Induction of renal endonuclease G by cisplatin is reduced in DNase I-deficient mice

Nephrotoxicity from the chemotherapeutic drug cisplatin is associated with DNA fragmentation and cell death. We have recently demonstrated that DNase I knockout mice are significantly protected against cisplatin nephrotoxicity, but it is unknown whether the DNA fragmentation that occurs is produced by DNase I or another endonuclease. In this study we assessed the expression of several endonucleases involved in cell death after injection of cisplatin and found that the expression of endonuclease G (EndoG) increased whereas the expression of DNase I decreased almost to zero. Immunostaining showed that some nuclei contained both fragmented DNA and EndoG, suggesting that EndoG may cause DNA fragmentation induced by cisplatin. The increase in expression of EndoG was greater in wild-type mice than in DNase I knockout mice, indicating a potential link between the two endonucleases. In support of such a link, overexpression of DNase I in cultured mouse tubular epithelial cells also induced EndoG. Furthermore, gene silencing of EndoG in vitro provided significant protection against cell death. Taken together, our data suggest that both DNase I and EndoG mediate cisplatin injury to tubular epithelial cells.

Improving outcomes of acute kidney injury: report of an initiative

Acute kidney injury (AKI) is a complex disorder comprising several etiological factors and occurring in multiple settings. The disorder has a variety of clinical manifestations that range from minimal elevation in serum creatinine level to anuric renal failure. We describe the formation of a multidisciplinary collaborative network focused on AKI. This Acute Kidney Injury Network has proposed uniform standards for diagnosing and classifying AKI. These proposed standards will need to be validated in future studies, a process that will be facilitated by the Acute Kidney Injury Network, which offers a forum that encourages acquisition of knowledge to improve patient outcomes.

Mcl-1 is downregulated in cisplatin-induced apoptosis, and proteasome inhibitors restore Mcl-1 and promote survival in renal tubular epithelial cells

Mcl-1 is an antiapoptotic member of the Bcl-2 family that plays an important role in cell survival. We demonstrate that proteasome-dependent regulation of Mcl-1 plays a critical role in renal tubular epithelial cell injury from cisplatin. Protein levels of Mcl-1 rapidly declined in a time-dependent manner following cisplatin treatment of LLC-PK1cells. However, mRNA levels of Mcl-1 were not altered following cisplatin treatment. Expression of other antiapoptotic members of the Bcl-2 family such as Bcl-2 and BclxL was not affected by cisplatin treatment. Cisplatin-induced loss of Mcl-1 occurs at the same time as the mitochondrial release of cytochrome c, activation of caspase-3, and initiation of apoptosis. Treatment of cells with cycloheximide, a protein synthesis inhibitor, revealed rapid turnover of Mcl-1. In addition, treatment with cycloheximide in the presence or absence of cisplatin demonstrated that cisplatin-induced loss of Mcl-1 results from posttranslational degradation rather than transcriptional inhibition. Overexpression of Mcl-1 protected cells from cisplatin-induced caspase-3 activation and apoptosis. Preincubating cells with the proteasome inhibitor MG-132 or lactacystin not only restored cisplatin-induced loss of Mcl-1 but also resulted in an accumulation of Mcl-1 that exceeded basal levels; however, Bcl-2 and BclxL levels did not change in response to MG-132 or lactacystin. The proteasome inhibitors effectively blocked cisplatin-induced mitochondrial release of cytochrome c, caspase-3 activation, and apoptosis. These studies suggest that proteasome regulation of Mcl-1 is crucial in the cisplatin-induced apoptosis via the mitochondrial apoptotic pathway and that Mcl-1 is an important therapeutic target in cisplatin injury to renal tubular epithelial cells.

