A Role for Erythropoietin in the Attenuation of Radiocontrast-Induced Acute Renal Failure in Rats

Astaxanthin attenuates contrast-induced acute kidney injury in rats via ROS/NLRP3 inflammasome

OBJECTIVE

To explore the protective effect and mechanism of astaxanthin on the kidney of rats with contrast-induced acute kidney injury.

METHODS

Forty SD rats were randomly divided into five groups: Control group (CON); Astaxanthin control group (AST); Contrast media group (CM); Astaxanthin pre-treatment group (AST + CM); N-acetylcysteine pre-treatment group (NAC + CM), each group with eight rats. The rats were killed 72 h after the modeling, the blood supernatant and kidneys were collected, and then the serum creatinine and blood urea nitrogen levels were measured; HE staining was used to observe the pathological changes in kidney tissue; TUNEL was used to detect apoptosis level in renal tubular epithelial cells; frozen section was used to observe the expression of ROS in renal tissue by reactive oxygen staining; the expression of NLRP3, ASC, caspase-1, IL-1β, IL-18 were detected by immunohistochemistry and western blot.

RESULTS

The CI-AKI rat model was induced by iohexol. Then the elevated level of ROS activated the inflammatory response mediated by NLRP3 inflammasome (NLRP3, ASC, caspase-1). Subsequently, the increase in renal tubular epithelial cell apoptosis caused the destruction of the pathological structure of the kidney and finally led to renal impairment. While after the pretreatment of astaxanthin, the level of ROS was decreased. The activation level of NLRP3 inflammasome and its mediated inflammatory response were alleviated significantly. Eventually, the level of renal tubular epithelial cell apoptosis and renal damage were significantly mitigated.

CONCLUSION

Astaxanthin can protect the kidney in CI-AKI by inhibiting the activation of NLRP3 inflammasome-IL-1β/IL-18 through inhibition of the production of ROS.

Darbepoetin alfa reduces cell death due to radiocontrast media in human renal proximal tubular cells

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Radiocontrast medium, sodium diatrizoate, reduces renal cell viability in vitro.

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Effect of darbepoetin on diatrizoate-treated cells was studied.

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Pre-treatment of renal cells with darbepoetin could reduce diatrizoate toxicity.

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Darbepoetin caused changes in the activation state of signaling molecules.

The hypersialylated erythropoiesis stimulating agent (ESA) darbepoetin alfa was developed for the treatment of anemia, and has also been reported to have other nonerythropoietic effects. This study outlines one such effect against the toxicity of the radiocontrast medium (RCM) sodium diatrizoate (NaD) in human renal proximal tubular (HK-2) cells in vitro. Using a standard cell viability assay, we observed that pre-incubation of HK-2 cells with darbepoetin (at concentrations of 0.25and 1.0 μg/mL) for 2.5 h prior to addition of NaD (75 mg I/mL, for 2 h) reduced the decrease in cell viability due to the RCM, assayed 22 h after removal of the NaD, whilst maintaining the cells incubated with darbepoetin. Western blot analysis showed that darbepoetin reduced the phosphorylation of c-Jun N-terminal kinases (JNK)1/2 over a period of 1 h incubation with NaD, but did not have an obvious effect on several other targets associated with cell death/survival. However, incubation of HK-2 cells with darbepoetin for a further 22 h after prior exposure to NaD (75 mg I/mL, for 2 h) and subsequent immunoblotting showed that darbepoetin: caused recovery of the activity (phosphorylation) of pro-proliferative/survival signalling molecules, such as Akt (Ser473), STAT (signal transducer and activator of transcription)3(Tyr705); decreased activation of the pro-apoptotic transcription factor FOXO3a by increasing its phosphorylation at Thr32; decreased phosphorylation (activation) of p38 Mitogen activated protein kinase; and reduced poly(ADP-ribose)polymerase (PARP)-1 cleavage. In summary, we present here a beneficial nonerythropoietic effect of darbepoetin alfa against radiocontrast-induced toxicity together with modulation of signalling molecules that play a crucial role in determining cell fate.

