Renal Hemodynamics in AKI: In Search of New Treatment Targets

Renal-Targeted Drug Delivery by Chitosan Oligosaccharide Micelles with HSA-Enriched Protein Corona for the Treatment of Ischemia/Reperfusion-Induced Acute Kidney Injury

Renal-specific nanoparticulate drug delivery systems have shown great potential in reducing systemic side effects and improving the safety and efficacy of treatments for renal diseases. Here, stearic acid-grafted chitosan oligosaccharide (COS-SA) was synthesized as a renal-targeted carrier due to the high affinity of the 2-glucosamine moiety on COS to the megalin receptor expressed on renal proximal tubular epithelial cells. Specifically, COS-SA/CLT micelles were prepared by encapsulating celastrol (CLT) with COS-SA, and different proportions of human serum albumin (HSA) were then adsorbed onto its surface to explore the interaction between the protein corona and cationic polymeric micelles. Our results showed that a multilayered protein corona, consisting of an inner "hard" corona and an outer "soft" corona, was formed on the surface of COS-SA/CLT@HSA8, which was beneficial in preventing its recognition and phagocytosis by macrophages. The formation of HSA protein corona on COS-SA/CLT micelles also increased its accumulation in the renal tubules. Furthermore, the electropositivity of COS-SA/CLT micelles affected the conformation of adsorbed proteins to various degrees. During the adsorption process, the protein corona on the surface of COS-SA/CLT@HSA1 was partially denatured. Overall, COS-SA/CLT and COS-SA/CLT@HSA micelles demonstrated sufficient safety with renal targeting potential, providing a viable strategy for the management of ischemia/reperfusion-induced acute kidney injury.

Renal medullary perfusion differs from that in renal cortex in patients with sepsis associated acute kidney injury and correlates with renal function prognosis: A prospective cohort study

BACKGROUND

Renal perfusion status remains poorly studied at the bedside during sepsis associated acute kidney injury (AKI). The aim of the study is to examine renal cortical and medullary perfusion using renal contrast enhanced ultrasound (CEUS) in septic patients.

METHODS

In this single-center, prospective longitudinal study, septic patients were enrolled. Renal ultrasonography was performed within 24 hours of ICU admission (D1), then repeated at D3, D5 and D7. Each measurement consisted of three destruction replenishment sequences that were recorded for delayed analysis with dedicated software (Vuebox). Renal cortex and medulla perfusion were quantified by measuring time to peak (TTP). Receiver operating characteristic (ROC) analysis was used to evaluate 28-day renal prognosis.

RESULTS

The study included 149 septic patients, including 70 non-AKI patients and 79 AKI patients. Both renal cortical and medullary TTP was longer in the AKI group than in the non-AKI group. The difference of TTP between renal cortex and medulla in AKI group was higher than that in the non-AKI group (p = 0.000). Medullary TTP on day 3 had the best performance in predicting the prognosis of 28-day renal function (AUC 0.673, 95% confidence interval 0.528-0.818, p = 0.024), and its cut-off value was 45 s with a sensitivity 52.2% and a specificity of 82.1%. Cortical TTP on day 3 also had the performance in predicting the prognosis of 28-day renal function (AUC 0.657, 95% confidence interval 0.514-0.800, p = 0.039), and its cut-off value was 33 s with a sensitivity 78.3% and a specificity of 55.0%.

CONCLUSION

Renal medullary perfusion alterations differ from those in cortex, with the medulla is worse. Simultaneous and dynamic assessment of cortical and medullary microcirculatory flow alterations necessary. TTP on day 3, especially medullary TTP, seems to be a relatively stable and useful indicator, which correlates with 28-day renal function prognosis in septic patients. Early correction of renal cortical and medullary perfusion alterations reduces the incidence of adverse renal events.

Dynamic parametric MRI and deep learning: Unveiling renal pathophysiology through accurate kidney size quantification

Renal pathologies often manifest as alterations in kidney size, providing a valuable avenue for employing dynamic parametric MRI as a means to derive kidney size measurements for the diagnosis, treatment, and monitoring of renal disease. Furthermore, this approach holds significant potential in supporting MRI data-driven preclinical investigations into the intricate mechanisms underlying renal pathophysiology. The integration of deep learning algorithms is crucial in achieving rapid and precise segmentation of the kidney from temporally resolved parametric MRI, facilitating the use of kidney size as a meaningful (pre)clinical biomarker for renal disease. To explore this potential, we employed dynamic parametric T2 mapping of the kidney in rats in conjunction with a custom-tailored deep dilated U-Net (DDU-Net) architecture. The architecture was trained, validated, and tested on manually segmented ground truth kidney data, with benchmarking against an analytical segmentation model and a self-configuring no new U-Net. Subsequently, we applied our approach to in vivo longitudinal MRI data, incorporating interventions that emulate clinically relevant scenarios in rats. Our approach achieved high performance metrics, including a Dice coefficient of 0.98, coefficient of determination of 0.92, and a mean absolute percentage error of 1.1% compared with ground truth. The DDU-Net enabled automated and accurate quantification of acute changes in kidney size, such as aortic occlusion (-8% ± 1%), venous occlusion (5% ± 1%), furosemide administration (2% ± 1%), hypoxemia (-2% ± 1%), and contrast agent-induced acute kidney injury (11% ± 1%). This approach can potentially be instrumental for the development of dynamic parametric MRI-based tools for kidney disorders, offering unparalleled insights into renal pathophysiology.

