Erythropoietin protects the kidneys against ischemia reperfusion injury by activating hypoxia inducible factor-1alpha

Suppressive effect erythropoietin on oxidative stress by targeting AMPK/Nox4/ROS pathway in renal ischemia reperfusion injury

OBJECTIVE

To explore the effect of erythropoietin (EPO) on the AMP-activated protein kinase (AMPK)/nicotinamide adenine dinucleotide phosphatase oxidase 4 (NOX4) signaling pathway during renal ischemia reperfusion injury (RIRI) in rats.

METHODS

A rat model of RIRI was established by clamping the left renal pedicle and removing the right kidney. The rats in the sham group did not have their left renal pedicle clamped. Rats with a model of RIRI were randomly divided into RIRI alone (control), erythropoietin treatment (EPO/RIRI), and Compound C treatment (CPC/RIRI) groups. Hematoxylin-eosin (H&E) staining was used to examine pathological kidney damage. Serum creatinine and urea nitrogen levels were measured to evaluate renal function. Western blotting was performed to detect the expression levels of phosphorylated p-AMPK and total AMPK protein in the kidneys. RT-PCR was used to evaluate the mRNA levels of Nox4 and p22 in the kidneys. Oxidative stress-related indices (ROS, CAT, GSH, SOD, and MDA) were also measured.

RESULTS

EPO treatment improved kidney function by preventing kidney damage induced by the RIRI model. Preventing ischemia/reperfusion injury in the RIRI model was correlated with an increased p-AMPK/AMPK ratio and elevated activity of CAT, GSH, and SOD, which ameliorated the expression of NOX4, p22, ROS, and MDA. Moreover, treatment with CPC (an AMPK inhibitor) reduced the effects of EPO in the RIRI model.

CONCLUSION

EPO treatment protected rats against RIRI in the RIRI model by alleviating oxidative stress by triggering the AMPK/NOX4/ROS pathway.

Minimizing Ischemia Reperfusion Injury in Xenotransplantation

The recent dramatic advances in preventing "initial xenograft dysfunction" in pig-to-non-human primate heart transplantation achieved by minimizing ischemia suggests that ischemia reperfusion injury (IRI) plays an important role in cardiac xenotransplantation. Here we review the molecular, cellular, and immune mechanisms that characterize IRI and associated "primary graft dysfunction" in allotransplantation and consider how they correspond with "xeno-associated" injury mechanisms. Based on this analysis, we describe potential genetic modifications as well as novel technical strategies that may minimize IRI for heart and other organ xenografts and which could facilitate safe and effective clinical xenotransplantation.

CXCL6 regulates cell permeability, proliferation, and apoptosis after ischemia-reperfusion injury by modulating Sirt3 expression via AKT/FOXO3a activation

Chemokine (C-X-C motif) ligand 6 (CXCL6), a member of the CXC chemokine family, reportedly mediates several processes such as inflammation, immunoreaction, cell growth, and metastasis through interaction with the chemokine receptors CXCR1 and CXCR2 in humans; further, CXCR1 and CXCR2 can promote repair and regeneration of organs or tissues after ischemia-reperfusion injury (IRI). In this study, we found that HIF-1α, CXCL6, and CXCR2 expression levels were elevated in human brain microvascular endothelial cells (HBMECs) after IRI, whereas silent information regulator of transcription (Sirt) 3 expression level had reduced. HIF-1α inhibition in an IRI model potently promoted HBMEC proliferation, accompanied by increased Sirt3 and decreased CXCL6/CXCR2 expression levels. CXCL6 knockdown in the IRI model significantly decreased HBMEC permeability and promoted HBMEC proliferation, concurrent with a decrease in apoptosis; it also increased Sirt3 expression levels and decreased CXCL6/CXCR2 protein and phosphorylated AKT (p-AKT) and class O of forkhead box (FOXO) 3a (p-FOXO3a) levels. In addition, CXCL6-induced HBMEC permeability and inhibition of HBMEC proliferation were counteracted by Sirt3 overexpression, and the AKT inhibitor LY294002 counteracted the effect of CXCL6 recombinant proteins on Sirt3, p-AKT, and p-FOXO3a expressions. These results suggest that CXCL6 and Sirt3 are downstream of HIF-1α and that CXCL6 regulatesHBMEC permeability, proliferation, and apoptosis after IRI by modulating Sirt3 expression via AKT/FOXO3a activation.

Cilastatin Preconditioning Attenuates Renal Ischemia-Reperfusion Injury via Hypoxia Inducible Factor-1α Activation

Cilastatin is a specific inhibitor of renal dehydrodipeptidase-1. We investigated whether cilastatin preconditioning attenuates renal ischemia-reperfusion (IR) injury via hypoxia inducible factor-1α (HIF-1α) activation. Human proximal tubular cell line (HK-2) was exposed to ischemia, and male C57BL/6 mice were subjected to bilateral kidney ischemia and reperfusion. The effects of cilastatin preconditioning were investigated both in vitro and in vivo. In HK-2 cells, cilastatin upregulated HIF-1α expression in a time- and dose-dependent manner. Cilastatin enhanced HIF-1α translation via the phosphorylation of Akt and mTOR was followed by the upregulation of erythropoietin (EPO) and vascular endothelial growth factor (VEGF). Cilastatin did not affect the expressions of PHD and VHL. However, HIF-1α ubiquitination was significantly decreased after cilastatin treatment. Cilastatin prevented the IR-induced cell death. These cilastatin effects were reversed by co-treatment of HIF-1α inhibitor or HIF-1α small interfering RNA. Similarly, HIF-1α expression and its upstream and downstream signaling were significantly enhanced in cilastatin-treated kidney. In mouse kidney with IR injury, cilastatin treatment decreased HIF-1α ubiquitination independent of PHD and VHL expression. Serum creatinine level and tubular necrosis, and apoptosis were reduced in cilastatin-treated kidney with IR injury, and co-treatment of cilastatin with an HIF-1α inhibitor reversed these effects. Thus, cilastatin preconditioning attenuated renal IR injury via HIF-1α activation.