Phosphodiesterase-5 inhibitors ameliorate structural kidney damage in a rat model of contrast-induced nephropathy

The aim of the study was to investigate the potential of sildenafil and tadalafil to ameliorate structural kidney damage in contrast-induced nephropathy (CIN). A rat model of CIN was developed by dehydration, administration of a nitric oxide inhibitor and a prostaglandin synthesis inhibitor (L-NAME/indomethacin) and contrast media exposure to iopromide. The effect of pre-treatment with sildenafil, tadalafil or N-acetyl cysteine (NAC) for 7 days prior to CIN induction was investigated. All animals were sacrificed at 24 h after CIN induction and both kidneys were collected. Histopathological examination was performed under light microscopy in serial tissue sections stained with hematoxylin and eosin. CIN group showed hydropic changes of the renal tubules (proximal and distal convoluted tubules and Henle's loop), an increased Bowman space with lobulated glomerulus and alteration of macula densa region of distal convolute tubules. The groups pretreated with sildenafil and tadalafil showed nearly normal histological aspects of renal tissue. The group pretreated with NAC showed similar but less intense histopathologic changes compared to CIN group. Sildenafil and tadalafil pre-treatment ameliorates CIN-related structural kidney damage and the protective potential of these agents is superior to NAC.

Atorvastatin protects against contrast-induced acute kidney injury via upregulation of endogenous hydrogen sulfide

Background

Contrast-induced acute kidney injury (CIAKI) is the third leading cause of acute renal failure in hospitalized patients. This study was aimed to investigate whether atorvastatin could upregulate the expression of hydrogen sulfide (H₂S) and hence protect against CIAKI.

Methods

We treated male rats and NRK-52E cells by iopromide to establish in vivo and in vitro models of CIAKI. Pretreatment with atorvastatin was given in CIAKI rats to investigate its effect on CIAKI. We collected serum and urine samples to detect renal function. We obtained kidney tissue for histological analysis and detection of protein concentration. We tested the serum concentration of H₂S and renal expression of two H₂S synthetases [cystathionine γ-lyase (CSE) and cystathionine-β synthase (CBS)]. NaHS was pretreated in NRK-52E cells to testify its underlying effect on contrast-induced injury.

Results

Atorvastatin significantly ameliorated renal dysfunction and morphological changes in CIAKI rats, as well as inflammation, apoptosis, and excessive oxidative stress. Atorvastatin also markedly increased the serum concentration of H₂S and renal expression of CSE and CBS. Moreover, pretreatment with NaHS in NRK-52E cells considerably attenuated contrast-induced cell death and inflammation.

Conclusion

Atorvastatin protects against CIAKI via upregulation of endogenous hydrogen sulfide.

Sildenafil and tadalafil reduce the risk of contrast-induced nephropathy by modulating the oxidant/antioxidant balance in a murine model

The aim of the study was to evaluate the potential protective role of sildenafil and tadalafil in contrast-induced nephropathy (CIN) by modulating oxidative stress. Thirty Wistar male rats were equally assigned into five groups: sham, CIN, CIN + sildenafil (10 mg/kg bw/day), CIN + tadalafil (5 mg/kg bw/day) and CIN + N-Acetyl Cysteine (NAC) (100 mg/kg bw/day) as a positive control. CIN was induced by 12 h dehydration and administration of indomethacin (10 mg/kg bw), N-ω- nitro-L-arginine methyl ester (10 mg/kg bw), and iopromide (3 g/kg bw iodine). Blood was drawn prior to and 24 h after CIN induction for evaluating renal function and oxidative stress. In the CIN group, total antioxidant capacity (TAC), reduced glutathione (GSH) and catalase (CAT) levels were significantly decreased; and protein carbonyl (PROTC) and thiobarbituric reactive species (TBARS) were significantly increased compared to the sham group. Pre- Sildenafil and tadalafil pre-treatment reduced CIN risk and reversed oxidative stress almost to the sham group levels. These results suggest that PDE5Is can be good candidates for preventing CIN based on their ability to modulate the oxidant/antioxidant balance.