Effect of Respiratory Failure on Peripheral and Organ Perfusion Markers in Severe COVID-19: A Prospective Cohort Study

Microvascular dysfunction and inflammation caused by COVID-19 disrupt organ function. The study aimed to investigate the association between the severity of SARS-CoV-2 pneumonia and peripheral and organ perfusion as a consequence of altered microcirculation. A total of 116 patients hospitalized due to severe COVID-19 were enrolled in the study. On admission, the patients underwent a Capillary Refill Time (CRT) examination, finger oxygen saturation measurement, thermal imaging of the hand (FIT), and a kidney Doppler ultrasound. Medical data were collected from the medical history. From the evaluated perfusion parameters, only renal cortex perfusion (RCP) was substantially correlated with the CT score (p < 0.010). The peripheral perfusion parameters of Sat., FIT, CRT, and RCP correlated with the ARDS stages (p = 0.0021; p = 0.038; p < 0.0006; p < 0.0002, respectively). The Oxygenation Ratio value (p < 0.001) was significantly associated with all the perfusion parameters (saturation, CRT, FIT, and RCP) in the multivariable regression analysis model. According to the stepwise retrograde regression analysis, RCP was an independent parameter linked with the Oxygenation Ratio (p < 0.001). Severe COVID-19 can result in microvascular dysfunction influencing peripheral and organ perfusion, which can be measured with various methods. The staging of COVID-19 assessed by CT and the Oxygenation Ratio correlates with RCP, CRT, FIT, and oxygen saturation.

Central venous pressure combined with renal venous impedance index in predicting the acute kidney injury after thoracic and abdominal (non-cardiac) surgery

BACKGROUND

In the 21st century, 13% of patients undergoing open abdominal surgery, 25% of patients undergoing heart surgery, and 57% of patients admitted to the intensive care unit (ICU) are affected by acute kidney injury (AKI).

METHODS

This prospective observational study included patients admitted directly to the ICU between June 2021 and December 2021.

RESULTS

A total of 81 patients were enrolled after thoracic and abdominal (non-cardiac) surgery; 36 patients (44.4%) were diagnosed with AKI occurred within 7 days after surgery. Six-hour postoperative central venous pressure(CVP) was a risk factor for AKI in thoracic and abdominal (non-cardiac) postoperative patients (odds ratio [OR], 1.418; 95% confidence intervals [CI], 1.106-1.819; P = 0.006). Six-hour postoperative vein impedance index(VII) and CVP were significantly positively correlated (P = 0.031). The combination of 6-h postoperative VII with CVP (VII ≥0.34, CVP ≥7.5 mmHg) showed an area under the curve (AUC) of 0.787, In the subgroup analysis of patients with 6-h postoperative CVP <7.5 mmHg, there was a significant statistical difference in 6-h postoperative VII between the groups and those without AKI (P = 0.048). At 6-h postoperative CVP <7.5 mmHg, VII of ≥0.44 had a predictive value for AKI after thoracic and abdominal (non-cardiac) surgery, with an AUC of 0.669, a sensitivity of 41.2%, and a specificity of 94.4%.

CONCLUSION

Six-hour postoperative CVP combined with VII can better predict the occurrence of AKI occurred within 7 days after thoracic and abdominal (non-cardiac) surgery but cannot predict the severity of AKI.

Acute Kidney Injury: Definition, Management, and Promising Therapeutic Target

Acute kidney injury (AKI) is caused by a sudden loss of renal function, resulting in the build-up of waste products and a significant increase in mortality and morbidity. It is commonly diagnosed in critically ill patients, with its occurrence estimated at up to 50% in patients hospitalized in the intensive critical unit. Despite ongoing efforts, the death rate associated with AKI has remained high over the past half-century. Thus, it is critical to investigate novel therapy options for preventing the epidemic. Many studies have found that inflammation and Toll-like receptor-4 (TLR-4) activation have a significant role in the pathogenesis of AKI. Noteworthy, challenges in the search for efficient pharmacological therapy for AKI have arisen due to the multifaceted origin and complexity of the clinical history of people with the disease. This article focuses on kidney injury's epidemiology, risk factors, and pathophysiological processes. Specifically, it focuses on the role of TLRs especially type 4 in disease development.

