Endothelial injury and dysfunction in ischemic acute renal failure

Utilizing pathophysiological concepts of ischemia-reperfusion injury to design renoprotective strategies and therapeutic interventions for normothermic ex vivo kidney perfusion

Normothermic machine perfusion (NMP) has emerged as a promising tool for the preservation, viability assessment, and repair of deceased-donor kidneys prior to transplantation. These kidneys inevitably experience a period of ischemia during donation, which leads to ischemia-reperfusion injury when NMP is subsequently commenced. Ischemia-reperfusion injury has a major impact on the renal vasculature, metabolism, oxygenation, electrolyte balance, and acid-base homeostasis. With an increased understanding of the underlying pathophysiological mechanisms, renoprotective strategies and therapeutic interventions can be devised to minimize additional injury during normothermic reperfusion, ensure the safe implementation of NMP, and improve kidney quality. This review discusses the pathophysiological alterations in the vasculature, metabolism, oxygenation, electrolyte balance, and acid-base homeostasis of deceased-donor kidneys and delineates renoprotective strategies and therapeutic interventions to mitigate renal injury and improve kidney quality during NMP.

Aspirin intervention before ICU admission reduced the mortality in critically ill patients with acute kidney injury: results from the MIMIC-IV

Background: Aspirin, with its pleiotropic effects such as anti-inflammatory and anti-platelet aggregation, has been widely used for anti-inflammatory, analgesic, and cardiovascular diseases. However, the association between the use of aspirin before the intensive care unit (ICU) and clinical outcomes in critically ill patients with acute kidney injury (AKI) is unknown. Methods: Patients with AKI in this retrospective observational study were selected from the Marketplace for Medical Information in Intensive Care IV (MIMIC-IV). The association between aspirin intervention and 30-day mortality was assessed using Cox proportional hazards model. Logistic regression models were used to assess the association of aspirin intervention with the risks of intracranial hemorrhage, gastrointestinal bleeding and blood transfusion. The propensity score matching (PSM) method was adopted to balance the baseline variables. Sensitivity analysis was performed to validate the results by multiple interpolations for the missing data. Results: The study included 4237 pre-ICU aspirin users and 9745 non-users. In multivariate models, we found a decreased risk of mortality in those who received aspirin before ICU compared to those who did not (30-day:hazard ratio [HR], 0.70; 95% CI, 0.62-0.79; p < 0.001; 90-day:HR, 0.70; 95% CI, 0.63-0.77, p < 0.001; 180-day:HR, 0.72; 95%CI,0.65-0.79, p < 0.001). This benefit was consistent in the post-PSM analyses, sensitivity analyses, and subgroup analyses. Moreover, aspirin intervention was associated with a reduced risk of intracranial hemorrhage and gastrointestinal bleeding (HR, 0.16; 95% CI, 0.10-0.25; p < 0.001; HR, 0.59; 95% CI, 0.38-0.88, p = 0.012) after being adjusted by relating covariates, whereas with a increased risk of blood transfusion (HR, 1.28; 95% CI, 1.16-1.46; p < 0.001). Conclusion: Patients with AKI treated with aspirin before ICU admission might have reduced 30-day, 90-day and 180-day mortality without increasing the risk of intracranial hemorrhage (ICH) or gastrointestinal bleeding, but may increase the risk of transfusion.

Prognostic value of C-reactive protein to albumin ratio for mortality in acute kidney injury

BACKGROUND

Inflammation plays an important role in the development of acute kidney injury (AKI). However, there are few studies exploring the prognostic influence of C-reactive protein to albumin ratio (CAR) among AKI patients. In this study, we investigated whether CAR could be a useful marker to predict the mortality of AKI.

METHODS

A total of 358 AKI patients were extracted from the Medical Information Mart for Intensive Care III (MIMIC III) database. C-reactive protein (CRP) and albumin were measured at ICU admission. The clinical outcome was 365-day mortality. Cox proportional hazards model and Kaplan-Meier survival analysis were conducted to evaluate the association between CAR and outcome.

RESULTS

Compared with patients in the survival group, nonsurvivors had higher CAR levels. The area under the receiver operating characteristic (ROC) curve of CAR was higher than that of CRP and albumin for mortality (0.64 vs. 0.63, 0.59, respectively). The cut-off point of CAR for mortality was 7.23. In Cox proportional-hazard regression analysis, CAR (hazards ratio (HR) =2.04, 95% confidence interval (CI) =1.47-2.85, p < 0.001 for higher CAR) and Simplified Acute Physiology Score II (HR = 1.02, 95%CI = 1.00-1.03, p = 0.004) were independent predictors of 365-day mortality.

CONCLUSIONS

Our study demonstrated that a higher level of CAR was associated with 365-day mortality in AKI patients.

Endothelial cells: potential novel regulators of renal inflammation

Substantial evidence has supported the role of endothelial cell (EC) activation and dysfunction in the development of hypertension, chronic kidney disease (CKD), and lupus nephritis (LN). In both humans and experimental models of hypertension, CKD, and LN, ECs become activated and release potent mediators of inflammation including cytokines, chemokines, and reactive oxygen species that cause EC dysfunction, tissue damage, and fibrosis. Factors that activate the endothelium include inflammatory cytokines, mechanical stretch, and pathological shear stress. These signals can activate the endothelium to promote upregulation of adhesion molecules, such as intercellular adhesion molecule-1 and vascular cell adhesion molecule-1, which promote leukocyte adhesion and migration to the activated endothelium. More importantly, it is now recognized that some of these signals may in turn promote endothelial antigen presentation through major histocompatibility complex II. In this review, we will consider in-depth mechanisms of endothelial activation and the novel mechanism of endothelial antigen presentation. Moreover, we will discuss these proinflammatory events in renal pathologies and consider possible new therapeutic approaches to limit the untoward effects of endothelial inflammation in hypertension, CKD, and LN.

Microcirculation during surgery

Throughout the long history of surgery, there has been great advancement in the hemodynamic management of surgical patients. Traditionally, hemodynamic management has focused on macrocirculatory monitoring and intervention to maintain appropriate oxygen delivery. However, even after optimization of macro-hemodynamic parameters, microcirculatory dysfunction, which is related to higher postoperative complications, occurs in some patients. Although the clinical significance of microcirculatory dysfunction has been well reported, little is known about interventions to recover microcirculation and prevent microcirculatory dysfunction. This may be at least partly caused by the fact that the feasibility of monitoring tools to evaluate microcirculation is still insufficient for use in routine clinical practice. However, considering recent advancements in these research fields, with more popular use of microcirculation monitoring and more clinical trials, clinicians may better understand and manage microcirculation in surgical patients in the future. In this review, we describe currently available methods for microcirculatory evaluation. The current knowledge on the clinical relevance of microcirculatory alterations has been summarized based on previous studies in various clinical settings. In the latter part, pharmacological and clinical interventions to improve or restore microcirculation are also presented.