Prevention of contrast-induced nephropathy with single bolus erythropoietin in patients with diabetic kidney disease: A randomized controlled trial

AIM

Contrast-induced-nephropathy (CIN) is associated with poor outcomes, thus prevention of CIN may be of clinical value. Erythropoietin (EPO) has been shown to elicit tissue-protective effects in experimental models and in clinical studies of acute kidney injury. We therefore evaluated its effectiveness for prevention of CIN after coronary angiography (CA) ± percutaneous coronary intervention (PCI) in diabetic patients with chronic kidney disease.

METHODS

A prospective, randomized, controlled trial was carried out in 138 diabetic patients with eGFR <60 mL/min who underwent non-urgent CA ± PCI. Patients received normal saline and n-acetyl cysteine before CA, with or without 50,000 U of EPO administered 30 min prior to CA. CIN was defined as an increase in serum creatinine of at least 0.5 mg/dL during the first 2 days after exposure to contrast media. Primary outcome was the incidence of CIN. Secondary outcomes were the sensitivity and positive predictive value (PPV) of Cystatin C (CC) and Neutrophil-gelatinase-associated-lipocalin (NGAL) for diagnosis of CIN.

RESULTS

The observed incidence of CIN was 8.7%, significantly lower than the expected for such high-risk population. The administration of EPO prior to CA did not reduce the incidence of CIN (9.7% vs. 7.6%, P = 0.65). CC and NGAL demonstrated a low sensitivity (16.6%) and low PPV (6.7 and 33.3%, respectively) for detecting CIN.

CONCLUSION

The administration of EPO prior to CA did not reduce the incidence of CIN. Additional prospective research with a larger sample size and in other patient categories is essential to further define the potential protective effect of EPO on prevention of CIN.

Bridging Translation by Improving Preclinical Study Design in AKI

Despite extensive research, no therapeutic interventions have been shown to prevent AKI, accelerate recovery of AKI, or reduce progression of AKI to CKD in patients. This failure in translation has led investigators to speculate that the animal models being used do not predict therapeutic responses in humans. Although this issue continues to be debated, an important concern that has not been addressed is whether improvements in preclinical study design can be identified that might also increase the likelihood of translating basic AKI research into clinical practice using the current models. In this review, we have taken an evidence-based approach to identify common weaknesses in study design and reporting in preclinical AKI research that may contribute to the poor translatability of the findings. We focused on use of N-acetylcysteine or sodium bicarbonate for the prevention of contrast-induced AKI and use of erythropoietin for the prevention of AKI, two therapeutic approaches that have been extensively studied in clinical trials. On the basis of our findings, we identified five areas for improvement in preclinical study design and reporting. These suggested and preliminary guidelines may help improve the quality of preclinical research for AKI drug development.

Evaluation of urine fibrinogen level in a murine model of contrast-induced nephropathy

OBJECTIVE

The mechanisms of contrast-induced nephropathy are not fully understood and sensitive biomarkers of contrast-induced nephropathy are yet to be found. We investigated whether urinary fibrinogen could be a potential biomarker for contrast-induced nephropathy.

METHODS

To create a contrast-induced nephropathy model, mice received a prostaglandin synthesis inhibitor (indomethacin) and a nitric oxide synthase inhibitor (Nω-Nitro-L-arginine methyl ester) intraperitoneally followed by a different dose of iodixanol. In the control group, normal saline was administered. Urinary fibrinogen and serum creatinine were analyzed using enzyme-linked immunosorbent assay. Kidneys were used to quantify fibrinogen using qRT-PCR and Western blot and for histopathological examination.

