Phosphodiesterase-5 inhibition prevents postcardiopulmonary bypass acute kidney injury in swine

Exploring the Multifaceted Potential of Sildenafil in Medicine

Phosphodiesterase type 5 (PDE5) is pivotal in cellular signalling, regulating cyclic guanosine monophosphate (cGMP) levels crucial for smooth muscle relaxation and vasodilation. By targeting cGMP for degradation, PDE5 inhibits sustained vasodilation. PDE5 operates in diverse anatomical regions, with its upregulation linked to various pathologies, including cancer and neurodegenerative diseases. Sildenafil, a selective PDE5 inhibitor, is prescribed for erectile dysfunction and pulmonary arterial hypertension. However, considering the extensive roles of PDE5, sildenafil might be useful in other pathologies. This review aims to comprehensively explore sildenafil's therapeutic potential across medicine, addressing a gap in the current literature. Recognising sildenafil's broader potential may unveil new treatment avenues, optimising existing approaches and broadening its clinical application.

Cyclic nucleotide phosphodiesterase inhibition as a potential therapeutic target in renal ischemia reperfusion injury

AIMS

Ischemia/reperfusion (I/R) occurs in renal artery stenosis, partial nephrectomy and most commonly during kidney transplantation. It brings serious consequences such as DGF (Delayed Graft Function) or organ dysfunction leading to renal failure and ultimate death. There is no effective therapy to handle the consequences of Renal Ischemia/Reperfusion (I/R) injury. Cyclic nucleotides, cAMP and cGMP are the important second messengers that stimulate intracellular signal transduction for cell survival in response to growth factors and peptide hormones in normal tissues and in kidneys plays significant role that involves vascular tone regulation, inflammation and proliferation of parenchymal cells. Renal ischemia and subsequent reperfusion injury stimulate signal transduction pathways involved in oxidative stress, inflammation, alteration in renal blood flow leading to necrosis and apoptosis of renal cell.

MATERIALS AND METHODS

An extensive literature review of various search engines like PubMed, Medline, Bentham, Scopus, and EMBASE (Elsevier) databases was carried out. To understand the functioning of Phosphodiesterases (PDEs) and its pharmacological modulation in Renal Ischemia-Reperfusion Injury.

KEY FINDINGS

Current therapeutic options may not be enough to treat renal I/R injury in group of patients and therefore, the current review has discussed the general characteristics and physiology of PDEs and preclinical-studies defining the relationship between PDEs expression in renal injury due to I/R and its outcome on renal function.

SIGNIFICANCE

The role of PDE inhibitors in renal I/R injury and the clinical status of drugs for various renal diseases have been summarized in this review.

Large animal models for translational research in acute kidney injury

While extensive research using animal models has improved the understanding of acute kidney injury (AKI), this knowledge has not been translated into effective treatments. Many promising interventions for AKI identified in mice and rats have not been validated in subsequent clinical trials. As a result, the mortality rate of AKI patients remains high. Inflammation plays a fundamental role in the pathogenesis of AKI, and one reason for the failure to translate promising therapeutics may lie in the profound difference between the immune systems of rodents and humans. The immune systems of large animals such as swine, nonhuman primates, sheep, dogs and cats, more closely resemble the human immune system. Therefore, in the absence of a basic understanding of the pathophysiology of human AKI, large animals are attractive models to test novel interventions. However, there is a lack of reviews on large animal models for AKI in the literature. In this review, we will first highlight differences in innate and adaptive immunities among rodents, large animals, and humans in relation to AKI. After illustrating the potential merits of large animals in testing therapies for AKI, we will summarize the current state of the evidence in terms of what therapeutics have been tested in large animal models. The aim of this review is not to suggest that murine models are not valid to study AKI. Instead, our objective is to demonstrate that large animal models can serve as valuable and complementary tools in translating potential therapeutics into clinical practice.

