Tubular kidney injury molecule-1 (KIM-1) in human renal disease

Biomarkers for the early detection of acute kidney injury

PURPOSE OF REVIEW

Acute kidney injury (AKI) is a common and serious condition, the diagnosis of which depends on serum creatinine, which is a delayed and unreliable indicator of AKI. Fortunately, understanding the early stress response of the kidney to acute injuries has revealed a number of potential biomarkers. The current status of the most promising of these novel AKI biomarkers, including neutrophil gelatinase-associated lipocalin (NGAL), kidney injury molecule-1 (KIM-1), liver-type fatty acid binding protein (L-FABP), and interleukin (IL)-18, is reviewed.

RECENT FINDINGS

In particular, NGAL is emerging as an excellent biomarker in the urine and plasma, for the early prediction of AKI, for monitoring clinical trials in AKI, and for the prognosis of AKI in several common clinical scenarios. However, biomarker combinations may be required to improve our ability to predict AKI and its outcomes in a context-specific manner.

SUMMARY

It is vital that additional large future studies demonstrate the association between biomarkers and hard clinical outcomes independent of serum creatinine concentrations and that randomization to a treatment for AKI based on high biomarker levels results in an improvement in clinical outcomes.

Urinary kidney injury molecule-1 in patients with IgA nephropathy is closely associated with disease severity

BACKGROUND

The pathological characteristics of IgA nephropathy (IgAN) are highly variable. Urinary kidney injury molecule-1 (KIM-1) is a sensitive biomarker for proximal tubule injury. The aim of the study is to investigate the value of KIM-1 as a biomarker for assessing the renal injury in IgAN.

METHODS

The levels of urinary KIM-1 in 202 patients with IgAN, 46 patients with other renal diseases as disease controls and 60 healthy blood donors as normal controls were measured. Correlations with clinical and histopathological features of patients with IgAN were evaluated.

RESULTS

The levels of urinary KIM-1 were significantly higher in patients with IgAN than in normal controls (P < 0.001) and in patients with non-IgAN (P = 0.011). Urinary levels of KIM-1 in IgAN positively correlated with levels of serum creatinine and proteinuria and negatively with creatinine clearance. The more severe the tubulointerstitial injury was, the higher the levels of urinary KIM-1. Patients with severe mesangial proliferation, crescents formation or endocapillary proliferation had higher levels of urinary KIM-1 than those without. The levels of tubular KIM-1 expression in immunohistochemistry closely correlated with the levels of urinary KIM-1 (r = 0.553, P = 0.032). Renal survival was significantly worse in patients with elevated urinary KIM-1 (P = 0.020).

CONCLUSION

Urinary KIM-1 may be a useful biomarker to evaluate kidney injury in IgAN.

Review: Serum and urine biomarkers of kidney disease: A pathophysiological perspective

The use of reliable biomarkers is becoming increasingly important for the improved management of patients with acute and chronic kidney diseases. Recent developments have identified a number of novel biomarkers in serum or urine that can determine the potential risk of kidney damage, distinguish different types of renal injury, predict the progression of disease and have the potential to assess the efficacy of therapeutic intervention. Some of these biomarkers can be used independently while others are more beneficial when used in combination with knowledge of other clinical risk factors. Advances in gene expression analysis, chromatography, mass spectrometry and the development of sensitive enzyme-linked immunosorbent assays have facilitated accurate quantification of many biomarkers. This review primarily focuses on describing new and established biomarkers, which identify and measure the various pathophysiological processes that promote kidney disease. It provides an overview of some of the different classes of renal biomarkers that can be assessed in serum/plasma and urine, including markers of renal function, oxidative stress, structural and cellular injury, immune responses and fibrosis. However, it does not explore the current status of these biomarkers in terms of their clinical validation.

Tubular markers do not predict the decline in glomerular filtration rate in type 1 diabetic patients with overt nephropathy

Recent studies have shown that both glomerular and tubulointerstitial damage are important factors in the pathophysiology and progression of diabetic nephropathy. To examine whether markers of tubular damage are useful in monitoring the progression of disease, we measured urinary levels of neutrophil gelatinase-associated lipocalin (NGAL), liver-fatty acid-binding protein (LFABP), and kidney injury molecule-1 (KIM-1) in a 3-year intervention study of 63 type 1 diabetic patients with kidney disease. The baseline mean glomerular filtration rate (GFR) was 87 ml/min per 1.73 m(2) and urinary albumin excretion 1141 mg/24 h. Patients with the highest compared with the lowest quartile of urinary NGAL at baseline had higher urinary KIM-1 levels and a significant decrease in their GFR each year. Using linear regression analysis, we found that elevated urinary NGAL and KIM-1 concentrations were associated with a faster decline in GFR, but not after adjustment for known promoters of progression. Urinary LFABP was not related to decline in GFR. Losartan treatment (100 mg/day) reduced urinary KIM-1 by 43% over a 12-month period. Thus, urine biomarker measurements in patients with type 1 diabetic nephropathy did not provide additional prognostic information to that of known progression promoters.