A Review of Natural Products for Prevention of Acute Kidney Injury

BACKGROUND AND OBJECTIVES

acute kidney injury (AKI), formerly called acute renal failure (ARF), is commonly defined as an abrupt decline in renal function, clinically manifesting as a reversible acute increase in nitrogen waste products-measured by blood urea nitrogen (BUN) and serum creatinine levels-over the course of hours to weeks. AKI occurs in about 20% of all hospitalized patients and is more common in the elderly. Therefore, it is necessary to prevent the occurrence of AKI, and to detect and treat early, since it is known that a prolonged period of kidney injury increases cardiovascular complications and the risk of death. Despite advances in modern medicine, there are no consistent treatment strategies for preventing the progression to chronic kidney disease. Through many studies, the safety and efficacy of natural products have been proven, and based on this, the time and cost required for new drug development can be reduced. In addition, research results on natural products are highly anticipated in the prevention and treatment of various diseases. In relation to AKI, many papers have reported that many natural products can prevent and treat AKI.

CONCLUSIONS

in this paper, the results of studies on natural products related to AKI were found and summarized, and the mechanism by which the efficacy of AKI was demonstrated was reviewed. Many natural products show that AKI can be prevented and treated, suggesting that these natural products can help to develop new drugs. In addition, we may be helpful to elucidate additional mechanisms and meta-analysis in future natural product studies.

Impact of Inhaled Oxygen on Reactive Oxygen Species Production and Oxidative Damage during Spontaneous Ventilation in a Murine Model of Acute Renal Ischemia and Reperfusion

Introduction

Acute kidney injury (AKI) affects 10% of patients following major surgery and is independently associated with extra-renal organ injury, development of chronic kidney disease, and death. Perioperative renal ischemia and reperfusion (IR) contributes to AKI by, in part, increasing production of reactive oxygen species (ROS) and leading to oxidative damage. Variations in inhaled oxygen may mediate some aspects of IR injury by affecting tissue oxygenation, ROS production, and oxidative damage. We tested the hypothesis that provision of air (normoxia) compared to 100% oxygen (hyperoxia) during murine renal IR affects renal ROS production and oxidative damage.

Methods

We administered 100% oxygen or 21% oxygen (air) to 8-9 week-old FVB/N mice and performed dorsal unilateral nephrectomy with contralateral renal ischemia/reperfusion surgery while mice spontaneously ventilated. We subjected mice to 30 minutes of ischemia and 30 minutes of reperfusion prior to sacrifice. We obtained an arterial blood gas (ABG) by performing sternotomy and left cardiac puncture. We stained the kidney with pimonidazole, a marker of tissue hypoxia; 4-HNE, a marker of ROS-production; and we measured F2-isoprostanes in homogenized tissue to quantify oxidative damage.

Results

Hyperoxia during IR increased arterial oxygen content compared to normoxia, but both groups of mice were hypoventilating at the time of ABG sampling. Renal tissue hypoxia following reperfusion was similar in both treatment groups. ROS production was similar in the cortex of mice (3.8% area in hyperoxia vs. 3.1% in normoxia, P=0.19) but increased in the medulla of hyperoxia-treated animals (6.3% area in hyperoxia vs. 4.5% in nomoxia, P=0.02). Renal F2-isoprostanes were similar in treatment groups (2.2 pg/mg kidney in hyperoxia vs. 2.1 pg/mg in normoxia, P=0.40).

Conclusions

Hyperoxia during spontaneous ventilation in murine renal IR did not appear to affect renal hypoxia following reperfusion, but hyperoxia increased medullary ROS production compared to normoxia.

The Potential Role of Exercise-Induced Muscle Damage in Exertional Heat Stroke

Exertional heat stroke (EHS) is a life-threatening condition that affects mainly athletes, military personnel, firefighters, and occupational workers. EHS is frequently observed in non-compensable conditions (where the body is unable to maintain a steady thermal balance) as a result of heavy heat stress and muscle contraction associated with prolonged and strenuous physical and occupational activities, resulting in central nervous system dysfunction followed by multi-organ damage and failure. Since the pathophysiology of EHS is complex and involves multiple organs and systems, any condition that changes the interrelated systems may increase the risk for EHS. It has been suggested that exercise-induced muscle damage (EIMD) can lead to thermoregulatory impairment and systemic inflammation, which could be a potential predisposing factor for EHS. In this review article, we aim to (1) address the evidence of EIMD as a predisposing factor for EHS and (2) propose a possible mechanism of how performing muscle-damaging exercise in the heat may aggravate muscle damage and subsequent risk of EHS and acute kidney injury (AKI). Such an understanding could be meaningful to minimize the risks of EHS and AKI for individuals with muscle damage due to engaging in physical work in hot environments.

Opioids Preconditioning Upon Renal Function and Ischemia-Reperfusion Injury: A Narrative Review

Kidneys have an important role in regulating water volume, blood pressure, secretion of hormones and acid-base and electrolyte balance. Kidney dysfunction derived from acute injury can, under certain conditions, progress to chronic kidney disease. In the late stages of kidney disease, treatment is limited to replacement therapy: Dialysis and transplantation. After renal transplant, grafts suffer from activation of immune cells and generation of oxidant molecules. Anesthetic preconditioning has emerged as a promising strategy to ameliorate ischemia reperfusion injury. This review compiles some significant aspects of renal physiology and discusses current understanding of the effects of anesthetic preconditioning upon renal function and ischemia reperfusion injury, focusing on opioids and its properties ameliorating renal injury. According to the available evidence, opioid preconditioning appears to reduce inflammation and reactive oxygen species generation after ischemia reperfusion. Therefore, opioid preconditioning represents a promising strategy to reduce renal ischemia reperfusion injury and, its application on current clinical practice could be beneficial in events such as acute renal injury and kidney transplantation.

G protein-coupled estrogen receptor activation improves contractile and diastolic functions in rat renal interlobular artery to protect against renal ischemia reperfusion injury

OBJECTIVE

This work aimed to investigate whether G protein-coupled estrogen receptor (GPER) can improve the renal interlobular artery vascular function by increasing the NO content, thereby protecting against renal ischemia-reperfusion (IR) injury.

METHODS

This study classified ovariectomised (OVX) female Sprague-Dawley rats into OVX, OVX + IR, OVX + IR + G1 (the GPER agonist G1), OVX + IR + G1+G15 (GPER blocker) and OVX + IR + G1+L-NAME (eNOS blocker) groups. Enzyme-linked immunosorbent assay was performed to detect the estrogen levels in the body and eliminate interference from endogenous estrogens. Terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end labelling (TUNEL) and HE staining, renal function test and Paller scoring were performed to identify the successful model and detect the degree of renal and renal interlobular arteries injury. The in vitro microvascular pressure diameter measurement technique was used to detect the contraction and diastolic activities of the renal interlobular arteries in each group. Immunofluorescence technique was used to observe the localisation and expression levels of GPER and eNOS in renal interlobular arteries. The GPER and eNOS protein expression levels in each group were detected by Western blot. The NO content in the serum of each group was detected by the nitrate reductase method.