Evaluation of Neutrophil Dynamics Change by Protective Effect of Tadalafil After Renal Ischemia/Reperfusion Using In Vivo Real-time Imaging

BACKGROUND

Neutrophils play a major role in ischemia/reperfusion injury (IRI) in renal transplantation and acute kidney injury. However, it has been difficult to observe changes in neutrophil dynamics over time in living mice kidney. We investigate neutrophil dynamics in IRI in living mice using novel in vivo multiphoton microscope imaging techniques and characterize the renoprotective effects of a selective phosphodiesterase (PDE) 5 inhibitor, tadalafil.

METHODS

Wild-type (WT) and eNOS knockout (eNOS-KO) mice, a model of endothelial dysfunction, were used to establish in vivo real-time imaging in living mouse kidneys. Neutrophils were labeled green with Ly-6G monoclonal antibody, and plasma flow was labeled red with bovine serum albumin. Tadalafil was administered orally 1 h before surgery. Both kidney pedicles were reperfused after 37° warm ischemia for 45 min.

RESULTS

Our novel approach revealed that neutrophils were trapped in glomerulus within a few minutes after reperfusion. They gradually increased over time and Infiltrated neutrophils were observed in the tubular lumen and peritubular capillary. The neutrophils were clearly visualized rolling on peritubular capillary plexus at 3 μm/min. The administration of tadalafil significantly reduced neutrophil influx into the glomerulus in both WT and eNOS-KO mice. Reduced neutrophil infiltration in tadalafil groups, which was confirmed by flow cytometry, resulted in histopathologically decreased tubular injury. The expression of VCAM-1 and KIM-1 was partially prevented by tadalafil.

CONCLUSIONS

Use of a novel technique contributed to elucidation of neutrophil dynamics after reperfusion. Tadalafil has a potential for inhibiting neutrophil infiltration in renal IRI.Supplemental Visual Abstract; http://links.lww.com/TP/C223.

Impact of pretreatment with carnitine and tadalafil on contrast-induced nephropathy in CKD patients

Objective: The present study assesses whether phosphodiesterase type 5 (PDE-5) inhibitor or carnitine exert nephroprotective effects against clinical contrast-induced nephropathy (CIN).

Materials and Methods: The present study consisted of three groups of CKD patients. The first group was control group, who were treated with N-acetyl-L-cysteine 1 day before and on the day of radiocontrast administration. The second one was carnitine group, where the patients were infused with carnitine over 10 min 2 h prior to the radiocontrast administration and 24 h post CT. The third one was PDE-5 inhibitor group, where patients were given tadalafil 2 h prior to the administration of the radiocontrast and in the subsequent day. Urine and blood samples were collected before and at the following time sequence: 2, 6, 12, 24, 48, and 120 h after the contrast administration, for creatinine and NGAL determination.

Results: Pretreated with N-acetyl-L-cysteine prior to administration of contrast media (CM) to CKD patients caused a significant increase in urinary but not of plasma neutrophil gelatinase-associated lipocalin (NGAL) and serum creatinine (SCr). In contrast, pretreatment with carnitine prevented the increase in urinary NGAL and reduced SCr below basal levels. Similarly, tadalafil administration diminished the elevation of CM-induced urinary NGAL.

Conclusions: These results indicate that carnitine and PDE-5 inhibitors may comprise potential therapeutic maneuvers for CIN.

Current Concepts on the Reno-Protective Effects of Phosphodiesterase 5 Inhibitors in Acute Kidney Injury: Systematic Search and Review

Acute kidney injury (AKI) is associated with increased morbidity, prolonged hospitalization, and mortality, especially in high risk patients. Phosphodiesterase 5 inhibitors (PDE5Is), currently available as first-line therapy of erectile dysfunction in humans, have shown a beneficial potential of reno-protection through various reno-protective mechanisms. The aim of this work is to provide a comprehensive overview of the available literature on the reno-protective properties of PDE5Is in the various forms of AKI. Medline was systematically searched from 1946 to November 2019 to detect all relevant animal and human studies in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) statement. In total, 83 studies were included for qualitative synthesis. Sildenafil is the most widely investigated compound (42 studies), followed by tadalafil (20 studies), icariin (10 studies), vardenafil (7 studies), zaprinast (4 studies), and udenafil (2 studies). Even though data are limited, especially in humans with inconclusive or negative results of only two clinically relevant studies available at present, the results of animal studies are promising. The reno-protective action of PDE5Is was evident in the vast majority of studies, independently of the AKI type and the agent applied. PDE5Is appear to improve the renal functional/histopathological alternations of AKI through various mechanisms, mainly by affecting regional hemodynamics, cell expression, and mitochondrial response to oxidative stress and inflammation.