Renal hemodynamic evaluation protocol based on the pathophysiological mechanism of acute kidney injury: Critical Care UltraSound Guided-A(KI)BCDE

The multiple etiological characteristics of acute kidney injury (AKI) have brought great challenges to its clinical diagnosis and treatment. Renal injury in critically ill patients always indicates hemodynamic injury. The Critical Care UltraSound Guided (CCUSG)-A(KI)BCDE protocol developed by the Chinese Critical Ultrasound Study Group (CCUSG), respectively, includes A(KI) diagnosis and risk assessment and uses B-mode ultrasound, Color doppler ultrasound, spectral Doppler ultrasound, and contrast Enhanced ultrasound to obtain the hemodynamic characteristics of the kidney so that the pathophysiological mechanism of the occurrence and progression of AKI can be captured and the prognosis of AKI can be predicted combined with other clinical information; therefore, the corresponding intervention and treatment strategies can be formulated to achieve targeted, protocolized, and individualized therapy.

Knockout of the C3a receptor protects against renal ischemia reperfusion injury by reduction of NETs formation

Renal ischemia/reperfusion (I/R) injury is a local sterile inflammatory response driven by innate immunity. Emerging data have revealed that complement and neutrophils contribute to hyperinflammation and oxidative stress in I/R induced acute kidney injury (AKI). However, the interplay between the C3a/C3aR axis and neutrophil extracellular traps (NETs) is imcompletelyunderstood. Here, we utilize genetically engineered mouse models and pharmacological inhibitors to investigate this association. The C3a/C3aR axis is found to promote neutrophil recruitment and NETs formation, thereby accelerating renal damage and dysfunction. Knockout of C3aR restores NETs release and improves renal function after I/R injury. Antibody-mediated blockade of NETs can also significantly ameliorate renal tubular injury and inflammation. Consistently, under stimulation by C3a, neutrophils are activated to promote NETs formation and subsequent renal tubular epithelial cell damage, and blocking C3aR rescued the injury. Interfering with reactive oxygen species (ROS) accumulation in neutrophils by antioxidant treatment significantly attenuates NETs formation. Our findings demonstrate that the C3a/C3aR-ROS-NETs axis constitutes a promising target for prevention or treatment of renal I/R injury.

Contrast-enhanced ultrasonography for identifying acute kidney injury in brain-dead donors

Background

Acute kidney injury (AKI) is frequently found in deceased donors; however, few studies have reported the use of imaging to detect and identify this phenomenon. The purpose of this study was to detect renal microcirculatory perfusion in brain-dead donors using contrast-enhanced ultrasonography (CEUS), investigate the value of CEUS in identifying AKI, and analyze the correlation between CEUS and preimplantation biopsy results and early post-transplant renal function of grafts.

Methods

This prospective study recruited 94 kidneys from brain-dead donors (AKI =44, non-AKI =50) from August 2020 to November 2022. The inclusion criteria were age ≥18 years and brain death. The exclusion criteria encompassed donors maintained with extracorporeal membrane oxygenation (ECMO) and the presence of irregular kidney anatomy. The mean age of the donors was 45.1±10.4 [standard deviation (SD)] years, and the majority were male (86.2%). CEUS was performed prior to organ procurement, and time-intensity curves (TICs) were constructed. The time to peak (TTP) and peak intensity (PI) of kidney segmental artery (KA), kidney cortex (KC), and kidney medulla (KM) were calculated using TIC analysis.

Results

Arrival time (AT) of KA (P<0.001) and TTP of kidney cortex (TTPKC) (P<0.001) of the non-AKI group were significantly shorter than those of the AKI group. The PI of the KA (P=0.003), KM (P=0.005), and kidney cortex (PIKC; P<0.001) of the non-AKI group were significantly higher than those of the AKI group. Multivariable logistic regression analysis showed that serum creatinine [odds ratio (OR) =1.06; 95% CI: 1.03-1.1; P<0.001], TTPKC (OR =1.38; 95% CI: 1.03-1.84; P=0.03), and PIKC (OR =0.95; 95% CI: 0.91-1; P=0.046) were the independent factors of AKI. The area under the receiver operating characteristic curve (AUC) for identifying AKI for TTPKC and PIKC was 0.73 and 0.71, respectively. TTPKC showed a weak correlation with interstitial fibrosis (r=0.23; P=0.03), PIKC showed a weak correlation with arterial intimal fibrosis ((r=-0.29; P=0.004) and arteriolar hyalinosis (r=-0.27; P=0.008), and PIKC showed the strongest correlation with eGFR on postoperative day 7 (r=-0.46; P=0.046) in the donor kidneys with AKI.

Conclusions

CEUS can be used to identify AKI in brain-dead donors. Furthermore, there is a correlation between CEUS-derived parameters and pretransplant biopsy results and early preimplantation renal function of grafts.

Contrast-Enhanced Ultrasonography for Acute Kidney Injury: A Systematic Review and Meta-Analysis

OBJECTIVE

The aim of the work described here was to provide an evidence-based evaluation of contrast-enhanced ultrasonography (CEUS) in acute kidney injury (AKI) and assess variations in renal microperfusion with CEUS quantitative parameters in patients at a high risk of developing AKI.

METHODS

A meta-analysis and systematic review were conducted following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, and the Embase, MEDLINE, Web of Science and the Cochrane Library databases were used to search the relevant articles systematically (2000-2022). Studies using CEUS to assess renal cortical microcirculation in AKI were included.

