The continuous erythropoietin receptor activator affects different pathways of diabetic renal injury

Kidney pericyte hypoxia-inducible factor regulates erythropoiesis but not kidney fibrosis

Prolyl hydroxylase domain enzyme (PHD) inhibitors are effective in the treatment of chronic kidney disease (CKD)-associated anemia by stabilizing hypoxia inducible factor (HIF), thereby increasing erythropoietin and consequently erythropoiesis. However, concern for CKD progression needs to be addressed in clinical trials. Although pre-clinical studies showed an anti-inflammatory effect in kidney disease models, the effect of PHD inhibitors on kidney fibrosis was inconsistent probably because the effects of HIF are cell type and context dependent. The major kidney erythropoietin-producing cells are pericytes that produce erythropoietin through HIF-2α-dependent gene transcription. The concern for the impact of HIF in pericytes on kidney fibrosis arises from the fact that pericytes are the major precursor cells of myofibroblasts in CKD. Since cells expressing Gli1 fulfill the morphologic and anatomic criteria for pericytes, we induced Gli1⁺ cell-specific HIF stabilization or knockout to study the impact of HIF in pericytes on kidney pathology of mice with or without fibrotic injury induced by unilateral ureteral obstruction. Compared with the littermate controls, mice with pericyte-specific HIF stabilization due to von Hippel-Lindau protein or PHD2 knockout showed increased serum erythropoietin and polycythemia rather than a discernible difference in kidney fibrosis. Compared with Gli1⁺ pericytes sorted from littermate controls, Gli1⁺ pericytes sorted from PHD2 knockout mice showed increased erythropoietin gene expression rather than discernible changes in Col1a1 or Acta2 expression. Furthermore, pericyte-specific knockout of HIF-1α or HIF-2α did not affect kidney fibrosis. Thus, our study supports the absence of negative effects of PHD inhibitors on kidney fibrosis of mice despite HIF stabilization in pericytes.

Effects of Allicin on Pathophysiological Mechanisms during the Progression of Nephropathy Associated to Diabetes

This study aimed to assess the impact of allicin on the course of diabetic nephropathy. Study groups included control, diabetes, and diabetes-treated rats. Allicin treatment (16 mg/kg day/p.o.) started after 1 month of diabetes onset and was administered for 30 days. In the diabetes group, the systolic blood pressure (SBP) increased, also, the oxidative stress and hypoxia in the kidney cortex were evidenced by alterations in the total antioxidant capacity as well as the expression of nuclear factor (erythroid-derived 2)-like 2/Kelch ECH associating protein 1 (Nrf2/Keap1), hypoxia-inducible factor 1-alpha (HIF-1α), vascular endothelial growth factor (VEGF), erythropoietin (Epo) and its receptor (Epo-R). Moreover, diabetes increased nephrin, and kidney injury molecule-1 (KIM-1) expression that correlated with mesangial matrix, the fibrosis index and with the expression of connective tissue growth factor (CTGF), transforming growth factor-β1 (TGF-β1), and α-smooth muscle actin (α-SMA). The insulin levels and glucose transporter protein type-4 (GLUT4) expression were decreased; otherwise, insulin receptor substrates 1 and 2 (IRS-1 and IRS-2) expression was increased. Allicin increased Nrf2 expression and decreased SBP, Keap1, HIF-1α, and VEGF expression. Concurrently, nephrin, KIM-1, the mesangial matrix, fibrosis index, and the fibrotic proteins were decreased. Additionally, allicin decreased hyperglycemia, improved insulin levels, and prevented changes in (GLUT4) and IRSs expression induced by diabetes. In conclusion, our results demonstrate that allicin has the potential to help in the treatment of diabetic nephropathy. The cellular mechanisms underlying its effects mainly rely on the regulation of antioxidant, antifibrotic, and antidiabetic mechanisms, which can contribute towards delay in the progression of renal disease.

Review of Alterations in Perlecan-Associated Vascular Risk Factors in Dementia

Perlecan is a heparan sulfate proteoglycan protein in the extracellular matrix that structurally and biochemically supports the cerebrovasculature by dynamically responding to changes in cerebral blood flow. These changes in perlecan expression seem to be contradictory, ranging from neuroprotective and angiogenic to thrombotic and linked to lipid retention. This review investigates perlecan's influence on risk factors such as diabetes, hypertension, and amyloid that effect Vascular contributions to Cognitive Impairment and Dementia (VCID). VCID, a comorbidity with diverse etiology in sporadic Alzheimer's disease (AD), is thought to be a major factor that drives the overall clinical burden of dementia. Accordingly, changes in perlecan expression and distribution in response to VCID appears to be injury, risk factor, location, sex, age, and perlecan domain dependent. While great effort has been made to understand the role of perlecan in VCID, additional studies are needed to increase our understanding of perlecan's role in health and in cerebrovascular disease.

