Osteopontin expression in acute renal allograft rejection

The development of lateral flow devices for urinary biomarkers to assess kidney health

Serum creatinine levels are insensitive to real-time changes in kidney function or injury. There is a growing interest in assessing kidney injury by measuring biomarkers in body fluid. From our previous studies, we identified and reported three urinary biomarkers namely Uromodulin (UMOD), Osteopontin (OPN), and Interleukin-9 (IL-9) to be associated with kidney health. The availability of a rapid point-of-care test for these urinary biomarkers will potentially accelerate its applicability and accessibility. In this study, we aimed to develop novel lateral flow device (LFD) for UMOD, OPN and IL-9. We tested paired antibodies using Enzyme Linked Immunosorbent Assay wherein we observed functionality only for UMOD and OPN and not for IL-9. A conjugation buffer pH of 7.8 and 8.5 was found suitable at a detection antibody concentration of 15 µg/mL for LFD development. The developed LFDs were found to quantitatively measure UMOD standard (LLOD of 80,000 pg/mL) and OPN standard (LLOD of 8600 pg/mL) respectively. The LFD was also able to measure human urinary UMOD and OPN with a percent CV of 12.12 and 5.23 respectively.

Drug induced nephrotoxicity- A mechanistic approach

The main goal of the treatment of patients is its effectiveness and safety. However, all currently prescribed drugs being used also have certain adverse effects, which might be seen as an unavoidable but necessary cost of pharmacotherapy. The kidney is the primary organ for xenobiotics elimination, making it particularly susceptible to the harmful effects of drugs and their metabolites during their excretion from the body. Moreover, certain medications have a preferential nephrotoxicity potential, which means that using them increases the risk of kidney injury. Drug nephrotoxicity is, therefore, both a significant problem and a complication of pharmacotherapy. It should be noted that, there is presently no accepted definition of drug-induced nephrotoxicity and no established diagnostic criteria. The current review briefly describes the pathogenic mechanism of drug-induced nephrotoxicity, the various basic drugs with nephrotoxicity potential and the renal biomarkers for the treatment of the drug-related kidney damage.

Monitoring of Serological, Cellular and Genomic Biomarkers in Transplantation, Computational Prediction Models and Role of Cell-Free DNA in Transplant Outcome

The process and evolution of an organ transplant procedure has evolved in terms of the prevention of immunological rejection with the improvement in the determination of immune response genes. These techniques include considering more important genes, more polymorphism detection, more refinement of the response motifs, as well as the analysis of epitopes and eplets, its capacity to fix complement, the PIRCHE algorithm and post-transplant monitoring with promising new biomarkers that surpass the classic serum markers such as creatine and other similar parameters of renal function. Among these new biomarkers, we analyze new serological, urine, cellular, genomic and transcriptomic biomarkers and computational prediction, with particular attention to the analysis of donor free circulating DNA as an optimal marker of kidney damage.

Role of Biomarkers in Detecting Acute Rejection in Kidney Transplantation

Medicine has evolved from the so-called experience-based medicine to evidence-based medicine, which is now evolving into precision-based medicine [...]

The Most Promising Biomarkers of Allogeneic Kidney Transplant Rejection

Clinical transplantology is a constantly evolving field of medicine. Kidney transplantation has become standard clinical practice, and it has a significant impact on reducing mortality and improving the quality of life of patients. Allogenic transplantation induces an immune response, which may lead to the rejection of the transplanted organ. The gold standard for evaluating rejection of the transplanted kidney by the recipient's organism is a biopsy of this organ. However, due to the high invasiveness of this procedure, alternative diagnostic methods are being sought. Therefore, the biomarkers may play an essential predictive role in transplant rejection. A review of the most promising biomarkers for early diagnosis and prognosis prediction of allogenic kidney transplant rejection summarizes novel data on neutrophil gelatinase-associated lipocalin (NGAL), kidney injury molecule-1 (KIM-1), C-X-C motif chemokine 10 (CXCL-10), cystatin C (CysC), osteopontin (OPN), and clusterin (CLU) and analyses the dynamics of changes of the biomarkers mentioned above in kidney diseases and the mechanism of rejection of the transplanted kidney.

Association of osteopontin with kidney function and kidney failure in chronic kidney disease patients: the GCKD study

BACKGROUND

Osteopontin (OPN), synthesized in the thick ascending limb of Henle's loop and in the distal tubule, is involved in the pathogenesis of kidney fibrosis, a hallmark of kidney failure (KF). In a cohort of chronic kidney disease (CKD) patients, we evaluated OPN's association with kidney markers and KF.