Role of meprin A in renal tubular epithelial cell injury

Meprins are zinc-dependent metalloproteinases that are highly expressed in the brush-border membranes of both the kidney and the intestines. Meprins are capable of proteolytically degrading extracellular matrix proteins, proteolytically processing bioactive proteins, and play a role in inflammatory processes. In this study, the function of meprin A in the acute kidney injury (AKI) model of cisplatin nephrotoxicity was examined. Normal linear localization of meprin A in the brush border membranes of proximal tubules was altered in AKI. The meprin A alpha-subunit was detected in the urine of both control and cisplatin-treated mice. A cleaved product of the meprin A beta-subunit, undetected in the urine of control mice, was found to be significantly increased in the urine during the progression of cisplatin nephrotoxicity. The excretion of this beta-fragment was found to be before the rise in serum creatinine and blood urea nitrogen (BUN) suggesting usefulness as a biomarker for AKI. Pretreatment of mice with a meprin A inhibitor afforded protection from cisplatin nephrotoxicity as reflected by significant decreases in serum creatinine, BUN, and the excretion of kidney injury molecule-1. These decreases in serum and urine biomarkers were accompanied by significant decreases in histologic markers such as leukocyte infiltration and apoptosis. Meprin A appears to be an important therapeutic target and urinary excretion appears to be a potential biomarker of AKI.

Carbamylated Low-Density Lipoprotein Induces Monocyte Adhesion to Endothelial Cells Through Intercellular Adhesion Molecule-1 and Vascular Cell Adhesion Molecule-1

Objective— Carbamylated low-density lipoprotein (LDL), the most abundant modified LDL isoform in human blood, has been recently implicated in causing the atherosclerosis-prone injuries to endothelial cells in vitro and atherosclerosis in humans. This study was aimed at testing the hypothesis that carbamylated LDL acts via inducing monocyte adhesion to endothelial cells and determining the adhesion molecules responsible for the recruitment of monocytes.

Methods and Results— Exposure of human coronary artery endothelial cells with carbamylated LDL but not native LDL caused U937 monocyte adhesion and the induction of intercellular adhesion molecule-1 and vascular cell adhesion molecule-1 adhesion molecules as measured by cell enzyme-linked immunosorbent assay. Silencing of intercellular adhesion molecule-1 by siRNA or its inhibition using neutralizing antibody resulted in decreased monocyte adhesion to the endothelial cells. Similar silencing or neutralizing of vascular cell adhesion molecule-1 alone did not have an effect but was shown to contribute to intercellular adhesion molecule-1 when tested simultaneously.

Conclusions— Taken together, these data provide evidence that intercellular adhesion molecule-1 in cooperation with vascular cell adhesion molecule-1 are essential for monocyte adhesion by carbamylated low-density lipoprotein-activated human vascular endothelial cells in vitro.

Modified LDLs induce proliferation-mediated death of human vascular endothelial cells through MAPK pathway

The ability of modified low-density lipoptoteins (LDLs) to induce both proliferation and death of endothelial cells is considered to be a mechanism of early atherosclerosis development. We previously showed that carbamylated LDL (cLDL) induces human coronary artery endothelial cell (HCAEC) death in vitro. This effect is similar to the atherogenic action of oxidized LDL (oxLDL) that induces the proliferation and death of endothelial cells. The present study was designed to analyze a potential proliferative effect of cLDL and whether proliferation caused by modified LDLs is related to cell death. Cultured HCAECs were exposed to different concentrations of modified LDL or native LDL for varying periods of time. Cell proliferation measured by bromodeoxyuridine incorporation and S-phase analysis was dose-dependently increased in the presence of cLDL (6.25–200 μg/ml). The proliferation induced by cLDL or oxLDL was associated with cell death and increased phosphorylation of extracellular signal-regulated kinase (ERK) and c-Jun NH2-terminal kinase (JNK). Inhibition of cLDL- or oxLDL-induced proliferation by aphidicolin (1 μg/ml) was protective against both short-term cell death measured by lactate dehydrogenase release into the medium and long-term cell viability visualized by cell multiplication. Inhibition of ERK phosphorylation led to a significant decrease of DNA synthesis and cell rescue from injury by modified LDLs, while inhibition of JNK phosphorylation had an only partial rescue effect without involvement in cell proliferation. These data are the first evidence that endothelial cell death induced by cLDL or oxLDL is mediated by cell proliferation through the mitogen-activated protein kinase pathway.

Salter-Harris type III fracture of the lateral femoral condyle with a ruptured posterior cruciate ligament: an uncommon injury pattern

We report a case of an obscure injury to the distal femoral epiphysis with an uncommon pattern in a 12-year-old boy following a road traffic accident. Initial plain radiographs of the knee were inconclusive. Further investigation with magnetic resonance imaging revealed Salter-Harris type III fracture of the lateral femoral condyle with a gap at the fracture site associated with avulsion of the posterior cruciate ligament. This potentially serious injury can be underestimated on plain radiographs and therefore any suspected injury to the distal femoral epiphysis should be thoroughly assessed and investigated to institute appropriate treatment and minimise the risk of long-term complications.