RESULTS

Histopathological examination demonstrated mild renal injury in the low-dose group, and moderate renal injury in the high-dose group. Urinary fibrinogen levels were significantly increased in an iodixanol dose-dependent manner (control vs. low-dose group, P < 0.05; control vs. high-dose group P < 0.01). Serum creatinine levels were only increased in the high-dose group (P < 0.01 compared to control), but not in the low-dose group. For fibrinogen-gene expression, in the low-dose group, Fgγ increased (qRT-PCR, Western blot, P < 0.05) in the high-dose group, Fgβ and Fgγ decreased (qRT-PCR, P < 0.01; Western blot, P < 0.05), and Fgα increased (qRT-PCR, P < 0.05; Western blot, P < 0.05).

CONCLUSIONS

We propose that urinary fibrinogen could be used as a potential biomarker for early contrast-induced nephropathy diagnosis.

Prevention of contrast-induced nephropathy through a knowledge of its pathogenesis and risk factors

Contrast-induced nephropathy (CIN) is an iatrogenic acute renal failure (ARF) occurring after the intravascular injection of iodinated radiographic contrast media. During the past several years, in many patients undergoing computed tomography, iodinated contrast media have not been used for the fear of ARF, thereby compromising the diagnostic procedure. But recent studies have demonstrated that CIN is rarely occurring in patients with normal renal function and that preexisting chronic renal failure and/or diabetes mellitus represent(s) predisposing condition(s) for its occurrence. After the description of CIN and its epidemiology and pathophysiology, underlying the important role played by dehydration and salt depletion, precautions for prevention of CIN are listed, suggested, and discussed. Maximum priority has to be given to adequate hydration and volume expansion prior to radiographic procedures. Other important precautions include the need for monitoring renal function before, during, and after contrast media injection, discontinuation of potentially nephrotoxic drugs, use of either iodixanol or iopamidol at the lowest dosage possible, and administration of antioxidants. A long list of references is provided that will enable readers a deep evaluation of the topic.

The utility of the additive EuroSCORE, RIFLE and AKIN staging scores in the prediction and diagnosis of acute kidney injury after cardiac surgery

BACKGROUND/AIMS

Acute kidney injury (AKI) following cardiac surgery is a complication associated with high rates of morbidity and mortality. We compared staging systems for the diagnosis of AKI after cardiac surgery, and assessed pre-operative factors predictive of post-operative AKI.

METHODS

Clinical data, surgical risk scores, procedure and clinical outcome were obtained on all 4,651 patients undergoing cardiac surgery to the Royal Infirmary of Edinburgh between April 2006 and March 2011, of whom 4,572 had sufficient measurements of creatinine before and after surgery to permit inclusion and analysis. The presence of AKI was assessed using the AKIN and RIFLE criteria.

RESULTS

By AKIN criteria, 12.4% of the studied population developed AKI versus 6.5% by RIFLE criteria. Any post-operation AKI was associated with increased mortality from 2.2 to 13.5% (relative risk 7.0, p < 0.001), and increased inpatient stay from a median of 7 (IQR 4) to 9 (IQR 11) days (p < 0.05). Patients identified by AKIN, but not RIFLE, had a mean peak creatinine rise of 34% from baseline and had a significantly lower mortality compared to RIFLE-'Risk' AKI (mortality 6.1 vs. 9.7%; p < 0.05). Pre-operative creatinine, diabetes, NYHA Class IV dyspnoea and EuroSCORE-1 (a surgical risk score) all predicted subsequent AKI on multivariate analysis. EuroSCORE-1 outperformed any single demographic factor in predicting post-operative AKI risk, equating to an 8% increase in relative risk for each additional point.

CONCLUSION

AKI after cardiac surgery is associated with delayed discharge and high mortality rates. The AKIN and RIFLE criteria identify patients at a range of AKI severity levels suitable for trial recruitment. The utility of EuroSCORE as a risk stratification tool to identify high AKI-risk subjects for prospective intervention merits further study.