CERA Attenuates Kidney Fibrogenesis in the db/db Mouse by Influencing the Renal Myofibroblast Generation

Tubulointerstitial fibrosis (TIF) is a pivotal pathophysiological process in patients with diabetic nephropathy (DN). Multiple profibrotic factors and cell types, including transforming growth factor beta 1 (TGF-β1) and interstitial myofibroblasts, respectively, are responsible for the accumulation of extracellular matrix in the kidney. Matrix-producing myofibroblasts can originate from different sources and different mechanisms are involved in the activation process of the myofibroblasts in the fibrotic kidney. In this study, 16-week-old db/db mice, a model for type 2 DN, were treated for two weeks with continuous erythropoietin receptor activator (CERA), a synthetic erythropoietin variant with possible non-hematopoietic, tissue-protective effects. Non-diabetic and diabetic mice treated with placebo were used as controls. The effects of CERA on tubulointerstitial fibrosis (TIF) as well as on the generation of the matrix-producing myofibroblasts were evaluated by morphological, immunohistochemical, and molecular biological methods. The placebo-treated diabetic mice showed significant signs of beginning renal TIF (shown by picrosirius red staining; increased connective tissue growth factor (CTGF), fibronectin and collagen I deposition; upregulated KIM1 expression) together with an increased number of interstitial myofibroblasts (shown by different mesenchymal markers), while kidneys from diabetic mice treated with CERA revealed less TIF and fewer myofibroblasts. The mechanisms, in which CERA acts as an anti-fibrotic agent/drug, seem to be multifaceted: first, CERA inhibits the generation of matrix-producing myofibroblasts and second, CERA increases the ability for tissue repair. Many of these CERA effects can be explained by the finding that CERA inhibits the renal expression of the cytokine TGF-β1.

Restricted Use of Erythropoiesis-Stimulating Agent is Safe and Associated with Deferred Dialysis Initiation in Stage 5 Chronic Kidney Disease

The effect of erythropoiesis-stimulating agent (ESA) on dialysis initiation in advanced chronic kidney disease (CKD) patients is not clear. We retrospectively analyzed the outcome of dialysis initiation in a stage 5 CKD cohort with ESA reimbursement limited to the maximal standardized monthly ESA dose equivalent to epoetin beta 20,000 U by the National Health Insurance program. Totally 423 patients were followed up for a median of 1.37 year. A time-dependent Cox regression model, adjusted for monthly levels of estimated glomerular filtration rate (eGFR) and hemoglobin, was constructed to investigate the association between ESA and outcome. The standardized monthly ESA dose in ESA users was 16,000 ± 3,900 U of epoetin beta. Annual changes of hemoglobin were −0.29 ± 2.19 and −0.99 ± 2.46 g/dL in ESA users and ESA non-users, respectively (P = 0.038). However, annual eGFR decline rates were not different between ESA users and non-users. After adjustment, ESA use was associated with deferred dialysis initiation (hazard ratio 0.63, 95% confidence interval 0.42–0.93, P = 0.021). The protective effect remained when the monthly ESA doses were incorporated. Our data showed that restricted use of ESA was safe and associated with deferred dialysis initiation in stage 5 CKD patients.

Erythropoietin, a novel versatile player regulating energy metabolism beyond the erythroid system

Erythropoietin (EPO), the required cytokine for promoting the proliferation and differentiation of erythroid cells to stimulate erythropoiesis, has been reported to act as a pleiotropic cytokine beyond hematopoietic system. The various activities of EPO are determined by the widespread distribution of its cell surface EPO receptor (EpoR) in multiple tissues including endothelial, neural, myoblasts, adipocytes and other cell types. EPO activity has been linked to angiogenesis, neuroprotection, cardioprotection, stress protection, anti-inflammation and especially the energy metabolism regulation that is recently revealed. The investigations of EPO activity in animals and the expression analysis of EpoR provide more insights on the potential of EPO in regulating energy metabolism and homeostasis. The findings of crosstalk between EPO and some important energy sensors and the regulation of EPO in the cellular respiration and mitochondrial function further provide molecular mechanisms for EPO activity in metabolic activity regulation. In this review, we will summarize the roles of EPO in energy metabolism regulation and the activity of EPO in tissues that are tightly associated with energy metabolism. We will also discuss the effects of EPO in regulating oxidative metabolism and mitochondrial function, the interactions between EPO and important energy regulation factors, and the protective role of EPO from stresses that are related to metabolism, providing a brief overview of previously less appreciated EPO biological function in energy metabolism and homeostasis.