METHODS

OPN was measured from baseline serum samples of German Chronic Kidney Disease study participants. Cross-sectional regression models for estimated glomerular filtration rate (eGFR) and urinary albumin-to-creatinine ratio (UACR) as well as Cox regression models for all-cause mortality and KF were evaluated to estimate the OPN effect. Additionally, predictive ability, of OPN and time-dependent population-attributable fraction were evaluated.

RESULTS

Over a median follow-up of 6.5 years, 471 KF events and 629 deaths occurred among 4,950 CKD patients. One-unit higher log(OPN) was associated with 5.5 mL/min/1.73m2 lower eGFR (95%CI: [-6.4,-4.6]) and 1% change in OPN with 0.7% higher UACR (estimated effect 0.7, 95%CI: [0.6,0.8]). Moreover, higher OPN levels were associated with a higher risk of KF (hazard ratio [HR] 1.4, 95%CI: [1.2,1.7]) and all-cause mortality (HR 1.5, 95%CI: [1.3,1.8]). After 6 years, 31% of the KF events could be attributed to higher OPN levels (95%CI: [3%,56%]).

CONCLUSIONS

In this study, higher OPN levels were associated with kidney function markers worsening, and a higher risk for adverse outcomes. A larger proportion of KF could be attributed to higher OPN levels warranting further research on OPN with regards to its role in CKD progression and possible treatment options.

Osteopontin and Transplantation: Where Are We Now?

Organ transplantation represents the optimal therapeutic tool for patients with end-stage organ failure. Hematopoietic stem cell transplantation (HSCT) is likewise an effective therapy for a wide range of malignant and non-malignant diseases. Better understanding of transplantation immunology and the use of multi-modal immunosuppression protocols, can decrease the risk of graft failure and graft-versus-host disease (GVHD) after HSCT. Nevertheless, a major challenge of modern transplantology still seems to be finding non-invasive biomarkers for recipients selection, monitoring of allograft function, and diagnosis of rejection. Since proinflammatory cytokine osteopontin (OPN) is closely involved in regulating both adaptive and innate immune responses, as well as the pathogenesis of inflammatory and autoimmune diseases, it is likely to play an important role in organ and HSC transplantation. This review is to summarize recent advances in our knowledge about OPN function in the kidney, heart, liver, lung, and HSC transplantation. Most studies found that elevated OPN is associated with poorer graft function in kidney, heart, liver and lung recipients. Moreover, some reports suggested that this protein can play role in GVHD pathogenesis. However, due to relatively small number of similar studies, as well as some inconclusive results, future investigation in this field is needed to verify if OPN can serve as a biomarker of organ and HSC transplantation. The knowledge about such markers will promote our understanding of the mechanisms underlying graft dysfunction and posttransplant mortality. In addition, such knowledge may be helpful in the development of new treatment strategies and identification of recipients with increased risk of allograft failure.

Prediction of acute renal allograft rejection by combined HLA-G 14-bp insertion/deletion genotype analysis and detection of kidney injury molecule-1 and osteopontin in the peripheral blood

INTRODUCTION

Acute renal rejection usually fails to be diagnosed before the increase in the serum creatinine levels, and the resultant damage to the renal tissues occur in varying degrees. We hypothesized that the combined detection of human leucocyte antigen-G (HLA-G) 14-bp insertion/deletion genotypes and kidney injury molecule-1 (KIM-1) and osteopontin (OPN) levels in serum might facilitate the prediction of acute renal allograft rejections in kidney transplant recipients.

METHODS

HLA-G 14-bp insertion/deletion genotypes and the serum KIM-1 and OPN levels of 77 kidney transplant recipients were determined and compared before operation and on days 1, 4, and 7 after the operation (32 in acute rejection [AR] group and 45 in stable allograft function [STA] group). These 3 indicators were combined to establish a model for the early prediction of AR.

RESULTS

The KIM-1 levels in the serum of patients were significantly higher in the AR group than in the STA group. The area under the receiver operator characteristics (ROC) curve (AUC) of KIM-1 for the prediction of rejection was maximized on the1st day after operation, with a sensitivity of 84.4% and a specificity of 86.7%. The OPN levels in the serum of patients were significantly higher in the AR group than in the STA group only before operation and on the 7th day after operation. The AUC of OPN for the prediction of rejection was maximized on 7th day after operation, with a sensitivity of 68.8% and a specificity of 88.9%. The HLA-G + 14-bp allele frequency was also significantly higher in the AR group than in the STA group. The results of these three indicators were converted into a qualitative method. If any two of the three indicators show as positive, it was diagnosed as acute rejection, and it has the highest ability to predict acute rejection with a sensitivity and specificity of 84.38% and 91.11%, respectively.