RESULT

After OVX, the estrogen level in the body decreased significantly (P < 0.01), and TUNEL staining showed a significant increase in the degree of renal tubular epithelial cell apoptosis in the IR group. Serum creatinine (SCr) and blood urea nitrogen (BUN) levels were significantly increased in the IR group (P < 0.01), and the Paller score showed significantly increased kidney damage. When performing drug treatment, the G1 intervention group significantly decreased serum BUN and SCr levels after IR injury (P < 0.01). The Paller score showed significantly decreased the degree of renal injury (P < 0.01). After IR, the renal interlobular artery contraction rate and systolic velocity of blood vessels were significantly decreased (P < 0.01). The G1 intervention group significantly restored contraction rate and systolic velocity of blood vessels (P < 0.01), and G15 and L-NAME partially reversed this effect (P < 0.01). Immunofluorescence technique showed that GPER was expressed in renal interlobular artery smooth muscle and endothelial cells. After IR injury, the GPER protein expression increased, and the eNOS protein expression decreased significantly (P < 0.01). Western blot showed that after IR injury, the GPER protein expression increased, and the eNOS protein expression decreased significantly. After G1 intervention, the GPER content did not change, and the eNOS content increased significantly (P < 0.01). After ischemia and reperfusion, the serum NO content decreased significantly, but it increased after G1 intervention. G15 and L-NAME reversed the effects of G1 to varying degrees (both at P < 0.01).

CONCLUSION

GPER may improve the renal interlobular artery vascular function by increasing the NO content, thereby protecting against renal IR injury.

The assessment of acute kidney injury in critically ill patients

Acute kidney injury (AKI) is common in critically ill patients and is associated with high morbidity and mortality. The availability of several biomarkers of kidney injury offers new tools for its early recognition and management. The early identification of high-risk patients provides an opportunity to develop strategies for the prevention, early diagnosis and treatment of AKI. Despite progress in critical care medicine over the past decade, the treatment strategies for AKI in critically ill patients, such as when to start renal replacement therapy, remain controversial. A recently proposed risk prediction score for AKI, based on routinely available clinical variables, presents a new means of identifying patients at high risk of AKI.

Farnesoid X receptor activation protects the kidney from ischemia-reperfusion damage

Farnesoid X receptor (FXR) activation has been reported to reduce inflammation and oxidative stress. Because both inflammation and oxidative stress are critical for tissue destruction during kidney ischemia reperfusion (I/R) injury, we investigated the protective role of FXR against kidney damage induced by I/R in mice. Mice undergoing renal I/R developed the typical features of acute kidney injury (AKI): increased creatinine, albuminuria, tubular necrosis and apoptosis. Inflammatory cytokine production and oxidative stress were also markedly increased. In mice pretreated with 6-ethyl-chenodeoxycholic acid (6-ECDCA), a selective FXR agonist, I/R induced changes were prevented and renal function and structure were improved. Moreover, FXR activation also effectively prevented the subsequent progression of AKI to chronic kidney disease (CKD) by ameliorating glomerulosclerosis and interstitial fibrosis and by suppressing fibrogenic gene expression. FXR mRNA levels were inversely correlated with the progression to CKD in mice and with the degree of interstitial fibrosis in human biopsies. In further experiments administering 6-ECDCA to renal proximal tubular cells cultured under hypoxia, the renoprotective effects of FXR activation were associated with inhibition of oxidative and ER stress and with increased antioxidant activity. In conclusion, FXR agonists may have a therapeutic role in conditions associated with ischemic kidney damage.

Hepatic ischemia/reperfusion injury associates with acute kidney injury in liver transplantation: Prospective cohort study

Solid clinical prospective studies investigating the association between hepatic ischemia/reperfusion injury (HIRI) and acute kidney injury (AKI) after liver transplantation are missing. HIRI, reflected by transaminase release, induces AKI in rodents, and retrospective studies suggest a similar association in humans. This prospective cohort study determined risk factors for AKI in 80 adult liver-only recipients. AKI defined by Risk, Injury, Failure, Loss, and End-Stage Kidney Disease (RIFLE) criteria developed in 21 (26%) recipients at 12 hours after reperfusion (interquartile range, 6 hours to postoperative day [POD] 1); 13 progressed from "risk" to "injury"; 5 progressed to "failure." In AKI patients, creatinine (Cr) increased during liver transplantation and was higher versus baseline at 6 hours to POD 4, whereas perioperative Cr remained stable in those without AKI. Plasma heart-type fatty acid-binding protein was higher 12 hours after reperfusion in AKI patients, though urinary kidney injury molecule 1 and neutrophil gelatinase-associated lipocalin were similar between those with or without AKI. Peak aspartate aminotransferase (AST), occurring at 6 hours, was the only independent risk factor for AKI (adjusted odds ratio, 2.42; 95% confidence interval, 1.24-4.91). Early allograft dysfunction occurred more frequently in AKI patients, and intensive care and hospital stays were longer. Patient survival at 1 year was 90% in those with AKI versus 98% in those without AKI. Chronic kidney disease stage ≥ 2 at 1 year was more frequent in patients who had had AKI (89% versus 58%, respectively). In conclusion, AKI is initiated early after liver reperfusion and its association with peak AST suggests HIRI as a determinant. Identifying operating mechanisms is critical to target interventions and to reduce associated morbidity. Liver Transplantation 23 634-644 2017 AASLD.

Endothelial colony-forming cells ameliorate endothelial dysfunction via secreted factors following ischemia-reperfusion injury

Damage to endothelial cells contributes to acute kidney injury (AKI) by leading to impaired perfusion. Endothelial colony-forming cells (ECFC) are endothelial precursor cells with high proliferative capacity, pro-angiogenic activity, and in vivo vessel forming potential. We hypothesized that ECFC may ameliorate the degree of AKI and/or promote repair of the renal vasculature following ischemia-reperfusion (I/R). Rat pulmonary microvascular endothelial cells (PMVEC) with high proliferative potential were compared with pulmonary artery endothelial cells (PAEC) with low proliferative potential in rats subjected to renal I/R. PMVEC administration reduced renal injury and hastened recovery as indicated by serum creatinine and tubular injury scores, while PAEC did not. Vehicle-treated control animals showed consistent reductions in renal medullary blood flow (MBF) within 2 h of reperfusion, while PMVEC protected against loss in MBF as measured by laser Doppler. Interestingly, PMVEC mediated protection occurred in the absence of homing to the kidney. Conditioned medium (CM) from human cultured cord blood ECFC also conveyed beneficial effects against I/R injury and loss of MBF. Moreover, ECFC-CM significantly reduced the expression of ICAM-1 and decreased the number of differentiated lymphocytes typically recruited into the kidney following renal ischemia. Taken together, these data suggest that ECFC secrete factors that preserve renal function post ischemia, in part, by preserving microvascular function.

