Nanotherapeutic kidney cell-specific targeting to ameliorate acute kidney injury.

Acute kidney injury (AKI) increases the risk of in-hospital death, adds to expense of care, and risk of early chronic kidney disease. AKI often follows an acute event such that timely treatment could ameliorate AKI and potentially reduce the risk of additional disease. Despite therapeutic success of dexamethasone in animal models, clinical trials have not demonstrated broad success. To improve the safety and efficacy of dexamethasone for AKI, we developed and characterized a novel, kidney-specific nanoparticle enabling specific within-kidney targeting to proximal tubular epithelial cells provided by the megalin ligand cilastatin. Cilastatin and dexamethasone were complexed to H-Dot nanoparticles, which were constructed from generally recognized as safe components. Cilastatin/Dexamethasone/H-Dot nanotherapeutics were found to be stable at plasma pH and demonstrated salutary release kinetics at urine pH. In vivo, they were specifically biodistributed to the kidney and bladder, with 75% recovery in the urine and with reduced systemic toxicity compared to native dexamethasone. Cilastatin complexation conferred proximal tubular epithelial cell specificity within the kidney in vivo and enabled dexamethasone delivery to the proximal tubular epithelial cell nucleus in vitro. The Cilastatin/Dexamethasone/H-Dot nanotherapeutic improved kidney function and reduced kidney cellular injury when administered to male C57BL/6 mice in two translational models of AKI (rhabdomyolysis and bilateral ischemia reperfusion). Thus, our design-based targeting and therapeutic loading of a kidney-specific nanoparticle resulted in preservation of the efficacy of dexamethasone, combined with reduced off-target disposition and toxic effects. Hence, our study illustrates a potential strategy to target AKI and other diseases of the kidney.

Harm! foul! How acute kidney injury SHReDDs patient futures.

PURPOSE OF REVIEW: Transition from acute kidney injury (AKI) to chronic kidney disease (CKD) is increasingly accepted. Less well recognized, but supported by very similar data, is development of disease of other organ systems after AKI. Awareness of other-organ sequelae of AKI may inform efforts to improve the care of patients after AKI. RECENT FINDINGS: Stroke, hypertension, reproductive risk, dementia, and death (SHReDD) are sequelae, which occur with increased risk relative to that of non-AKI within 6 months-3 years after AKI diagnosis, and which are supported by preclinical/mechanistic study. Adjusted hazard ratios for these sequelae are strikingly similar to that of AKI-CKD, ranging from 1.2 to 3.0. Mechanistic studies suggest kidney-centric mechanisms including sodium regulation, volume status regulation, and the renin-angiotensin system are drivers of long-term, extra-renal, change. SUMMARY: Further clinical characterization and mechanistic insight is necessary, and may have considerable translational impact. Programs which screen or follow post-AKI patients may increase clinical utility if focus is expanded to include the SHReDD complications.

Cilastatin Ameliorates Rhabdomyolysis-induced AKI in Mice.

BACKGROUND: Rhabdomyolysis, the destruction of skeletal muscle, is a significant cause of AKI and death in the context of natural disaster and armed conflict. Rhabdomyolysis may also initiate CKD. Development of specific pharmacologic therapy is desirable because supportive care is nearly impossible in austere environments. Myoglobin, the principal cause of rhabdomyolysis-related AKI, undergoes megalin-mediated endocytosis in proximal tubule cells, a process that specifically injures these cells. METHODS: To investigate whether megalin is protective in a mouse model of rhabdomyolysis-induced AKI, we used male C57BL/6 mice and mice (14-32 weeks old) with proximal tubule-specific deletion of megalin. We used a well-characterized rhabdomyolysis model, injection of 50% glycerol in normal saline preceded by water deprivation. RESULTS: Inducible proximal tubule-specific deletion of megalin was highly protective in this mouse model of rhabdomyolysis-induced AKI. The megalin knockout mice demonstrated preserved GFR, reduced proximal tubule injury (as indicated by kidney injury molecule-1), and reduced renal apoptosis 24 hours after injury. These effects were accompanied by increased urinary myoglobin clearance. Unlike littermate controls, the megalin-deficient mice also did not develop progressive GFR decline and persistent new proteinuria. Administration of the pharmacologic megalin inhibitor cilastatin to wild-type mice recapitulated the renoprotective effects of megalin deletion. This cilastatin-mediated renoprotective effect was dependent on megalin. Cilastatin administration caused selective proteinuria and inhibition of tubular myoglobin uptake similar to that caused by megalin deletion. CONCLUSIONS: We conclude that megalin plays a critical role in rhabdomyolysis-induced AKI, and megalin interference and inhibition ameliorate rhabdomyolysis-induced AKI. Further investigation of megalin inhibition may inform translational investigation of a novel potential therapy.