CONCLUSIONS

The HLA-G 14-bp insertion/deletion genotype and KIM-1 and OPN levels in the patients' serum were significantly different between the AR and STA groups. The power of predicting acute renal allograft rejection could be improved by combined these three biomarkers.

The role of osteopontin in kidney diseases

BACKGROUND

Osteopontin (OPN) is a pleiotropic glycoprotein expressed in various cell types in animals and in humans, including bone, immune, smooth muscle, epithelial and endothelial cells. Moreover, OPN is found in kidneys (in the thick ascending limbs of the loop of Henle and in distal nephrons) and urine. The protein plays an important role in mineralization and bone resorption. In addition, OPN is involved in the regulation of immunity and inflammation, angiogenesis and apoptosis. It was demonstrated that OPN and some OPN gene polymorphic variants are associated with the pathogenesis and progression of multiple disorders, such as cancer, autoimmune, neurodegenerative and cardiovascular diseases. Moreover, recent studies suggested that OPN is associated with the pathogenesis of renal failure.

METHODS

In this review, I briefly discussed the role of OPN and its gene polymorphisms in kidney physiology, as well as in various kidney diseases.

FINDINGS AND CONCLUSION

Most studies reported that OPN expression is elevated in urolithiasis, and also in acute and chronic kidney diseases, and in renal allograft dysfunction. Moreover, it was demonstrated that polymorphic variants of the OPN gene may be associated with renal failure. However, some reports suggested that OPN is essential for tubulogenesis, and that it inhibits calcium oxalate crystal formation and retention, nitric oxide synthesis, cell apoptosis and promotes cell regeneration. Thus, further studies are required to fully understand the role of OPN in kidney physiology and pathology. Eventually, these studies may result in the identification of OPN as a valuable marker for renal dysfunction prognosis and treatment.

Pyruvate Kinase M2: A Novel Biomarker for the Early Detection of Acute Kidney Injury

The identification of biomarkers for the early detection of acute kidney injury (AKI) is clinically important. Acute kidney injury (AKI) in critically ill patients is closely associated with increased morbidity and mortality. Conventional biomarkers, such as serum creatinine (SCr) and blood urea nitrogen (BUN), are frequently used to diagnose AKI. However, these biomarkers increase only after significant structural damage has occurred. Recent efforts have focused on identification and validation of new noninvasive biomarkers for the early detection of AKI, prior to extensive structural damage. Furthermore, AKI biomarkers can provide valuable insight into the molecular mechanisms of this complex and heterogeneous disease. Our previous study suggested that pyruvate kinase M2 (PKM2), which is excreted in the urine, is a sensitive biomarker for nephrotoxicity. To appropriately and optimally utilize PKM2 as a biomarker for AKI requires its complete characterization. This review highlights the major studies that have addressed the diagnostic and prognostic predictive power of biomarkers for AKI and assesses the potential usage of PKM2 as an early biomarker for AKI. We summarize the current state of knowledge regarding the role of biomarkers and the molecular and cellular mechanisms of AKI. This review will elucidate the biological basis of specific biomarkers that will contribute to improving the early detection and diagnosis of AKI.

Drug-induced nephrotoxicity and its biomarkers

Nephrotoxicity occurs when kidney-specific detoxification and excretion do not work properly due to the damage or destruction of kidney function by exogenous or endogenous toxicants. Exposure to drugs often results in toxicity in kidney which represents the major control system maintaining homeostasis of body and thus is especially susceptible to xenobiotics. Understanding the toxic mechanisms for nephrotoxicity provides useful information on the development of drugs with therapeutic benefi ts with reduced side effects. Mechanisms for drug-induced nephrotoxicity include changes in glomerular hemodynamics, tubular cell toxicity, inflammation, crystal nephropathy, rhabdomyolysis, and thrombotic microangiopathy. Biomarkers have been identifi ed for the assessment of nephrotoxicity. The discovery and development of novel biomarkers that can diagnose kidney damage earlier and more accurately are needed for effective prevention of drug-induced nephrotoxicity. Although some of them fail to confer specificity and sensitivity, several promising candidates of biomarkers were recently proved for assessment of nephrotoxicity. In this review, we summarize mechanisms of drug-induced nephrotoxicity and present the list of drugs that cause nephrotoxicity and biomarkers that can be used for early assessment of nephrotoxicity.

Macrophages in renal transplantation: Roles and therapeutic implications

The presence of macrophages within transplanted renal allografts has been appreciated for some time, whereby macrophages were viewed primarily as participants in the process of cell-mediated allograft rejection. Recent insights into macrophage biology have greatly expanded our conceptual understanding of the multiple roles of macrophages within the allograft. Distinct macrophage subsets are present within the kidney and these sub-serve discrete functions in promoting and attenuating inflammation, immune modulation and tissue repair. Unraveling the complex roles macrophages play in transplantation will allow identification of potential therapeutic targets to prevent and treat allograft rejection and maximize graft longevity.

