs into first-in human studies. Although mouse models are widely employed in preclinical studies, few urinary biomarker studies have been performed in mice due to limited urine availability and lack of sensitive assays. Here, we report the development and validation of two different assays for quantitative assessment of mouse urinary KIM-1 (uKIM-1) and compare the sensitivity of KIM-1 relative to other standard markers in ischemia reperfusion and aristolochic acid (AA)-induced kidney injury in mice. A sensitive, reproducible, and quantitative microbead-based KIM-1 ELISA was established, which requires only 10 μl urine for triplicate determination with an assay range of 12.21 pg/ml to 50 ng/ml. The second assay is a laminar flow dipstick assay, which has an assay range of 195 pg/ml to 50 ng/ml and provides quantitative assessment of KIM-1 in 15 min. uKIM-1 levels increased with increasing time of ischemia or time after AA administration. After only 10-min ischemia followed by 24-h reperfusion, uKIM-1 was significantly elevated by 13-fold, whereas serum creatinine (sCr), blood urea nitrogen, N-acetyl-β-glucosaminidase (NAG), and proteinuria levels did not change. After AA administration, uKIM-1 levels were significantly upregulated by greater than threefold within 12 h, whereas sCr and NAG levels were unchanged. Mouse KIM-1 was stable for multiple freeze-thaw cycles, for up to 5 days at room temperature and up to at least an year when stored at -80°C.

Qualified kidney biomarkers and their potential significance in drug safety evaluation and prediction

The kidney is one of the major organs drug toxicity may target. Some renal safety biomarkers have been proposed to measure kidney injury and function accordingly. Despite the widespread use for diagnosis and monitoring of renal injury and function for decades, serum creatinine and blood urea nitrogen are nonspecific biomarkers with insensitive and delayed response in the clinical setting. There is an urgent need to identify and qualify novel kidney safety biomarkers that would be used to detect and predict drug-induced nephrotoxicity in preclinical toxicological studies, clinical trials and patient care in sequence. To do that, eight novel renal safety biomarkers have been well characterized and qualified for preclinical drug safety screening, and their clinical bridging validation is underway as well. Of them, some are used to detect or predict proximal tubular injury, and others are used to diagnose and monitor glomerular damage. Thus, measurement of a panel of kidney safety biomarkers in parallel would help maximally capture all potential safety signals for a more informative decision to be made in drug research and development as well as for optimal selection of the drug and its dose in clinical practice.

Selective stabilization of HIF-1α in renal tubular cells by 2-oxoglutarate analogues

The role of proximal versus distal tubular injury in the pathogenesis of acute kidney injury (AKI) is debatable. Inhibition of prolyl hydroxylases that regulate the degradation of hypoxia-inducible transcription factors (HIFs) is a promising therapeutic approach to optimize energy preservation under hypoxia and has successfully been applied to protect kidney structure and function in AKI models. Presently used prolyl hydroxylase inhibitors are lipophilic 2-oxoglutarate analogues (2OGAs) that are widely taken up in cells of most organs. Given the selective expression of organic anion transporters (OATs) in renal proximal tubular cells, we hypothesized that hydrophilic 2OGAs can specifically target proximal tubular cells. We found that cellular hydrophilic 2OGAs uptake depended on OATs and largely confined to the kidney, where it resulted in activation of HIF target genes only in proximal tubular cells. When applied in ischemia-reperfusion experiments, systemically active 2OGA preserved kidney structure and function, but OAT1-transported 2OGA was not protective, suggesting that HIF stabilization in distal tubular rather than proximal tubular cells and/or nontubular cells mediates protective effects. This study provides proof of concept for selective drug targeting of proximal tubular cells on the basis of specific transporters, gives insights into the role of different nephron segments in AKI pathophysiology, and may offer options for long-term HIF stabilization in proximal tubules without confounding effects of erythropoietin induction in peritubular cells and unwarranted extrarenal effects.

Substituent effects on desferrithiocin and desferrithiocin analogue iron-clearing and toxicity profiles

Desferrithiocin (DFT, 1) is a very efficient iron chelator when given orally. However, it is severely nephrotoxic. Structure-activity studies with 1 demonstrated that removal of the aromatic nitrogen to provide desazadesferrithiocin (DADFT, 2) and introduction of either a hydroxyl group or a polyether fragment onto the aromatic ring resulted in orally active iron chelators that were much less toxic than 1. The purpose of the current study was to determine if a comparable reduction in renal toxicity could be achieved by performing the same structural manipulations on 1 itself. Accordingly, three DFT analogues were synthesized. The iron-clearing efficiency and ferrokinetics were evaluated in rats and primates; toxicity assessments were carried out in rodents. The resulting DFT ligands demonstrated a reduction in toxicity that was equivalent to that of the DADFT analogues and presented with excellent iron-clearing properties.