Critical care and ventilatory management of deceased organ donors impact lung use and recipient graft survival.

Current risk-adjusted models for donor lung use and lung graft survival do not include donor critical care data. We sought to identify modifiable donor physiologic and mechanical ventilation parameters that predict donor lung use and lung graft survival. This is a prospective observational study of donors after brain death (DBDs) managed by 19 Organ Procurement Organizations from 2016 to 2019. Demographics, mechanical ventilation parameters, and critical care data were recorded at standardized time points during donor management. The lungs were transplanted from 1811 (30%) of 6052 DBDs. Achieving ≥7 critical care endpoints was a positive predictor of donor lung use. After controlling for recipient factors, donor blood pH positively predicted lung graft survival (OR 1.48 per 0.1 unit increase in pH) and the administration of dopamine during donor management negatively predicted lung graft survival (OR 0.19). Tidal volumes ≤8 ml/kg predicted body weight (OR 0.65), and higher positive end-expiratory pressures (OR 0.91 per cm H2 O) predicted decreased donor lung use without affecting lung graft survival. A randomized clinical trial is needed to inform optimal ventilator management strategies in DBDs.

The CAT-1 is out of the bag: endothelial Cationic Amino Acid Transporter-1 is a critical player in cardiorenal syndrome type 2.

Although the numbers of patients affected by cardiorenal syndrome keeps increasing, we lack a complete understanding of the molecular pathways involved in its development and progression. Nitric oxide synthase (NOS) may play a role in cardiorenal syndrome, particularly cardiorenal syndrome type 2 (CRS2). However, complexities and paradoxical clinical findings have limited translation. In the current Clinical Science, Giam et al. (Clinical Science (2020) 134, 2755-2769) highlight the role of a key NOS substrate transporter, the cationic amino acid transporter-1, in preserving renal function in CRS2. In this commentary, we introduce the cardiorenal syndrome and the putative role that nitric oxide (NO) may play in the development of this disease and discuss the exciting findings of Giam et al. (Clinical Science (2020) 134, 2755-2769) and their tantalizing translational implications.

The acute kidney injury to chronic kidney disease transition in a mouse model of acute cardiorenal syndrome emphasizes the role of inflammation.

Acute cardiorenal syndrome is a common complication of acute cardiovascular disease. Studies of acute kidney injury (AKI) to chronic kidney disease (CKD) transition, including patients suffering acute cardiovascular disease, report high rates of CKD development. Therefore, acute cardiorenal syndrome associates with CKD, but no study has established causation. To define this we used a murine cardiac arrest (CA) and cardiopulmonary resuscitation (CPR) model or sham procedure on male mice. CA was induced with potassium chloride while CPR consisted of chest compressions and epinephrine eight minutes later. Two weeks after AKI was induced by CA/CPR, the measured glomerular filtration rate (GFR) was not different from sham. However, after seven weeks the mice developed CKD, recapitulating clinical observations. One day, and one, two, and seven weeks after CA/CPR, the GFR was measured, and renal tissue sections were evaluated for various indices of injury and inflammation. One day after CA/CPR, acute cardiorenal syndrome was indicated by a significant reduction of the mean GFR (649 in sham, vs. 25 µL/min/100g in CA/CPR animals), KIM-1 positive tubules, and acute tubular necrosis. Renal inflammation developed, with F4/80 positive and CD3-positive cells infiltrating the kidney one day and one week after CA/CPR, respectively. Although there was functional recovery with normalization of GFR two weeks after CA/CPR, deposition of tubulointerstitial matrix proteins α-smooth muscle actin and fibrillin-1 progressed, along with a significantly reduced mean GFR (623 in sham vs. 409 µL/min/100g in CA/CPR animals), proteinuria, increased tissue transforming growth factor-ß, and fibrosis establishing the development of CKD seven weeks after CA/CPR. Thus, murine CA/CPR, a model of acute cardiorenal syndrome, causes an AKI-CKD transition likely due to prolonged renal inflammation.