Increased Intra-abdominal Pressure Induces Acute Kidney Injury in an Experimental Model of Congestive Heart Failure

BACKGROUND

Congestive heart failure (CHF) entails a complex interaction between the heart and the kidney that represents a clinical entity called cardiorenal syndrome (CRS). One of the mechanisms underlying CRS includes increased intra-abdominal pressure (IAP). We examined the effect of elevated IAP on kidney function in rats with low- and high-output CHF.

METHODS AND RESULTS

Rats with compensated and decompensated CHF induced by means of aortocaval fistula, rats with myocardial infraction (MI) induced by means of left anterior descending artery ligation, and sham control rats were subjected to either 10 or 14 mm Hg IAP. Urine flow (V), Na⁺ excretion (U_NaV), glomerular filtration rate (GFR), and renal plasma flow (RPF) were determined. The effects of pretreatment with tadalafil (10 mg/kg orally for 4 days) on the adverse renal effects of IAP were examined in decompensated CHF and MI. Basal V and GFR were significantly lower in rats with decompensated CHF compared with sham control rats. Decompensated CHF rats and MI rats subjected to 10 and 14 mm Hg IAP exhibited more significant declines in V, U_NaV, GFR and RPF than compensated and sham controls. Elevated IAP also induced tubular injury, as evidenced by significantly increased absolute urinary excretion of neutrophil gelatinase-associated lipocalin. In addition, in a nonquantitative histologic analysis, elevated IAP was associated with increase in necrosis and cell shedding to the tubule lumens, especially in the decompensated CHF subgroup. Pretreatment of decompensated CHF rats and MI rats with tadalafil ameliorated the adverse renal effects of high IAP.

CONCLUSIONS

Elevated IAP contributes to kidney dysfunction in high- and low-cardiac output CHF. IAP induces both hemodynamic alterations and renal tubular dysfunction. These deleterious effects are potentially reversible and can be ameliorated with the use of phosphodiesterase-5 inhibition.

Effect of sildenafil (Revatio) on postcardiac surgery acute kidney injury: a randomised, placebo-controlled clinical trial: the REVAKI-2 trial protocol

Introduction

Acute kidney injury (AKI) is a common and severe complication of cardiac surgery. The administration of pharmacological renoprotective agents during the perioperative period could prevent or reduce the severity of AKI and improve clinical outcomes. Experimental studies suggest that sildenafil may have therapeutic potential for the prevention of AKI. This trial will test the hypothesis that postoperative AKI will be reduced in cardiac surgery patients if they receive sildenafil compared with placebo.

Methods and analysis

Adult cardiac surgery patients 18 years of age or above undergoing cardiac surgery with cardiopulmonary bypass and cardioplegic arrest at a single tertiary cardiac centre in the UK will be randomised in a 1:1 ratio to receive either sildenafil or placebo. The primary outcome is serum creatinine concentration measured at preoperation and daily for up to 7 days postoperatively. Secondary outcomes will include measures of inflammation, organ injury, volumes of blood transfused and resource use. Allocation concealment, internet-based randomisation stratified by operation type, and blinding of outcome assessors will reduce the risk of bias. A sample size of 112 patients will have a 90% power to detect a mean difference of 10 μmol/L for serum creatinine values between treatment and placebo control groups with an alpha value of 0.05.

Ethics and dissemination

The trial protocol was approved by a UK ethics committee (reference 15/YH/0489). The trial findings will be disseminated in scientific journals and meetings.

Trial registration number

ISRCTN18386427.