Delayed ischemic preconditioning contributes to renal protection by upregulation of miR-21

Delayed ischemic preconditioning effectively protects kidneys from ischemia-reperfusion injury but the mechanism underlying renal protection remains poorly understood. Here we examined the in vivo role of microRNA miR-21 in the renal protection conferred by delayed ischemic preconditioning in mice. A 15 minute renal ischemic preconditioning significantly increased the expression of miR-21 by 4 hours and substantially attenuated ischemia-reperfusion injury induced 4 days later. A locked nucleic acid-modified anti-miR-21 given at the time of ischemic preconditioning knocked down miR-21 and significantly exacerbated subsequent ischemia-reperfusion injury in the mouse kidney. Knockdown of miR-21 resulted in significant upregulation of programmed cell death protein 4, a pro-apoptotic target gene of miR-21, and substantially increased tubular cell apoptosis. Hypoxia inducible factor-1α in the kidney was activated after ischemic preconditioning and blockade of its activity with a decoy abolished the up-regulation of miR-21 in cultured human renal epithelial cells treated with the inducer cobalt chloride. In the absence of ischemic preconditioning, knockdown of miR-21 alone did not significantly affect ischemia-reperfusion injury in the mouse kidney. Thus, upregulation of miR-21 contributes to the protective effect of delayed ischemic preconditioning against subsequent renal ischemia-reperfusion injury.

Tubular markers are associated with decline in kidney function in proteinuric type 2 diabetic patients

Our aim was to investigate u-NGAL, u-KIM1 and p-FGF23 and prediction of decline in kidney function in type 2 diabetic patients with proteinuria.

METHODS

We performed a follow-up study, follow-up median (range) 3.5 (1-5) years. At baseline u-NGAL, u-KIM1 and p-FGF23 (ELISA) was measured and patients were followed yearly with estimated(e)-GFR (MDRD) and u-albumin.

RESULTS

We included 177 patients (44 women), mean age (SD) 59 (9) years. eGFR 90 (24) ml/min/1.73 m(2) at baseline, u-albumin: median (interquartile range) 104 (39-238) mg/24 h. Patients with levels of u-KIM1 in the highest quartile had a greater decline in eGFR than patients with the lowest quartile 6.0 (5.4) versus 3.2 (5.5) ml/min/1.73 m(2) per year (p=0.02). u-NGAL in the highest versus lowest quartile eGFR decline: 5.1 (4.7) and 2.8 (7.1)ml/min/1.73 m(2) per year (p=0.07). Higher values of u-NGAL and u-KIM1 were associated with enhanced decline in eGFR (R=0.16 and R=0.19, p<0.05), however not after adjustment for progression promoters. p-FGF23 was not predictive of decline in eGFR.

CONCLUSION

Higher levels of markers of tubular damage are associated with a faster decline in eGFR. However, since this is not independent of known progression promoters, measurement of tubular markers does not give additional prognostic information.

Urinary vanin-1 as a novel biomarker for early detection of drug-induced acute kidney injury

Drug-induced nephrotoxicity is a serious problem in patients with hospital-acquired acute kidney injury (AKI). A new renal biomarker is needed because traditional markers are not sensitive for early detection of drug-induced AKI. In a recent study, we demonstrated that vanin-1 is a novel candidate biomarker of nephrotoxicant-induced kidney injury. The objective of the present study is to determine whether the increase in urinary vanin-1 is detected before the elevations of serum creatinine or urinary N-acetyl-β-glucosaminidase (NAG), kidney injury molecule-1 (Kim-1), and neutrophil gelatinase-associated lipocalin (NGAL) in the two well established animal models of drug-induced AKI. After the administration of a higher dose of cisplatin (10 mg/kg, a single intraperitoneal dose) or gentamicin (120 mg/kg per day, once daily intraperitoneal dose for 9 days), urinary vanin-1 was detected earlier than the other biomarkers. In rats treated with a lower dose of cisplatin (5 mg/kg, a single intraperitoneal dose) or gentamicin (40 mg/kg per day, once daily intraperitoneal dose for 9 days), serum creatinine and urinary NAG were not changed throughout the study period, whereas urinary vanin-1, Kim-1, and NGAL were significantly increased. The renal vanin-1 protein levels were significantly decreased in rats treated with the higher dose of cisplatin on day 5 and gentamicin on day 9, and the immunofluorescence analyses confirmed that vanin-1 immunoreactivity in tubular cells was reduced with the time after the dose of cisplatin, indicating that urinary vanin-1 was leaked from tubular cells. These results suggest that, compared with urinary Kim-1 and NGAL, urinary vanin-1 is an earlier and equally sensitive biomarker for drug-induced AKI.