Hydrodynamic Isotonic Fluid Delivery Ameliorates Moderate-to-Severe Ischemia-Reperfusion Injury in Rat Kidneys

Highly aerobic organs like the kidney are innately susceptible to ischemia-reperfusion (I/R) injury, which can originate from sources including myocardial infarction, renal trauma, and transplant. Therapy is mainly supportive and depends on the cause(s) of damage. In the absence of hypervolemia, intravenous fluid delivery is frequently the first course of treatment but does not reverse established AKI. Evidence suggests that disrupting leukocyte adhesion may prevent the impairment of renal microvascular perfusion and the heightened inflammatory response that exacerbate ischemic renal injury. We investigated the therapeutic potential of hydrodynamic isotonic fluid delivery (HIFD) to the left renal vein 24 hours after inducing moderate-to-severe unilateral IRI in rats. HIFD significantly increased hydrostatic pressure within the renal vein. When conducted after established AKI, 24 hours after I/R injury, HIFD produced substantial and statistically significant decreases in serum creatinine levels compared with levels in animals given an equivalent volume of saline via peripheral infusion (P<0.05). Intravital confocal microscopy performed immediately after HIFD showed improved microvascular perfusion. Notably, HIFD also resulted in immediate enhancement of parenchymal labeling with the fluorescent dye Hoechst 33342. HIFD also associated with a significant reduction in the accumulation of renal leukocytes, including proinflammatory T cells. Additionally, HIFD significantly reduced peritubular capillary erythrocyte congestion and improved histologic scores of tubular injury 4 days after IRI. Taken together, these results indicate that HIFD performed after establishment of AKI rapidly restores microvascular perfusion and small molecule accessibility, with improvement in overall renal function.

Multiphoton imaging of kidney pathophysiology

The number of people being diagnosed with end-stage renal disease is increasing globally. Therapeutic options to slow or halt the progression of kidney disease are limited and are not always successful, despite the increasing body of research and number of basic scientific reports in this field. Further studies are required to investigate new approaches to renal pathophysiology. State of the art optical imaging is a powerful tool used to non-invasively observe the pathophysiology of small animals and has the potential to elucidate the unknown mechanisms of renal disease and aid in our understanding of the disease. This paper is a brief summary of the current usefulness of intravital imaging using multiphoton microscopy and discusses possible future applications of the technique.

Renal ischemia/reperfusion against nephrectomy for induction of acute lung injury in rats

PURPOSE

Acute kidney injury (AKI) induces acute lung injury (ALI) through releasing injurious mediators or impairing clearance of systemic factors. To determine the links between AKI and ALI, pulmonary and blood variables were evaluated following induction of AKI via different experimental models of bilateral renal ischemia/reperfusion (BIR: renal ischemia with uremia), unilateral renal ischemia/reperfusion (UIR: renal ischemia without uremia), bilateral nephrectomy (BNX: uremia without renal ischemia), and unilateral nephrectomy (UNX: without uremia and renal ischemia).

METHODS

Ninety male Sprague-Dawley rats were divided into six groups. Animals had 1-h bilateral or 2-h unilateral renal ischemia followed by 24-h reperfusion in the BIR and UIR groups, respectively, and 24-h period following bilateral or unilateral nephrectomy in the BNX and UNX groups, respectively. There were also sham and control groups with and without sham-operation, respectively.

RESULTS

Plasma malondialdehyde and nitric oxide were elevated by BIR more than UIR, but not changed by UNX and BNX. UIR slightly increased plasma creatinine, whereas BIR and BNX largely increased plasma creatinine, urea, K⁺and osmolality and decreased arterial HCO₃^-, pH, and CO₂. UNX and UIR did not affect lung, but BIR and BNX induced ALI with equal capillary leak and macrophages infiltration. However, there were more prominent lung edema and vascular congestion following BNX and more severe neutrophils infiltration and P_aO₂/F_iO₂ reduction following BIR.

CONCLUSION

Acutely accumulated systemic mediators following renal failure in the absence of kidneys vary from those due to combined renal failure with ischemic-reperfused kidneys and consequently they induce ALI with distinct characteristics.

Acute kidney injury: Renal disease in the ICU

Acute kidney injury (AKI) in the ICU frequently requires costly supportive therapies, has high morbidity, and its long-term prognosis is not as good as it has been presumed so far. Consequently, AKI generates a significant burden for the healthcare system. The problem is that AKI lacks an effective treatment and the best approach relies on early secondary prevention. Therefore, to facilitate early diagnosis, a broader definition of AKI should be established, and a marker with more sensitivity and early-detection capacity than serum creatinine - the most common marker of AKI - should be identified. Fortunately, new classification systems (RIFLE, AKIN or KDIGO) have been developed to solve these problems, and the discovery of new biomarkers for kidney injury will hopefully change the way we approach renal patients. As a first step, the concept of renal failure has changed from being a "static" disease to being a "dynamic process" that requires continuous evaluation of kidney function adapted to the reality of the ICU patient.

Semi-automated rapid quantification of brain vessel density utilizing fluorescent microscopy

BACKGROUND

Measurement of vascular density has significant value in characterizing healthy and diseased tissue, particularly in brain where vascular density varies among regions. Further, an understanding of brain vessel size helps distinguish between capillaries and larger vessels like arterioles and venules. Unfortunately, few cutting edge methodologies are available to laboratories to rapidly quantify vessel density.

NEW METHOD

We developed a rapid microscopic method, which quantifies the numbers and diameters of blood vessels in brain. Utilizing this method we characterized vascular density of five brain regions in both mice and rats, in two tumor models, using three tracers.

RESULTS

We observed the number of sections/mm(2) in various brain regions: genu of corpus callosum 161±7, hippocampus 266±18, superior colliculus 300±24, frontal cortex 391±55, and inferior colliculus 692±18 (n=5 animals). Regional brain data were not significantly different between species (p>0.05) or when using different tracers (70kDa and 2000kDa Texas Red; p>0.05). Vascular density decreased (62-79%) in preclinical brain metastases but increased (62%) a rat glioma model.

COMPARISON WITH EXISTING METHODS

Our values were similar (p>0.05) to published literature. We applied this method to brain-tumors and observed brain metastases of breast cancer to have a ∼2.5-fold reduction (p>0.05) in vessels/mm(2) compared to normal cortical regions. In contrast, vascular density in a glioma model was significantly higher (sections/mm(2) 736±84; p<0.05).

CONCLUSIONS

In summary, we present a vascular density counting method that is rapid, sensitive, and uses fluorescence microscopy without antibodies.