Biomarkers of acute kidney injury in children: discovery, evaluation, and clinical application

Acute kidney injury (AKI) in children is associated with increased mortality and prolonged length of hospital stay and may also be associated with long-term chronic kidney disease development. Despite encouraging results on AKI treatment in animal studies, no specific treatment has yet been successful in humans. One of the important factors contributing to this problem is the lack of an early AKI diagnostic test. Serum creatinine, the current main diagnostic test for AKI, rises late in AKI pathophysiology and is an inaccurate marker of acute changes in glomerular filtration rate. Therefore, new biomarkers of AKI are needed. With great advancements in genomics, proteomics, and metabolomics, new AKI biomarkers, mainly consisting of urinary proteins that appear in response to renal tubular cell injury, have been, and continue to be, discovered. These new biomarkers offer promise for early AKI diagnosis and for the depiction of severity of renal injury occurring with AKI. This review provides a summary of what a biomarker is, why we need new biomarkers of AKI, and how biomarkers are discovered and should be evaluated. The review also provides a summary of selected AKI biomarkers that have been studied in children.

The use of targeted biomarkers for chronic kidney disease

There is a paucity of sensitive and specific biomarkers for the early prediction of CKD progression. The recent application of innovative technologies such as functional genomics, proteomics, and biofluid profiling has uncovered several new candidates that are emerging as predictive biomarkers of CKD. The most promising among these include urinary proteins such as neutrophil gelatinase-associated lipocalin, kidney injury molecule-1, and liver-type fatty acid binding protein. In addition, an improved understanding of the complex pathophysiologic processes underlying CKD progression has also provided discriminatory biomarkers of CKD progression that are being actively evaluated. Candidates included in this category are plasma proteins such as asymmetric dimethylarginine, adiponectin, apolipoprotein A-IV, fibroblast growth factor 23, neutrophil gelatinase-associated lipocalin, and the natriuretic peptides, as well as urinary N-acetyl-β-d-glucosaminidase. This review represents a critical appraisal of the current status of these emerging CKD biomarkers. Currently, none of these are ready for routine clinical use. Additional large, multicenter prospective studies are needed to validate the biomarkers, identify thresholds and cut-offs for prediction of CKD progression and adverse events, assess the effects of confounding variables, and establish the ideal assays.

Serum and Urinary Biomarkers Determination and Their Significance in Diagnosis of Kidney Diseases

Chronic kidney disease (CKD) is becoming a major public health problem worldwide due to the epidemic increase of patients on renal replacement therapy and their high cardiovascular morbidity and mortality. The only effective approach to this problem is prevention and early detection of CKD. In addition, despite significant improvements in therapeutics, the mortality and morbidity associated with acute kidney injury (AKI) remain high. A major reason for this is the lack of early markers for AKI, and hence an unacceptable delay in initiating therapy. Therefore, there is a pressing need to develop biomarkers (proteins and other molecules in the blood or urine) for renal disease, which might assist in diagnosis and prognosis and might provide endpoints for clinical trials of drugs designed to slow the progression of renal insufficiency. Besides serum creatinine, promising novel biomarkers for AKI include a plasma panel (neutrophil gelatinase-associated lipocalin-NGAL and cystatin C) and a urine panel (NGAL, kidney injury molecule-1, interleukin-18, cystatin C, alpha 1-microglobulin, Fetuin-A, Gro-alpha, and meprin). For CKD, these include a similar plasma panel and a urine panel (NGAL, asymmetric dimethylarginine, and liver-type fatty acid-binding protein). Increased plasma and urinary TGF-β1 levels might contribute to the development of chronic tubulointerstitial disease, indicating the possible therapeutic implications. Furthermore, to differentiate lower urinary tract infection and pyelonephritis interleukin-6 and serum procalcitonin levels were introduced. It will be important in future studies to validate the sensitivity and specificity of these biomarker panels in clinical samples from large cohorts and in multiple clinical situations.

Neutrophil Gelatinase-Associated Lipocalin (NGAL) and Kidney Injury Molecule 1 (KIM1) in patients with diabetic nephropathy: a cross-sectional study and the effects of lisinopril

AIMS

Our aim was to evaluate the markers of tubulointerstitial damage, neutrophil gelatinase-associated lipocalin (NGAL) and kidney injury molecule1 (KIM1) in Type 1 diabetic patients with different levels of albuminuria and in control subjects. In addition, the effect of renoprotective treatment on urinary NGAL was evaluated in diabetic nephropathy.

METHODS

This was a cross-sectional study in 58 normoalbuminuric (u-albumin <30 mg/24 h), 45 microalbuminuric (30-300 mg/24 h) and 45 macroalbuminuric (>300 mg/24 h) Type 1 diabetic patients and 55 non-diabetic control subjects. Furthermore, in a second study, urine-NGAL was measured in a randomized cross-over study of 56 Type 1 diabetic patients with diabetic nephropathy treated with lisinopril 20, 40 and 60 mg daily.

RESULTS

  Urine-NGAL levels were [geometric mean (95% CI)]: control subjects 74 (52-104) (pg/mmol creatinine), normoalbuminuric 146 (97-221), microalbuminuric 222 (158-312) and macroalbuminuric group 261 (175-390). Urine-NGAL increased significantly from the normo- to the micro- and further to the macroalbuminuric group (P<0.05). Urine-NGAL was higher in normoalbuminuric vs. control subjects (P<0.01). Plasma-NGAL was significantly higher in the normoalbuminuric and macroalbuminuric groups than in the control group. Urine-KIM1 was higher in all diabetic groups than in the control group (P<0.001), with no difference between diabetic groups. During lisinopril treatment, urine-NGAL was reduced (95% CI) 17% (11-50) (not significant).