Dynamic transcriptomic analysis of Ischemic Injury in a Porcine Pre-Clinical Model mimicking Donors Deceased after Circulatory Death

Due to organ shortage, clinicians are prone to consider alternative type of organ donors among them donors deceased after circulatory death (DCD). However, especially using these organs which are more prone to graft dysfunction, there is a need to better understand mechanistic events ocuring during ischemia phase and leading to ischemia/reperfusion injuries (IRI). The aim of this study is to provide a dynamic transcriptomic analysis of preclinical porcine model kidneys subjected to ischemic stress mimicking DCD donor. We compared cortex and corticomedullary junction (CMJ) tissues from porcine kidneys submitted to 60 min warm ischemia (WI) followed by 0, 6 or 24 hours of cold storage in University of Wisconsin solution versus control non-ischemic kidneys (n = 5 per group). 29 cortex genes and 113 CMJ genes were significantly up or down-regulated after WI versus healthy kidneys, and up to 400 genes were regulated after WI followed by 6 or 24 hours of cold storage (p < 0.05). Functionnal enrichment analysis (home selected gene kinetic classification, Gene-ontology-biological processes and Gene-ontology-molecular-function) revealed relevant genes implication during WI and cold storage. We uncovered targets which we will further validate as biomarkers and new therapeutic targets to optimize graft kidney quality before transplantation and improve whole transplantation outcome.

FGF23 modulates the effects of erythropoietin on gene expression in renal epithelial cells

Background

FGF23 plays an important role in calcium–phosphorus metabolism. Other roles of FGF23 have recently been reported, such as commitment to myocardium enlargement and immunological roles in the spleen. In this study, we aimed to identify the roles of FGF23 in the kidneys other than calcium–phosphorus metabolism.

Methods

DNA microarrays and bioinformatics tools were used to analyze gene expression in mIMCD3 mouse renal tubule cells following treatment with FGF23, erythropoietin and/or an inhibitor of ERK.

Results

Three protein-coding genes were upregulated and 12 were downregulated in response to FGF23. Following bioinformatics analysis of these genes, PPARγ and STAT3 were identified as candidate transcript factors for mediating their upregulation, and STAT1 as a candidate for mediating their downregulation. Because STAT1 and STAT3 also mediate erythropoietin signaling, we investigated whether FGF23 and erythropoietin might show interactive effects in these cells. Of the 15 genes regulated by FGF23, 11 were upregulated by erythropoietin; 10 of these were downregulated following cotreatment with FGF23. Inhibition of ERK, an intracellular mediator of FGF23, reversed the effects of FGF23. However, FGF23 did not influence STAT1 phosphorylation, suggesting that it impinges on erythropoietin signaling through other mechanisms.

Conclusion

Our results suggest cross talk between erythropoietin and FGF23 signaling in the regulation of renal epithelial cells.

Erythropoietin and Its Angiogenic Activity

Erythropoietin (EPO) is the main hematopoietic hormone acting on progenitor red blood cells via stimulation of cell growth, differentiation, and anti-apoptosis. However, its receptor (EPOR) is also expressed in various non-hematopoietic tissues, including endothelium. EPO is a pleiotropic growth factor that exhibits growth stimulation and cell/tissue protection on numerous cells and tissues. In this article we review the angiogenesis potential of EPO on endothelial cells in heart, brain, and leg ischemia, as well as its role in retinopathy protection and tumor promotion. Furthermore, the effect of EPO on bone marrow and adipose tissue is also discussed.

Delayed graft function and its management in children

Delayed graft function (DGF) is commonly defined as the requirement for dialysis within the first 7 days following renal transplantation. The major underlying mechanism is related to ischaemia/reperfusion injury, which includes microvascular inflammation and cell death and apoptosis, and to the regeneration processes. Several clinical factors related to donor, recipient and organ procurement/transplantation procedures may increase the risk of DGF, including donor cardiovascular instability, older donor age, donor creatinine concentration, long cold ischaemia time and marked body mass index of both the donor and recipient. Some of these parameters have been used in specific predictive formulas created to assess the risk of DGF. A variety of other pre-, intra- and post-transplant clinical factors may also increase the risk of DGF, such as potential drug nephrotoxicity, surgical problems and/or hyperimmunization of the recipient. DGF may decrease the long-term graft function, but data on this effect are inconsistent, partially due to the many different types of organ donation. Relevant management strategies may be classified into the classic clinical approach, which has the aim of minimizing the individual risk factors of DGF, and specific pharmacologic strategies, which are designed to prevent or treat ischaemia/reperfusion injury. Both strategies are currently being evaluated in clinical trials.

Mitochondria-targeted antioxidant MitoQ reduced renal damage caused by ischemia-reperfusion injury in rodent kidneys: Longitudinal observations of T2 -weighted imaging and dynamic contrast-enhanced MRI

Purpose

To investigate the effect of mitochondria‐targeted antioxidant MitoQ in reducing the severity of renal ischemia‐reperfusion injury (IRI) in rats using T₂‐weighted imaging and dynamic contrast‐enhanced MRI (DCE‐MRI).