Serum and Tissue HIF-2 Alpha Expression in CIN, N-Acetyl Cysteine, and Sildenafil-Treated Rat Models: An Experimental Study

Background and Objectives: Contrast-induced nephropathy (CIN), is acute renal damage due to contrast agents. This study is conducted to evaluate serum and renal heterodimeric nuclear transcription factor (HIF)-2 alpha levels and its tissue expression in contrast-induced nephropathy, and in N-acetyl cysteine (NAC)-and Sildenafil-treated rat models. Materials/Methods: This randomized, controlled, interventional animal study was conducted on Wistar rats. Rats (n = 36) were randomly assigned to four groups: control (n = 9), CIN group (n = 9), CIN + NAC group (n = 9), and sildenafil (n = 9). The rat model was used to form iohexol-originated CIN. During the modeling, prophylactic treatment was performed at the 24th and 48th h. After 48 h of modeling, blood, urine, and tissue samples were obtained for biochemical analyses. HIF-2-α levels were measured in renal tissue, serum, and urine samples. Renal sections were also performed for histopathologic and immunohistochemical evaluations of renal injury and HIF-2-α expression. Results: In the CIN model, HIF-2α levels and other biochemical parameters were significantly increased (p < 0.01). Both sildenafil and NAC efficiently decreased renal damage due to contrast agents, as shown in histopathologic examinations (p < 0.05). Similarly, after treatment with sildenafil and NAC, HIF-2α levels were significantly decreased (p < 0.05). Conclusions: The current study shows that serum and tissue HIF-2α levels decrease in CIN. Besides, the levels and tissue expression of HIF-2α decrease with both NAC and sildenafil treatments. With further studies, HIF-2α can be investigated as a biomarker of CIN and can be used in the follow-up of patients with CIN.

Differences in acute kidney injury ascertainment for clinical and preclinical studies

Background

Acute kidney injury (AKI) is a common clinical condition directly associated with adverse outcomes. Several AKI biomarkers have been discovered, but their use in clinical and preclinical studies has not been well examined. This study aims to investigate the differences between clinical and preclinical studies on AKI biomarkers.

Methods

We performed a systematic review of clinical and preclinical interventional studies that considered AKI biomarkers in enrollment criteria and/or outcome assessment and described the main differences according to their setting, the inclusion of biomarkers in the definition of AKI and the use of biomarkers as primary or secondary end points.

Results

In the 151 included studies (76 clinical, 75 preclinical), clinical studies have prevalently focused on cardiac surgery (38.1%) and contrast-associated AKI (17.1%), while the majority of preclinical studies have focused on ether ischemia-reperfusion injury or drug-induced AKI (42.6% each). A total of 57.8% of clinical studies defined AKI using the standard criteria and only 19.7% of these studies used AKI biomarkers in the definition of renal injury. Conversely, the majority of preclinical studies defined AKI according to the increase in serum creatinine and blood urea nitrogen, and 32% included biomarkers in that definition. The percentage of both clinical and preclinical studies with biomarkers as a primary end point has not significantly increased in the last 10 years; however, preclinical studies are more likely to use AKI biomarkers as a primary end point compared with clinical studies [odds ratio 2.31 (95% confidence interval 1.17-4.59); P  =  0.016].

Conclusion

Differences between clinical and preclinical studies are evident and may affect the translation of preclinical findings in the clinical setting.

Renal haemodynamics and oxygenation during and after cardiac surgery and cardiopulmonary bypass

Acute kidney injury (AKI) is a common complication following cardiac surgery performed on cardiopulmonary bypass (CPB) and has important implications for prognosis. The aetiology of cardiac surgery-associated AKI is complex, but renal hypoxia, particularly in the medulla, is thought to play at least some role. There is strong evidence from studies in experimental animals, clinical observations and computational models that medullary ischaemia and hypoxia occur during CPB. There are no validated methods to monitor or improve renal oxygenation during CPB, and thus possibly decrease the risk of AKI. Attempts to reduce the incidence of AKI by early transfusion to ameliorate intra-operative anaemia, refinement of protocols for cooling and rewarming on bypass, optimization of pump flow and arterial pressure, or the use of pulsatile flow, have not been successful to date. This may in part reflect the complexity of renal oxygenation, which may limit the effectiveness of individual interventions. We propose a multi-disciplinary pathway for translation comprising three components. Firstly, large-animal models of CPB to continuously monitor both whole kidney and regional kidney perfusion and oxygenation. Secondly, computational models to obtain information that can be used to interpret the data and develop rational interventions. Thirdly, clinically feasible non-invasive methods to continuously monitor renal oxygenation in the operating theatre and to identify patients at risk of AKI. In this review, we outline the recent progress on each of these fronts.