Probucol inhibited Nox2 expression and attenuated podocyte injury in type 2 diabetic nephropathy of db/db mice

The present study was conducted to investigate the effects of probucol on the progression of diabetic nephropathy and the underlying mechanism in type 2 diabetic db/db mice. Eight weeks db/db mice were treated with regular diet or probucol-containing diet (1%) for 12 weeks. Non-diabetic db/m mice were used as controls. We examined body weight, blood glucose, and urinary albumin. At 20 weeks, experimental mice were sacrificed and their blood and kidneys were extracted for the analysis of blood chemistry, kidney histology, oxidative stress marker, and podocyte marker. As a result, 24 h urinary albumin excretions were reduced after probucol treatment. There were improvements of extracellular matrix accumulation and fibronectin and collagen IV deposition in glomeruli in the probucol-treated db/db mice. The reduction of nephrin and the loss of podocytes were effectively prevented by probucol in db/db mice. Furthermore, probucol significantly decreased the production of thiobarbituric acid-reactive substances (TBARS), an index of reactive oxygen species (ROS) generation and down-regulated the expression of Nox2. Taken together, our findings support that probucol may have the potential to protect against type 2 diabetic nephropathy via amelioration of podocyte injury and reduction of oxidative stress.

Erythropoietin action in stress response, tissue maintenance and metabolism

Erythropoietin (EPO) regulation of red blood cell production and its induction at reduced oxygen tension provides for the important erythropoietic response to ischemic stress. The cloning and production of recombinant human EPO has led to its clinical use in patients with anemia for two and half decades and has facilitated studies of EPO action. Reports of animal and cell models of ischemic stress in vitro and injury suggest potential EPO benefit beyond red blood cell production including vascular endothelial response to increase nitric oxide production, which facilitates oxygen delivery to brain, heart and other non-hematopoietic tissues. This review discusses these and other reports of EPO action beyond red blood cell production, including EPO response affecting metabolism and obesity in animal models. Observations of EPO activity in cell and animal model systems, including mice with tissue specific deletion of EPO receptor (EpoR), suggest the potential for EPO response in metabolism and disease.

Renoprotective effect of epoetin beta pegol by the prevention of M2 macrophage recruitment in Thy-1 rats

BACKGROUND

Glomerulonephritis (GN) develops via accumulation of extracellular matrix through macrophage recruitment in glomeruli. It is unclear whether epoetin beta pegol (continuous erythropoietin receptor activator, CERA), a long-acting erythropoiesis-stimulating agent, exerts a renoprotective effect by preventing glomerulosclerosis. We examined the renoprotective effect of CERA in rats with Thy-1 glomerulonephritis (Thy-1-GN), an animal model for mesangial proliferative glomerulonephritis.

METHODS

Thy-1-GN was induced in F344 rats by injection of anti-Thy1.1 antibody. CERA (25 µg/kg) was intravenously administered 4 h before anti-Thy1.1 antibody injection. After 6 days, blood and urine was collected for biochemical analysis and kidneys harvested for analysis of histopathology and mRNA expression.

RESULTS

In Thy-1-GN rats, CERA suppressed increased urinary total protein, urea nitrogen, and N-acetyl-β-(D)-glucosaminidase. CERA significantly prevented glomerulosclerosis and expression of α-smooth muscle actin, collagen-1, and fibronectin. Increased macrophage infiltration and up-regulated monocyte chemotactic protein-1 were significantly suppressed by CERA. Furthermore, CERA also suppressed up-regulation of arginase-1, a marker of M2 macrophages. Arginase-1 expression levels strongly correlated with levels of collagen-1 and fibronectin mRNA.

CONCLUSIONS

These results suggest that CERA has potential to protect kidney function through the prevention of glomerulosclerosis, accompanied by prevention of M2 macrophage recruitment.

Glutaraldehyde erythropoietin protects kidney in ischaemia/reperfusion injury without increasing red blood cell production

BACKGROUND AND PURPOSE

Recombinant human erythropoietin (rHuEPO) is currently the mainstay of renal anaemia treatment. Recently, rHuEPO has been shown to provide pleiotrophic tissue protection in various pathological conditions. However, the benefits of rHuEPO beyond anaemia treatment are limited because it increases red blood cell mass. Carbamylated erythropoietin (CEPO) is the first rHuEPO derivative that lacks erythropoietic activity but retains tissue protection properties. Since carbamylation targets lysine residues on rHuEPo, we hypothesized that targeted lysine modifications of rHuEPO may result in a novel non-erythropoietic erythropoietin.