Methods

Ischemia‐reperfusion injury was induced by temporarily clamping the left renal artery. Rats were pretreated with MitoQ or saline. The MRI examination was performed before and after IRI (days 2, 5, 7, and 14). The T₂‐weighted standardized signal intensity of the outer stripe of the outer medulla (OSOM) was measured. The unilateral renal clearance rate k_cl was derived from DCE‐MRI. Histopathology was evaluated after the final MRI examination.

Results

The standardized signal intensity of the OSOM on IRI kidneys with MitoQ were lower than those with saline on days 5 and 7 (P = 0.004, P < 0.001, respectively). K_cl values of IRI kidneys with MitoQ were higher than those with saline at all time points (P = 0.002, P < 0.001, P = 0.001, P < 0.001). Histopathology showed that renal damage was the most predominant on the OSOM of IRI kidneys with saline, which was less obvious with MitoQ (P < 0.001).

Conclusions

These findings demonstrate that MitoQ can reduce the severity of renal damage in rodent IRI models using T₂‐weighted imaging and DCE‐MRI. Magn Reson Med 79:1559–1667, 2018. © 2017 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

Soluble Uric Acid Activates the NLRP3 Inflammasome

Uric acid is a damage-associated molecular pattern (DAMP), released from ischemic tissues and dying cells which, when crystalized, is able to activate the NLRP3 inflammasome. Soluble uric acid (sUA) is found in high concentrations in the serum of great apes, and even higher in some diseases, before the appearance of crystals. In the present study, we sought to investigate whether uric acid, in the soluble form, could also activate the NLRP3 inflammasome and induce the production of IL-1β. We monitored ROS, mitochondrial area and respiratory parameters from macrophages following sUA stimulus. We observed that sUA is released in a hypoxic environment and is able to induce IL-1β release. This process is followed by production of mitochondrial ROS, ASC speck formation and caspase-1 activation. Nlrp3^-/- macrophages presented a protected redox state, increased maximum and reserve oxygen consumption ratio (OCR) and higher VDAC protein levels when compared to WT and Myd88^-/- cells. Using a disease model characterized by increased sUA levels, we observed a correlation between sUA, inflammasome activation and fibrosis. These findings suggest sUA activates the NLRP3 inflammasome. We propose that future therapeutic strategies for renal fibrosis should include strategies that block sUA or inhibit its recognition by phagocytes.

Update on ischemia-reperfusion injury in kidney transplantation: Pathogenesis and treatment

Ischemia/reperfusion injury is an unavoidable relevant consequence after kidney transplantation and influences short term as well as long-term graft outcome. Clinically ischemia/reperfusion injury is associated with delayed graft function, graft rejection, chronic rejection and chronic graft dysfunction. Ischemia/reperfusion affects many regulatory systems at the cellular level as well as in the renal tissue that result in a distinct inflammatory reaction of the kidney graft. Underlying factors of ischemia reperfusion include energy metabolism, cellular changes of the mitochondria and cellular membranes, initiation of different forms of cell death-like apoptosis and necrosis together with a recently discovered mixed form termed necroptosis. Chemokines and cytokines together with other factors promote the inflammatory response leading to activation of the innate immune system as well as the adaptive immune system. If the inflammatory reaction continues within the graft tissue, a progressive interstitial fibrosis develops that impacts long-term graft outcome. It is of particular importance in kidney transplantation to understand the underlying mechanisms and effects of ischemia/reperfusion on the graft as this knowledge also opens strategies to prevent or treat ischemia/reperfusion injury after transplantation in order to improve graft outcome.

Restoration of Haemoglobin Level Using Hydrodynamic Gene Therapy with Erythropoietin Does Not Alleviate the Disease Progression in an Anaemic Mouse Model for TGFβ1-Induced Chronic Kidney Disease

Erythropoietin, Epo, is a 30.4 kDa glycoprotein hormone produced primarily by the fetal liver and the adult kidney. Epo exerts its haematopoietic effects by stimulating the proliferation and differentiation of erythrocytes with subsequent improved tissue oxygenation. Epo receptors are furthermore expressed in non-haematopoietic tissue and today, Epo is recognised as a cytokine with many pleiotropic effects. We hypothesize that hydrodynamic gene therapy with Epo can restore haemoglobin levels in anaemic transgenic mice and that this will attenuate the extracellular matrix accumulation in the kidneys. The experiment is conducted by hydrodynamic gene transfer of a plasmid encoding murine Epo in a transgenic mouse model that overexpresses TGF-β1 locally in the kidneys. This model develops anaemia due to chronic kidney disease characterised by thickening of the glomerular basement membrane, deposition of mesangial matrix and mild interstitial fibrosis. A group of age matched wildtype littermates are treated accordingly. After a single hydrodynamic administration of plasmid DNA containing murine EPO gene, sustained high haemoglobin levels are observed in both transgenic and wildtype mice from 7.5 ± 0.6 mmol/L to 9.4 ± 1.2 mmol/L and 10.7 ± 0.3 mmol/L to 15.5 ± 0.5 mmol/L, respectively. We did not observe any effects in the thickness of glomerular or tubular basement membrane, on the expression of different collagen types in the kidneys or in kidney function after prolonged treatment with Epo. Thus, Epo treatment in this model of chronic kidney disease normalises haemoglobin levels but has no effect on kidney fibrosis or function.