CONCLUSIONS

Urine-NGAL and urine-KIM1 (u-KIM1) are elevated in Type1 diabetic patients, with or without albuminuria, indicating tubular damage at an early stage. Urine-NGAL increases significantly with increasing albuminuria. The ACE inhibitor lisinopril reduced urine-NGAL, but this was not statistically significant.

Tubular damage in chronic systolic heart failure is associated with reduced survival independent of glomerular filtration rate

BACKGROUND

The prognostic impact of reduced glomerular filtration rate (GFR) in chronic heart failure (CHF) is increasingly recognised, but little is known about tubular damage in these patients.

OBJECTIVE

To investigate the prevalence of tubular damage, and its association with GFR, and prognosis in patients with CHF.

METHODS AND RESULTS

In 90 patients with CHF, GFR and effective renal plasma flow (ERPF) were measured ([(125)I]iothalamate and [(131)I]hippuran clearances). The tubular markers neutrophil gelatinase-associated lipocalin (NGAL), N-acetyl-beta-D-glucosaminidase (NAG) and kidney injury molecule 1 (KIM-1) as well as urinary albumin excretion were determined in 24 h urine collections. Mean GFR was 78+/-26 ml/min/1.73 m(2). Urinary NGAL (175 (70-346) microg/g creatinine (gCr)), NAG (12 (6-17) U/gCr) and KIM-1 (277 (188-537) ng/gCr) levels were increased compared with 20 healthy controls (all p<0.001). Urinary NAG, but not NGAL or KIM-1 correlated with GFR (r=-0.34, p=0.001) and ERPF (r=-0.29, p=0.006). Both NAG (r=0.21, p=0.048) and KIM-1 (r=0.23, p=0.033) correlated with plasma N-terminal pro-brain natriuretic peptide levels. Both urinary KIM-1 (HR=1.15 (95% CI 1.02 to 1.30) per 100 ng/gCr increase, p=0.025) and NAG (HR=1.42 (95% CI 1.02 to 1.94) per 5 U/gCr increase, p=0.039), were associated with an increased risk of death or heart failure hospitalisations, independent of GFR.

CONCLUSION

Tubular damage, as indicated by increased urinary concentrations of NGAL, NAG and KIM-1 is common in patients with CHF and mildly reduced GFR. Both urinary KIM-1 and NAG showed prognostic information additional to GFR. These findings suggest an important role for tubular damage and tubular markers in cardiorenal interaction in heart failure.

Successes achieved and challenges ahead in translating biomarkers into clinical applications

Biomarkers are important tools for identifying and stratifying diseases, predicting their progression and determining the effectiveness, safety, and doses of therapeutic interventions. This is important for common chronic diseases such as diabetic nephropathy, osteoporosis, and rheumatoid arthritis which affect large numbers of patients worldwide. This article summarizes the current knowledge of established and novel biomarkers for each of these diseases as presented at the 2008 AAPS/ACCP joint symposium "Success Achieved and Challenges Ahead in Translating Biomarkers into Clinical Applications," in Atlanta, Georgia. The advantages and disadvantages of various proteomic, metabolomic, genomic, and imaging biomarkers are discussed in relation to disease diagnosis and stratification, prognosis, drug development, and potential clinical applications. The use of biomarkers as a means to determine therapeutic interventions is also considered. In addition, we show that biomarkers may be useful for adapting therapies for individual needs by allowing the selection of patients who are most likely to respond or react adversely to a particular treatment. They may also be used to determine whether the development of a novel therapy is worth pursuing by informing crucial go/no go decisions around safety and efficacy. Indeed, regulatory bodies now suggest that effective integration of biomarkers into clinical drug development programs is likely to promote the development of novel therapeutics and more personalized medicine.

Emerging risk factors and markers of chronic kidney disease progression

Chronic kidney disease (CKD) is a common condition with an increasing prevalence. A number of comorbidities are associated with CKD and prognosis is poor, with many patients experiencing disease progression. Recognizing the factors associated with CKD progression enables high-risk patients to be identified and given more intensive treatment if necessary. The identification of new predictive markers might improve our understanding of the pathogenesis and progression of CKD. This Review discusses a number of emerging factors and markers for which epidemiological evidence from prospective studies indicates an association with progression of CKD. The following factors and markers are discussed: asymmetric dimethylarginine, factors involved in calcium-phosphate metabolism, adrenomedullin, A-type natriuretic peptide, N-terminal pro-brain natriuretic peptide, liver-type fatty acid binding protein, kidney injury molecule 1, neutrophil gelatinase-associated lipocalin, apolipoprotein A-IV, adiponectin and some recently identified genetic polymorphisms. Additional epidemiological and experimental data are required before these markers can be broadly used for the prediction of CKD progression and before the risk factors can be considered as potential drug targets in clinical interventional trials.