Postischemic microvasculopathy and endothelial progenitor cell-based therapy in ischemic AKI: update and perspectives

Acute kidney injury (AKI) dramatically increases mortality of hospitalized patients. Incidences have been increased in recent years. The most frequent cause is transient renal hypoperfusion or ischemia which induces significant tubular cell dysfunction/damage. In addition, two further events take place: interstitial inflammation and microvasculopathy (MV). The latter evolves within minutes to hours postischemia and may result in permanent deterioration of the peritubular capillary network, ultimately increasing the risk for chronic kidney disease (CKD) in the long term. In recent years, our understanding of the molecular/cellular processes responsible for acute and sustained microvasculopathy has increasingly been expanded. The methodical approaches for visualizing impaired peritubular blood flow and increased vascular permeability have been optimized, even allowing the depiction of tissue abnormalities in a three-dimensional manner. In addition, endothelial dysfunction, a hallmark of MV, has increasingly been recognized as an inductor of both vascular malfunction and interstitial inflammation. In this regard, so-called regulated necrosis of the endothelium could potentially play a role in postischemic inflammation. Endothelial progenitor cells (EPCs), represented by at least two major subpopulations, have been shown to promote vascular repair in experimental AKI, not only in the short but also in the long term. The discussion about the true biology of the cells continues. It has been proposed that early EPCs are most likely myelomonocytic in nature, and thus they may simply be termed proangiogenic cells (PACs). Nevertheless, they reliably protect certain types of tissues/organs from ischemia-induced damage, mostly by modulating the perivascular microenvironment in an indirect manner. The aim of the present review is to summarize the current knowledge on postischemic MV and EPC-mediated renal repair.

Renal endothelial injury and microvascular dysfunction in acute kidney injury

The kidney is comprised of heterogeneous cell populations that function together to perform a number of tightly controlled, complex and interdependent processes. Renal endothelial cells contribute to vascular tone, regulation of blood flow to local tissue beds, modulation of coagulation and inflammation, and vascular permeability. Both ischemia and sepsis have profound effects on the renal endothelium, resulting in microvascular dysregulation resulting in continued ischemia and further injury. In recent years, the concept of the vascular endothelium as an organ that is both the source of and target for inflammatory injury has become widely appreciated. Here we revisit the renal endothelium in the light of ever evolving molecular advances.

Ascorbic acid improves renal microcirculatory oxygenation in a rat model of renal I/R injury

Background and objectives

Acute kidney injury (AKI) is a clinical condition associated with a degree of morbidity and mortality despite supportive care, and ischemia/reperfusion injury (I/R) is one of the main causes of AKI. The pathophysiology of I/R injury is a complex cascade of events including the release of free oxygen radicals followed by damage to proteins, lipids, mitochondria, and deranged tissue oxygenation. In this study, we investigated whether the antioxidant ascorbic acid would be able to largely prevent oxidative stress and consequently, reduce I/R-related injury to the kidneys in terms of oxygenation, inflammation, and renal failure.

Materials and methods

Rats were divided into three groups (n = 6/group): (1) a time control group; (2) a group subjected to renal ischemia for 60 min by high aortic occlusion followed by 2 h of reperfusion (I/R); and (3) a group subjected to I/R and treated with an i.v. 100 mg/kg bolus ascorbic acid 15 min before ischemia and continuous infusion of 50 mg/kg/hour for 2 h during reperfusion (I/R + AA). We measured renal tissue oxidative stress, microvascular oxygenation, renal oxygen delivery and consumption, and renal expression of inflammatory and injury markers.

Results

We demonstrated that aortic clamping and release resulted in increased oxidative stress and inflammation that was associated with a significant fall in systemic and renal hemodynamics and oxygenation parameters. The treatment of ascorbic acid completely abrogated oxidative stress and inflammatory parameters. However, it only partly improved microcirculatory oxygenation and was without any effect on anuria.

Conclusion

The ascorbic acid treatment partly improves microcirculatory oxygenation and prevents oxidative stress without restoring urine output in a severe I/R model of AKI.

Strategies to optimize kidney recovery and preservation in transplantation: specific aspects in pediatric transplantation

In renal transplantation, live donor kidney grafts are associated with optimum success rates due to the shorter period of ischemia during the surgical procedure. The current shortage of donor organs for adult patients has caused a shift towards deceased donors, often with co-morbidity factors, whose organs are more sensitive to ischemia-reperfusion injury, which is unavoidable during transplantation. Donor management is pivotal to kidney graft survival through the control of the ischemia-reperfusion sequence, which is known to stimulate numerous deleterious or regenerative pathways. Although the key role of endothelial cells has been established, the complexity of the injury, associated with stimulation of different cell signaling pathways, such as unfolded protein response and cell death, prevents the definition of a unique therapeutic target. Preclinical transplant models in large animals are necessary to establish relationships and kinetics and have already contributed to the improvement of organ preservation. Therapeutic strategies using mesenchymal stem cells to induce allograft tolerance are promising advances in the treatment of the pediatric recipient in terms of reducing/withdrawing immunosuppressive therapy. In this review we focus on the different donor management strategies in kidney graft conditioning and on graft preservation consequences by highlighting the role of endothelial cells. We also propose strategies for preventing ischemia-reperfusion, such as cell therapy.

Biliary tract external drainage alleviates kidney injury in shock

BACKGROUND

Kidney injury is common in hemorrhagic shock (HS). Kidney injury leads to a systemic increase in serum chemokines and cytokines and causes injuries to other vital organs. Our previous studies showed that vitamin C led to organ protection and inflammation inhibitory effects in rat models of HS via induction heme oxygenase-1 (HO-1). We also found that biliary tract external drainage (BTED) increased the expression levels of HO-1 in rat livers. We investigated roles of BTED in kidney injury and its relationship with the HO-1 pathway in HS in this research.

METHODS

Rat models of HS were induced by drawing blood from the femoral artery. BTED was performed by inserting a catheter into the bile duct. Thirty-six Sprague-Dawley rats were randomized to sham group; HS group; zinc protoporphyrin IX (Znpp) group; BTED group; BTED + Znpp group, and BTED + bile infusion group. The expression levels of HO-1 in the kidney were analyzed by Western blotting. The expression levels of occludin messenger RNA in the kidney were analyzed by real-time reverse transcription-polymerase chain reaction. The expression levels of occludin in the kidney were analyzed by immunohistochemistry. Histology of renal was performed by hematoxylin and eosin staining.

RESULTS

Occludin messenger RNA and protein levels in the kidney increased markedly after BTED under HS conditions. Renal histopathologic scores decreased significantly after BTED under HS conditions. Znpp significantly inhibited all mentioned effects.

CONCLUSIONS

BTED alleviates kidney injury in rats of HS via the HO-1 pathway.