Innate and adaptive immune responses subsequent to ischemia-reperfusion injury in the kidney

Understanding innate immune responses and their correlation to alloimmunity after solid organ transplantation is key to optimizing long term graft outcome. While Ischemia/Reperfusion injury (IRI) has been well studied, new insight into central mechanisms of innate immune activation, i.e. chemokine mediated cell trafficking and the role of Toll-like receptors have evolved recently. The mechanistic implications of Neutrophils, Macrophages/Monocytes, NK-cells, Dendritic cells in renal IRI has been proven by selective depletion of these cell types, thereby offering novel therapeutic interventions. At the same time, the multi-faceted role of different T-cell subsets in IRI has gained interest, highlighting the dichotomous effects of differentiated T-cells and suggesting more selective therapeutic approaches. Targeting innate immune cells and their activation and migration pathways, respectively, has been promising in experimental models holding translational potential. This review will summarize the effects of innate immune activation and potential strategies to interfere with the immunological cascade following renal IRI.

Administration of erythropoietin exerts protective effects against glucocorticoid-induced osteonecrosis of the femoral head in rats

Accumulating evidence has indicated that erythropoietin (EPO) plays a role in anti-apoptosis and tissue protection in a number of human diseases. The present study was implemented to evaluate these anti-apoptotic and tissue-protective effects in glucocorticoid-induced osteonecrosis in rats. Osteonecrosis was induced by low-dose lipopolysaccharide and subsequent high-dose methylprednisolone pulse. Rats in the preventive group were treated with 500 U/kg/day recombinant human EPO (rhuEPO) for 1 week. Hematological and histomorphometric methods were then used to determine the effects of the administration of rhuEPO. An analysis of trabecular bone architecture was performed to evaluate bone mass change in the osteonecrosis zone. Terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL) assay was performed to determine the apoptotic index of osteoblasts and osteocytes. Immunoblot analysis was performed to assess the expression of caspase-3 and vascular endothelial growth factor (VEGF) in the femoral head. Treatment with rhuEPO greatly improved the histological performance. Additionally, the incidence of osteonecrosis markedly decreased in the rats in the rhuEPO-treated group (22.2%) compared with the control group (66.7%). Furthermore, the expression of caspase-3 markedly decreased in the rhuEPO-treated group. Consistently, the apoptosis of osteoblasts and osteocytes, as determined by TUNEL assays, was inhibited following the administration of rhuEPO. By contrast, the expression of VEGF increased in the osteonecrosis zone in the rats treated with rhuEPO. The results from the present study demonstrate that EPO exerts prominent protective effects against glucocorticoid-induced osteonecrosis of the femoral head in rats by inhibiting the apoptosis of osteoblasts and osteocytes and increasing the expression of VEGF.

Antioxidant and antigenotoxic role of recombinant human erythropoeitin against alkylating agents: Cisplatin and mitomycin C in cultured Vero cells

Cisplatin (CDDP) and mitomycin C (MMC), two alkylating agents used against various solid tumours, are a common source of acute kidney injury. Thus, strategies for minimizing CDDP and MMC toxicity are of a clinical interest. In this study, we aimed to investigate the protective role of recombinant human erythropoietin (rhEPO) against oxidative stress and genotoxicity induced by CDDP and MMC in cultured Vero cells. Three types of treatments were performed: (i) cells were treated with rhEPO 24 h before exposure to CDDP/MMC (pre-treatment), (ii) cells were treated with rhEPO and CDDP/MMC simultaneously (co-treatment), (iii) cells were treated with rhEPO 24 h after exposure to CDDP/MMC (post-treatment). Our results showed that rhEPO decreased the reactive oxygen species levels, the malondialdehyde levels and ameliorated glutathione (reduced and oxidized glutathione) modulation induced by CDDP and MMC in cultured Vero cells. Furthermore, rhEPO administration prevented alkylating agents-induced DNA damage accessed by comet test. Altogether, our results suggested a protective role of rhEPO, against CDDP- and MMC-induced oxidative stress and genotoxicity, especially in pre-treatment condition.

The erythropoietin receptor is a downstream effector of Klotho-induced cytoprotection

Although the role of the erythropoietin (EPO) receptor (EpoR) in erythropoiesis has been known for decades, its role in nonhematopoietic tissues is still not well defined. Klotho has been shown and EPo has been suggested to protect against acute ischemia-reperfusion injury in the kidney. Here we found in rat kidney and in a rat renal tubular epithelial cell line (NRK cells) EpoR transcript and antigen, and EpoR activity signified as EPo-induced phosphorylation of Jak2, ErK, Akt, and Stat5 indicating the presence of functional EpoR. Transgenic overexpression of Klotho or addition of exogenous recombinant Klotho increased kidney EpoR protein and transcript. In NRK cells, Klotho increased EpoR protein, enhanced EPo-triggered phosphorylation of Jak2 and Stat5, the nuclear translocation of phospho-Stat5, and protected NRK cells from hydrogen peroxide cytotoxicity. Knockdown of endogenous EpoR rendered NRK cells more vulnerable, and overexpression of EpoR more resistant to peroxide-induced cytotoxicity, indicating that EpoR mitigates oxidative damage. Knockdown of EpoR by siRNA abolished Epo-induced Jak2, and Stat5 phosphorylation, and blunted the protective effect of Klotho against peroxide-induced cytotoxicity. Thus in the kidney, EpoR and its activity are downstream effectors of Klotho enabling it to function as a cytoprotective protein against oxidative injury.

Erythropoietin attenuates cardiac dysfunction by increasing myocardial angiogenesis and inhibiting interstitial fibrosis in diabetic rats

Background

Recent studies revealed that erythropoietin (EPO) has tissue-protective effects in the heart by increasing vascular endothelial growth factor (VEGF) expression and attenuating myocardial fibrosis in ischemia models. In this study, we investigated the effect of EPO on ventricular remodeling and blood vessel growth in diabetic rats.