Acute Kidney Injury Network: report of an initiative to improve outcomes in acute kidney injury

INTRODUCTION

Acute kidney injury (AKI) is a complex disorder for which currently there is no accepted definition. Having a uniform standard for diagnosing and classifying AKI would enhance our ability to manage these patients. Future clinical and translational research in AKI will require collaborative networks of investigators drawn from various disciplines, dissemination of information via multidisciplinary joint conferences and publications, and improved translation of knowledge from pre-clinical research. We describe an initiative to develop uniform standards for defining and classifying AKI and to establish a forum for multidisciplinary interaction to improve care for patients with or at risk for AKI.

METHODS

Members representing key societies in critical care and nephrology along with additional experts in adult and pediatric AKI participated in a two day conference in Amsterdam, The Netherlands, in September 2005 and were assigned to one of three workgroups. Each group's discussions formed the basis for draft recommendations that were later refined and improved during discussion with the larger group. Dissenting opinions were also noted. The final draft recommendations were circulated to all participants and subsequently agreed upon as the consensus recommendations for this report. Participating societies endorsed the recommendations and agreed to help disseminate the results.

RESULTS

The term AKI is proposed to represent the entire spectrum of acute renal failure. Diagnostic criteria for AKI are proposed based on acute alterations in serum creatinine or urine output. A staging system for AKI which reflects quantitative changes in serum creatinine and urine output has been developed.

CONCLUSION

We describe the formation of a multidisciplinary collaborative network focused on AKI. We have proposed uniform standards for diagnosing and classifying AKI which will need to be validated in future studies. The Acute Kidney Injury Network offers a mechanism for proceeding with efforts to improve patient outcomes.

Prevention of cisplatin-induced kidney epithelial cell apoptosis with a Cu superoxide dismutase-mimetic [copper2II(3,5-ditertiarybutylsalicylate)4(ethanol)4]

Copper(2)(II)(3,5-ditertiarybutylsalicylate)(4)(ethanol)(4), Cu(2)(II)(3,5-DTBS)(4)(Eth)(4), was synthesized and characterized for evaluation as an anti-apoptotic superoxide dismutase (SOD)-mimetic in an in vitro 50 microM cis-diamminedichloroplatinum(II), [Pt(II)(NH(3))(2)(Cl)(2)]-treated kidney proximal tubule epithelial cell (LLC-PK) preparation. Synthesized Cu(2)(II)(3,5-DTBS)(4)(Eth)(4) was characterized by elemental analysis, FTIR spectrophotometry, and X-ray crystallography. The IC(50) for SOD-mimetic reactivity of Cu(2)(II)(3,5-DTBS)(4)(Eth)(4), determined with the xanthine/xanthine oxidase/nitroblue tetrazolium (NBT) system, was found to be 2.69 microM for the binuclear chelate. Pretreatment of LLC-PK cells with 20 microM Cu(2)(II)(3,5-DTBS)(4)(Eth)(4) prevented 50 microM Pt(II)(NH(3))(2)(Cl)(2)-induced and superoxide-mediated apoptosis. This SOD-mimetic significantly suppressed Pt(II)(NH(3))(2)(Cl)(2)-induced translocation of pro-apoptotic Bax from the cytosol to the inner mitochondrial membrane, prevented Pt(II)(NH(3))(2)(Cl)(2)-induced release of cytochrome c from the inner mitochondrial membrane and the appearance of cytochrome c in the cytosol, and prevented conversion of procaspase-3 to active caspase-3. Cu(2)(II)(3,5-DTBS)(4)(Eth)(4) treatment inhibited Pt(II)(NH(3))(2)(Cl)(2)-mediated tubular cell injury by preventing activation of cellular mechanisms that lead to proximal tubule kidney cell death. Based on these observations, Pt(II)(NH(3))(2)(Cl)(2)- induced O(2)(-)-mediated apoptosis can be mechanistically overcome with a small molecular mass SOD-mimetic, Cu(2)(II)(3,5-DTBS)(4)(Eth)(4). Prior treatment of patients who are to undergo treatment with Pt(II)(NH(3))(2)(Cl)(2) for their neoplastic disease with Cu(2)(II)(3,5-DTBS)(4)(Eth)(4) may be beneficial to these patients.