Deceased organ donor factors influencing pancreatic graft transplantation and survival.

Criteria for organ acceptance in brain-dead organ donors remain inconsistent, especially when concerning pancreatic transplants. We sought to examine donor-specific predictors of pancreatic graft use and survival to better guide the selection and management of potential donors. A prospective observational study of all donors from ten organ procurement organizations was conducted from March 2012 to January 2015. Critical care endpoints were collected at 4 standardized time points. Data associated with pancreatic transplantation and graft survival rates were first determined using univariate analyses, and then logistic regression was used to identify independent predictors of these two outcomes. From 1819 donors, 238 (13.1%) pancreata were transplanted, and at a mean follow-up of 192 days, 218 (91.6%) grafts had survived. After regression analysis, donor age (OR = 0.89), HgbA1C (OR = 0.07), and achieving the donor management goal (DMG) for ejection fraction at allocation of ≥50% (OR = 3.29) remained as independent predictors of pancreatic utilization. On regression analysis, graft survival was independently predicted by lower donor age (OR = 0.93) and achieving the DMGs for mean arterial pressure (60-110 mm Hg) and glucose (≤180 mg/dL) at separate time points. These results may help guide the management and selection of potential pancreatic donors after brain death.

Right Ventricular Systolic Performance Determined by 2D Speckle-Tracking Echocardiography and Acute Kidney Injury After Cardiac Surgery.

OBJECTIVE: An association between central venous pressure and acute kidney injury (AKI) has been observed following cardiac surgery, but it is unknown whether this reflects intravascular volume status or impaired right ventricular (RV) myocardial performance. This study was performed to test the hypothesis that decreased RV peak longitudinal strain (PLSS), as measured by 2-dimensional speckle-tracking echocardiography, is associated with AKI following cardiac surgery. DESIGN: Retrospective observational cohort study. SETTING: Cardiovascular intensive care unit in a 576-bed referral hospital. PARTICIPANTS: Adult patients having undergone cardiac surgery in whom a transthoracic echocardiogram (TTE) was performed within 48 hours after chest closure. INTERVENTIONS: This was a retrospective study. Urine output and serum creatinine values were recorded at baseline and for 48 hours after surgery. Statistical analysis was performed to identify differences in baseline demographic and echo-derived values between patients with and without postoperative AKI criteria. MEASUREMENTS AND MAIN RESULTS: One hundred ninety-nine subjects had postprocessing of TTE performed. AKI was observed in 87% of patients (173 of 199). Age, body mass index, and preoperative serum creatinine were higher in the AKI group. The mean PLSS was -17.2% ± 4.3% versus -17.1% ± 3.7% in patients with AKI versus those without (p = 0.95). The calculated RV systolic pressure was elevated in the AKI group compared to the non-AKI group (38.9 ± 9.9 v 34.6 ± 7.9 mmHg, p = 0.02). CONCLUSION: In this cohort of cardiac surgery patients, speckle-tracking analysis of RV myocardial performance was feasible. Elevated RV systolic pressure associated with AKI, while speckle tracking-derived echocardiography measurements did not.

Impact of Isolyte Versus 0.9% Saline on Postoperative Event of Acute Kidney Injury Assayed by Urinary [TIMP-2] × [IGFBP7] in Patients Undergoing Cardiac Surgery.