EXPERIMENTAL APPROACH

rHuEPO was subjected to various targeted lysine modifications. In vitro cytoprotection and apoptosis were evaluated using P19 and HEK293 cells. In vivo erythropoiesis was performed by administering the derivatives to animals for 2 weeks. Renoprotection was tested on an ischaemia/reperfusion (I/R) model.

KEY RESULTS

We synthesized a novel derivative, a glutaraldehyde erythropoietin (GEPO). This construct abolished in vivo erythropoiesis. Biochemical characterization showed that GEPO was more electrostatically negative than rHuEPO. Immunoprecipitation experiments revealed that GEPO bound to the IL3RB/EPOR heterotrimeric receptor and ameliorated cellular apoptosis via the activation of Bcl-2. Notably, Bcl-2 activation was suppressed by the JAK2 inhibitor, tyrphostin AG490. In vivo experiments showed that GEPO also ameliorated kidney damage due to I/R injury both functionally and histologically.

CONCLUSIONS AND IMPLICATIONS

Herein, we describe a novel lysine-modified rHuEPO, glutaradehyde-EPO (GEPO), obtained from a simple reaction. This derivative has no erythropoietic properties but retains cell-protective characteristics both in vitro and in vivo, with promise for future use as an adjunctive treatment of kidney disease.

Effect of methoxy polyethylene glycol-epoetin beta on oxidative stress in predialysis patients with chronic kidney disease

Background

There is data in the literature indicating increased oxidative stress in chronic kidney disease (CKD). Erythropoiesis-stimulating agents (ESAs), which are commonly used to treat anemia in patients with CKD, seem to have an antioxidant action, which could be a part of nephroprotection. The aim of the current study was to investigate the effect of a long half-life ESA, methoxy polyethylene glycol-epoetin beta (Mircera), on some markers of oxidative stress in predialysis patients with CKD.

Material/Methods

Peripheral blood was collected from 28 predialysis CKD patients 2 times, before Mircera treatment and after achieving target hemoglobin (Hb), and 15 healthy subjects (control group). Superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), and catalase (CAT) activity in erythrocytes were measured according to commonly used methods as a function of the antioxidant defense system. To assess reactive oxygen species (ROS) production, malondialdehyde (MDA) concentration in erythrocytes and in plasma was measured according to a commonly used method.

Results

SOD, GSH-Px, and CAT activity were similar, but plasma and erythrocyte MDA concentrations were significantly higher in CKD patients before ESA treatment in comparison to the control group. SOD, GSH-Px, and CAT activity was significantly higher, but plasma and erythrocyte MDA concentrations were significantly lower, in CKD patients after ESA treatment in comparison to these patients before treatment. We did not find a significant correlation between Hb concentration and SOD, GSH-Px, and CAT activity and plasma, as well as erythrocyte MDA concentrations. Analysis of all investigated groups showed a significant negative correlation between Hb concentration and plasma MDA concentration.

Conclusions

Our results suggest that treatment of anemia with methoxy polyethylene glycol-epoetin beta may inhibit oxidative stress in predialysis patients with CKD by enhancing the antioxidant defense system and reducing ROS production.

Erythropoietin ameliorates podocyte injury in advanced diabetic nephropathy in the db/db mouse

Podocyte damage and accumulation of advanced glycation end products (AGEs) are characteristics of diabetic nephropathy (DN). The pathophysiology of AGE-challenged podocytes, such as hypertrophy, apoptosis, and reduced cell migration, is closely related to the induction of the cell cycle inhibitor p27Kip1 and to the inhibition of neuropilin 1 (NRP1). We have previously demonstrated that treatment with erythropoietin is associated with protective effects for podocytes in vitro. db/ db mice with overt DN aged 15–16 wk were treated with either placebo, epoetin-β, or continuous erythropoietin receptor activator (CERA) for 2 wk. db/ db mice compared with nondiabetic db/ m control mice revealed the expected increases in body weight, blood glucose, albumin-to-creatinine ratio, and AGE accumulation. Whereas there were no differences in body weight, hyperglycemia and AGEs were observed among diabetic mice that received epoetin-β compared with CERA and placebo treatment, indicating that epoetin-β/CERA treatment does not interfere with the development of diabetes in this model. However, the albumin-to-creatinine ratio was significantly lower in db/ db mice treated with epoetin-β or CERA. Furthermore, kidney weights in db/ db mice were increased compared with db/ m control mice, indicating renal hypertrophy, whereas the increase in renal weight in epoetin-β- or CERA-treated db/ db mice was significantly lower than in placebo-treated control mice. Induction of p27Kip1 and suppression of NRP1 were significantly reduced in the epoetin-β treatment group versus the CERA treatment group. Furthermore, erythropoietin treatment diminished the diabetes-induced podocyte loss. Together, independently from hematopoetic effects, epoetin-β or CERA treatment was associated with protective changes in DN, especially that NRP1 and p27Kip1 expressions as well as numbers of podocytes returned to normal levels. Our data show, for the first time, that medication of overt DN with erythropoietin for a short time can ameliorate albuminuria and podocyte loss.