Methods

Male SD rats were randomly divided into 3 groups: control rats, streptozotocin (STZ)-induced diabetic rats, and diabetic rats treated with 1000 U/kg EPO by subcutaneous injection once per week. Twelve weeks later, echocardiography was conducted, and blood samples were collected for counting of peripheral blood endothelial progenitor cells (EPCs). Myocardial tissues were collected, quantitative real-time PCR (RT-PCR) was used to detect the mRNA expression of VEGF and EPO-receptor (EPOR), and Western blotting was used to detect the protein expression of VEGF and EPOR. VEGF, EPOR, transforming growth factor beta (TGF-β), and CD31 levels in the myocardium were determined by immunohistochemistry. To detect cardiac hypertrophy, immunohistochemistry of collagen type I, collagen type III, and Picrosirius Red staining were performed, and cardiomyocyte cross-sectional area was measured.

Results

After 12 weeks STZ injection, blood glucose increased significantly and remained consistently elevated. EPO treatment significantly improved cardiac contractility and reduced diastolic dysfunction. Rats receiving the EPO injection showed a significant increase in circulating EPCs (27.85 ± 3.43%, P < 0.01) compared with diabetic untreated animals. EPO injection significantly increased capillary density as well as EPOR and VEGF expression in left ventricular myocardial tissue from diabetic rats. Moreover, EPO inhibited interstitial collagen deposition and reduced TGF-β expression.

Conclusions

Treatment with EPO protects cardiac tissue in diabetic animals by increasing VEGF and EPOR expression levels, leading to improved revascularization and the inhibition of cardiac fibrosis.

Splenectomy protects the kidneys against ischemic reperfusion injury in the rat

BACKGROUND

Ischemic reperfusion (I/R) injury of the kidney is closely associated with delayed graft function, increased acute rejection, and late allograft dysfunction. Splenectomy reduced hepatic I/R injury by inhibiting leukocyte infiltration in the liver, release of TNF-α, cell apoptosis, and expression of caspase-3. Thus, we investigated the effects of splenectomy on renal I/R injury in the rat.

METHODS

Male Wistar rats were assigned to four groups: sham operation (sham group), sham operation+splenectomy (sham+SPLN group), right nephrectomy followed by clamping the left renal pedicle for 30min (I/R 30 group), and I/R 30+splenectomy (I/R 30+SPLN group). Renal function was determined by measuring the concentration of blood urea nitrogen (BUN) and serum creatinine (S-Cr). The serum level of tumor necrosis factor-α (TNF-α) was measured as the marker for inflammation. Left kidneys were obtained 24h after reperfusion. TUNEL assay was assessed for cell apoptosis. Spleens were obtained immediately (0-h group) and 3h after reperfusion (3-h group). The removed spleens were histologically evaluated.

RESULTS

The BUN and S-Cr levels were significantly lower in the I/R 30+SPLN group than in the I/R 30 group (p<0.05 for both). Apoptotic cells were significantly lower in the I/R 30+SPLN group than in the I/R 30 group. The serum level of TNF-α, which was increased after I/R, was significantly lower in the I/R 30+SPLN group than in the I/R 30 group (p<0.05). Spleen weights were significantly lower in the 3-h group than in the 0-h group (p<0.05).

CONCLUSION

These results suggest that splenectomy reduces renal I/R injury, and this effect may occur by an anti-inflammatory pathway and inhibition of cell apoptosis.

Carbamylated Erythropoietin Ameliorates Cyclosporine Nephropathy without Stimulating Erythropoiesis

The introduction of cyclosporine (CsA) has improved graft survival, but it causes nephropathy, which limits its clinical utility. Recently, we reported that carbamylated erythropoietin (CEPO) protected kidneys from ischemia reperfusion injury as well as EPO. To investigate the clinical applications of CEPO, we next evaluated the long-term therapeutic effect of CEPO using a CsA-induced nephropathy model. CsA caused renal dysfunction, while EPO/CEPO administration significantly improved renal function. EPO treatment significantly increased Hb concentration, while CEPO treatment neither enhanced nor reduced Hb concentration. CsA treatment induced tubular apoptosis, while EPO/CEPO administration inhibited it and increased PI3 kinase activation and Akt phosphorylation. In parallel, morphological assessment revealed that EPO/CEPO significantly reduced CsA-induced interstitial fibrosis and inhibited interstitial macrophage infiltration. In addition, real-time RT-PCR demonstrated that cortical mRNA levels of TGF-β1 and type I collagen were suppressed in the EPO/CEPO group. These results suggest a new therapeutic approach using CEPO to protect kidneys from CsA-induced nephropathy.

Amelioration of renal ischemia-reperfusion injury with a novel protective cocktail

PURPOSE

Extended warm ischemia during partial nephrectomy can lead to considerable renal injury. Using a rat model of renal ischemia we examined the ability of a unique renoprotective cocktail to ameliorate warm ischemia-reperfusion injury.

MATERIALS AND METHODS

A warm renal ischemia model was developed using 60 Sprague-Dawley® rats. The left renal artery was clamped for 40 minutes, followed by 48 hours of reperfusion. A renoprotective cocktail of a mixture of specific growth factors, mitochondria protecting biochemicals and Manganese-Porphyrin (MnTnHex-2-PyP(5+)) was given intramuscularly at -24, 0 and 24 hours after surgery. At 48 hours the 2 kidneys were harvested and examined with hematoxylin and eosin, and periodic acid-Schiff stains. Protein and gene expression were also analyzed to determine ischemia markers and the antioxidant response.