The effects of MyD88 deficiency on disease phenotype in dysferlin-deficient A/J mice: role of endogenous TLR ligands

An absence of dysferlin leads to activation of innate immune receptors such as Toll-like receptors (TLRs) and skeletal muscle inflammation. Myeloid differentiation primary response gene 88 (MyD88) is a key mediator of TLR-dependent innate immune signalling. We hypothesized that endogenous TLR ligands released from the leaking dysferlin-deficient muscle fibres engage TLRs on muscle and immune cells and contribute to disease progression. To test this hypothesis, we generated and characterized dysferlin and MyD88 double-deficient mice. Double-deficient mice exhibited improved body weight, grip strength, and maximum muscle contractile force at 6-8 months of age when compared to MyD88-sufficient, dysferlin-deficient A/J mice. Double-deficient mice also showed a decrease in total fibre number, which contributed to the observed increase in the number of central nuclei/fibres. These results indicate that there was less regeneration in the double-deficient mice. We next tested the hypothesis that endogenous ligands, such as single-stranded ribonucleic acids (ssRNAs), released from damaged muscle cells bind to TLR-7/8 and perpetuate the disease progression. We found that injection of ssRNA into the skeletal muscle of pre-symptomatic mice (2 months old) resulted in a significant increase in degenerative fibres, inflammation, and regenerating fibres in A/J mice. In contrast, characteristic histological features were significantly decreased in double-deficient mice. These data point to a clear role for the TLR pathway in the pathogenesis of dysferlin deficiency and suggest that TLR-7/8 antagonists may have therapeutic value in this disease.

Urinary OPN excretion in children with glomerular proteinuria

PURPOSE

The aim of the study was to investigate urinary levels and clinical significance of osteopontin (uOPN) in children with different glomerular diseases according to histological diagnosis and degree of proteinuria.

MATERIALS AND METHODS

The examinations were conducted in 3 groups of children: I - 20 children with minimal change disease (MCD) examined twice: A - in relapse; B - in remission, group II - 17 children with focal segmental glomerulosclerosis (FSGS), III - 12 children with IgA nephropathy (IgAN). The control group (C) contained 20 healthy children. OPN was measured in the urine using ELISA commercial available kit (R&D Quantikine) and was expressed in ng/ mg cr.

RESULTS

The median uOPN/ cr. in MCD children in relapse (IA) was median 134.98 ng/ mg cr. and was higher when compared to controls (p< 0.01). In exam IB, when proteinuria subsided, OPN/ cr. increased to median 172.96 ng/ mg cr. and was higher in comparison to healthy subjects (p< 0.01) and MCD children in relapse (p<0.05). Children from group II revealed higher uOPN/ cr. levels when compared to groups I, III and C (p< 0.01). UOPN/ cr. positively correlated with protein/ creatinine ratio in all examined groups of children (p< 0.01).

CONCLUSION

We found significantly higher uOPN/ cr. in all the groups of children with glomerulonephritis. The highest uOPN/ cr. levels were found in patients with FSGS and correlated significantly with both interstitial changes and mesangial expansion found in kidney biopsy.

Donor phosphorus levels and recipient outcomes in living-donor kidney transplantation

BACKGROUND AND OBJECTIVES

In living-donor kidney transplantation, various donor factors, including gender, age, and baseline kidney function, predict allograft function and recipient outcomes after transplantation. Because higher phosphorus is predictive of vascular injury in healthy adults, the effect of donor phosphorus levels on recipient renal function after transplantation was investigated.

DESIGN, SETTING, PARTICIPANTS, AND MEASUREMENTS

Phosphorus levels in 241 living donors were analyzed from a 7-year period, and recipient renal function and acute rejection at 1 year posttransplantation were examined controlling for other influencing factors, including multiple donor variables, HLA matching, and acute rejection.

RESULTS

Female and African-American donors had significantly higher phosphorus levels predonation. By multivariable analysis, higher donor phosphorus correlated with higher recipient serum creatinine (slope=0.087, 95% confidence interval [CI]: 0.004 to 0.169, P=0.041) and lower recipient estimated GFR (slope=-4.321, 95% CI: -8.165 to -0.476, P=0.028) at 12 months. Higher donor phosphorus also displayed an independent correlation with biopsy-proven acute rejection and delayed or slow graft function after transplantation.