OBJECTIVE: Administration of excess chloride in 0.9% normal saline (NS) decreases renal perfusion and glomerular filtration rate, thereby increasing the risk for acute kidney injury (AKI). In this study, the effect of NS versus Isolyte use during cardiac surgery on urinary levels of tissue inhibitor of metalloproteinase 2 and insulin-like growth factor-binding protein 7 [TIMP-2] × [IGFBP7] and postoperative risk of AKI were examined. DESIGN: Prospective, randomized, and single-blinded trial. SETTING: Single university medical center. PARTICIPANTS: Thirty patients over 18 years without chronic renal insufficiency or recent AKI undergoing elective cardiac surgery. INTERVENTIONS: Subjects were randomized to receive either NS or Isolyte during the intraoperative period. MEASUREMENTS AND MAIN RESULTS: The primary outcome was the change in urinary levels of [TIMP2] × [IGFBP7] from before surgery to 24 hours postoperatively. Secondary outcomes included serum creatinine pre- and postoperatively at 24 and 48 hours, serum chloride pre- and postoperatively at 24 and 48 hours, need for dialysis prior to discharge, and arterial pH measured 24 hours postoperatively. Sixteen patients received NS and 14 patients received Isolyte. Three patients developed AKI within the first 3 postoperative days, all in the NS group. The authors found increases in [TIMP-2] × [IGFBP7] in both groups. However, the difference in this increase between study arms was not significant (p = 0.92; -0.097 to 0.107). CONCLUSION: The authors observed no change in urinary [TIMP-] × [IGFBP7] levels in patients receiving NS versus Isolyte during cardiac surgery. Future larger studies in patients at higher risk for AKI are recommended to evaluate the impact of high- versus lower-chloride solutions on the risk of postoperative AKI after cardiac surgery.

Determination of renal function and injury using near-infrared fluorimetry in experimental cardiorenal syndrome.

Cardiorenal syndrome type 1 causes acute kidney injury but is poorly understood; animal models and diagnostic aids are lacking. Robust noninvasive measurements of glomerular filtration rate are required for injury models and clinical use. Several have been described but are untested in translational models and suffer from biologic interference. We developed a mouse model of cardiorenal syndrome and tested the novel near-infrared fluorophore ZW800-1 to assess renal and cardiac function. We performed murine cardiac arrest and cardiopulmonary resuscitation followed by transthoracic echocardiography, 2 and 24 h later. Transcutaneous fluorescence of ZW800-1 bolus dispersion and clearance was assessed with whole animal imaging and compared with glomerular filtration rate (GFR; inulin clearance), tubular cell death (using unbiased stereology), and serum creatinine. Correlation, Bland-Altman, and polar analyses were used to compare GFR with ZW800-1 clearance. Cardiac arrest and cardiopulmonary resuscitation caused reversible cardiac failure, halving fractional shortening of the left ventricle (n = 12, P = 0.03). Acute kidney injury resulted with near-zero GFR and sixfold increase in serum creatinine 24 h later (n = 16, P < 0.01). ZW800-1 biodistribution and clearance were exclusively renal. ZW800-1 t1/2 and clearance correlated with GFR (r = 0.92, n = 31, P < 0.0001). ZW800-1 fluorescence was reduced in cardiac arrest, and cardiopulmonary resuscitation-treated mice compared with sham animals 810 s after injection (P < 0.01) and bolus time-dispersion curves demonstrated that ZW800-1 fluorescence dispersion correlated with left ventricular function (r = 0.74, P < 0.01). Cardiac arrest and cardiopulmonary resuscitation lead to experimental cardiorenal syndrome type 1. ZW800-1, a small near-infrared fluorophore being developed for clinical intraoperative imaging, is favorable for evaluating cardiac and renal function noninvasively.

A Structured Transfer of Care Process Reduces Perioperative Complications in Cardiac Surgery Patients.