RESULTS

Compared to ischemic controls, kidneys treated with the renoprotective cocktail showed significant reversal of morphological changes and a significant decrease in the specific ischemic markers lipocalin-2, mucin-1 and galectin-3. Quantitative reverse transcriptase-polymerase chain reaction revealed up-regulation of several antioxidant genes in treated animals.

CONCLUSIONS

According to histopathological and several molecular measures our unique renoprotective cocktail mitigated ischemia-reperfusion injury.

Protective effect of recombinant human erythropoeitin against cisplatin cytotoxicity and genotoxicity in cultured Vero cells

Cisplatin is an effective agent against various solid tumors. Despite its effectiveness, the dose of cisplatin that can be administered is limited by its nephrotoxicity. Therefore, strategies for minimising the toxicity of cisplatin are of a clinical interest. The aim of this study was to investigate the protective effect of recombinant human erythropoietin (rhEPO) against the cytotoxicity and apoptosis induced by cisplatin in cultured Vero cells. Three types of treatments were performed: (i) cells were treated with rhEPO 24 h before exposure to cisplatin (pre-treatment), (ii) cells were treated with rhEPO and cisplatin simultaneously (co-treatment), (iii) cells were treated with rhEPO 24 h after exposure to cisplatin (post-treatment). Our results showed that rhEPO reduced cisplatin-induced cell mortality. Besides, rhEPO administration prevented cisplatin-induced DNA damage. Furthermore, rhEPO decreased the caspase-3 activity and pro-apoptotic factors levels (p53 and Bax) induced by cisplatin. It increased also the expression of the anti-apoptotic factor Bcl2 in Vero cells. Altogether, our results suggest a protective action of rhEPO against cisplatin cytotoxicity and genotoxicity via an anti-apoptotic process. The most protective effect was observed with rhEPO when it was administrated 24 h before cisplatin treatment.

Intra-operative erythropoietin during laparoscopic partial nephrectomy is not renoprotective

PURPOSE

In pre-clinical studies, acute erythropoietin (EPO) administration has been shown to mitigate the deleterious effects of ischemia/reperfusion injury. We reviewed our clinical experience with intraoperative EPO administration as a potential renoprotective agent during laparoscopic partial nephrectomy (LPN).

METHODS

Patients who underwent LPN at our institution between August 2008 and March 2010 received 500 IU/kg EPO 30 min prior to hilar occlusion. Those who underwent LPN between August 2006 and July 2008 without receiving EPO were selected as controls. Demographic, clinical, perioperative, and estimated glomerular filtration rate (eGFR) data were compared for the cohorts preoperatively, and during short-term (<6 months) and long-term (≥6 months) follow-up.

RESULTS

Short-term eGFR was evaluable for 39 EPO and 29 controls, while long-term eGFR was evaluable for 26 EPO and 27 controls. Baseline demographic and clinical features of the cohorts were similar. For EPO versus controls, median short and long-term follow-up was 19 days versus 22 days and 10.2 months versus 11.9 months, respectively. Mean preoperative, postoperative, and % change in eGFR were statistically similar for the cohorts during short- and long-term follow-up, without and with adjustment for baseline renal function (unadjusted P-values = 0.28, 0.095, and 0.38, respectively, short term, and 0.61, 0.50, and 0.69, respectively, long term).

CONCLUSIONS

In this retrospective study, a single dose of EPO prior to hilar occlusion during LPN had no added protective impact on postoperative eGFR in the short or long term. Prospective evaluation in patients with solitary kidneys may better elucidate its potential renoprotective role in this setting.

Erythropoietin as a novel brain and kidney protective agent

Erythropoietin is a 30.4 kDa glycoprotein produced by the kidney, which is mostly known for its physiological function in regulating red blood cell production in the bone marrow Accumulating evidence, however suggests that erythropoietin has additional organ protective effects, which may specifically be useful in protecting the brain and kidneys from injury. Experimental evidence suggests that these protective mechanisms are multi-factorial in nature and may include inhibition of apoptotic cell death, stimulation of cellular regeneration, inhibition of deleterious pathways and promotion of recovery. In this article we review the physiology of erythropoietin, assess previous work that supports the role of erythropoietin as a general tissue protective agent and explain the mechanisms by which it may achieve this tissue protective effect. We then focus on specific laboratory and clinical data that suggest that erythropoietin has a strong brain protective and kidney protective effect. In addition, we comment on the implications of these studies for clinicians at the bedside and for researchers designing controlled trials to further elucidate the true clinical utility of erythropoietin as a neuroprotective and nephroprotective agent. Finally, we describe EPO-TBI, a double-blinded multi-centre randomised controlled trial involving the authors that is being conducted to investigate the organ protective effects of erythropoietin on the brain, and also assesses its effect on the kidneys.

Erythropoietin: a hormone with multiple functions

Erythropoietin (EPO), the main hemopoietic hormone synthesized by the kidney as well as by the liver in fetal life, is implicated in mammalian erythropoiesis. Production and secretion of EPO and the expression of its receptor (EPO-R) are regulated by tissue oxygenation. EPO and EPO-R, expressed in several tissues, exert pleiotropic activities and have different effects on nonhemopoietic cells. EPO is a cytokine with antiapoptotic activity and plays a potential neuroprotective and cardioprotective role against ischemia. EPO is also involved in angiogenesis, neurogenesis, and the immune response. EPO can prevent metabolic alterations, neuronal and vascular degeneration, and inflammatory cell activation. Consequently, EPO may be of therapeutic use for a variety of disorders. Many tumors express EPO and/or EPO-R, but the action of EPO on tumor cells remains controversial. It has been suggested that EPO promotes the proliferation and survival of cancer cells expressing EPO-R. On the other hand, other reports have concluded that EPO-R plays no role in tumor progression. This review provides a detailed insight into the nonhemopoietic role of EPO and its mechanism(s) of action which may lead to a better understanding of its potential therapeutic value in diverse clinical settings.