CONCLUSIONS

In a cohort of living kidney donors, higher donor phosphorus correlated with female gender and African-American ethnicity and was an independent risk factor for early allograft dysfunction after living-donor kidney transplantation.

Peroxisome proliferator-activated receptor (PPAR)gamma can inhibit chronic renal allograft damage

Chronic inflammation and fibrosis are the leading causes of chronic allograft failure. The nuclear receptor peroxisome proliferator-activated receptor (PPAR)gamma is a transcription factor known to have antidiabetogenic and immune effects, and PPARgamma forms obligate heterodimers with the retinoid X receptor (RXR). We have reported that a retinoic acid (RAR)/RXR-agonist can potently influence the course of renal chronic allograft dysfunction. In this study, in a Fischer to Lewis rat renal transplantation model, administration of the PPARgamma-agonist, rosiglitazone, independent of dose (3 or 30 mg/kgBW/day), lowered serum creatinine, albuminuria, and chronic allograft damage with a chronic vascular damage score as follows: 35.0 +/- 5.8 (controls) vs. 8.1 +/- 2.4 (low dose-Rosi; P < 0.05); chronic tubulointerstitial damage score: 13.6 +/- 1.8 (controls) vs. 2.6 +/- 0.4 (low dose-Rosi; P < 0.01). The deposition of extracellular matrix proteins (collagen, fibronectin, decorin) was strikingly lower. The expression of transforming growth factor-beta1 was inhibited, whereas that of bone morphogenic protein-7 (BMP-7) was increased. Intragraft mononuclear cells and activated fibroblast numbers were reduced by 50%. In addition, the migratory and proliferative activity of these cells was significantly inhibited in vitro. PPARgamma activation diminished the number of cells expressing the proinflammatory and fibrogenic proteoglycan biglycan. In macrophages its secretion was blocked by rosiglitazone in a predominantly PPARgamma-dependent manner. The combination of PPARgamma- and RAR/RXR-agonists resulted in additive effects in the inhibition of fibrosis. In summary, PPARgamma activation was potently immunosuppressive and antifibrotic in kidney allografts, and these effects were enhanced by a RAR/RXR-agonist.

Maintenance of donor-specific chimerism despite osteopontin-associated bone fibrosis in a vascularized bone marrow transplantation model

BACKGROUND

The role of vascularized bone allografting is not established in plastic and reconstructive surgery. The authors evaluated the contribution by osteopontin to fibrosis of allografted bone in a vascularized bone marrow transplantation model across a major histocompatibility complex barrier.

METHODS

Thirty-six transplantations were performed between Brown Norway (RT1 n) donors and Lewis (RT1 l) recipients divided into three groups: group 1, isografts between Lewis rats (n = 12); group 2, allografts without treatment (n = 8); and group 3, allografts under a 7-day alphabeta-T-cell receptor/cyclosporine protocol (n = 16). Flow cytometry assessed the presence of chimerism for donor major histocompatibility complex class I (RT1 n) antigens. Immunostaining was used to determine osteopontin expression in grafted and recipient bone, and histologic examination was used to assess bone architecture.

RESULTS

Early engraftment of donor bone marrow cells (RT1 n) into the recipient bone marrow compartment was achieved at posttransplantation day 7. This corresponded with osteopontin expression restricted to the endosteum of trabecular bone and was associated with the preservation of hematopoietic cells within donor bone. Cell migration between donor and recipient bone marrow compartments was confirmed by the presence of recipient cells (RT1 l) within the allografted bone and donor-origin cells (RT1 n) within the recipient bone. At posttransplantation day 63, osteopontin expression within allografted bone was associated with allograft bone fibrosis and lack of hematopoietic properties. In contrast, the recipient's contralateral bone demonstrated a highly localized osteopontin expression pattern within the endosteum and active hematopoiesis with the presence of donor-specific (RT1 n) cells and correlated with chimerism maintenance.

CONCLUSIONS

These results confirm that despite up-regulation of osteopontin expression and fibrosis of allografted bone, vascularized bone marrow transplantation resulted in efficient engraftment of donor cells into the recipient's bone marrow compartment, leading to chimerism maintenance.