A Comparison of Red Cell Rejuvenation versus Mechanical Washing for the Prevention of Transfusion-associated Organ Injury in Swine

Background

We evaluated the effects of two interventions that modify the red cell storage lesion on kidney and lung injury in experimental models of transfusion.

Methods

White–landrace pigs (n = 32) were allocated to receive sham transfusion (crystalloid), 14-day stored allogeneic red cells, 14-day red cells washed using the red cells washing/salvage system (CATS; Fresenius, Germany), or 14-day red cells rejuvenated using the inosine solution (Rejuvesol solution; Zimmer Biomet, USA) and washed using the CATS device. Functional, biochemical, and histologic markers of organ injury were assessed for up to 24 h posttransfusion.

Results

Transfusion of 14 day red cells resulted in lung injury (lung injury score vs. sham, mean difference −0.3 (95% CI, −0.6 to −0.1; P = 0.02), pulmonary endothelial dysfunction, and tissue leukocyte sequestration. Mechanical washing reduced red cell–derived microvesicles but increased cell-free hemoglobin in 14-day red cell units. Transfusion of washed red cells reduced leukocyte sequestration but did not reduce the lung injury score (mean difference −0.2; 95% CI, −0.5 to 0.1; P = 0.19) relative to 14-day cells. Transfusion of washed red cells also increased endothelial activation and kidney injury. Rejuvenation restored adenosine triphosphate to that of fresh red cells and reduced microvesicle concentrations without increasing cell-free hemoglobin release. Transfusion of rejuvenated red cells reduced plasma cell-free hemoglobin, leukocyte sequestration, and endothelial dysfunction in recipients and reduced lung and kidney injury relative to 14-day or washed 14-day cells.

Conclusions

Reversal of the red cell storage lesion by rejuvenation reduces transfusion-associated organ injury in swine.

Vascular endothelial cell changes in postcardiac surgery acute kidney injury

Acute kidney injury (AKI) is common complication of cardiac surgery; however, the phenotype of this condition is poorly defined. The aim of this study was to characterize changes in endothelial structure and function that underlie postcardiopulmonary bypass (post-CPB) AKI. Adult pigs ( n = 16) were randomized to undergo the following procedures ( n = 8 per group): group 1: sham operation, neck dissection with 2.5 h of general anesthesia; and group 2: CPB, 2.5 h of cardiopulmonary bypass. CPB resulted in the depletion of specific epitopes of glycosaminoglycans side chains of the endothelial glycocalyx: Dolichos biflorus agglutinin: mean difference (MD) [95% confidence interval (CI)], P value: -0.26 (-0.42, -0.09), P = 0.0024, Triticum vulgaris (wheat germ) agglutinin: -0.83 (-1.2, -0.38), P = 0.0005, and Ulex europaeus agglutinin 1: -0.25 (-0.49, -0.009), P = 0.041; endothelial membrane protein: thrombomodulin: -3.13 (-5.6, -0.65), P = 0.02; and adherens junction: VE-cadherin: -1.06 (-1.98, -0.145), P = 0.02. CPB also resulted in reductions in microvascular cortical perfusion: -0.62 (-1.02, -0.22), P = 0.006, and increased renal cortex adenosine levels: 2.32 (0.83, 3.8), P = 0.0059. These changes were accompanied by significant reduction in creatinine clearance at 1.5 h postintervention, MD 95% CI; -51.7 (-99.7, -3.7), P = 0.037, and at 24 h, MD (95% CI): -47.3 (-87.7, -7.6), P = 0.023, and proteinuria immediately postintervention MD (95% CI): 18.79 (2.17, 35.4), P = 0.03 vs. sham. In our experimental CPB model, endothelial injury was associated with loss of autoregulation, increase in microvascular permeability, and reduced glomerular filtration. Interventions that promote endothelial homeostasis may have clinical utility in the prevention of postcardiac surgery AKI.