Combined peri-ischemic administration of Bβ15-42 in treating ischemia reperfusion injury of the mouse kidney

The disruption of endothelial integrity is a crucial step for the development of vascular leakage and consequently ischemia-reperfusion injury (IRI). Regarding the molecular cell-cell interaction, the fibrinopeptide Bβ15-42 prevents vascular leakage by stabilizing the inter-endothelial junctions via association with the vascular endothelial-cadherin. In a previous study we showed that a renoprotective effect in early IRI may be achieved by intravenous administration of Bβ15-42 at the time of reperfusion. We now aimed to investigate whether additional pre-ischemic application of Bβ15-42 could enhance this effect. Therefore C57BL/6 mice were subjected to 0.5h bilateral renal ischemia followed by reperfusion. The animals were randomized into 6 groups (n=6): two control groups treated with i.v. administration of NaCl at reperfusion for 0.5h (NaCl 1h) and 2.5h (NaCl 3h), two groups with Bβ15-42 at reperfusion for 0.5h (Bβ(rep) 1h) and 2.5h (Bβ(rep) 3h), and two groups with administration of Bβ15-42 immediately pre-ischemic as well as at reperfusion for 0.5h (Bβ(peri) 1h) and 2.5h (Bβ(peri) 3h). We found that both Bβ(rep) and Bβ(peri) mice displayed reduced early renal damage compared with NaCl treated mice. However, there was no further reduction of the IR damage through added pre-ischemic application of Bβ15-42. Overall, we detected significantly reduced endothelial activation, lower tissue infiltration of neutrophils as well as lower tissue levels of neutrophil gelatinase-associated lipocalin (NGAL) in all mice treated with Bβ15-42 compared to mice treated with NaCl. Our data confirm the renoprotective effect of Bβ15-42 in the early therapeutic treatment of acute kidney injury due to ischemia and reperfusion. However, a combined pre-and post-ischemic administration of Bβ15-42 appears to provide no additional benefit compared with a sole administration at reperfusion.

Ischemia-reperfusion: From cell biology to acute kidney injury

Ischemia reperfusion injury occurs in the kidney when blood supply is interrupted in clinical settings such as kidney transplantation or nephron sparing surgery for renal tumors. These lesions lead to acute kidney injury (AKI) a detrimental situation associated with impaired short-term allograft function (delayed graft function or primary non function) but also long-term transplant survival through the onset of chronic allograft nephropathy. The present review details the cellular and molecular consequences of ischemia reperfusion in a native kidney as well as in a kidney graft after cold ischemia time, giving a comprehensive description of biological pathways involved during the phase of ischemia and during the reperfusion period where the rapid return to normoxia leads to a large burst of reactive oxygen species along with a dramatic reduction in antioxidant defenses. This work also focuses on the distinct susceptibilities of kidney cells to ischemia (endothelial vs epithelial) and the outcome of acute kidney injury.

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.

TIGAR regulates glycolysis in ischemic kidney proximal tubules

Tp53-induced glycolysis and apoptosis regulator (TIGAR) activation blocks glycolytic ATP synthesis by inhibiting phosphofructokinase-1 activity. Our data indicate that TIGAR is selectively induced and activated in renal outermedullary proximal straight tubules (PSTs) after ischemia-reperfusion injury in a p53-dependent manner. Under severe ischemic conditions, TIGAR expression persisted through 48 h postinjury and induced loss of renal function and histological damage. Furthermore, TIGAR upregulation inhibited phosphofructokinase-1 activity, glucose 6-phosphate dehydrogenase (G6PD) activity, and induced ATP depletion, oxidative stress, autophagy, and apoptosis. Small interfering RNA-mediated TIGAR inhibition prevented the aforementioned malevolent effects and protected the kidneys from functional and histological damage. After mild ischemia, but not severe ischemia, G6PD activity and NADPH levels were restored, suggesting that TIGAR activation may redirect the glycolytic pathway into gluconeogenesis or the pentose phosphate pathway to produce NADPH. The increased level of NADPH maintained the level of GSH to scavenge ROS, resulting in a lower sensitivity of PST cells to injury. Under severe ischemia, G6PD activity and NADPH levels were reduced during reperfusion; however, blockade of TIGAR enhanced their levels and reduced oxidative stress and apoptosis. Collectively, these results demonstrate that inhibition of TIGAR may protect PST cells from energy depletion and apoptotic cell death in the setting of severe ischemia-reperfusion injury. However, under low ischemic burden, TIGAR activation induces the pentose phosphate pathway and autophagy as a protective mechanism.

Stanniocalcin-1 inhibits renal ischemia/reperfusion injury via an AMP-activated protein kinase-dependent pathway

AKI is associated with increased morbidity, mortality, and cost of care, and therapeutic options remain limited. Reactive oxygen species are critical for the genesis of ischemic AKI. Stanniocalcin-1 (STC1) suppresses superoxide generation through induction of uncoupling proteins (UCPs), and transgenic overexpression of STC1 inhibits reactive oxygen species and protects from ischemia/reperfusion (I/R) kidney injury. Our observations revealed high AMP-activated protein kinase (AMPK) activity in STC1 transgenic kidneys relative to wild-type (WT) kidneys; thus, we hypothesized that STC1 protects from I/R kidney injury through activation of AMPK. Baseline activity of AMPK in the kidney correlated with the expression of STCs, such that the highest activity was observed in STC1 transgenic mice followed (in decreasing order) by WT, STC1 knockout, and STC1/STC2 double-knockout mice. I/R in WT kidneys increased AMPK activity and the expression of STC1, UCP2, and sirtuin 3. Inhibition of AMPK by administration of compound C before I/R abolished the activation of AMPK, diminished the expression of UCP2 and sirtuin 3, and aggravated kidney injury but did not affect STC1 expression. Treatment of cultured HEK cells with recombinant STC1 activated AMPK and increased the expression of UCP2 and sirtuin 3, and concomitant treatment with compound C abolished these responses. STC1 knockout mice displayed high susceptibility to I/R, whereas pretreatment of STC1 transgenic mice with compound C restored the susceptibility to I/R kidney injury. These data suggest that STC1 is important for activation of AMPK in the kidney, which mediates STC1-induced expression of UCP2 and sirtuin 3 and protection from I/R.

Therapeutic translation in acute kidney injury: the epithelial/endothelial axis

Acute kidney injury (AKI) remains a major clinical event with rising incidence, severity, and cost; it now has a morbidity and mortality exceeding acute myocardial infarction. There is also a documented conversion to and acceleration of chronic kidney disease to end-stage renal disease. The multifactorial nature of AKI etiologies and pathophysiology and the lack of diagnostic techniques have hindered translation of preclinical success. An evolving understanding of epithelial, endothelial, and inflammatory cell interactions and individualization of care will result in the eventual development of effective therapeutic strategies. This review focuses on epithelial and endothelial injury mediators, interactions, and targets for therapy.

Perioperative steroids administration in pediatric cardiac surgery: a meta-analysis of randomized controlled trials*

OBJECTIVE

To evaluate the effects of prophylactic perioperative corticosteroid administration, compared with placebo, on postoperative mortality and clinical outcomes (renal dysfunction, duration of mechanical ventilation, and ICU length of stay) in pediatric patients undergoing cardiac surgery with cardiopulmonary bypass.