Immuno-localization of CD44 and osteopontin in developing human kidney

CD44 is observed in ureteric bud structures and is implicated in branching morphogenesis during early mouse renal development. Healthy adult kidney demonstrates minimal CD44, but CD44 is up-regulated in renal diseases. CD44 may mediate binding of calcium oxalate crystals to tubular epithelia via the ligands osteopontin (OPN) and hyaluronan. Because 15% of premature infants develop nephrocalcinosis, developmental tubular CD44 expression might promote nephrocalcinosis. We studied CD44 and OPN immuno-localization in developing human kidney by immunohistochemical analysis. Human renal tissue between 18 and 40 wk of gestation showed CD44 immuno-localization in ureteric buds, with staining decreasing with increasing gestational age; CD44 was rarely observed in developing renal tubules. OPN was diffusely observed in proximal tubules, rarely observed in distal tubules, ureteric buds or metanephric structures. These data support the role of CD44 in early human nephron formation and branching morphogenesis. Rare CD44 staining in developing tubular epithelium suggests no role for CD44 in promoting calcium oxalate adherence to tubular epithelia in premature infants. Immuno-localization of OPN in tubules supports its role in tubular differentiation, but OPN does not seem to be necessary during early nephron formation.

The role of osteopontin in the development of albuminuria

Several gene array studies have suggested that osteopontin (Opn) expression strongly correlates with albuminuria and glomerular disease. Urinary Opn concentration and kidney Opn immunoreactivity were found to be increased in patients with steroid-sensitive nephrotic syndrome. In addition, renal Opn mRNA was increased in the Ins2(Akita) mouse model of type 1 diabetic nephropathy, in the LPS-induced albuminuria model, and in glomeruli of puromycin aminonucleotide-induced nephrotic rats. Opn knockout mice did not develop albuminuria in response to LPS injection, and Opn knockout mice were protected from diabetes-induced albuminuria and mesangial expansion. In the glomerulus, Opn immunostaining was increased specifically in podocytes. Treatment of podocytes with recombinant Opn activated the NF-kappaB pathway, increased expression of urokinase plasminogen activator and matrix metalloproteinases 2 and 9, and increased podocyte motility. Taken together, these results indicate that Opn plays an important role in the development of albuminuria, possibly by modulating podocyte signaling and motility.

Urinary biomarkers as a diagnostic tool for acute kidney injury

Acute kidney injury is a common condition in hospitalized patients with significant associated morbidity and mortality. Although impressive progress has been made in the understanding of the molecular and biochemical mechanisms of kidney injury, the ability to effectively treat and thus impact on the outcomes of acute kidney injury has been disappointing. One of the major reasons for this has been the reliance on current measures of renal dysfunction, such as serum creatinine and blood urea nitrogen, which are insensitive to small changes in renal function and subtle signs of kidney injury. This insensitivity of commonly used biomarkers of renal dysfunction not only prevents timely diagnosis and estimation of injury severity, but also delays administration of putative therapeutic agents. A number of serum and urinary proteins have been identified that may herald acute kidney injury prior to a rise in serum creatinine. Further characterization of these candidate biomarkers will clarify their utility and define new diagnostic and prognostic paradigms for acute kidney injury, facilitate clinical trials and lead to novel effective therapies.

Biomarkers of nephrotoxic acute kidney injury

Acute kidney injury (AKI) is a common condition with significant associated morbidity and mortality. Epidemiologic data suggest that a significant proportion of AKI cases is at least partially attributable to nephrotoxin exposure. This is not surprising given intrinsic renal susceptibility to toxicant-induced injury, a consequence of the unique physiologic and biochemical properties of the normally functioning kidney. A number of pathophysiologic mechanisms have been identified that mediate toxic effects on the kidney, resulting in a variety of clinical syndromes ranging from subtle changes in tubular function to fulminant renal failure. Unfortunately, standard metrics used to diagnose and monitor kidney injury, such as blood urea nitrogen and serum creatinine, are insensitive and nonspecific, resulting in delayed diagnosis and intervention. Considerable effort has been made to identify biomarkers that will allow the earlier diagnosis of AKI. Further characterization of these candidate biomarkers will clarify their utility in the setting of acute nephrotoxicity, define new diagnostic and prognostic paradigms for kidney injury, facilitate clinical trials, and lead to novel effective therapies.

Anti-inflammatory effects of alphav integrin antagonism in acute kidney allograft rejection

Integrin-mediated cell adhesion and signaling is essential to vascular development and inflammatory processes. Elevated expression of integrin alpha(v)beta(3) has been detected in ischemia-reperfusion injury and rejecting heart allografts. We thus hypothesized that the inhibition of alpha(v)-associated integrins may have potent anti-inflammatory effects in acute kidney allograft rejection. We studied the effects of a peptidomimetic antagonist of alpha(v) integrins in two rat models of renal allotransplantation, differing in degree of major histocompatibility complex mismatch. Integrin alpha(v)beta(3) was up-regulated in rejecting renal allografts. Integrin antagonist reduced the histological signs of acute rejection, the intensity of the mononuclear cell infiltration, and cell proliferation in the grafted kidneys. This could be correlated to a reduced leukocyte-endothelial interaction and an improved peritubular microcirculation observed by intravital microscopy. In vitro under laminar flow conditions, the arrest of monocytes to interleukin-1beta-activated endothelium was decreased. Furthermore, in co-culture models the proliferation and transmigration of monocytes/macrophages, endothelium, and fibroblasts induced by renal tubular epithelia was efficiently inhibited by alpha(v) integrin antagonism. These data reveal an important role of this integrin subclass in leukocyte recruitment and development and maintenance of acute rejection; blockade of alpha(v) integrins may provide a new therapeutic strategy to attenuate acute allograft rejection.