Urinary L-FABP and anaemia: distinct roles of urinary markers in type 2 diabetes

BACKGROUND

Urinary liver-type fatty acid binding protein (L-FABP) and kidney injury molecule (KIM)-1, novel urinary biomarkers of renal tubulointerstitial function, have previously been associated with acute ischaemic kidney injury. We studied the clinical significance of urinary L-FABP, KIM-1 and N-acetyl-beta-glucosaminidase (NAG) as potential markers of renal function and chronic ischaemic injury in patients with diabetic nephropathy.

MATERIAL AND METHODS

A total of 130 type 2 diabetes patients with early diabetic nephropathy and 40 healthy controls were studied. Urinary L-FABP, KIM-1, NAG, albumin excretion rate (AER) and creatinine clearance were obtained from 24-h urine samples, and correlated with measures of red blood cell count, renal function and metabolic control.

RESULTS

Urinary L-FABP was significantly increased in diabetes patients compared with healthy controls [8.1 (interquartile 0.6-11.6) vs. 2.4 (0.5-3.6) microg/g creatinine, P < 0.001] and correlated with AER (r = 0.276, P = 0.002), creatinine clearance (r = -0.189, P = 0.033) and haemoglobin levels (r = -0.190, P = 0.030). In multivariable linear regression analysis, haemoglobin (beta = -0.247, P = 0.015) and AER (beta = 0.198, P = 0.046) were significant predictors of urinary L-FABP. Prevalent anaemia was independently associated with a 6-fold risk for increased tubulointerstitial kidney damage (upper vs. lower two L-FABP tertiles: OR, 6.06; 95% CI: 1.65-22.23; P = 0.007). Urinary KIM-1 was not significantly associated with kidney function, AER, or measures of red blood cell count while urinary NAG was associated with parameters of glucose control and renal function.

CONCLUSIONS

Different urinary biomarkers may reflect distinct pathophysiological mechanisms of tubulointerstitial damage in early diabetic nephropathy: Urinary L-FABP could be a novel biomarker for chronic intrarenal ischaemia.

Cell-specific biomarkers in renal medicine and research

Histopathology is the gold standard for defining renal injury, but it is invasive, time-consuming and expensive, plus it is seldom used in subjects with mild renal injury. Using biomarkers linked to distinct, defined cell types and tissues provides a direct link to histopathology without its drawbacks, plus it provides increased sensitivity, and specificity. The nephron consists of several sections, each with its own specific biomarkers; therefore, by the use of a battery of tests injuries can be localised to distinct areas of it. Using urine samples simplifies repeated sampling from the same subject or animal leading to better defined toxicokinetics and disease monitoring.Serum creatinine is the most widely used renal biomarker in spite of its known shortcomings. Cell-specific biomarkers are more specific and sensitive and have been known for over 40 years, but they are still underused in renal medicine and research. In particular, while many studies have shown cell-specific biomarkers to be valuable in diagnosis, there are few studies where they have been used to guide therapy or linked to quantitative changes in the kidney. Furthermore, the great majority of cell-specific biomarkers are from the proximal tubule, which may have hindered research into the study of conditions where the distal tubules are affected. Recently, the range of biomarkers and their applications has been expanded by the introduction of indicators of cellular regeneration.This chapter will discuss how using biomarkers with a known cellular origin, renal effects may be found earlier and at lower levels of injury. Their use in both renal medicine and drug research will be presented. Knowledge of these existing markers lays the foundation for evaluation, comparison, and characterisation of new markers that will be identified in the future.

Novel biomarkers of acute kidney toxicity

Novel biomarkers of kidney toxicity are powerful tools not only with respect to their clinical applications but also because of their impact on drug development. These biomarkers can influence the assessment of efficacy of new drugs for kidney diseases as well as the risk management for new drugs. The science behind these novel biomarkers reflects the evolution over the past decade of genomic and proteomic platforms that have transformed the discovery and development of new biomarkers for preclinical and clinical applications in drug development. Several of these biomarkers are in use as transcriptomic biomarkers in animal models as well as translational proteomic biomarkers in animal models and in humans. Their ability to detect kidney damage earlier than is possible with currently accessible biomarkers is being given qualification through regulatory biomarker-qualification programs, which will help establish consensus for their widespread use.

Kidney injury molecule-1 is an early noninvasive indicator for donor brain death-induced injury prior to kidney transplantation

With more marginal deceased donors affecting graft viability, there is a need for specific parameters to assess kidney graft quality at the time of organ procurement in the deceased donor. Recently, kidney injury molecule-1 (Kim-1) was described as an early biomarker of renal proximal tubular damage. We assessed Kim-1 in a small animal brain death model as an early and noninvasive marker for donor-derived injury related to brain death and its sequelae, with subsequent confirmation in human donors. In rat kidney, real-time PCR revealed a 46-fold Kim-1 gene upregulation after 4 h of brain death. In situ hybridization showed proximal tubular Kim-1 localization, which was confirmed by immunohistochemistry. Also, Luminex assay showed a 6.6-fold Kim-1 rise in urine after 4 h of brain death. In human donors, 2.5-fold kidney injury molecule-1 (KIM-1) gene upregulation and 2-fold higher urine levels were found in donation after brain death (DBD) donors compared to living kidney donors. Multiple regression analysis showed that urinary KIM-1 at brain death diagnosis was a positive predictor of recipient serum creatinine, 14 days (p < 0.001) and 1 year (p < 0.05) after kidney transplantation. In conclusion, we think that Kim-1 is a promising novel marker for the early, organ specific and noninvasive detection of brain death-induced donor kidney damage.