RESULTS

Six prospective studies (374 patients) were included. The overall quality of included studies was moderate to high. CEUS measures, maximum intensity (standard mean difference [SMD]: -1.37, 95% confidence interval [CI]: -1.64 to -1.09) and wash-in rate (SMD: -0.77, 95% CI: -1.09 to -0.45) were lower in the AKI+ group than in the AKI- group, and mean transit time (SMD: 0.76, 95% CI: 0.11-1.40) and time to peak (SMD: 1.63, 95% CI: 0.99-2.27) were higher in the AKI+ group. Moreover, maximum intensity and wash-in rate values changed before creatinine changed in the AKI+ group.

CONCLUSION

Patients with AKI had reduced microcirculatory perfusion, prolonged perfusion time and a reduced rising slope in the renal cortex, which occurred before serum creatinine changes. And they could be measured using CEUS, indicating that CEUS could help in the diagnosis of AKI.

Monitoring kidney size to interpret MRI-based assessment of renal oxygenation in acute pathophysiological scenarios

AIM

Tissue hypoxia is an early key feature of acute kidney injury. Assessment of renal oxygenation using magnetic resonance imaging (MRI) markers T₂ and T₂ * enables insights into renal pathophysiology. This assessment can be confounded by changes in the blood and tubular volume fractions, occurring upon pathological insults. These changes are mirrored by changes in kidney size (KS). Here, we used dynamic MRI to monitor KS for physiological interpretation of T₂ * and T₂ changes in acute pathophysiological scenarios.

METHODS

KS was determined from T₂ *, T₂ mapping in rats. Six interventions that acutely alter renal tissue oxygenation were performed directly within the scanner, including interventions that change the blood and/or tubular volume. A biophysical model was used to estimate changes in O₂ saturation of hemoglobin from changes in T₂ * and KS.

RESULTS

Upon aortic occlusion KS decreased; this correlated with a decrease in T₂ *, T₂ . Upon renal vein occlusion KS increased; this negatively correlated with a decrease in T₂ *, T₂ . Upon simultaneous occlusion of both vessels KS remained unchanged; there was no correlation with decreased T₂ *, T₂ . Hypoxemia induced mild reductions in KS and T₂ *, T₂ . Administration of an X-ray contrast medium induced sustained KS increase, with an initial increase in T₂ *, T₂ followed by a decrease. Furosemide caused T₂ *, T₂ elevation and a minor increase in KS. Model calculations yielded physiologically plausible calibration ratios for T₂ *.

CONCLUSION

Monitoring KS allows physiological interpretation of acute renal oxygenation changes obtained by T₂ *, T₂ . KS monitoring should accompany MRI-oximetry, for new insights into renal pathophysiology and swift translation into human studies.

SARS-CoV-2 infection and diabetes: Pathophysiological mechanism of multi-system organ failure

Since the discovery of the coronavirus disease 2019 outbreak, a vast majority of studies have been carried out that confirmed the worst outcome of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection in people with preexisting health conditions, including diabetes, obesity, hypertension, cancer, and cardiovascular diseases. Likewise, diabetes itself is one of the leading causes of global public health concerns that impose a heavy global burden on public health as well as socio-economic development. Both diabetes and SARS-CoV-2 infection have their independent ability to induce the pathogenesis and severity of multi-system organ failure, while the co-existence of these two culprits can accelerate the rate of disease progression and magnify the severity of the disease. However, the exact pathophysiology of multi-system organ failure in diabetic patients after SARS-CoV-2 infection is still obscure. This review summarized the organ-specific possible molecular mechanisms of SARS-CoV-2 and diabetes-induced pathophysiology of several diseases of multiple organs, including the lungs, heart, kidneys, brain, eyes, gastrointestinal system, and bones, and sub-sequent manifestation of multi-system organ failure.

Urine biochemistry assessment in the sequential evaluation of renal function: Time to think outside the box

Urine biochemistry (UB) remains a controversial tool in acute kidney injury (AKI) monitoring, being considered to be of limited value both in terms of AKI diagnosis and prognosis. However, many criticisms can be made to the studies that have established the so called “pre-renal paradigm” (used for decades as the essential physiological basis for UB assessment in AKI) as well as to more recent studies suggesting that UB has no utility in daily clinical practice. The aim of this article is to describe our hypothesis on how to interpret simple and widely recognized urine biochemical parameters from a novel perspective, propose the rationale for their sequential assessment and demonstrate their usefulness in AKI monitoring, especially in the critical care setting.

Diagnostic value of ultrasound and contrast-enhanced ultrasound in septic acute kidney injury

PURPOSE

This study aimed to explore the clinical value of ultrasonic Doppler examination and contrast-enhanced ultrasound (US) in the circulation of septic acute kidney injury (AKI).

METHODS

Patients with intensive care unit-related infection were divided into AKI group and control groups. The AKI group was divided into three subgroups according to the serum creatinine value: stage 1, stage 2, and stage 3. Relevant parameters and blood flow of the renal artery were measured, and further contrast-enhanced US was performed and time-intensity curve was analyzed.