A Phase I study to determine the pharmacokinetic profile, safety and tolerability of sildenafil (Revatio® ) in cardiac surgery: the REVAKI-1 study

AIMS

Acute kidney injury (AKI) is a common and severe complication of cardiac surgery. There is no effective prevention or treatment. Sildenafil citrate (Revatio^® , Pfizer Inc.), a phosphodiesterase type 5 inhibitor, prevents post cardiac surgery AKI in pre-clinical studies, however its use is contraindicated in patients with symptomatic cardiovascular disease. The aim of this study is to assess the safety and pharmacokinetics of intravenous sildenafil in cardiac surgery patients.

METHODS

We conducted an open label, dose escalation study with six patients per dose level. The six doses were 2.5 mg, 5 mg or 10 mg as a bolus, either alone or followed by an additional 2 h infusion of 2.5 mg sildenafil.

RESULTS

Thirty-six patients entered the trial, of which 33 completed it. The mean age was 69.9 years. One patient died during surgery, two others were removed from the trial before dosing (all at dose level 5 mg + 2.5 mg). The pharmacokinetic profile of sildenafil was similar to previously published studies. For a dose of 10 mg administered as a bolus followed by 2.5 mg administered over 2 h the results were AUC_∞ 537 ng h ml^-1 , C_max 189.4 ng ml^-1 and t_1/2 10.5 h. The drug was well tolerated with no serious adverse events related to drug administration. Higher sildenafil doses stabilized post-surgery nitric oxide bioavailability.

CONCLUSIONS

Pharmacokinetics of sildenafil during cardiopulmonary bypass were comparable to those of other patient groups. The drug was well tolerated at therapeutic plasma levels. These results support the further evaluation of sildenafil for the prevention of AKI in cardiac surgery.

Sildenafil prevents renal dysfunction in contrast media-induced nephropathy in Wistar rats

Contrast-induced nephropathy (CIN) is an iatrogenic medical event in stable cardiology patients that may lead to acute renal failure. There is no current successful therapy to manage CIN. Increasing evidence in experimental models and humans has suggested that this disease is associated with renal tubular and vascular injury triggered by oxidative stress. Considering the importance of reactive oxygen species (ROS) generation in the pathogenesis of CIN, the goal of the present study was to evaluate the effects of sildenafil on CIN development. Male Wistar rats were divided into control, CIN, and CIN pretreated with sildenafil (50 mg/kg/day). CIN was induced by water deprivation, NG-nitro-L-arginine methyl ester + indomethacin injections (10 mg/kg, intraperitoneally) and intravenous iohexol administration (3 g/kg). Renal function was evaluated through glomerular filtration rate (GFR), renal blood flow (RBF), plasma creatinine, uremia, and proteinuria. Oxidative stress was assessed by flow cytometry for intracellular ROS. Treatment with sildenafil attenuated the marked reduction of GFR and RBF in the CIN group. Moreover, sildenafil treatment in CIN rats reduced plasma creatinine, uremia, and proteinuria. Flow cytometry demonstrated that sildenafil attenuated the ROS production in the CIN group. These data suggest that sildenafil may be a new therapeutic agent to prevent CIN through its ability to preserve renal function and attenuate oxidative stress.

Bridging translation for acute kidney injury with better preclinical modeling of human disease

The current lack of effective therapeutics for patients with acute kidney injury (AKI) represents an important and unmet medical need. Given the importance of the clinical problem, it is time for us to take a few steps back and reexamine current practices. The focus of this review is to explore the extent to which failure of therapeutic translation from animal studies to human studies stems from deficiencies in the preclinical models of AKI. We will evaluate whether the preclinical models of AKI that are commonly used recapitulate the known pathophysiologies of AKI that are being modeled in humans, focusing on four common scenarios that are studied in clinical therapeutic intervention trials: cardiac surgery-induced AKI; contrast-induced AKI; cisplatin-induced AKI; and sepsis associated AKI. Based on our observations, we have identified a number of common limitations in current preclinical modeling of AKI that could be addressed. In the long term, we suggest that progress in developing better preclinical models of AKI will depend on developing a better understanding of human AKI. To this this end, we suggest that there is a need to develop greater in-depth molecular analyses of kidney biopsy tissues coupled with improved clinical and molecular classification of patients with AKI.