Pentobarbital reduces rhabdomyolysis-induced acute renal failure in conscious rats

BACKGROUND

Rhabdomyolysis is one of the causes of acute renal failure. Pentobarbital enhances the action of gamma-aminobutyric acid and suppresses the activities of nuclear factor (NF)-kappaB pathways. In this study, we used pentobarbital to study the effects on the glycerol-induced rhabdomyolysis with acute renal failure in conscious rats.

METHODS

Rhabdomyolysis was induced by intramuscular injection of 10 mL/kg of 50% glycerol in conscious rats. Ten minutes later, the rats received an intravenous injection of pentobarbital (10 mg/kg in 0.5 mL/h normal saline) or normal saline (0.5 mL/h). Biochemical substances, including blood urea nitrogen (BUN), creatinine (Cre), glutamic oxaloacetic transaminase (GOT), glutamic pyruvic transaminase (GPT), and creatine phosphokinase (CPK) were measured at 0 hour, 1 hour, 3 hours, 6 hours, 12 hours, 24 hours, and 48 hours. Rats were killed by decapitation at 48 hours after glycerol administration, and the kidneys were removed immediately for pathological findings and immunohistochemistry.

RESULTS

Intramuscular injection of glycerol significantly increased blood BUN, Cre, GOT, GPT, CPK levels and induced severe histopathologic damage in the kidneys. NF-kappaB and inducible nitric oxide synthase (iNOS) were increased, and E-cadherin was decreased after glycerol administration, as detected by immunohistochemistry in the kidneys. Posttreatment with pentobarbital decreased blood BUN, Cre, GOT, GPT, CPK levels, decreased the markers of kidney injury, and suppressed the release of NF-kappaB and iNOS after rhabdomyolysis.

CONCLUSION

Posttreatment with pentobarbital suppressed the activities of NF-kappaB and iNOS, decreased BUN, Cre, GOT, GPT, CPK levels, and decreased the markers of kidney injury after rhabdomyolysis. These actions ameliorated rhabdomyolysis-induced acute renal failure in conscious rats.

Therapeutic and predictive targets of AKI

Acute kidney injury (AKI) is a very common condition encountered in a hospital setting. AKI is an independent risk factor for in-hospital mortality. In this review, we discuss in detail about the tubular, inflammatory and vascular molecular targets of AKI which may result in therapies to improve mortality and biomarkers for earlier diagnosis of AKI.

Reduction of proteinuria in adriamycin-induced nephropathy is associated with reduction of renal kidney injury molecule (Kim-1) over time

Tubulointerstitial lesions are important in the progression of proteinuric renal disease. Tubular kidney injury molecule-1 (Kim-1) is induced in acute renal injury and reversible as a natural course. Kim-1 is also present in chronic renal damage; however, the dynamics of Kim-1 in chronic renal damage and effects of antiproteinuric treatment on Kim-1 are unknown. We studied Kim-1 in adriamycin nephrosis (AN) before and after renin-angiotensin system blockade. A renal biopsy was taken 6 wk after adriamycin injection to study renal damage and Kim-1 expression. Subsequently, ACE inhibition (ACEi; n = 23), angiotensin II antagonist (AT(1A); n = 23), or vehicle (n = 10) was given for 6 wk; healthy rats served as controls (CON; n = 8). In AN, renal Kim-1 mRNA was induced 26-fold vs. CON at week 6, with further increase in vehicle to week 12 (40-fold) but was reduced by ACEi and AT(1A) to 10- and 12-fold vs. CON (P < 0.05 vs. week 6). Kim-1 protein was undetectable in CON; in AN, it was present in brush border of dilated tubules in areas with adjacent interstitial lesions. Renal Kim-1 protein levels increased from weeks 6-12 in vehicle and decreased in ACEi- and AT(1A)-treated groups (P < 0.05). In vehicle, urinary Kim-1 was increased (P < 0.05 vs. CON), with a reduction by ACEi and AT(1A) (P < 0.05 vs. vehicle). Renal and urinary Kim-1 correlated with proteinuria and interstitial damage cross-sectionally. Reductions in proteinuria and renal Kim-1 correlated, which was not associated by corresponding changes in tubulointerstitial fibrosis. In conclusion, on longitudinal follow-up during antiproteinuric treatment increased renal Kim-1 expression is reversible in proportion to proteinuria reduction, likely reflecting reversibility of early tubular injury, supporting its potential as a biomarker for tubulointerstitial processes of damage and repair.

The future of pediatric acute kidney injury management--biomarkers

Acute kidney injury (AKI) represents a common and devastating problem in clinical medicine. A major reason is the lack of early biomarkers for AKI, and hence an unacceptable delay in initiating therapy. Fortunately, the application of innovative technologies has uncovered several novel biomarkers. The most promising of these are included in a putative AKI biomarker panel, consisting of neutrophil gelatinase-associated lipocalin, interleukin-18, and kidney injury molecule-1. These biomarkers have completed initial validation, and have entered the prospective screening stage in the biomarker development process, facilitated by the development of commercial tools for their reproducible measurement across laboratories. The availability of a panel of validated biomarkers will revolutionize renal and critical care, and enable the practice of personalized and predictive medicine at an unprecedented level.