RESULTS

The renal blood flow (RBF) and time-averaged velocity decreased significantly in the AKI group compared with the control group (p = .021 and p = .001). The peak value decreased and time to peak (TTP) prolonged in the AKI group (p < .001). With the aggravation of the disease, the RBF decreased slightly among subgroups (p = 0.124). However, the peak value gradually decreased and the TTP prolonged (all p < .05). The multiple linear regression model showed that only PI, RI, and TTP were independently and linearly correlated with the serum creatinine value.

CONCLUSIONS

Doppler US and contrast-enhanced US are of great help in the detection of condition changes and prognosis of patients with sepsis-induced AKI.

Central venous pressure and acute kidney injury in critically ill patients with multiple comorbidities: a large retrospective cohort study

Background

Given the traditional acceptance of higher central venous pressure (CVP) levels, clinicians ignore the incidence of acute kidney injury (AKI). The objective of this study was to assess whether elevated CVP is associated with increased AKI in critically ill patients with multiple comorbidities.

Methods

This was a retrospective observational cohort study using data collected from the Medical Information Mart for Intensive Care (MIMIC)-III open-source clinical database (version 1.4). Critically ill adult patients with CVP and serum creatinine measurement records were included. Linear and multivariable logistic regression were performed to determine the association between elevated CVP and AKI.

Results

A total of 11,135 patients were enrolled in our study. Critically ill patients in higher quartiles of mean CVP presented greater KDIGO AKI severity stages at 2 and 7 days. Linear regression showed that the CVP quartile was positively correlated with the incidence of AKI within 2 (R² = 0.991, P = 0.004) and 7 days (R² = 0.990, P = 0.005). Furthermore, patients in the highest quartile of mean CVP exhibited an increased risk of AKI at 7 days than those in the lowest quartile of mean CVP with an odds ratio of 2.80 (95% confidence interval: 2.32–3.37) after adjusting for demographics, treatments and comorbidities. The adjusted odds of AKI were 1.10 (95% confidence interval: 1.08–1.12) per 1 mmHg increase in mean CVP.

Conclusions

Elevated CVP is associated with an increased risk of AKI in critically ill patients with multiple comorbidities. The optimal CVP should be personalized and maintained at a low level to avoid AKI in critical care settings.

Heart, kidney and left ventricular assist device: a complex trio

BACKGROUND

Heart failure (HF) is a complex syndrome affecting the whole body, kidneys included. The left ventricular assist device (LVAD) is a valid option for patients with very severe HF. Focusing on renal function, LVAD implantation could theoretically reverse the detrimental effects of HF syndrome on kidneys. However, implanting an LVAD is a high-risk surgical procedure, and LVAD patients have higher risk of bleeding, device thrombosis, strokes, renal impairment, multi-organ failure and infections. Furthermore, an LVAD has its own particular effects on the renal system.

METHODS

In this review, we provide a comprehensive overview of the complex interaction between LVAD and the kidneys from the pathophysiological and clinical perspectives. An analysis of the different effects of pulsatile-flow and continuous-flow LVAD is provided.

RESULTS

Despite their limitations, creatinine-based estimated glomerular filtration rate (eGFR) formulas help to stratify patients by their post-LVAD placement prognosis. Poor basal renal function, the onset of acute kidney injury or the need for renal replacement therapy after LVAD implantation negatively influences a patient's prognosis. LVAD can also prompt an improvement in renal function, however, with some counterintuitive effects on a patient's prognosis.

CONCLUSION

It is still hard to say whether different trends in eGFR depend on different renal conditions before LVAD placement, on a patient's better overall status or on a particular patient management strategy before and/or after the device's implantation. Steps should be taken to solve this question because finding the best candidates for LVAD implantation is of paramount importance to ensure the best outcomes.

Reliable kidney size determination by magnetic resonance imaging in pathophysiological settings

AIM

Kidney diseases constitute a major health challenge, which requires noninvasive imaging to complement conventional approaches to diagnosis and monitoring. Several renal pathologies are associated with changes in kidney size, offering an opportunity for magnetic resonance imaging (MRI) biomarkers of disease. This work uses dynamic MRI and an automated bean-shaped model (ABSM) for longitudinal quantification of pathophysiologically relevant changes in kidney size.

METHODS

A geometry-based ABSM was developed for kidney size measurements in rats using parametric MRI (T₂ , T₂ * mapping). The ABSM approach was applied to longitudinal renal size quantification using occlusion of the (a) suprarenal aorta or (b) the renal vein, (c) increase in renal pelvis and intratubular pressure and (d) injection of an X-ray contrast medium into the thoracic aorta to induce pathophysiologically relevant changes in kidney size.

RESULTS

The ABSM yielded renal size measurements with accuracy and precision equivalent to the manual segmentation, with >70-fold time savings. The automated method could detect a ~7% reduction (aortic occlusion) and a ~5%, a ~2% and a ~6% increase in kidney size (venous occlusion, pelvis and intratubular pressure increase and injection of X-ray contrast medium, respectively). These measurements were not affected by reduced image quality following administration of ferumoxytol.