Renal endothelial dysfunction in acute kidney ischemia reperfusion injury

Acute kidney injury is associated with alterations in vascular tone that contribute to an overall reduction in GFR. Studies in animal models indicate that ischemia triggers alterations in endothelial function that contribute significantly to the overall degree and severity of a kidney injury. Putative mediators of vasoconstriction that may contribute to the initial loss of renal blood flow and GFR are highlighted. In addition, there is discussion of how intrinsic damage to the endothelium impairs homeostatic responses in vascular tone as well as promotes leukocyte adhesion and exacerbating the reduction in renal blood flow. The timing of potential therapies in animal models as they relate to the evolution of AKI, as well as the limitations of such approaches in the clinical setting are discussed. Finally, we discuss how acute kidney injury induces permanent alterations in renal vascular structure. We posit that the cause of the sustained impairment in kidney capillary density results from impaired endothelial growth responses and suggest that this limitation is a primary contributing feature underlying progression of chronic kidney disease.

Sildenafil citrate in a donation after circulatory death experimental model of renal ischemia-reperfusion injury

INTRODUCTION

Phosphodiesterase-5 inhibitors prevent the breakdown of cyclic guanosine 3',5'-monophosphate (cGMP) and therefore may be useful in reducing the detrimental effects of ischemia-reperfusion (I/R) injury. The aim of this study was to assess the effects of the phosphodiesterase-5 inhibitor sildenafil, on I/R injury in a porcine model of donation after circulatory death kidney transplantation.

METHODS

Kidneys were subjected to 20 min warm ischemia followed by 2 or 18 hr of cold storage (n=6 kidneys per group). After preservation kidneys were reperfused on an ex vivo perfusion system for 3 hr with an oxygenated blood based solution. Kidneys were treated with 1.4 mg/kg sildenafil infused 10 min before and for 20 min after reperfusion (n=6 kidneys per group). Renal function and injury markers were measured throughout reperfusion.

RESULTS

Prolonged cold ischemia (CI) significantly reduced levels of cGMP (2 hr 3.5 [1.5-5.7] vs. 18 hr 1.2 [0.3-2.8] pmol/mL; P=0.010). The administration of sildenafil significantly increased the levels (P=0.047, 0.064). Sildenafil improved the renal blood flow for the first 30 min in the 2-hr group (sildenafil, 81.8 [43.8-101.9] vs. control 40.2 [6.4-76.9] mL/min/100 g; P=0.026) and up to 60 min in the 18-hr group (sildenafil, 67.4 [38.0-87.0] vs. control 36.2 [30.5-50.0] mL/min/100 g; P=0.009) during reperfusion. Renal function was significantly impaired after 18-hr CI (P=0.0.26), and treatment with sildenafil did not improve renal function in the 2-hr (P=0.384) or 18-hr CI (P=0.099) groups.

CONCLUSION

Sildenafil had a vasodilatory action and increased levels of cGMP but did not affect recovery of renal function or protect against I/R injury.

Changes in renal medulla gene expression in a pre-clinical model of post cardiopulmonary bypass acute kidney injury

BACKGROUND

Acute kidney injury (AKI) is a common and serious complication of cardiac surgery using cardiopulmonary bypass (CPB). The pathogenesis is poorly understood and the study of AKI in rodent models has not led to improvements in clinical outcomes. We sought to determine the changes in renal medullary gene expression in a novel and clinically relevant porcine model of CPB-induced AKI.