The protective effects of erythropoietin on rat glomerular podocytes in culture are modulated by extracellular matrix proteins

BACKGROUND/AIMS

Podocytes are typically cultured on collagen I; however, collagen I is absent from healthy glomerular basement membranes. Erythropoietin (EPO) is thought to protect podocytes in vivo. Here, we studied how various types of extracellular matrix (ECM) proteins and EPO affect podocytes in culture.

METHODS

Primary rat podocytes were replated on collagen I, collagen IV, whole ECM extract, laminin, or bare plastic. Cellular adhesion (8 hours after plating), proliferation (5 days, 10 % serum), and resistance to serum deprivation (3 days, 0.5 % serum) were assessed. BrdU incorporation and expression of podocyte-specific markers were employed as measures of cellular proliferation and differentiation, respectively. qPCR was used to verify expression of EPO receptor in cultured podocytes.

RESULTS

Cellular adhesion was similar on all ECM proteins and unaffected by EPO. Proliferation was accelerated by laminin and the ECM extract, but the final cell density was similar on all ECM surfaces. Collagen IV supported the serum-deprived cells better than the other ECM proteins. EPO (2-20 ng/ml) improved viability of serum-deprived podocytes on collagen I, collagen IV, and ECM, but not on laminin or bare plastic. The cells expressed mRNA for EPO receptor.

CONCLUSION

The physiological ECM proteins are more supportive of primary podocytic cultures compared with collagen I. The protective effects of EPO during serum deprivation are modulated by the cultivation surface.

The nephroprotective properties of recombinant human erythropoietin in kidney transplantation: experimental facts and clinical proofs

Adaptive responses to hypoxia, including hypoxia-inducible factor signaling, allow the cell to satisfy its basal metabolic demand and avoid death, but these responses can also be deleterious by promoting inflammation, cell dedifferentiation and fibrogenesis. Therefore, targeting hypoxia constitutes a promising therapeutic avenue. Recombinant human erythropoietin (rhEPO) appeared as a good candidate therapy because its hematopoietic properties could reverse anemia, and its tissue-protective properties could reduce cell death and limit maladaptive cellular responses to hypoxia. Despite experimental evidence on the nephroprotecive properties of rhEPO, recent clinical trials provided evidence that rhEPO was ineffective in preventing delayed graft function after ischemic acute injury but that the normalization of hemoglobin values preserved kidney function deterioration and reduced graft loss. Our aim here is to provide a survey of the rationale for evaluating the administration of rhEPO in the setting of kidney transplantation. We will discuss the intriguing findings that emerged from the clinical trials and the discrepancies between promising experimental results and negative clinical studies, as well as the differences in terms of the benefits and safety profiles of the normalization of hemoglobin values in chronic kidney disease patients and kidney transplant patients.

Renoprotection by continuous erythropoietin receptor activator in puromycin aminonucleoside-induced nephrotic syndrome

BACKGROUND/AIMS

Recent studies have demonstrated that erythropoiesis-stimulating agents (ESAs) induce a tissue-protective effect in the kidney. In this study, we examined whether continuous erythropoietin receptor activator (CERA), a long-acting ESA, could prevent kidney injury, especially podocyte damage, in a rat model of nephrotic syndrome induced by puromycin aminonucleoside (PAN).

METHODS

Rats were injected with CERA (30 µg/kg) or vehicle 4 h before the injection of PAN (50 mg/kg). Renal function, kidney injury, and podocyte damage were assessed at 7 days.

RESULTS

The levels of proteinuria, BUN, and plasma creatinine significantly increased in rats with PAN-induced nephrosis. Treatment with CERA significantly prevented these deteriorations induced by PAN. Glomerular lesions, especially vacuolation of podocytes, and the increase of desmin expression in PAN-treated rats were significantly ameliorated by treatment with CERA. Treatment with CERA also significantly prevented the decrease in the protein productions of nephrin and podocin in the kidneys of PAN-treated rats. We found persistent activation of the Akt signaling pathway in the kidneys of CERA-treated rats.