Involvement of caspase-12-dependent apoptotic pathway in ionic radiocontrast urografin-induced renal tubular cell injury

Contrast medium (CM) induces a direct toxic effect on renal tubular cells. This toxic effect subjects in the disorder of CM-induced nephropathy. Our previous work has demonstrated that CM shows to activate the endoplasmic reticulum (ER)-related adaptive unfolding protein response (UPR) activators. Glucose-regulated protein 78 (GRP78)/eukaryotic initiation factor 2α (eIF2α)-related pathways play a protective role during the urografin (an ionic CM)-induced renal tubular injury. However, the involvement of ER stress-related apoptotic signals in the urografin-induced renal tubular cell injury remains unclear. Here, we examined by the in vivo and in vitro experiments to explore whether ER stress-regulated pro-apoptotic activators participate in urografin-induced renal injury. Urografin induced renal tubular dilation, tubular cells detachment, and necrosis in the kidneys of rats. The tubular apoptosis, ER stress-related pro-apoptotic transcriptional factors, and kidney injury marker-1 (kim-1) were also conspicuously up-regulated in urografin-treated rats. Furthermore, treatment of normal rat kidney (NRK)-52E tubular cells with urografin augmented the expressions of activating transcription factor-6 (ATF-6), C/EBP homologous protein (CHOP), Bax, caspase-12, JNK, and inositol-requiring enzyme (IRE) 1 signals. Urografin-induced renal tubular cell apoptosis was not reversed by the inhibitors of ATF-6, JNK signals or CHOP siRNA transfection, but it could be partially reversed by the inhibitor of caspase-12. Taken together, the present results and our previous findings suggest that exposure of CM/urografin activates the ER stress-regulated survival- and apoptosis-related signaling pathways in renal tubular cells. Caspase-12-dependent apoptotic pathway may be partially involved in the urografin-induced nephropathy.

Erythropoietin ameliorates genetamicin-induced renal toxicity: A biochemical and histopathological study

BACKGROUND

Investigations have attempted to modify the outcome of tubular injury by either ameliorating renal tubular damage or promoting tubular regeneration in the case of acute tubular necrosis.

OBJECTIVES

We investigated the protective effect of Eprex an erythropoietin analogue on tubular injury induced by gentamicin (GM).

MATERIALS AND METHODS

Forty male Wistar rats were randomly divided into four groups. In group 1,rats were served as a sham group. In group 2, rats were injected intraperitoneally with 100 mg/kg of GM for 10 consecutive days (positive control group) and then were sacrificed. In group 3, rats received GM for 10 days then Eprex 100U/kg was injected intraperitoneally for the next 10 days and then they were sacrificed at the day 20th. In group 4 rats were injected a combination of GM (80 mg/kg) and Eprex 100U/kg intraperitoneally for 10 days and then were sacrificed.

RESULTS

The results indicated that, Eprex prevented the increase in serum creatinine (Cr) and blood urea nitrogen (BUN). The effect of Eprex on damage score, showed that co-administration of GM and Eprex (group 3 and 4) reduced the kidney tissue damage compared to positive control group (P<0.05). This result indicat that Eprex potentially can reduce or prevent the kidney tissue damage.

CONCLUSIONS

Ameliorative effect of Eprex when the drug was given in combination with GM and also when the drug was applied after GM-induced tubular damage, revealed the renoprotective potency of Eprex. Eprex is a promising drug to prevent or attenuate tubular damage induced by GM or other nephrotoxic agents which act through the same mechanisms as gentamicin.

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 (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.

Renoprotective effect of erythropoietin against ischaemia-reperfusion injury in a non-human primate model

BACKGROUND

The renoprotective effect of erythropoietin (Epo) against ischaemia-reperfusion injury (IR/I) was evaluated in a non-human primate model.