INTRODUCTION: Serious complications are common during the intensive care of postoperative cardiac surgery patients. Some of these complications may be influenced by communication during the process of handover of care from the operating room to the intensive care unit (ICU) team. A structured transfer of care process may reduce the rate of communication errors and perioperative complications. METHODS: We hypothesized that a collaborative, comprehensive, structured handover of care from the intraoperative team to the ICU team would reduce a specific set of postoperative complications. We tested this hypothesis by developing and introducing a comprehensive multidisciplinary transfer of care process. We measured patient outcomes before and after the intervention using a linkage between 2 care databases: an Anesthesia Information Management System and a critical care complication registry database. RESULTS: There were 1127 total postoperative cardiac surgery admissions during the study period, 550 before and 577 after the intervention. There was no statistical difference between overall complications before and after the intervention (P = .154). However, there was a statistically significant reduction in preventable complications after the intervention (P = .023). DISCUSSION: The main finding of this investigation is that the introduction of a collaborative, comprehensive transfer of care process from the operating room to the ICU was associated with patients suffering fewer preventable complications.

Vapor Pressures of Anesthetic Agents at Temperatures Below 0°C and a Novel Anesthetic Delivery Device.

At room temperature, the vapor pressures of desflurane, isoflurane, and sevoflurane are well above the clinically useful range. We hypothesized that therapeutic concentrations of these agents could be achieved at temperatures below 0°C, but the vapor pressure-temperature relationship is unknown below 0. Second, we hypothesized that this relationship could be exploited to deliver therapeutic-range concentrations of anesthetic vapor. We therefore set out to determine the low temperature-vapor pressure relationships of each anesthetic agent, thereby identifying the saturated vapor concentration of each agent at any temperature below 0°C. To test our hypothesis, we measured the saturated vapor concentration at 1 atm of pressure for temperatures between -60 and 0°C, thus developing an empiric relationship for each agent. There was consistency in repeated experiments for all 3 agents. To test the empiric data, we constructed a digitally controlled thermoelectric anesthetic vaporizer, characterized the device, and used it to deliver anesthetic vapor to laboratory mice. We report, for the first time, the temperature-vapor pressure relationship at temperatures below 0°C for desflurane, isoflurane, and sevoflurane as well as the TMAC of these agents: the temperature at which the vapor pressure is equal to the minimum alveolar concentration. We describe the construction and limited validation of an anesthetic vaporizer prototype on the basis of this principle. We conclude that clinically relevant concentrations of volatile anesthetics may be achieved at low temperatures.

Estrogen administered after cardiac arrest and cardiopulmonary resuscitation ameliorates acute kidney injury in a sex- and age-specific manner.

INTRODUCTION: There is a sex difference in the risk of ischemic acute kidney injury (AKI), and estrogen mediates the protective effect of female sex. We previously demonstrated that preprocedural chronic restoration of physiologic estrogen to ovariectomized female mice ameliorated AKI after cardiac arrest and cardiopulmonary resuscitation (CA/CPR). In the present study, we hypothesized that male mice and aged female mice would benefit from estrogen administration after CA/CPR. We tested the effect of estrogen in a clinically relevant manner by administrating it after CA/CPR. METHODS: CA/CPR was performed in young (10-15 weeks), middle-aged (43-48 weeks), and aged (78-87 weeks) C57BL/6 male and female mice. Mice received intravenous 17ß-estradiol or vehicle 15 min after resuscitation. Serum chemistries and unbiased stereological assessment of renal injury were completed 24 h after CA. Regional renal cortical blood flow was measured by a laser Doppler, and renal levels of estrogen receptor alpha (ERα) and G protein-coupled estrogen receptor (GPER) were evaluated with immunoblotting. RESULTS: Post-arrest estrogen administration reduced injury in young males without significant changes in renal blood flow (percentage reduction compared with vehicle: serum urea nitrogen, 30 %; serum creatinine (sCr), 41 %; volume of necrotic tubules (VNT), 31 %; P < 0.05). In contrast, estrogen did not affect any outcomes in young females. In aged mice, estrogen significantly reduced sCr (80 %) and VNT (73 %) in males and VNT (51 %) in females. Serum estrogen levels in aged female mice after CA/CPR were the same as levels in male mice. With age, renal ERα was upregulated in females. CONCLUSIONS: Estrogen administration after resuscitation from CA ameliorates renal injury in young males and aged mice in both sexes. Because injury was small, young females were not affected. The protective effect of exogenous estrogen may be detectable with loss of endogenous estrogen in aged females and could be mediated by differences in renal ERs. Post-arrest estrogen administration is renoprotective in a sex- and age-dependent manner.