Oxidants in chronic kidney disease

Chronic kidney disease is a worldwide public health problem that affects approximately 10% of the US adult population and is associated with a high prevalence of cardiovascular disease and high economic cost. Chronic renal insufficiency, once established, tends to progress to end-stage kidney disease, suggesting some common mechanisms for ultimately causing scarring and further nephron loss. This review defines the term reactive oxygen metabolites (ROM), or oxidants, and presents the available experimental evidence in support of the role of oxidants in diabetic and nondiabetic glomerular disease and their role in tubulointerstitial damage that accompanies progression. It concludes by reviewing the limited human data that provide some proof of concept that the observations in experimental models may be relevant to human disease.

Endonuclease G promotes cell death of non-invasive human breast cancer cells

The invasiveness of breast cancer cells was shown to be associated with the suppressed ability to develop apoptosis. The role of cell death DNases/endonucleases has not been previously examined in relation with the invasiveness of breast cancer cells. We have compared the activity of the endonucleases in seven human breast cancer cell lines different in the level of invasiveness and differentiation. The invasiveness of cell lines was confirmed by an in vitro Matrigel-based assay. The total endonuclease activity in the differentiated non-invasive (WDNI) cell lines was higher than that in the poorly differentiated invasive (PDI) cells. The expression of EndoG strongly correlated with the degree of estrogen receptor expression and showed an inverse correlation with vimentin and matrix metalloproteinase-13. The EndoG-positive WDNI cells were more sensitive to etoposide- or camptothecin-induced cell death than EndoG-negative PDI cells. Silencing of EndoG caused inhibited of SK-BR-3 WDNI cell death induced by etoposide. Human ductal carcinomas in situ expressed high levels of EndoG, while invasive medullar and ductal carcinomas had significantly decreased expression of EndoG. This correlated with decreased apoptosis as measured by TUNEL assay. Our findings suggest that the presence of EndoG in non-invasive breast cancer cells determines their sensitivity to apoptosis, which may be taken into consideration for developing the chemotherapeutic strategy for cancer treatment.

Kidney disease as an independent risk factor for cardiovascular events

Although the high risk for cardiovascular events in patients with end-stage renal disease (ESRD) is well known, recent data provide compelling evidence that even mild to moderate kidney disease is an important and independent risk factor for cardiac events. This increased risk does not seem to be explained by traditional risk factors as defined by the Framingham cohort. The examination of nontraditional risk factors has resulted in the identification of, among others, oxidant stress, hyperhomocystinemia, carbamylation, nitric oxide synthase inhibitors, and abnormal lipoproteins as potential pathways to explain the accelerated atherosclerosis in patients with kidney disease. Well-designed clinical trials should lead to the clarification of the relative importance of these factors in the pathogenesis of atherosclerotic disease.

Oxidants and Iron in Progressive Kidney Disease

Oxidants derived either from leukocytes in proliferative glomerulonephritis or from resident glomerular cells in nonproliferative glomerulonephritis have been shown to have several biological effects relevant to chronic kidney disease. These include the ability of oxidants to damage the glomerular basement membrane and directly induce proteinuria, effects that would lead to a fall in the glomerular filtration rate and account for the morphologic changes observed in chronic kidney disease. In experimental models, the role of oxidants has been shown in both proliferative glomerulonephritis (eg, antiglomerular basement membrane antibody disease) as well as experimental models of minimal change disease and membranous nephropathy. Oxidants have also been shown to be an important mediator of the various pathways that have been implicated in diabetic nephropathy. Antioxidants and iron chelators have also been shown to retard functional and morphologic changes observed in progressive kidney disease. Taken together, these experimental studies suggest an important role of oxidants in chronic kidney disease.

Carbamylated low-density lipoprotein induces death of endothelial cells: a link to atherosclerosis in patients with kidney disease

BACKGROUND

The presence of accelerated atherosclerosis in patients with kidney disease cannot be entirely explained by traditional cardiovascular risk factors. Exposure to urea, which is normally present in human blood plasma and elevated in patients with kidney disease, leads to the carbamylation of proteins. We postulated that low-density lipoprotein (LDL) carbamylated by urea has biologic effects relevant to atherosclerosis.