METHODS

Crab-eating macaques were divided into two groups: Control (n = 10), treated with saline, and EPO (n = 10), treated with Epo. Epo was injected intravenously at a dose of 12,000 units, 5 min before clamping the renal pedicle and 5 min before declamping. Renal IR/I was created by clamping the left renal artery for 90 min following right nephrectomy. Haemoglobin (Hb), haematocrit (Ht), creatinine (Cr), blood urea nitrogen (BUN), cystatin C and interleukin-6 (IL-6) were measured before (Pre) and after (Day 0) the operation, and on post-operative days: Day 1, Day 3, Day 5 and Day 7. Apoptotic cells were counted on Day 1.

RESULTS

There were no differences in Hb and Ht between the two groups. Cr, BUN, cystatin C and IL-6 levels in the EPO group were lower than those in the Control group at most of the observation points. The number of apoptotic cells in the Control was significantly higher than that of and EPO group.

CONCLUSIONS

Epo significantly ameliorates renal IR/I in this non-human primate model. Our findings justify the clinical application of Epo, not only for acute renal failure, but also in transplantation.

Reactive oxygen species and the pathogenesis of radiocontrast-induced nephropathy

Experimental findings in vitro and in vivo illustrate enhanced hypoxia and the formation of reactive oxygen species (ROS) within the kidney following the administration of iodinated contrast media, which may play a role in the development of contrast media-induced nephropathy. Clinical studies indeed support this possibility, suggesting a protective effect of ROS scavenging or reduced ROS formation with the administration of N-acetyl cysteine and bicarbonate infusion, respectively. Furthermore, most risk factors, predisposing to contrast-induced nephropathy are prone to enhanced renal parenchymal hypoxia and ROS formation. In this review, the association of renal hypoxia and ROS-mediated injury is outlined. Generated during contrast-induced renal parenchymal hypoxia, ROS may exert direct tubular and vascular endothelial injury and might further intensify renal parenchymal hypoxia by virtue of endothelial dysfunction and dysregulation of tubular transport. Preventive strategies conceivably should include inhibition of ROS generation or ROS scavenging.

Mitigating contrast-induced acute kidney injury associated with cardiac catheterization

Contrast-induced nephropathy, also referred to as contrast-induced acute kidney injury (CIAKI), is among the most common causes of AKI, especially in patients with underlying chronic kidney disease. In addition to the increased cost engendered by the development of CIAKI, several studies have suggested the occurrence of AKI after cardiac procedures is associated with an increase in both morbidity and mortality. This increase in morbidity and mortality occurs after both intravenous and intra-arterial studies. This review focuses on relevant proposed pathophysiological mechanisms, risk factors, and current prophylactic strategies, which may reduce the incidence of CIAKI during cardiac angiographic imaging studies.

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.

Therapeutic and predictive targets of AKI

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

Physiological basis for the use of erythropoietin in critically ill patients at risk for acute kidney injury

PURPOSE OF REVIEW

Acute kidney injury (AKI) frequently occurs in critically ill patients and is an independent risk factor for poor outcome. The prevention of kidney injury in intensive care remains a great challenge as specific nephroprotective therapies are still lacking. The present review summarizes recent evidence for the use of erythropoietin as a promising candidate to provide protection from AKI.

RECENT FINDINGS

Beyond the known hematopoietic actions of erythropoietin, a number of preclinical studies demonstrated that erythropoietin possesses pleiotropic, organ-protecting properties. Preconditional and postconditional erythropoietin treatment was shown to protect from ischemic, toxic and septic AKI. Despite heterogeneities in study design and dose, erythropoietin consistently ameliorated renal injury. The mechanisms of protection remain largely unclear but may involve reduction of apoptosis, induction of cellular proliferation and tissue repair as well as mobilization of stem cells.

SUMMARY

Animal studies revealed a physiological basis for the use of erythropoietin in AKI, which may be clinically applicable to prevent AKI in critically ill patients, but clinical studies are still lacking.