RESULTS

Adult pigs (n = 12 per group) were randomised to undergo sham procedure, or 2.5 hours CPB. AKI was determined using biochemical (Cr51 EDTA clearance, CrCl, urinary IL-18 release) and histological measures. Transcriptomic analyses were performed on renal medulla biopsies obtained 24 hours post intervention or from sham group. Microarray results were validated with real-time polymerase chain reaction and Western Blotting.Of the transcripts examined, 66 were identified as differentially expressed in CPB versus Sham pig's kidney samples, with 19 (29%) upregulated and 47 (71%) down-regulated. Out of the upregulated and downregulated transcripts 4 and 16 respectively were expression sequence tags (EST). The regulated genes clustered into three classes; Immune response, Cell adhesion/extracellular matrix and metabolic process. Upregulated genes included Factor V, SLC16A3 and CKMT2 whereas downregulated genes included GST, CPE, MMP7 and SELL.

CONCLUSION

Post CPB AKI, as defined by clinical criteria, is characterised by molecular changes in renal medulla that are associated with both injury and survival programmes. Our observations highlight the value of large animal models in AKI research and provide insights into the failure of findings in rodent models to translate into clinical progress.

The protective effect of single dose tadalafil in contrast-induced nephropathy: an experimental study

Objective:

Contrast-induced nephropathy (CIN) is one of the most common causes of acute renal failure in hospitalized patients. The direct toxic effect of contrast media; ischemic damage caused by reactive oxygen species; increased perivascular hydrostatic pressure; high viscosity and changes in the activity of vasoactive substances play important roles in the pathogenesis. Tadalafil inhibits the phosphodiesterase enzyme which destroys nitric oxide. Nitric oxide causes renal vasodilatation, increases renal medullar blood flow and mediates the removal of free oxygen radicals. Drugs that increase levels of nitric oxide are expected to reduce the development of contrast nephropathy due to contrast media. We aimed to test the hypothesis that tadalafil reduces the development of contrast nephropathy due to contrast toxicity.

Methods:

A total of 24 female Wistar albino rats, three groups of eight, were included in the study. After 48 hours of dehydration, contrast media (meglumine diatrozoate, 6 mL/kg) was administered to the first group, and contrast media with tadalafil (10 mg/kg) was administered to the second group. The third group served as the control group. Blood and tissue samples were taken 48 hours after this procedure.

Results:

Serum cystatin C, serum creatinine and blood urea nitrogen (BUN) values were significantly lower in the contrast with tadalafil group compared to the group given only contrast. Serum and tissue malondialdehyde (MDA) levels were significantly lower in the contrast with tadalafil group than in the contrast only group.

Conclusion:

These results demonstrate the protective effect of tadalafil in the prevention of CIN in rats.

Phosphodiesterase-5 inhibition attenuates early renal ischemia-reperfusion-induced acute kidney injury: assessment by quantitative measurement of urinary NGAL and KIM-1

Acute kidney injury (AKI) is a common clinical problem that still lacks effective treatment. Phosphodiesterase-5 (PDE5) inhibitors possess anti-apoptotic and anti-oxidant properties, making it a promising therapy for ischemia-reperfusion (I/R) injury of various organs. The present study evaluated the early nephroprotective effects of Tadalafil, a PDE5 inhibitor, in an experimental model of renal I/R. Sprague-Dawley rats were divided into two groups: vehicle-treated I/R (n = 10), and Tadalafil (10 mg/kg po)-treated I/R group (n = 11). After removal of the right kidney and collection of two baseline urine samples, the left renal artery was clamped for 45 min followed by reperfusion for 60, 120, 180, and 240 min. Functional and histological parameters of the kidneys from the various groups were determined. In the vehicle-treated I/R group, glomerular filtration rate was significantly reduced compared with that in normal kidneys. In addition, the ischemic kidney showed remarkable cast formation, necrosis, and congestion, a consistent pattern of acute tubular necrosis. Furthermore, urinary excretion of NGAL and KIM-1, two novel biomarkers of kidney injury, substantially increased following I/R insult. In contrast, Tadalafil treatment resulted in a significant improvement in kidney function and amelioration of the adverse histological alterations of the ischemic kidney. Noteworthy, the urinary excretion of NGAL and KIM-1 markedly decreased in the Tadalafil-treated I/R group. These findings demonstrate that Tadalafil possesses early nephroprotective effects in rat kidneys subjected to I/R insult. This approach may suggest a prophylactic therapy for patients with ischemic AKI.