CONCLUSION

Dynamic MRI in conjunction with renal segmentation using an ABSM supports longitudinal quantification of changes in kidney size in pathophysiologically relevant experimental setups mimicking realistic clinical scenarios. This can potentially be instrumental for developing MRI-based diagnostic tools for various kidney disorders and for gaining new insight into mechanisms of renal pathophysiology.

Atorvastatin (ATV)-Loaded Lipid Bilayer-Coated Mesoporous Silica Nanoparticles Enhance the Therapeutic Efficacy of Acute Kidney Injury

Background: Acute kidney injury (AKI) increases the risk of chronic kidney disease. Atorvastatin (ATV)-loaded lipid bilayer-coated mesoporous silica nanoparticles (L-AMSNs) were synthesized, and their physicochemical parameters were characterized. L-AMSNs exhibited excellent stability; it did not increase in size over time, indicating that the lipid membrane coating prohibited mesoporous silica nanoparticles (MSNs) coalescence. Results: The rate of drug release differed significantly between AMSNs and L-AMSNs at all tested time points. A remarkable improvement in hydrogen peroxide (H₂O₂)-treated human umbilical vein endothelial cell (HUVEC) viability was observed after treatment with L-AMSNs; the malondialdehyde (MDA) level was significantly reduced compared to control cells. The extent of apoptosis was only 15% that of control H₂O₂-treated cells. L-AMSNs induced a remarkable decrease in the levels of pro-inflammatory cytokines (tumor necrosis factor [TNF]-α and interleukin [IL]-6), showing the therapeutic potential of nanocarrier-based ATV. L-AMSNs significantly increased the superoxide dismutase level and decreased the MDA level, indicating superior anti-inflammatory activity under conditions of oxidative stress. The L-AMSN showed a remarkable improvement in the outer stripe of outer medulla (OSOM) region and maintained the tubular structure of the kidney tissue. Besides, kidney injury score of L-AMSN is significantly lower compared to that of LPS-AKI and ATV indicating the excellent therapeutic efficacy of nanoparticulate system based L-AMSN. Conclusions: Nanoparticles system-based L-AMSNs maintained the tubular structure of kidney tissue, indicating excellent therapeutic efficacy. After clinical translation, L-AMSNs could serve as a promising treatment for AKI.

Docosahexaenoic Acid-Acylated Astaxanthin Esters Exhibit Superior Renal Protective Effect to Recombination of Astaxanthin with DHA via Alleviating Oxidative Stress Coupled with Apoptosis in Vancomycin-Treated Mice with Nephrotoxicity

Prevention of acute kidney injury caused by drugs is still a clinical problem to be solved urgently. Astaxanthin (AST) and docosahexaenoic acid (DHA) are important marine-derived active ingredients, and they are reported to exhibit renal protective activity. It is noteworthy that the existing forms of AST in nature are mainly fatty acid-acylated AST monoesters and diesters, as well as unesterified AST, in which DHA is an esterified fatty acid. However, no reports focus on the different bioactivities of unesterified AST, monoesters and diesters, as well as the recombination of DHA and unesterified AST on nephrotoxicity. In the present study, vancomycin-treated mice were used to evaluate the effects of DHA-acylated AST monoesters, DHA-acylated AST diesters, unesterified AST, and the recombination of AST and DHA in alleviating nephrotoxicity by determining serum biochemical index, histopathological changes, and the enzyme activity related to oxidative stress. Results found that the intervention of DHA-acylated AST diesters significantly ameliorated kidney dysfunction by decreasing the levels of urea nitrogen and creatinine, alleviating pathological damage and oxidative stress compared to AST monoester, unesterified AST, and the recombination of AST and DHA. Further studies revealed that dietary DHA-acylated AST esters could inhibit the activation of the caspase cascade and MAPKs signaling pathway, and reduce the levels of pro-inflammatory cytokines. These findings indicated that the administration of DHA-acylated AST esters could alleviate vancomycin-induced nephrotoxicity, which represented a potentially novel candidate or therapeutic adjuvant for alleviating acute kidney injury.

Continuous diffusion spectrum computation for diffusion-weighted magnetic resonance imaging of the kidney tubule system

Background

The use of rigid multi-exponential models (with a priori predefined numbers of components) is common practice for diffusion-weighted MRI (DWI) analysis of the kidney. This approach may not accurately reflect renal microstructure, as the data are forced to conform to the a priori assumptions of simplified models. This work examines the feasibility of less constrained, data-driven non-negative least squares (NNLS) continuum modelling for DWI of the kidney tubule system in simulations that include emulations of pathophysiological conditions.

Methods

Non-linear least squares (LS) fitting was used as reference for the simulations. For performance assessment, a threshold of 5% or 10% for the mean absolute percentage error (MAPE) of NNLS and LS results was used. As ground truth, a tri-exponential model using defined volume fractions and diffusion coefficients for each renal compartment (tubule system: D_tubules , f_tubules ; renal tissue: D_tissue , f_tissue ; renal blood: D_blood , f_blood ;) was applied. The impact of: (I) signal-to-noise ratio (SNR) =40-1,000, (II) number of b-values (n=10-50), (III) diffusion weighting (b-range_small =0-800 up to b-range_large =0-2,180 s/mm²), and (IV) fixation of the diffusion coefficients D_tissue and D_blood was examined. NNLS was evaluated for baseline and pathophysiological conditions, namely increased tubular volume fraction (ITV) and renal fibrosis (10%: grade I, mild) and 30% (grade II, moderate).