Clinical significance and preventive strategies for contrast-induced nephropathy

PURPOSE OF REVIEW

Contrast-induced nephropathy continues to be a common cause of in-hospital acute kidney injury. Published studies on pathogenesis, clinical significance, diagnosis, and preventive measures have dramatically increased significantly in the past several years. This review will focus on new developments in contrast-induced nephropathy.

RECENT FINDINGS

Studies on the clinical significance of contrast-induced nephropathy are reviewed along with initial reports of biomarkers in diagnosing this complication of iodinated contrast administration. Emerging literature on the relative nephrotoxicity of iso-osmolar versus low-osmolar contrast media and the value of bicarbonate hydration are discussed. More recent preventive measures using prostacyclin, 'statins', and erythropoietin are also reviewed.

SUMMARY

Contrast-induced nephropathy is an increasing cause of acute kidney injury and is associated with significant mortality and morbidity. Future developments in this field will focus on refining the clinical significance of this complication, earlier diagnosis with biomarkers, clarifying the role for bicarbonate and iso-osmolar contrast agents as preventive strategies, and the introduction of new prophylactic techniques on the basis of an improved understanding of pathogenesis at the cellular level.

Asialoerythropoietin prevents contrast-induced nephropathy

Strategies to prevent contrast-induced nephropathy (CIN) are suboptimal. Erythropoietin was recently found to be cytoprotective in a variety of nonhematopoietic cells, so it was hypothesized that the nonhematopoietic erythropoietin derivative asialoerythropoietin would prevent CIN. Nephropathy was induced in rats by injection of the radiocontrast medium Ioversol in addition to inhibition of prostaglandin and nitric oxide synthesis. Administration of a single dose of asialoerythropoietin before the induction of nephropathy significantly attenuated the resulting renal dysfunction and histologic renal tubular injury. Contrast-induced apoptosis of renal tubular cells was inhibited by asialoerythropoietin both in vivo and in vitro, and this effect was blocked by a Janus kinase 2 (JAK2) inhibitor in vitro. Furthermore, phospho-JAK2/signal transducer and activator of transcription 5 (STAT5) and heat-shock protein 70 increased after injection of asialoerythropoietin, suggesting that the effects of asialoerythropoietin may be mediated by the activation of the JAK2/STAT5 pathway. Overall, these findings suggest that asialoerythropoietin may have potential as a new therapeutic approach to prevent CIN given its ability to preserve renal function and directly protect renal tissue.

RENAL PARENCHYMAL OXYGENATION AND HYPOXIA ADAPTATION IN ACUTE KIDNEY INJURY

The pathogenesis of acute kidney injury (AKI), formally termed acute tubular necrosis, is complex and, phenotypically, may range from functional dysregulation without overt morphological features to literal tubular destruction. Hypoxia results from imbalanced oxygen supply and consumption. Increasing evidence supports the view that regional renal hypoxia occurs in AKI irrespective of the underlying condition, even under circumstances basically believed to reflect 'direct' tubulotoxicity. However, at present, it is remains unclear whether hypoxia per se or, rather, re-oxygenation (possibly through reactive oxygen species) causes AKI. Data regarding renal hypoxia in the clinical situation of AKI are lacking and our current concepts regarding renal oxygenation during acute renal failure are presumptive and largely derived from experimental studies. There is robust experimental evidence that AKI is often associated with altered intrarenal microcirculation and oxygenation. Furthermore, renal parenchymal oxygen deprivation seems to participate in the pathogenesis of experimental AKI, induced by exogenous nephrotoxins (such as contrast media, non-steroidal anti-inflammatory drugs or amphotericin), sepsis, pigment and obstructive nephropathies. Sub-lethal cellular hypoxia engenders adaptational responses through hypoxia-inducible factors (HIF). Forthcoming technologies to modulate the HIF system form a novel potential therapeutic approach for AKI.