Aquaporin-2 water channel in developing quail kidney: possible role in programming adult fluid homeostasis

Avian kidneys have loopless and looped nephrons; a countercurrent multiplier mechanism operates in the latter by NaCl recycling. We identified an aquaporin-2 (AQP2) homolog in apical/subapical regions of cortical and medullary collecting duct (CD) cells in kidneys of Japanese quail (q), Coturnix japonica. We investigated whether undernutrition during the embryonic/maturation period retards kidney and AQP2 development in quail and programs impaired volume regulation in adults. Protocols included 1) time course and 2) effects of 5-10% egg white withdrawal (EwW) or 48-h post-hatch food deprivation (FD) on nephron growth and qAQP2 mRNA expression, and 3) effects of EwW and FD on qAQP2 mRNA responses to 72-h water deprivation in adults. In metanephric kidneys, qAQP2 mRNA is expressed in medullary CDs at embryonic day 10; distribution and intensity increase during maturation. The number and size of glomeruli continue to increase after birth, whereas nephrogenic zones decrease. In EwW embryos, qAQP2 mRNA expression is initially delayed, then restored; birth weight and hatching rate are lower than in controls. Adults from EwW embryos and FD chicks have fewer (P < 0.01) glomeruli. Water deprivation reduces body weight more in EwW birds than in controls. The results suggest that qAQP2 evolved in metanephric kidneys and that undernutrition may retard nephrogenesis, leading to impaired adult water homeostasis.

Genomewide expression profiles of rat model renal isografts from brain dead donors

BACKGROUND

It has been well documented that two factors, brain death (BD) and ischemia/reperfusion (I/R) injury, have distinct but overlapping adverse influences on the clinical outcome of renal transplantation.

METHOD

We previously established a rat model of renal isografting from brain dead donors. In the present study, we performed genomic expression profiling with a high-density oligonucleotide microarray to identify genes that were upregulated or downregulated by BD and/or I/R injury.

RESULTS

Among a total of 20,550 genes, most of those upregulated by BD were genes for adhesion molecules and cytokines or for chemokines such as Gro1 and IP-10. When overexpression of these genes was assessed by real-time reverse transcriptase-polymerase chain reaction, it was only observed one hr after the engraftment of kidneys from BD donors and returned to baseline thereafter, indicating the presence of an acute systemic inflammatory response to BD. Analysis of biologic networks demonstrated the activation of specific pathways that were clearly different for BD and I/R injury. The p53 and NFkappaB pathway was involved in the acute response to BD, whereas the Myc, Jun, and c-fos pathway was involved in I/R injury. Investigation of secretory protein genes identified LCN2 and SPP1 as candidate genes for biologic markers.

CONCLUSION

Because our experimental system is a good model of renal transplantation from brain dead or living human donors, our data may be useful for elucidating the pathologic processes involved and for identification of novel markers for graft dysfunction of renal transplantation.

Beneficial effects of CCR1 blockade on the progression of chronic renal allograft damage

The biology of chemokines and their receptors have been linked to the development of chronic allograft damage. Effects of CCR1 antagonist BX 471 were studied in a Fischer to Lewis renal transplantation model at days 10, 21 and 42 after transplantation. BX 471 treatment did not effectively reduce signs of acute rejection at day 10 but significantly improved allograft function and morphology at day 21 posttransplantation. When therapy was initiated on day 21 after transplantation, glomerulosclerosis and tubulointerstitial fibrosis were significantly inhibited by day 42 posttransplantation. Parallel decrease in infiltrating and proliferating mononuclear cells (ED1, CD8 and Ki67) was observed in treated allografts. Expression of acute phase reactive and proinflammatory genes (HO-1, osteopontin) and molecules associated with fibrosis (PAI-1, TGF-beta1, biglycan) was downregulated at day 21; reduced collagen deposition was observed, parallel to a significant lower number of alpha-SMA+ interstitial myofibroblasts. In situ hybridization demonstrated that biglycan expression was reduced following CCR1 blockade in interstitium of treated allografts. CCR1 antagonism was found to inhibit CCL5-induced secretion of biglycan by macrophages in vitro. CCR1 blockade significantly inhibited development and progression of chronic allograft damage. CCR1 antagonists may represent a therapeutic option for chronic inflammation and fibrosis in renal grafts.