CONCLUSION

CERA could ameliorate renal dysfunction in PAN-induced nephrosis, which might be due to the amelioration of podocyte injury. CERA inhibited the depletion of nephrin and podocin, key components of the glomerular filtration barrier, and alleviated proteinuria. Activation of the Akt signaling pathway might be involved in the renoprotective effect of CERA.

Effects of continuous erythropoietin receptor activator in sepsis-induced acute kidney injury and multi-organ dysfunction

BACKGROUND

Despite advances in supportive care, sepsis-related mortality remains high, especially in patients with acute kidney injury (AKI). Erythropoietin can protect organs against ischemia and sepsis. This effect has been linked to activation of intracellular survival pathways, although the mechanism remains unclear. Continuous erythropoietin receptor activator (CERA) is an erythropoietin with a unique pharmacologic profile and long half-life. We hypothesized that pretreatment with CERA would be renoprotective in the cecal ligation and puncture (CLP) model of sepsis-induced AKI.

METHODS

RATS WERE RANDOMIZED INTO THREE GROUPS: control; CLP; and CLP+CERA (5 µg/kg body weight, i.p. administered 24 h before CLP). At 24 hours after CLP, we measured creatinine clearance, biochemical variables, and hemodynamic parameters. In kidney tissue, we performed immunoblotting--to quantify expression of the Na-K-2Cl cotransporter (NKCC2), aquaporin 2 (AQP2), Toll-like receptor 4 (TLR4), erythropoietin receptor (EpoR), and nuclear factor kappa B (NF-κB)--and immunohistochemical staining for CD68 (macrophage infiltration). Plasma interleukin (IL)-2, IL-1β, IL-6, IL-10, interferon gamma, and tumor necrosis factor alpha were measured by multiplex detection.

RESULTS

Pretreatment with CERA preserved creatinine clearance and tubular function, as well as the expression of NKCC2 and AQP2. In addition, CERA maintained plasma lactate at normal levels, as well as preserving plasma levels of transaminases and lactate dehydrogenase. Renal expression of TLR4 and NF-κB was lower in CLP+CERA rats than in CLP rats (p<0.05 and p<0.01, respectively), as were CD68-positive cell counts (p<0.01), whereas renal EpoR expression was higher (p<0.05). Plasma levels of all measured cytokines were lower in CLP+CERA rats than in CLP rats.

CONCLUSION

CERA protects against sepsis-induced AKI. This protective effect is, in part, attributable to suppression of the inflammatory response.

High glucose stimulates the expression of erythropoietin in rat glomerular epithelial cells

It has been reported that the levels of erythropoietin are associated with diabetes mellitus. Glomerular epithelial cells, located in the renal cortex, play an important role in the regulation of kidney function and hyperglycemia-induced cell loss of glomerular epithelial cells is implicated in the onset of diabetic nephropathy. This study investigated the effect of high glucose on erythropoietin and erythropoietin receptor expression in rat glomerular epithelial cells. We found that 25 mM D-glucose, but not mannitol or L-glucose, stimulated erythropoietin mRNA and protein expression in a time dependent manner (>4 h) in rat glomerular epithelial cells. In addition, 25 mM glucose, but not mannitol or L-glucose, also increased the phosphorylation of erythropoietin receptor, suggesting a role for erythropoietin receptor phosphorylation in erythropoietin synthesis. We conclude that high glucose stimulates erythropoietin production and erythropoietin receptor phosphorylation in rat glomerular epithelial cells.

The effect of low-dose Continuous Erythropoietin receptor activator in an experimental model of acute Cyclosporine A induced renal injury

The use of Cyclosporine A (CsA) as rejection prophylaxis following organ transplantation is limited by its nephrotoxicity. CsA induces renal damage that is associated with tubulo-interstitial injury and parenchymal sequestration of macrophages, perpetuating pro-inflammatory processes. Furthermore, CsA exerts a diabetogenic effect by damaging pancreatic islet cell integrity. Continuous Erythropoietin Receptor Activator (CERA) was shown to mediate tissue-protective and anti-inflammatory effects in various settings of organ injury. Here, we investigated the effect of low dose CERA in a model of CsA-induced renal and pancreatic injury. Rats were exposed to medium-dose CsA for 28 days. Low-dose CERA was given to the treatment group (CERA) (n=6) once per week vs. a CsA-treated control group (CONTROL) (n=6). The effect of CERA on renal and pancreatic injuries was analyzed by organ function, histology, immunohistochemistry (CD68(+)-macrophages, insulin), ELISA (TGF-β1) and RT-PCR (TGF-β1, Osteopontin, IL-10). CsA induced functional kidney damage. Low dose CERA did not lead to improved kidney function in the treatment group. However, low dose CERA showed a trend toward upregulation of osteopontin accompanied by increased renal macrophage-infiltration and enhanced parenchymal TGF-β1 and IL-10 when compared to controls. Moreover, CERA treated animals showed amelioration of pancreatic islet cell injury. In this model of acute CsA-mediated renal injury, low dose CERA administration was associated with anti-inflammatory effects and preservation of pancreatic islet cell viability.