Dog as model for down-expression of E-cadherin and beta-catenin in tubular epithelial cells in renal fibrosis

Mechanism of renal fibrosis leading to end stage kidney remains still a challenge of interest in humans. The pathogenesis of chronic kidney disease is characterized by progressive loss of kidney function and fibrosis. The mechanism of epithelial-mesenchymal transition (EMT) has been predominantly studied in in vitro studies, and we previously demonstrated the EMT of tubular epithelial cells in dogs. In this study, we examined and quantified the modifications of cadherin-catenin complex by immunohistochemistry of E-cadherin and beta-catenin and the mesenchymal marker vimentin in 25 dogs with three different spontaneous inflammatory renal diseases. Results showed a significant down-expression of levels of E-cadherin and beta-catenin directly correlated with the tubular-interstitial damage (TID). In TID grades 2 and 3, E-cadherin expression was significantly reduced (p < 0.001). beta-catenin expression was overall similar to E-cadherin. The mesenchymal-associated protein, vimentin, was de novo identified in tubules within areas of inflammation. In this work, we identified the loss of cadherin or catenin expression as a progressive mechanism in tubulo-interstitial fibrosis, which allows dissociation of structural integrity of renal epithelia and loss of epithelial polarity. The dog might result more significant as model for new therapies.

Effect of renin-angiotensin-aldosterone system inhibition, dietary sodium restriction, and/or diuretics on urinary kidney injury molecule 1 excretion in nondiabetic proteinuric kidney disease: a post hoc analysis of a randomized controlled trial

BACKGROUND

Tubulointerstitial damage plays an important role in chronic kidney disease (CKD) with proteinuria. Urinary kidney injury molecule 1 (KIM-1) reflects tubular KIM-1 and is considered a sensitive biomarker for early tubular damage. We hypothesized that a decrease in proteinuria by using therapeutic interventions is associated with decreased urinary KIM-1 levels.

STUDY DESIGN

Post hoc analysis of a randomized, double-blind, placebo-controlled, crossover trial.

SETTING & PARTICIPANTS

34 proteinuric patients without diabetes from our outpatient renal clinic.

INTERVENTION

Stepwise 6-week interventions of losartan, sodium restriction (low-sodium [LS] diet), their combination, losartan plus hydrochlorothiazide (HCT), and the latter plus an LS diet.

OUTCOMES & MEASUREMENTS

Urinary excretion of KIM-1, total protein, and N-acetyl-beta-d-glucosaminidase (NAG) as a positive control for tubular injury.

RESULTS

Mean baseline urine protein level was 3.8 +/- 0.4 (SE) g/d, and KIM-1 level was 1,706 +/- 498 ng/d (increased compared with healthy controls; 74 ng/d). KIM-1 level was decreased by using placebo/LS (1,201 +/- 388 ng/d; P = 0.04), losartan/high sodium (1,184 +/- 296 ng/d; P = 0.09), losartan/LS (921 +/- 176 ng/d; P = 0.008), losartan/high sodium plus HCT (862 +/- 151 ng/d; P = 0.008) and losartan/LS plus HCT (743 +/- 170 ng/d; P = 0.001). The decrease in urinary KIM-1 levels paralleled the decrease in proteinuria (R = 0.523; P < 0.001), but not blood pressure or creatinine clearance. 16 patients reached target proteinuria with protein less than 1 g/d, whereas KIM-1 levels normalized in only 2 patients. Urinary NAG level was increased at baseline and significantly decreased during the treatment periods of combined losartan plus HCT only. The decrease in urinary NAG levels was not closely related to proteinuria.

LIMITATIONS

Post hoc analysis.

CONCLUSIONS

Urinary KIM-1 level was increased in patients with nondiabetic CKD with proteinuria and decreased in parallel with proteinuria by using losartan, sodium restriction, their combination, losartan plus HCT, and the latter plus sodium restriction. These results are consistent with the hypothesis of amelioration of proteinuria-induced tubular damage. Long-term studies are warranted to evaluate whether targeting treatment on KIM-1 can improve outcomes in patients with CKD with proteinuria.

Biomarkers for the diagnosis of acute kidney injury

The identification of acute kidney injury relies on tests like blood urea nitrogen and serum creatinine that were identified and incorporated into clinical practice several decades ago. This review summarizes clinical studies of newer biomarkers that may permit earlier and more accurate identification of acute kidney injury. The urine may contain sensitive and specific markers of kidney injury that are present due to either impaired tubular reabsorption and catabolism of filtered molecules or release of tubular cell proteins in response to ischemic or nephrotoxic injury. Many potential markers have been studied. Promising injury markers in the urine include N-acetyl-beta-D-glucosaminidase, neutrophil gelatinase-associated lipocalin, kidney injury molecule-1, and interleukin-18. New biomarkers of kidney injury hold the promise of substantially improving the diagnostic approach to acute kidney injury. Adequately powered clinical studies of multiple biomarkers are needed to qualify the biomarkers before they can be fully adopted in clinical practice. Once adopted, more sensitive biomarkers of acute kidney injury hold the potential to transform the care of patients with renal disease.