Postcardiac arrest temperature management: infectious risks.

PURPOSE OF REVIEW: Therapeutic hypothermia following out-of-hospital cardiac arrest improves neurological recovery. Coupled with neurological benefit, multiple complications including infection have been associated with therapeutic hypothermia following out-of-hospital cardiac arrest. In this review, we will discuss therapeutic hypothermia, and more broadly, temperature management, as a risk for ICU infection. RECENT FINDINGS: The application of therapeutic hypothermia following out-of-hospital cardiac arrest has been associated with infectious complications. Studies of hypothermic animal models have provided useful insights into mechanisms by which therapeutic hypothermia confers neuroprotection. Ironically, the same mechanisms through which therapeutic hypothermia provides neuroprotection have been implicated in the risk of infection associated with therapeutic hypothermia. Studies have demonstrated types of infections, pathogens, and the impact of infections on mortality and neurological recovery. SUMMARY: Studies demonstrate increased rate of pneumonia and bacteremia but decreased rate of other infections, suggesting redistribution but no overall increased risk of infection per se. The diagnosis of infection during therapeutic hypothermia does not impact mortality or neurological recovery.

Parental recovered acute kidney injury causes prenatal renal dysfunction and fetal growth restriction with sexually dimorphic implications for adult offspring.

Introduction: Acute kidney injury (AKI) is rapidly increasing in global incidence and a healthcare burden. Prior maternal AKI diagnosis correlates with later pregnancy complications. As pregnancy influences developmental programming, we hypothesized that recovered parental AKI results in poor pregnancy outcomes, impaired fetal growth, and adult offspring disease. Methods: Using a well-characterized model of rhabdomyolysis-induced acute kidney injury (RIAKI), a form of AKI commonly observed in young people, we confirmed functional renal recovery by assessing glomerular filtration rate (GFR) 2 weeks following RIAKI. We bred sham and recovered RIAKI sires and dams in timed, matched matings for gestational day (GD) 16.5 and offspring (birth-12 weeks, 6 months) study. Results: Despite a normal GFR pre-pregnancy, recovered RIAKI dams at GD16.5 had impaired renal function, resulting in reduced fetoplacental ratios and offspring survival. Pregnant RIAKI dams also had albuminuria and less renal megalin in the proximal tubule brush border than shams, with renal subcapsular fibrosis and higher diastolic blood pressure. Growth-restricted offspring had a reduced GFR as older adults, with evidence of metabolic inefficiency in male offspring; this correlated with reduced renal AngII levels in female offspring from recovered RIAKI pairings. However, the blood pressures of 6-month-old offspring were unaffected by parental RIAKI. Conclusions: Our mouse model demonstrated a causal relationship among RIAKI, gestational risk, and developmental programming of the adult-onset offspring GFR and metabolic dysregulation despite parental recovery.

Molecular Mechanisms of Rhabdomyolysis-Induced Kidney Injury: From Bench to Bedside.

Rhabdomyolysis-induced acute kidney injury (RIAKI) occurs following damage to the muscular sarcolemma sheath, resulting in the leakage of myoglobin and other metabolites that cause kidney damage. Currently, the sole recommended clinical treatment for RIAKI is aggressive fluid resuscitation, but other potential therapies, including pretreatments for those at risk for developing RIAKI, are under investigation. This review outlines the mechanisms and clinical significance of RIAKI, investigational treatments and their specific targets, and the status of ongoing research trials.

Legal Performance-enhancing Drugs Alter Course and Treatment of Rhabdomyolysis-induced Acute Kidney Injury.