Results

NNLS showed the same high degree of reliability as the non-linear LS. MAPE of the tubular volume fraction (f_tubules ) decreased with increasing SNR. Increasing the number of b-values was beneficial for f_tubules precision. Using the b-range_large led to a decrease in MAPE _ftubules compared to b-range_small. The use of a medium b-value range of b=0-1,380 s/mm² improved f_tubules precision, and further b_max increases beyond this range yielded diminishing improvements. Fixing D_blood and D_tissue significantly reduced MAPE _ftubules and provided near perfect distinction between baseline and ITV conditions. Without constraining the number of renal compartments in advance, NNLS was able to detect the (fourth) fibrotic compartment, to differentiate it from the other three diffusion components, and to distinguish between 10% vs. 30% fibrosis.

Conclusions

This work demonstrates the feasibility of NNLS modelling for DWI of the kidney tubule system and shows its potential for examining diffusion compartments associated with renal pathophysiology including ITV fraction and different degrees of fibrosis.

Porcine models of acute kidney injury

Pigs represent a potentially attractive model for medical research. Similar body size and physiological patterns of kidney injury that more closely mimic those described in humans make larger animals attractive for experimentation. Using larger animals, including pigs, to investigate the pathogenesis of acute kidney injury (AKI) also serves as an experimental bridge, narrowing the gap between clinical disease and preclinical discoveries. This article compares the advantages and disadvantages of large versus small AKI animal models and provides a comprehensive overview of the development and application of porcine models of AKI induced by clinically relevant insults, including ischemia-reperfusion, sepsis, and nephrotoxin exposure. The primary focus of this review is to evaluate the use of pigs for AKI studies by current investigators, including areas where more information is needed.

Dl-3-n-butylphthalide pretreatment attenuates renal ischemia/reperfusion injury

BACKGROUND

Renal ischemia reperfusion injury (IRI) has become a growing concern in clinical practice with high morbidity and mortality rates. There is currently no effective prophylactic regimen available to prevent its occurrence and to improve its clinical prognosis. Dl-3-n-butylphthalide (NBP) has been used for stroke treatment in China for years. Little is known about its role in preventing kidney injury.

METHODS

The kidneys of male C57BL/6J mice were subjected to 33 min of ischemia followed by 24 h of reperfusion. NBP was administered by gavage prior to surgery. The reno-protective effect of NBP was evaluated by serum creatinine, kidney injury markers and renal pathological changes. Furthermore, the inflammation, oxidative stress, and apoptosis markers in kidney tissue were examined. In vitro, HK2 cells were treated prophylactically with NBP and then exposed to hypoxia/reoxygenation (H/R). Cell viability and apoptosis related protein were quantified to verify the protective effect of NBP. Pro-inflammation genes expression as well as ROS generation were further investigated also.

RESULTS

NBP pretreatment significantly improved renal dysfunction and alleviated pathological injury, renal inflammation response, oxidative stress and cell apoptosis. Consistently, NBP attenuated H/R induced increases in ROS, pro-inflammatory genes expression, apoptosis and cleaved caspase-3 levels in HK2 cells.

CONCLUSION

Our promising results validated for the first time that NBP could ameliorate renal IRI via attenuating inflammation, oxidative stress, and apoptosis, which indicated that NBP might be a good candidate against AKI.

Restoration of afferent arteriolar autoregulatory behavior in ischemia-reperfusion injury in rat kidneys