Progression from acute kidney injury to chronic kidney disease: a pediatric perspective

Although emerging evidence indicates that the incidence of both acute kidney injury (AKI) and chronic kidney disease (CKD) in children is rising and the etiologies are dramatically changing, relatively little is currently known regarding the potential for transition from AKI to CKD. In both situations, early intervention can significantly improve the dismal prognosis. However, the lack of a uniform AKI definition and the paucity of early, predictive biomarkers have impaired our ability diagnose AKI early to institute potentially effective therapies in a timely manner. Fortunately, recent data has validated a multidimensional AKI classification system for children. In addition, the application of innovative technologies has identified candidates that are emerging as early biomarkers of both AKI and CKD. These include neutrophil gelatinase-associated lipocalin, liver-type fatty acid-binding protein, and kidney injury molecule-1. Studies to validate the sensitivity and specificity of these biomarkers in clinical samples from large cohorts and from multiple clinical situations are currently in progress, facilitated by the development of commercial tools for the reproducible measurement of these biomarkers across different laboratories.

Biomarkers of acute kidney injury

The diagnosis of acute kidney injury (AKI) is usually based on measurements of blood urea nitrogen (BUN) and serum creatinine. BUN and serum creatinine are not very sensitive or specific for the diagnosis of AKI because they are affected by many renal and nonrenal factors that are independent of kidney injury or kidney function. Biomarkers of AKI that are made predominantly by the injured kidney have been discovered in preclinical studies. In clinical studies of patients with AKI, some of these biomarkers (eg, interleukin-18, neutrophil gelatinase-associated lipocalin, and kidney injury molecule-1) have been shown to increase in the urine before the increase in serum creatinine. These early biomarkers of AKI are being tested in different types of AKI and in larger clinical studies. Biomarkers of AKI may also predict long-term kidney outcomes and mortality.

Immunolocalization of Kim-1, RPA-1, and RPA-2 in kidney of gentamicin-, mercury-, or chromium-treated rats: relationship to renal distributions of iNOS and nitrotyrosine

Immunohistochemical studies for kidney injury molecule-1 (Kim-1), renal papillary antigen-1 (RPA-1), and renal papillary antigen-2 (RPA-2) were conducted to explore their relationship to inducible nitric oxide synthase (iNOS) and nitrotyrosine expression. Male Sprague-Dawley rats were exposed to gentamicin (100 mg/kg/day Gen, sc, for 3 days), mercury (0.25 mg Hg/kg, iv, single dose), or chromium (5 mg Cr/kg, sc, single dose) and kidney tissue was examined 24 hours or 72 hours after the last dose of the nephrotoxicant. Another group of kidneys was evaluated 24 hours after rats were administered 3 daily doses (50, 100, 150, 200, or 300 mg/kg/day) of Gen. Gen- and Cr-treated rats exhibited increased immunoreactivity of Kim-1, RPA-1, and RPA-2 largely in the S1/S2 segments and to a lesser extent in the S3 segments of the proximal tubule of the kidney, whereas Hg-treated rats showed increased immunoreactivity of Kim-1, RPA-1, and RPA-2 in the S3 segments. Up-regulation of Kim-1, RPA-1, and RPA-2 expression correlated with injured tubular epithelial cells and also correlated with immunoreactivity of iNOS and nitrotyrosine. It is possible that iNOS activation with nitrotyrosine production in injured nephron segments may be involved in the induction of Kim-1, RPA-1, and RPA-2 following exposure to nephrotoxicants.

Emerging urinary biomarkers in the diagnosis of acute kidney injury

BACKGROUND: Acute kidney injury (AKI) represents a common and devastating problem in clinical medicine. The lack of early biomarkers for AKI has led to a delay in initiating potentially effective therapies. OBJECTIVE: Identification of novel urinary biomarkers for AKI that have progressed to the clinical phase of the biomarker discovery process. METHODS: A literature review (PubMed, MedLine) from 2000 to the present. RESULTS/CONCLUSIONS;: The most promising AKI biomarkers include neutrophil gelatinase-associated lipocalin, IL-18, kidney injury molecule-1 and liver-type fatty acid binding protein. Studies to validate the sensitivity and specificity of these biomarkers in clinical samples from large cohorts and from multiple clinical situations are in progress, facilitated by the development of commercial tools for their measurement.

Biomarkers of acute kidney injury

Acute kidney injury (AKI) is a common condition with a high risk of death. The standard metrics used to define and monitor the progression of AKI, such as serum creatinine and blood urea nitrogen levels, are insensitive, nonspecific, and change significantly only after significant kidney injury and then with a substantial time delay. This delay in diagnosis not only prevents timely patient management decisions, including administration of putative therapeutic agents, but also significantly affects the preclinical evaluation of toxicity thereby allowing potentially nephrotoxic drug candidates to pass the preclinical safety criteria only to be found to be clinically nephrotoxic with great human costs. Studies to establish effective therapies for AKI will be greatly facilitated by two factors: (a) development of sensitive, specific, and reliable biomarkers for early diagnosis/prognosis of AKI in preclinical and clinical studies, and (b) development and validation of high-throughput innovative technologies that allow rapid multiplexed detection of multiple markers at the bedside.