DATA SOURCES

MEDLINE and Cochrane Library were screened through August 2013 for randomized controlled trials in which perioperative steroid treatment was adopted.

STUDY SELECTION

Included were randomized controlled trials conducted on pediatric population that reported clinical outcomes about mortality and morbidity.

DATA EXTRACTION

Eighty citations (PubMed, 48 citations; Cochrane, 32 citations) were identified, of which 14 articles were analyzed in depth and six articles fulfilled eligibility criteria and reported mortality data (232 patients), two studies reported ICU length of stay and mechanical ventilation duration (60 patients), and two studies reported renal dysfunction (49 patients).

DATA SYNTHESIS

A nonsignificant trend of reduced mortality was observed in steroid-treated patients (11 [4.7%] vs 4 [1.7%] patients; odds ratio, 0.41; 95% CI, 0.14-1.15; p = 0.089). Steroids had no effects on mechanical ventilation time (117.4 ± 95.9 hr vs 137.3 ± 102.4 hr; p = 0.43) and ICU length of stay (9.6 ± 4.6 d vs 9.9 ± 5.9 d; p = 0.8). Perioperative steroid administration reduced the prevalence of renal dysfunction (13 [54.2%] vs 2 [8%] patients; odds ratio, 0.07; 95% CI, 0.01-0.38; p = 0.002).

CONCLUSION

Despite a demonstrated attenuation of cardiopulmonary bypass-induced inflammatory response by steroid administration, a systematic review of randomized controlled trials performed so far reveals that steroid administration has potential clinical advantages (lower mortality and significant reduction of renal function deterioration). A larger prospective randomized study is needed to verify clearly the effects of steroid prophylaxis in pediatric patients.

Global consequences of liver ischemia/reperfusion injury

Liver ischemia/reperfusion injury has been extensively studied during the last decades and has been implicated in the pathophysiology of many clinical entities following hepatic surgery and transplantation. Apart from its pivotal role in the pathogenesis of the organ's post reperfusion injury, it has also been proposed as an underlying mechanism responsible for the dysfunction and injury of other organs as well. It seems that liver ischemia and reperfusion represent an event with “global” consequences that influence the function of many remote organs including the lung, kidney, intestine, pancreas, adrenals, and myocardium among others. The molecular and clinical manifestation of these remote organs injury may lead to the multiple organ dysfunction syndrome, frequently encountered in these patients. Remote organ injury seems to be in part the result of the oxidative burst and the inflammatory response following reperfusion. The present paper aims to review the existing literature regarding the proposed mechanisms of remote organ injury after liver ischemia and reperfusion.

Protection of NAD(P)H:quinone oxidoreductase 1 against renal ischemia/reperfusion injury in mice

Ischemia/reperfusion (I/R) is the most common cause of acute renal injury. I/R-induced reactive oxygen species (ROS) are thought to be a major factor in the development of acute renal injury by promoting the initial tubular damage.

NAD(P)H

quinone oxidoreductase 1 (NQO1) is a well-known antioxidant protein that regulates ROS generation. The purpose of this study was to investigate whether NQO1 modulates the renal I/R injury (IRI) associated with NADPH oxidase (NOX)-derived ROS production in an animal model. We analyzed renal function, oxidative stress, and tubular apoptosis after IRI. NQO1(-/-) mice showed increased blood urea nitrogen and creatinine levels, tubular damage, oxidative stress, and apoptosis. In the kidneys of NQO1(-/-) mice, the cellular NADPH/NADP(+) ratio was significantly higher and NOX activity was markedly higher than in those of NQO1(+/+) mice. The activation of NQO1 by β-lapachone (βL) significantly improved renal dysfunction and reduced tubular cell damage, oxidative stress, and apoptosis by renal I/R. Moreover, the βL treatment significantly lowered the cellular NADPH/NADP(+) ratio and dramatically reduced NOX activity in the kidneys after IRI. From these results, it was concluded that NQO1 has a protective role against renal injury induced by I/R and that this effect appears to be mediated by decreased NOX activity via cellular NADPH/NADP(+) modulation. These results provide convincing evidence that NQO1 activation might be beneficial for ameliorating renal injury induced by I/R.

The small fibrinopeptide Bβ15-42 as renoprotective agent preserving the endothelial and vascular integrity in early ischemia reperfusion injury in the mouse kidney

Disruption of the renal endothelial integrity is pivotal for the development of a vascular leak, tissue edema and consequently acute kidney injury. Kidney ischemia amplifies endothelial activation and up-regulation of pro-inflammatory mechanisms. After restoring a sufficient blood flow, the kidney is damaged through complex pathomechanisms that are classically referred to as ischemia and reperfusion injury, where the disruption of the inter-endothelial connections seems to be a crucial step in this pathomechanism. Focusing on the molecular cell-cell interaction, the fibrinopeptide Bβ_15–42 prevents vascular leakage by stabilizing these inter-endothelial junctions. The peptide associates with vascular endothelial-cadherin, thus preventing early kidney dysfunction by preserving blood perfusion efficacy, edema formation and thus organ dysfunction. We intended to demonstrate the early therapeutic benefit of intravenously administered Bβ_15–42 in a mouse model of renal ischemia and reperfusion. After 30 minutes of ischemia, the fibrinopeptide Bβ_15–42 was administered intravenously before reperfusion was commenced for 1 and 3 hours. We show that Bβ_15–42 alleviates early functional and morphological kidney damage as soon as 1 h and 3 h after ischemia and reperfusion. Mice treated with Bβ_15–42 displayed a significantly reduced loss of VE-cadherin, indicating a conserved endothelial barrier leading to less neutrophil infiltration which in turn resulted in significantly reduced structural renal damage. The significant reduction in tissue and serum neutrophil gelatinase-associated lipocalin levels reinforced our findings. Moreover, renal perfusion analysis by color duplex sonography revealed that Bβ_15–42 treatment preserved resistive indices and even improved blood velocity. Our data demonstrate the efficacy of early therapeutic intervention using the fibrinopeptide Bβ_15–42 in the treatment of acute kidney injury resulting from ischemia and reperfusion. In this context Bβ_15–42 may act as a potent renoprotective agent by preserving the endothelial and vascular integrity.