Erythropoietin (EPO) in acute kidney injury

Erythropoietin (EPO) is a 30.4 kDa glycoprotein produced by the kidney, and is mostly well-known for its physiological function in regulating red blood cell production in the bone marrow. Accumulating evidence, however, suggests that EPO has additional organ protective effects, which may be useful in the prevention or treatment of acute kidney injury. These protective mechanisms are multifactorial in nature and include inhibition of apoptotic cell death, stimulation of cellular regeneration, inhibition of deleterious pathways, and promotion of recovery.

In this article, we review the physiology of EPO, assess previous work that supports the role of EPO as a general tissue protective agent, and explain the mechanisms by which it may achieve this tissue protective effect. We then focus on experimental and clinical data that suggest that EPO has a kidney protective effect.

Effect of noble gases on oxygen and glucose deprived injury in human tubular kidney cells

The noble gas xenon has been shown to be protective in preconditioning settings against renal ischemic injury. The aims of this study were to determine the protective effects of the other noble gases, helium, neon, argon, krypton and xenon, on human tubular kidney HK2 cells in vitro. Cultured human renal tubular cells (HK2) were exposed to noble gas preconditioning (75% noble gas; 20% O(2); 5% CO(2)) for three hours or mock preconditioning. Twenty-four hours after gas exposure, cell injury was provoked with oxygen-glucose deprived (OGD) culture medium for three hours. Cell viability was assessed 24 h post-OGD by a 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide assay. Other cohorts of cultured cells were incubated in the absence of OGD in 75% noble gas, 20% O(2) and 5% CO(2) and cellular signals phospho-Akt (p-Akt), hypoxia-inducible factor-1alpha (HIF-1alpha) and Bcl-2 were assessed by Western blotting. OGD caused a reduction in cell viability to 0.382 +/- 0.1 from 1.0 +/- 0.15 at control (P < 0.01). Neon, argon and krypton showed no protection from injury (0.404 +/- 0.03; 0.428 +/- 0.02; 0.452 +/- 0.02; P > 0.05). Helium by comparison significantly enhanced cell injury (0.191 +/- 0.05; P < 0.01). Xenon alone exerted a protective effect (0.678 +/- 0.07; P < 0.001). In the absence of OGD, helium was also detrimental (0.909 +/- 0.07; P < 0.01). Xenon caused an increased expression of p-Akt, HIF-1alpha and Bcl-2, while the other noble gases did not modify protein expression. These results suggest that unlike other noble gases, preconditioning with the anesthetic noble gas xenon may have a role in protection against renal ischemic injury.

Differential resolution of inflammation and recovery after renal ischemia-reperfusion injury in Brown Norway compared with Sprague Dawley rats

To investigate mechanisms conferring susceptibility or resistance to renal ischemia, we used two rat strains known to exhibit different responses to ischemia-reperfusion. We exposed proximal tubule cells isolated from Sprague Dawley or Brown Norway rats, to a protocol of hypoxia, followed by reoxygenation in vitro. The cells isolated from both rat strains exhibited comparable responses in the disruption of intercellular adhesions and cytoskeletal damage. In vivo, after 24 h of reperfusion, both strains showed similar degrees of injury. However, after 7 days of reperfusion, renal function and tubular structure almost completely recovered and inflammation resolved, but only in Brown Norway rats. Hypoxia-inducible factor-dependent gene expression, ERK1/2, and Akt activation were different in the two strains. Inflammatory mediators MCP-1, IL-10, INF-gamma, IL-1beta, and TNF-alpha were similarly induced at 24 h in both strains but were downregulated earlier in Brown Norway rats, which correlated with shorter NFkappaB activation in the kidney. Moreover, VLA-4 expression in peripheral blood lymphocytes and VCAM-1 expression in kidney tissues were initially similar at 24 h but reached basal levels earlier in Brown Norway rats. The faster resolution of inflammation in Brown Norway rats suggests that this strain might be a useful experimental model to determine the mechanisms that promote repair of renal ischemia-reperfusion injury.

Impact of innate and adaptive immunity on rejection and tolerance

Until recently, research on transplantation rejection and tolerance has been directed toward deciphering the mechanisms of the adaptive immune system. However, the emergence that the innate immune system, the body's first-line defense against pathogens, has a strong influence on adaptive immunity has galvanized interest in elucidating the interplay between these two arms of the immune system. The discovery of Toll-like receptors and the characterization of the cellular mediators involved in innate immunity have provided growing evidence that innate immunity affects the adaptive immune response. Emerging evidence has also shown that early "danger signals"' associated with ischemia-reperfusion injury or brain death contribute to innate immune activation, promoting rejection, and inhibiting tolerance induction. In addition, nonspecific stimuli such as increased donor age or patient disease may also serve to exert a synergistic influence on innate immune activation. Ultimately, controlling the events in innate immune activation may help drive tolerance induction and reduce the rate of rejection.