METHODS

To produce carbamylated LDL (cLDL), human native LDL (nLDL) was chemically modified in vitro by exposure to potassium cyanate. Human coronary artery endothelial cells (HCAECs) and human coronary artery smooth muscle cells (CASMCs) were treated in vitro with cLDL or nLDL. Irreversible cell death was measured using the lactate dehydrogenase (LDH) assay, apoptosis was assessed by annexin V binding, and proliferation was determined using bromodeoxyuridine (BrdU) incorporation. Total plasma protein carbamylation and plasma cLDL were measured in hemodialysis patients using the homocitrulline assay and enzyme-linked immunosorbent assay (ELISA).

RESULTS

Our studies demonstrated that cLDL but not nLDL induced dose-dependent vascular cell injuries relevant to atherosclerosis, which included the proliferation of vascular smooth muscle cells and endothelial cell death. Under light microscopy, endothelial cells treated with cLDL showed signs of morphologic alterations. The injury to endothelial cells measured by LDH release was time-dependent and correlated with the degree of LDL carbamylation. At least a part of the endothelial cell population treated with cLDL died by apoptosis. In patients with advanced renal disease on hemodialysis, total plasma protein carbamylation and plasma cLDL were several times higher than in control healthy individuals.

CONCLUSION

Collectively these data suggest the potential role of carbamylated LDL in accelerated atherosclerosis in patients with chronic renal disease and, possibly, in healthy individuals.

p53-dependent caspase-2 activation in mitochondrial release of apoptosis-inducing factor and its role in renal tubular epithelial cell injury

We demonstrate the role of p53-mediated caspase-2 activation in the mitochondrial release of apoptosis-inducing factor (AIF) in cisplatin-treated renal tubular epithelial cells. Gene silencing of AIF with its small interfering RNA (siRNA) suppressed cisplatin-induced AIF expression and provided a marked protection against cell death. Subcellular fractionation and immunofluorescence studies revealed cisplatin-induced translocation of AIF from the mitochondria to the nuclei. Pancaspase inhibitor benzyloxycarbonyl-Val-Ala-Asp-fluoromethylketone or p53 inhibitor pifithrin-alpha markedly prevented mitochondrial release of AIF, suggesting that caspases and p53 are involved in this release. Caspase-2 and -3 that were predominantly activated in response to cisplatin provided a unique model to study the role of these caspases in AIF release. Cisplatin-treated caspase-3 (+/+) and caspase-3 (-/-) cells exhibited similar AIF translocation to the nuclei, suggesting that caspase-3 does not affect AIF translocation, and thus, caspase-2 may be involved in the translocation. Caspase-2 inhibitor benzyloxycarbonyl-Val-Asp-Val-Ala-Asp-fluoromethylketone or down-regulation of caspase-2 by its siRNA significantly prevented translocation of AIF. Caspase-2 activation was a critical response from p53, which was markedly induced and phosphorylated in cisplatin-treated cells. Overexpression of p53 not only resulted in caspase-2 activation but also mitochondrial release of AIF. The p53 inhibitor pifithrin-alpha or p53 siRNA prevented both cisplatin-induced caspase-2 activation and mitochondrial release of AIF. Caspase-2 activation was dependent on the p53-responsive gene, PIDD, a death domain-containing protein that was induced by cisplatin in a p53-dependent manner. These results suggest that caspase-2 activation mediated by p53 is an important pathway involved in the mitochondrial release of AIF in response to cisplatin injury.

Oxidants and iron in chronic kidney disease

Oxidants derived either from leukocytes in proliferative glomerular nephritis or from resident glomerular cells in nonproliferative glomerulonephritis have been shown to have several biologic effects relevant to chronic kidney disease. These include: the ability of oxidants to damage glomerular basement membrane (GBM) and to directly induce proteinuria; effects that would lead to a fall in the glomerular filtration rate; and effects that would account for the morphologic changes observed in chronic kidney disease. In experimental models the role of oxidants has been demonstrated in both proliferative glomerulonephritis (e.g., anti-GBM antibody disease) as well as experimental models of minimal change disease and membranous nephropathy. Oxidants have also been shown to be an important mediator of the various pathways that have been implicated in diabetic nephropathy. Antioxidants and iron chelators have also been shown to retard functional and morphologic changes observed in progressive kidney disease. Taken together, these experimental studies suggest an important role of oxidants in chronic kidney disease.