Anti-inflammatory strategies to reduce acute kidney injury in cardiac surgery patients: a meta-analysis of randomized controlled trials

Acute kidney injury (AKI) after cardiac operations is a serious complication associated with postoperative mortality. Multiple factors contribute to AKI development, principally ischemia-reperfusion injury and inflammatory response. It is well proven that glucocorticoid administration, leukocyte filter application, and miniaturized extracorporeal circuits (MECC) modulate inflammatory response. We conducted a systematic review of randomized controlled trials (RCTs) in which one of these inflammatory system modulation strategies was used, with the aim to evaluate the effects on postoperative AKI. MEDLINE and Cochrane Library were screened through November 2011 for RCTs in which an inflammatory system modulation strategy was adopted. Included were trials that reported data about postoperative renal outcomes. Because AKI was defined by different criteria, including biochemical determinations, urine output, or dialysis requirement, we unified renal outcome as worsening renal function (WRF). We identified 14 trials for steroids administration (931 patients, WRF incidence [treatment vs. placebo]: 2.7% vs. 2.4%; OR: 1.13; 95% CI: 0.53-2.43; P = 0.79), 9 trials for MECC (947 patients, WRF incidence: 2.4% vs. 0.9%; OR: 0.47; 95% CI: 0.18-1.25; P = 0.13), 6 trials for leukocyte filters (374 patients, WRF incidence: 1.1% vs. 7.5%; OR: 0.18; 95% CI: 0.05-0.64; P = 0.008). Only leukocyte filters effectively reduced WRF incidence. Not all cardiopulmonary bypass-related anti-inflammatory strategies analyzed reduced renal damage after cardiac operations. In adult patients, probably other factors are predominant on inflammation in determining AKI, and only leukocyte filters were effective. Large multicenter RCTs are needed in order to better evaluate the role of inflammation in AKI development after cardiac operations.

Updates on Hepato-Renal Syndrome

Hepato-renal syndrome (HRS) is one of the most detrimental conditions in patients with end stage liver failure. Historically, HRS was considered a terminal disease associated with cirrhosis and was termed "liver-death syndrome". Furthermore, despite the improved understanding of pathophysiology and the reversibility of renal dysfunction in HRS, mortality remains extremely high especially for type 1 HRS. This review summarizes the recent advances in the pathophysiology, diagnosis and management of HRS and also provides an evolving area of research in the pathophysiologic mechanisms of HRS, which may open the door for new therapeutic approaches.

Mannitol increases renal blood flow and maintains filtration fraction and oxygenation in postoperative acute kidney injury: a prospective interventional study

Introduction

Acute kidney injury (AKI), which is a major complication after cardiovascular surgery, is associated with significant morbidity and mortality. Diuretic agents are frequently used to improve urine output and to facilitate fluid management in these patients. Mannitol, an osmotic diuretic, is used in the perioperative setting in the belief that it exerts reno-protective properties. In a recent study on uncomplicated postcardiac-surgery patients with normal renal function, mannitol increased glomerular filtration rate (GFR), possibly by a deswelling effect on tubular cells. Furthermore, experimental studies have previously shown that renal ischemia causes an endothelial cell injury and dysfunction followed by endothelial cell edema. We studied the effects of mannitol on renal blood flow (RBF), glomerular filtration rate (GFR), renal oxygen consumption (RVO₂), and extraction (RO₂Ex) in early, ischemic AKI after cardiac surgery.

Methods

Eleven patients with AKI were studied during propofol sedation and mechanical ventilation 2 to 6 days after complicated cardiac surgery. All patients had severe heart failure treated with one (100%) or two (73%) inotropic agents and intraaortic balloon pump (36%). Systemic hemodynamics were measured with a pulmonary artery catheter. RBF and renal filtration fraction (FF) were measured by the renal vein thermo-dilution technique and by renal extraction of chromium-51-ethylenediaminetetraacetic acid (⁵¹Cr-EDTA), respectively. GFR was calculated as the product of FF and renal plasma flow RBF × (1-hematocrit). RVO₂ and RO₂Ex were calculated from arterial and renal vein blood samples according to standard formulae. After control measurements, a bolus dose of mannitol, 225 mg/kg, was given, followed by an infusion at a rate of 75 mg/kg/h for two 30-minute periods.

Results

Mannitol did not affect cardiac index or cardiac filling pressures. Mannitol increased urine flow by 61% (P < 0.001). This was accompanied by a 12% increase in RBF (P < 0.05) and a 13% decrease in renal vascular resistance (P < 0.05). Mannitol increased the RBF/cardiac output (CO) relation (P = 0.040). Mannitol caused no significant changes in RO₂Ext or renal FF.

Conclusions

Mannitol treatment of postoperative AKI induces a renal vasodilation and redistributes systemic blood flow to the kidneys. Mannitol does not affect filtration fraction or renal oxygenation, suggestive of balanced increases in perfusion/filtration and oxygen demand/supply.

Overexpression of stanniocalcin-1 inhibits reactive oxygen species and renal ischemia/reperfusion injury in mice

Reactive oxygen species, endothelial dysfunction, inflammation, and mitogen-activated protein kinases have important roles in the pathogenesis of ischemia/reperfusion kidney injury. Stanniocalcin-1 (STC1) suppresses superoxide generation in many systems through induction of mitochondrial uncoupling proteins and blocks the cytokine-induced rise in endothelial permeability. Here we tested whether transgenic overexpression of STC1 protects from bilateral ischemia/reperfusion kidney injury. This injury in wild type mice caused a halving of the creatinine clearance; severe tubular vacuolization and cast formation; increased infiltration of macrophages and T cells; higher vascular permeability; greater production of superoxide and hydrogen peroxide; and higher ratio of activated ERK/activated JNK and p38, all compared to sham-treated controls. Mice transgenic for human STC1 expression, however, had resistance to equivalent ischemia/reperfusion injury indicated as no significant change from controls in any of these parameters. Tubular epithelial cells in transgenic mice expressed higher mitochondrial uncoupling protein 2 and lower superoxide generation. Pre-treatment of transgenic mice with paraquat, a generator of reactive oxygen species, before injury restored the susceptibility to ischemia/reperfusion kidney injury, suggesting that STC1 protects by an anti-oxidant mechanism. Thus, STC1 may be a therapeutic target for ischemia/reperfusion kidney injury.

Pathophysiology of acute kidney injury

Acute kidney injury (AKI) is the leading cause of nephrology consultation and is associated with high mortality rates. The primary causes of AKI include ischemia, hypoxia, or nephrotoxicity. An underlying feature is a rapid decline in glomerular filtration rate (GFR) usually associated with decreases in renal blood flow. Inflammation represents an important additional component of AKI leading to the extension phase of injury, which may be associated with insensitivity to vasodilator therapy. It is suggested that targeting the extension phase represents an area potential of treatment with the greatest possible impact. The underlying basis of renal injury appears to be impaired energetics of the highly metabolically active nephron segments (i.e., proximal tubules and thick ascending limb) in the renal outer medulla, which can trigger conversion from transient hypoxia to intrinsic renal failure. Injury to kidney cells can be lethal or sublethal. Sublethal injury represents an important component in AKI, as it may profoundly influence GFR and renal blood flow. The nature of the recovery response is mediated by the degree to which sublethal cells can restore normal function and promote regeneration. The successful recovery from AKI depends on the degree to which these repair processes ensue and these may be compromised in elderly or chronic kidney disease (CKD) patients. Recent data suggest that AKI represents a potential link to CKD in surviving patients. Finally, earlier diagnosis of AKI represents an important area in treating patients with AKI that has spawned increased awareness of the potential that biomarkers of AKI may play in the future.