INTRODUCTION: Rhabdomyolysis-induced acute kidney injury (RIAKI) can interrupt physical training and increase mortality in injured warfighters. The legal performance-enhancing drugs caffeine and ibuprofen, which can cause renal injury, are widely used by service members. Whether caffeine or ibuprofen affects RIAKI is unknown. Cilastatin treatment was recently identified as an experimental treatment to prevent RIAKI at injury. To determine potential interacting factors in RIAKI treatment, we test the hypothesis that caffeine and ibuprofen worsen RIAKI and interfere with treatment. MATERIALS AND METHODS: In mice, RIAKI was induced by glycerol intramuscular injection. Simultaneously, mice received caffeine (3 mg/kg), ibuprofen (10 mg/kg), or vehicle. A second cohort received volume resuscitation (PlasmaLyte, 20 mL/kg) in addition to caffeine or ibuprofen. In a third cohort, cilastatin (200 mg/kg) was administered concurrently with drug and glycerol administration. Glomerular filtration rate (GFR), blood urea nitrogen (BUN), urine output (UOP), renal pathology, and renal immunofluorescence for kidney injury molecule 1 were quantified after 24 hours. RESULTS: Caffeine did not worsen RIAKI; although BUN was modestly increased by caffeine administration, 24-hour GFR, UOP, and renal histopathology were similar between vehicle-treated, caffeine-treated, and caffeine + PlasmaLyte-treated mice. Ibuprofen administration greatly worsened RIAKI (GFR 14.3 ± 19.5 vs. 577.4 ± 454.6 µL/min/100 g in control, UOP 0.5 ± 0.4 in ibuprofen-treated mice vs. 2.7 ± 1.7 mL/24 h in control, and BUN 264 ± 201 in ibuprofen-treated mice vs. 66 ± 21 mg/dL in control, P < .05 for all); PlasmaLyte treatment did not reverse this effect. Cilastatin with or without PlasmaLyte did not reverse the deleterious effect of ibuprofen in RIAKI. CONCLUSIONS: Caffeine does not worsen RIAKI. The widely used performance-enhancing drug ibuprofen greatly worsens RIAKI in mice. Standard or experimental treatment of RIAKI including the addition of cilastatin to standard resuscitation is ineffective in mice with RIAKI exacerbated by ibuprofen. These findings may have clinical implications for the current therapy of RIAKI and for translational studies of novel treatment.

Estrogen protects renal endothelial barrier function from ischemia-reperfusion in vitro and in vivo.

Emerging evidence suggests that renal endothelial function may be altered in ischemia-reperfusion injury. Acute kidney injury is sexually dimorphic, and estrogen protects renal tubular function after experimental ischemic injury. This study tested the hypothesis that during ischemia-reperfusion, estrogen alters glomerular endothelial function to prevent hyperpermeability. Glomerular endothelial cells were exposed to 8-h oxygen-glucose deprivation (OGD) followed by 4- and 8-h reoxygenation-glucose repletion. After 4-h reoxygenation-glucose repletion, transendothelial permeability to Ficoll-70 was reduced, and transendothelial resistance increased, by 17ß-estradiol vs. vehicle treatment during OGD (OGD-vehicle: 91.0 ± 11.8%, OGD-estrogen: 102.6 ± 10.8%, P < 0.05). This effect was reversed by coadministration of G protein-coupled receptor 30 (GPR30) antagonist G15 with 17ß-estradiol (OGD-estrogen-G15: 89.5 ± 6.9, P < 0.05 compared with 17ß-estradiol). To provide preliminary confirmation of this result in vivo, Ficoll-70 was administered to mice 24 h after cardiac arrest and cardiopulmonary resuscitation (CA/CPR). Blood urea nitrogen (BUN) and serum creatinine (SCr) in these mice were elevated within 12 h following CA/CPR and reduced at 24 h by pretreatment with 17ß-estradiol (BUN/SCr 17ß-estradiol: 34 ± 19/0.2 ± 0.1 vehicle: 92 ± 49/0.5 ± 0.3, n = 8-12, P < 0.05). Glomerular sieving of Ficoll 70 was increased by CA/CPR within 2 h of injury and 17ß-estradiol treatment (θ; 17ß-estradiol: 0.74 ± 0.26 vs. vehicle: 1.05 ± 0.53, n = 14-15, P < 0.05). These results suggest that estrogen reduces postischemic glomerular endothelial hyperpermeability at least in part through GPR30 and that estrogen may regulate post CA/CPR glomerular permeability in a similar fashion in vivo.