The erythropoietin receptor in normal and cancer tissues

The hormone erythropoietin (EPO) is essential for the survival, proliferation and differentiation of the erythrocytic progenitors. The EPO receptor (EPO-R) of erythrocytic cells belongs to the cytokine class I receptor family and signals through various protein kinases and STAT transcription factors. The EPO-R is also expressed in many organs outside the bone marrow, suggesting that EPO is a pleiotropic anti-apoptotic factor. The controversial issue as to whether the EPO-R is functional in tumor tissue is critically reviewed. Importantly, most studies of EPO-R detection in tumor tissue have provided falsely positive results because of the lack of EPO-R specific antibodies. However, endogenous EPO appears to be necessary to maintain the viability of endothelial cells and to promote tumor angiogenesis. Although there is no clinical proof that the administration of erythropoiesis stimulating agents (ESAs) promotes tumor growth and mortality, present recommendations are that (i) ESAs should be administered at the lowest dose sufficient to avoid the need for red blood cell transfusions, (ii) ESAs should not be used in patients with active malignant disease not receiving chemotherapy or radiotherapy, (iii) ESAs should be discontinued following the completion of a chemotherapy course, (iv) the target Hb should be 12 g/dL and not higher and (v) the risks of shortened survival and tumor progression have not been excluded when ESAs are dosed to target Hb <12 g/dL.

Renal repair and recovery

OBJECTIVE

To review the cellular and molecular mechanisms of renal repair and recovery after acute kidney injury (AKI).

DATA SOURCE

The data were summarized from published research articles.

RESULTS

In AKI, there is an acute inflammatory response, epithelial cell necrosis and apoptosis, and shedding of epithelial cells into the tubular lumen. Recent work demonstrates that repopulation of damaged renal tubules occurs primarily from proliferation of tubular epithelial cells and resident renal-specific stem cells, with some contribution of paracrine factors from bone marrow-derived mesenchymal stem cells. In addition, growth factors seem to play a critical role in the repair process in animal models of renal injury. However, attempts to use growth factors in the clinical setting to attenuate human AKI or accelerate renal repair have not yet been successful. The endothelium also plays a critical role in the pathogenesis of AKI. Lastly, in human studies, the effect of dialysis on renal recovery remains poorly understood.

CONCLUSIONS

Experimental animal models of AKI demonstrate that renal recovery and repair involves proliferation of tubular epithelial cells and stem cell populations and the coordinated contribution of multiple growth factors. Future efforts to improve recovery from AKI and improve patient outcomes may include novel therapies based on manipulation of populations of stem cells and augmenting repopulation of renal tubules.

Erythropoietin stimulates normal endothelial progenitor cell-mediated endothelial turnover, but attributes to neovascularization only in the presence of local ischemia

PURPOSE

We aimed to evaluate whether ischemia is required for erythropoietin (EPO) induced stimulation of endothelial progenitor cells (EPCs) and their related effects on endothelial and cardiac function.

METHODS

Bone marrow of rats was replaced by transgenic cells to allow tracking of EPCs. Ischemic heart failure was induced by left coronary artery ligation to induce myocardial infarction (MI) and control rats received a sham procedure. Three weeks after surgery, rats were randomized to receive EPO (darbepoetin alfa 40 microg/kg per 3 weeks) or vehicle and were sacrificed 9 weeks after surgery.

RESULTS

In all treated groups, EPO significantly increased circulating EPCs and their incorporation into the endothelium of the ischemic and non-ischemic hearts as well as in the control organs; kidney and liver. This was associated with significantly improved endothelial function, which was strongly correlated with circulating EPCs (R = 0.7, p < 0.01). However, additional EPCs preferentially homed to the ischemic MI borderzone (p < 0.01) resulting in specific EPO-induced improvement of cardiac microvascularization and performance only in ischemic hearts (all p < 0.05). The differential stimulation of neovascularization by EPO was associated with increased EPO-receptor and VEGF expression in ischemic hearts only.

CONCLUSIONS

In general, EPO stimulates normal endothelial progenitor cell-mediated endothelial turnover, but improves cardiac microvascularization and function only in the presence of ischemia.

Novel pharmacological approaches to the treatment of renal ischemia-reperfusion injury: a comprehensive review

Renal ischemia-reperfusion (I-R) contributes to the development of ischemic acute renal failure (ARF). Multi-factorial processes are involved in the development and progression of renal I-R injury with the generation of reactive oxygen species, nitric oxide and peroxynitrite, and the decline of antioxidant protection playing major roles, leading to dysfunction, injury, and death of the cells of the kidney. Renal inflammation, involving cytokine/adhesion molecule cascades with recruitment, activation, and diapedesis of circulating leukocytes is also implicated. Clinically, renal I-R occurs in a variety of medical and surgical settings and is responsible for the development of acute tubular necrosis (a characteristic feature of ischemic ARF), e.g., in renal transplantation where I-R of the kidney directly influences graft and patient survival. The cellular mechanisms involved in the development of renal I-R injury have been targeted by several pharmacological interventions. However, although showing promise in experimental models of renal I-R injury and ischemic ARF, they have not proved successful in the clinical setting (e.g., atrial natriuretic peptide, low-dose dopamine). This review highlights recent pharmacological developments, which have shown particular promise against experimental renal I-R injury and ischemic ARF, including novel antioxidants and antioxidant enzyme mimetics, nitric oxide and nitric oxide synthase inhibitors, erythropoietin, peroxisome-proliferator-activated receptor agonists, inhibitors of poly(ADP-ribose) polymerase, carbon monoxide-releasing molecules, statins, and adenosine. Novel approaches such as recent research involving combination therapies and the potential of non-pharmacological strategies are also considered.