Aliskiren enhances protective effects of valsartan against type 2 diabetic nephropathy in mice

OBJECTIVES

Addition of aliskiren, a direct renin inhibitor, to losartan provides additive reduction of urinary albumin excretion in type 2 diabetic patients. However, the detailed effect of aliskiren on type 2 diabetic nephropathy is still unknown. This study was undertaken to examine the efficacy of aliskiren and the combination of aliskiren with valsartan on type 2 diabetic nephropathy.

METHODS

db/db mice were treated with aliskiren (3 mg/kg per day), valsartan (5 or 10 mg/kg per day), combined aliskiren (3 mg/kg per day) and valsartan (5 mg/kg per day), and hydralazine (80 mg/kg per day), for 6 weeks, and the protective effects against diabetic nephropathy were compared among each group.

RESULTS

Aliskiren significantly attenuated albuminuria and glomerular mesangial matrix expansion in db/db mice, which was associated with the improvement of the increased glomerular transforming growth factor-beta and type IV collagen expressions, the increased macrophage infiltration, and the decreased glomerular nephrin expression of db/db mice. These protective effects of aliskiren in db/db mice were attributed to the attenuation of p22(phox)-related nicotinamide adenine dinucleotide phosphate oxidase-induced superoxide. Addition of aliskiren to valsartan treatment provided more beneficial effects on all the above-mentioned parameters than valsartan monotherapy.

CONCLUSION

Aliskiren protected against type 2 diabetic nephropathy, through pleiotropic effects, and significantly enhanced the protective effects of valsartan against diabetic nephropathy in db/db mice.

Akt2/PKBbeta-sensitive regulation of renal phosphate transport

AIM

The protein kinase B (PKB)/Akt is known to stimulate the cellular uptake of glucose and amino acids. The kinase is expressed in proximal renal tubules. The present study explored the influence of Akt/PKB on renal tubular phosphate transport.

METHODS

The renal phosphate transporter NaPi-IIa was expressed in Xenopus oocytes with or without PKB/Akt and Na(+) phosphate cotransport determined using dual electrode voltage clamp. Renal phosphate excretion was determined in Akt2/PKBbeta knockout mice (akt2(-/-)) and corresponding wild-type mice (akt2(+/+)). Transporter protein abundance was determined using Western blotting and phosphate transport by (32)P uptake into brush border membrane vesicles.

RESULTS

The phosphate-induced current in NaPi-IIa-expressing Xenopus oocytes was significantly increased by the coexpression of Akt/PKB. Phosphate excretion [micromol per 24 h per g BW] was higher by 91% in akt2(-/-) than in akt2(+/+) mice. The phosphaturia of akt2(-/-) mice occurred despite normal transport activity and expression of the renal phosphate transporters NaPi-IIa, NaPi-IIc and Pit2 in the brush border membrane, a significantly decreased plasma PTH concentration (by 46%) and a significantly enhanced plasma 1,25-dihydroxyvitamin D(3) concentration (by 46%). Moreover, fractional renal Ca(2+) excretion was significantly enhanced (by 53%) and bone density significantly reduced (by 11%) in akt2(-/-) mice.

CONCLUSIONS

Akt2/PKBbeta plays a role in the acute regulation of renal phosphate transport and thus contributes to the maintenance of phosphate balance and adequate mineralization of bone.

Regulation of renal tubular glucose reabsorption by Akt2/PKBβ

Akt/PKB is known to regulate the facilitative glucose carrier GLUT4. Nothing is known, however, of the role of Akt/PKB in the regulation of renal epithelial transport. To explore whether Akt2/PKBβ influences the Na(+)-coupled glucose cotransporter SGLT1, human SGLT1 was expressed in Xenopus laevis oocytes with or without Akt/PKB, and electrogenic glucose transport was determined by dual-electrode voltage clamp. The coexpression of Akt/PKB in SGLT1-expressing oocytes was followed by an increase in glucose-induced currents. To study the functional significance of Akt/PKB-sensitive renal glucose transport, further experiments were performed in gene-targeted mice lacking functional Akt2/PKBβ (akt2(-/-)) and in their wild-type littermates (akt2(+/+)). Plasma glucose concentration was significantly higher in akt2(-/-) mice than in akt2(+/+) mice but was virtually identical to the plasma glucose concentration in fructose-treated akt2(+/+) mice. Urinary glucose excretion was significantly higher in akt2(-/-) mice compared with akt2(+/+) mice with or without fructose treatment. Moreover, the glucose-induced depolarization of proximal tubular cells was significantly smaller in isolated, perfused renal tubules from akt2(-/-) mice than in those from akt2(+/+) mice. In conclusion, Akt2/PKBβ plays a role in the regulation of renal glucose transport.