Mechanistic biomarkers for cytotoxic acute kidney injury

Acute kidney injury is a common condition and is associated with a high mortality rate. It has been recognised that routinely used measures of renal function, such as levels of blood urea nitrogen and serum creatinine, increase significantly only after substantial kidney injury occurs and then with a time delay. Insensitivity of such tests delays the diagnosis in humans, making it particularly challenging to administer putative therapeutic agents in a timely fashion. Furthermore, this insensitivity affects the evaluation of toxicity in preclinical studies by allowing drug candidates, which have low, but nevertheless important, nephrotoxic side effects in animals, to pass the preclinical safety criteria only to be found to be clinically nephrotoxic with great human costs. This review presents the current status of sensitive and specific biomarkers to detect preclinical and clinical renal injury and summarises the techniques used to quantitate these biomarkers in biological fluids.

Up-Regulation of Osteopontin, Chemokines, Adhesion Molecule, and Heat Shock Proteins in 1-Hour Biopsy From Cardiac Death Donor Kidneys

AIMS

Since April 1979, 471 kidneys were retrieved from donors after cardiac death (DCD) using an in situ regional cooling technique, with excellent renal function and good long-term graft survival. However, the precise cascade of events following transplantation of DCD kidneys and the influence of ischemia-reperfusion injury remain unclear. In this study, we performed gene expression profiling using 1-hour biopsy samples from DCD kidneys versus those from living sources.

METHODS

All kidney grafts were procured at our center using an in situ regional cooling technique from DCD. Living donor kidneys (LD) were harvested by open nephrectomy. All graft biopsies were performed 1 hour after reperfusion (DCD n = 8, LD n = 9). We analyzed the expression profile of 20,173 genes.

RESULTS

One hundred seventy eight genes were up-regulated (>2-fold difference and DCD/LD > 1.5) and 120 down-regulated (<1/2-fold and LD/DCD > 1.5) in DCD kidneys. Expression of osteopontin (22.5 +/- 2.6-fold DCD vs 7.7 +/- 1.7 LD; P < .001), chemokines (CCL4 4.4 +/- 0.7 vs 2.5 +/- 0.3; P < .01), (CCL2 6.0 +/- 1.3 vs 2.8 +/- 0.5), CXCL1 (9.5 +/- 0.4 vs 2.0 +/- 0.2), and CXCL2 (16.7 +/- 5.3 vs 4.8 +/- 1.3; P < .05), adhesion molecule (ICAM-1 4.7 +/- 0.7 vs 2.5 +/- 0.4; P < .05), and heat shock proteins (HSPA1L 6.7 +/- 0.7 vs 1.6 +/- 0.3, HSPA1A 17.7 +/- 2.6 vs 2.4 +/- 0.5, HSPA1B 13.3 +/- 0.2 vs 3.0 +/- 0.7, HSPA5 6.7 +/- 0.8 vs 3.2 +/- 0.3, HSPB1 2.9 +/- 0.2 vs 1.0 +/- 0.1, and HSPH1 19.4 +/- 3.0 vs 5.9 +/- 1.1; P < .001) were up-regulated in the kidneys from DCD.

CONCLUSION

This report analyzed global gene expression using 1-hour biopsy samples from DCD kidneys. These results may provide new insight into the identification of novel target genes for the development of therapeutic approaches and for determining graft viability of kidneys from DCD.

Renal expression of CD44 correlates with acute renal allograft rejection

As CD44 is involved in the activation, proliferation, adhesion, and extravasation of lymphocytes, we hypothesized that CD44 could be involved in the pathogenesis of acute renal allograft rejection. Renal biopsies and plasma were collected from patients suffering an episode of acute renal allograft rejection. CD44 and its ligands, hyaluronic acid (HA) and osteopontin, were analyzed retrospectively by immunohistochemistry and, computer-aided, morphometric analysis. Soluble CD44 (sCD44) and osteopontin in the plasma were determined by enzyme-linked immunosorbent assay. During acute rejection episodes, CD44 and its ligands, HA and osteopontin, were upregulated in the renal allograft. Also, increased sCD44 plasma levels were observed, which correlated with both tubular expression of CD44 and the extent of infiltrate. No differences could be detected between the different pathologic grades of rejection. Upregulation of tubular CD44 and increased levels of circulating sCD44 may reflect a common pathogenic mechanism during acute renal rejection and could be useful markers in the diagnosis of acute renal rejection.