Renal injury in cardiorenal syndrome type 1 is mediated by albumin.

Cardiorenal syndrome type 1 (CRS-1) acute kidney injury (AKI) is a critical complication of acute cardiovascular disease but is poorly understood. AKI induces acute albuminuria. As chronic albuminuria is associated with worsening kidney disease and albumin has been implicated in tubular epithelial injury, we investigated whether albumin participates in CRS-1, and whether CRS-1 alters renal albumin handling. We report the role of albumin in in vivo and in vitro CRS-1 models. An established translational model, cardiac arrest and cardiopulmonary resuscitation (CA/CPR) induced severe acute albuminuria which correlated with tubular epithelial cell death. In vivo microscopy demonstrated CA/CPR-induced glomerular filtration of exogenous albumin, while administration of exogenous albumin after CA/CPR worsened AKI compared to iso-oncotic control. Increased albumin signal was observed in the proximal tubules of CA/CPR mice compared to sham. Comparison of albumin flux from tubular lumen to epithelial cells revealed saturated albumin transport within minutes of albumin injection after CA/CPR. In vitro, HK2 cells (human kidney tubular epithelial cells), exposed to oxygen-glucose deprivation were injured by albumin in a dose dependent fashion. This interference was unchanged by the tubular endocytic receptor megalin. In conclusion, CRS-1 alters albumin filtration and tubular uptake, leading to increased tubular exposure to albumin, which is injurious to tubular epithelial cells, worsening AKI. Our findings shed light on the pathophysiology of renal albumin and may guide interventions such as albumin resuscitation to improve CRS-1 outcomes. This investigation may have important translational relevance for patients that receive exogenous albumin as part of their CRS-1 treatment regimen.

Soluble ACE2 Is Filtered into the Urine.

Background: ACE2 is a key enzyme in the renin-angiotensin system (RAS) capable of balancing the RAS by metabolizing angiotensin II (AngII). First described in cardiac tissue, abundance of ACE2 is highest in the kidney, and it is also expressed in several extrarenal tissues. Previously, we reported an association between enhanced susceptibility to hypertension and elevated renal AngII levels in global ACE2-knockout mice. Methods: To examine the effect of ACE2 expressed in the kidney, relative to extrarenal expression, on the development of hypertension, we used a kidney crosstransplantation strategy with ACE2-KO and WT mice. In this model, both native kidneys are removed and renal function is provided entirely by the transplanted kidney, such that four experimental groups with restricted ACE2 expression are generated: WT→WT (WT), KO→WT (KidneyKO), WT→KO (SystemicKO), and KO→KO (TotalKO). Additionally, we used nanoscale mass spectrometry-based proteomics to identify ACE2 fragments in early glomerular filtrate of mice. Results: Although significant differences in BP were not detected, a major finding of our study is that shed or soluble ACE2 (sACE2) was present in urine of KidneyKO mice that lack renal ACE2 expression. Detection of sACE2 in the urine of KidneyKO mice during AngII-mediated hypertension suggests that sACE2 originating from extrarenal tissues can reach the kidney and be excreted in urine. To confirm glomerular filtration of ACE2, we used micropuncture and nanoscale proteomics to detect peptides derived from ACE2 in the Bowman's space. Conclusions: Our findings suggest that both systemic and renal tissues may contribute to sACE2 in urine, identifying the kidney as a major site for ACE2 actions. Moreover, filtration of sACE2 into the lumen of the nephron may contribute to the pathophysiology of kidney diseases characterized by disruption of the glomerular filtration barrier.