Morg1 heterozygous mice are protected from acute renal ischemia-reperfusion injury

Renal ischemia and reperfusion injury leads to acute renal failure when proinflammatory and apoptotic processes in the kidney are activated. The increase in hypoxia-inducible transcription factor-alpha (HIF-alpha), an important transcription factor for several genes, can attenuate ischemic renal injury. We recently identified a novel WD-repeat protein designated Morg1 (MAPK organizer 1) that interacts with prolyl hydroxylase 3 (PHD3), an important enzyme involved in the regulation of HIF-1alpha and HIF-2alpha expression. While homozygous Morg1 -/- mice are embryonic lethal, heterozygous Morg1 +/- mice have a normal phenotype. We show here that Morg1 +/- were partially protected from renal ischemia-reperfusion injury compared with wild-type Morg1 +/+ animals. Morg1 +/- mice compared with wild-type animals revealed a stronger increase in HIF-1alpha and HIF-2alpha expression in the ischemic-reperfused kidney associated with enhanced serum erythropoietin levels. However, no significant expression of HIF-1alpha and HIF-2alpha was found in nonischemic kidneys without any difference between Morg1 +/- and Morg1 +/+ mice. Ischemic kidneys of Morg1 +/- mice expressed more erythropoietin mRNA than ischemic kidneys from wild-type animals. Renal ischemia in Morg1 +/- mice resulted in a decrease in renal inflammation and reduction of proinflammatory cytokines (MCP-1, IP-10, MIP-2) compared with wild-type mice. Furthermore, there was significantly less apoptosis and tubular damage in Morg1 +/- kidneys after ischemia-reperfusion, and this was also reflected in significantly improved renal function compared with wild-type. Thus Morg1 may be a novel therapeutic target to limit renal injury after ischemia-reperfusion.

Chronic erythropoietin treatment affects different molecular pathways of diabetic cardiomyopathy in mouse

BACKGROUND

Recent studies in mice experimental models with acute ischaemic injury revealed that erythropoietin (EPO) has numerous tissue-protective effects in the heart, brain and kidneys. We therefore explored the tissue-protective properties of chronic EPO treatment in an experimental model of the db/db mouse with diabetic heart injury.

MATERIAL AND METHODS

We randomly treated 11 db/db mice with placebo (saline), 0.4 microg of the continuous erythropoietin receptor activator (CERA) per week (n = 11) or 1.2 microg CERA per week (n = 11) for 14 weeks, and analysed cardiac tissue. The lower CERA dose was a non-haematologically effective dose, whereas the second increased the haematocrit.

RESULTS

Compared with mice in the placebo group, CERA-treated mice had a reduction in TGF-beta(1) and collagen I expression in cardiac tissue (P < 0.01 vs. higher dose CERA). In addition, an increased expression of the pro-survival intracellular pathway p-AKT was observed (P < 0.05 vs. higher dose CERA). The values for the lower C.E.R.A had an intermediate nonsignificant effect. Furthermore, we were able to show that atrial natriuretic peptide (ANP) expression was increased in both CERA groups.

CONCLUSIONS

Chronic treatment with CERA protects cardiac tissue in diabetic animals, i.e. it inhibits molecular pathways of cardiac fibrosis, and the effects are dose-dependent.

Erythropoietin and renoprotection

In the haematopoietic system, the principal function of erythropoietin (EPO) is the regulation of RBC production. Consequently, following the cloning of the EPO gene, recombinant human EPO (rHuEPO) forms have been widely used for treatment of anaemia in chronic kidney disease and chemotherapy-induced anaemia in cancer patients. However, a steadily growing body of evidence indicates that the therapeutic benefits of rHuEPO could be far beyond the correction of anaemia. Several articles have been recently published on the tissue-protective, nonhaematological effects of rHuEPO that prevent ischaemia-induced tissue damage in several organs including the kidney.In this review, we focus on nonhaematological effects of rHuEPO in various experimental settings of acute and chronic kidney injury. Because this tissue-protective action of rHuEPO is not the result of correction of anaemia-related tissue hypoxia, we will also discuss potential molecular pathways involved. Finally, we will review the current literature on clinical studies with rHuEPO or analogous substances and progression of chronic kidney disease, and propose possible clinical renoprotective strategies.