KIM-1 expression in kidney allograft biopsies: Improving the gold standard

Long-term outcomes of kidney allografts have shown only marginal improvement over the last three decades, despite the remarkable improvement in acute rejection and one-year graft survival. Novel biomarkers of tubular injury may prevent irreversible damage to the tubulointerstitial compartment and improve allograft survival.

Diagnosis, epidemiology and outcomes of acute kidney injury

Acute kidney injury is an increasingly common and potentially catastrophic complication in hospitalized patients. Early observational studies from the 1980s and 1990s established the general epidemiologic features of acute kidney injury: the incidence, prognostic significance, and predisposing medical and surgical conditions. Recent multicenter observational cohorts and administrative databases have enhanced our understanding of the overall disease burden of acute kidney injury and trends in its epidemiology. An increasing number of clinical studies focusing on specific types of acute kidney injury (e.g., in the setting of intravenous contrast, sepsis, and major surgery) have provided further details into this heterogeneous syndrome. Despite our sophisticated understanding of the epidemiology and pathobiology of acute kidney injury, current prevention strategies are inadequate and current treatment options outside of renal replacement therapy are nonexistent. This failure to innovate may be due in part to a diagnostic approach that has stagnated for decades and continues to rely on markers of glomerular filtration (blood urea nitrogen and creatinine) that are neither sensitive nor specific. There has been increasing interest in the identification and validation of novel biomarkers of acute kidney injury that may permit earlier and more accurate diagnosis. This review summarizes the major epidemiologic studies of acute kidney injury and efforts to modernize the approach to its diagnosis.

High urinary excretion of kidney injury molecule-1 is an independent predictor of graft loss in renal transplant recipients

BACKGROUND

Chronic transplant dysfunction is characterized by renal function decline and proteinuria. Kidney injury molecule (KIM)-1, a transmembrane tubular protein with unknown function, is undetectable in normal kidneys, but markedly induced after injury. Urinary KIM-1 excretion has been quantified as biomarker of renal damage. We prospectively studied whether urinary KIM-1 predicts graft loss, independent of renal function and proteinuria.

METHODS

Renal transplant recipients (n=145) visiting our outpatient clinic between August 2001 and July 2003 collected 24-hour urine samples for assessment of baseline urinary KIM-1 excretion (microsphere-based Luminex technology), and were followed for graft loss.

RESULTS

Recipients participated at a median (interquartile range) of 6.0 (2.5-12.0) years posttransplant in baseline measurements. Follow-up beyond baseline was 4.0 (3.2-4.5) years. Urinary KIM-1 excretion was 0.72 (0.42-1.37) ng per 24 hours. Occurrence of graft loss increased over tertiles of KIM-1 excretion: 3 (6.3%), 11 (22.4%), and 17 cases (35.4%; P=0.001), respectively. High KIM-1 excretion was associated with proteinuria, low creatinine clearance, and high donor age (all P<0.01). In multivariate Cox regression analyses, prediction of graft loss by KIM-1 appeared independent of creatinine clearance, proteinuria, and donor age. Hazard ratios (95% CI) for the second and third tertile of KIM-1 excretion were 3.6 (0.9-13.5) and 5.1 (1.5-17.8) in the final model.

CONCLUSIONS

Urinary excretion of KIM-1 is an independent predictor of long-term graft loss and therefore a promising new biomarker in early prediction of graft loss.

Evaluation of putative biomarkers of nephrotoxicity after exposure to ochratoxin a in vivo and in vitro

The kidney is one of the main targets of xenobiotic-induced toxicity, but early detection of renal damage is difficult. Recently, several novel biomarkers of nephrotoxicity have been identified by transcription profiling, including kidney injury molecule-1 (Kim-1), lipocalin-2, tissue inhibitor of metalloproteinases-1 (Timp-1), clusterin, osteopontin (OPN), and vimentin, and suggested as sensitive endpoints for acute kidney injury in vivo. However, it is not known if these cellular marker molecules may also be useful to predict chronic nephrotoxicity or to detect nephrotoxic effects in vitro. In this study, a panel of new biomarkers of renal toxicity was assessed via quantitative real-time PCR, immunohistochemistry, and immunoblotting in rats treated with the nephrotoxin ochratoxin A (OTA) for up to 90 days and in rat proximal tubule cells (NRK-52E) treated with OTA in vitro. Repeated administration of OTA to male F344/N rats for 14, 28, or 90 days resulted in a dose- and time-dependent increase in the expression of Kim-1, Timp-1, lipocalin-2, OPN, clusterin, and vimentin. Changes in gene expression were found to correlate with the progressive histopathological alterations and preceded effects on traditional clinical parameters indicative of impaired kidney function. Induction of Kim-1 messenger RNA expression was the earliest and most prominent response observed, supporting the use of this marker as sensitive indicator of chronic kidney injury. In contrast, no significant increase in the expression of putative marker genes and proteins were evident in NRK-52E cells after exposure to OTA for up to 48 h, suggesting that they may not be suitable endpoints for sensitive detection of nephrotoxic effects in vitro.