Renal autoregulation is critical in maintaining stable renal blood flow (RBF) and glomerular filtration rate (GFR). Renal ischemia-reperfusion (IR)-induced kidney injury is characterized by reduced RBF and GFR. The mechanisms contributing to renal microvascular dysfunction in IR have not been fully determined. We hypothesized that increased reactive oxygen species (ROS) contributed to impaired renal autoregulatory capability in IR rats. Afferent arteriolar autoregulatory behavior was assessed using the blood-perfused juxtamedullary nephron preparation. IR was induced by 60 min of bilateral renal artery occlusion followed by 24 h of reperfusion. Afferent arterioles from sham rats exhibited normal autoregulatory behavior. Stepwise increases in perfusion pressure caused pressure-dependent vasoconstriction to 65 ± 3% of baseline diameter (13.2 ± 0.4 μm) at 170 mmHg. In contrast, pressure-mediated vasoconstriction was markedly attenuated in IR rats. Baseline diameter averaged 11.7 ± 0.5 µm and remained between 90% and 101% of baseline over 65-170 mmHg, indicating impaired autoregulatory function. Acute antioxidant administration (tempol or apocynin) to IR kidneys for 20 min increased baseline diameter and improved autoregulatory capability, such that the pressure-diameter profiles were indistinguishable from those of sham kidneys. Furthermore, the addition of polyethylene glycol superoxide dismutase or polyethylene glycol-catalase to the perfusate blood also restored afferent arteriolar autoregulatory responsiveness in IR rats, indicating the involvement of superoxide and/or hydrogen peroxide. IR elevated mRNA expression of NADPH oxidase subunits and monocyte chemoattractant protein-1 in renal tissue homogenates, and this was prevented by tempol pretreatment. These results suggest that ROS accumulation, likely involving superoxide and/or hydrogen peroxide, impairs renal autoregulation in IR rats in a reversible fashion.NEW & NOTEWORTHY Renal ischemia-reperfusion (IR) leads to renal microvascular dysfunction manifested by impaired afferent arteriolar autoregulatory efficiency. Acute administration of scavengers of reactive oxygen species, polyethylene glycol-superoxide dismutase, or polyethylene glycol-catalase following renal IR restored afferent arteriolar autoregulatory capability in IR rats, indicating that renal IR led to reversible impairment of afferent arteriolar autoregulatory capability. Intervention with antioxidant treatment following IR may improve outcomes in patients by preserving renovascular autoregulatory function and potentially preventing the progression to chronic kidney disease after acute kidney injury.

Oil-In-Water Microemulsion Encapsulation of Antagonist Drugs Prevents Renal Ischemia-Reperfusion Injury in Rats

Developing new therapeutic drugs to prevent ischemia/reperfusion (I/R)-induced renal injuries is highly pursued. Liposomal encapsulation of spironolactone (SP) as a mineralocorticoid antagonist increases dissolution rate, bioavailability and prevents the drug from degradation. In this context, this work develops a new formulation of oil-in-water type microemulsions to enhance the bioavailability of SP. The size of the SP-loaded microemulsion was about 6.0 nm by dynamic light scattering analysis. Briefly, we investigated the effects of nano-encapsulated SP (NESP) on renal oxidative stress, biochemical markers and histopathological changes in a rat model of renal I/R injury. Forty eight male Wistar rats were divided into six groups. Two groups served as control and injury model (I/R). Two groups received “conventional” SP administration (20 mg/kg) and NESP (20 mg/kg), respectively, for two days. The remaining two groups received SP (20 mg/kg) and NESP (20 mg/kg) two days before induction of I/R. At the end of the experiments, serum and kidneys of rats underwent biochemical, molecular and histological examinations. Our results showed that I/R induces renal oxidative stress, abnormal histological features and altered levels of renal biomarkers. Administration of SP in healthy animals did not cause any significant changes in the measured biochemical and histological parameters compared to the control group. However, SP administration in the I/R group caused some corrections in renal injury, although it could not completely restore I/R-induced renal oxidative stress and kidney damage. On the contrary, NESP administration restored kidney oxidative injury via decreasing renal lipid peroxidation and enhancing glutathione, superoxide dismutase and catalase in kidneys of the I/R group. The deviated serum levels of urea, creatinine, total proteins and uric acid were also normalized by NESP administration. Furthermore, NESP protected against renal abnormal histology features induced by I/R. Therefore, NESP has beneficial effects in preventing kidney damage and renal oxidative stress in a rat model of I/R, which deserves further evaluations in the future.

New drugs for acute kidney injury

PURPOSE OF REVIEW

To describe recent advances in the development of therapeutic agents for acute kidney injury (AKI).

RECENT FINDINGS

Traditional care for AKI is mostly supportive. At present, no specific therapy has been developed to prevent or treat AKI. However, based on a better understanding of the pathophysiology of AKI, various potential compounds have been recently identified and tested. A variety of pathways has been targeted, including oxidative and mitochondrial stress, cellular metabolism and repair, inflammation, apoptosis and hemodynamics. Many of these potential agents are currently ongoing early-phase clinical trials, and the purpose of this review is to provide a summary of those with the most potential.

SUMMARY

Despite the lack of therapies specifically approved for AKI, many interesting potential agents are entering clinical trials, with the potential to transform the care of patients with AKI.

Clinical phenotypes of acute kidney injury are associated with unique outcomes in critically ill septic children

BACKGROUND

Assessment of acute kidney injury (AKI) in septic patients remains imprecise. In adults, the classification of septic patients by clinical AKI phenotypes (severity and timing) demonstrates unique associations with patient outcome vs. broadly defined AKI.

METHODS

In a multinational prospective observational study, AKI diagnosis in critically ill septic children was stratified by duration (transient vs. persistent) and severity (mild vs. severe by creatinine change and urine output). The outcomes of interest were mortality and intensive care unit resource complexity at 28 days.

RESULTS

Seven hundred and fifty-seven septic children were studied (male 52.7%, age 4.6 years (1.5-11.9)). Mortality (overall 12.1%) was different between severe AKI and mild AKI (18.3 vs. 4.4%, p < 0.001) as well as intensive care unit (ICU) complexity (overall 34.5%, 45 vs. 21.7%, p < 0.001). Patients with Persistent AKI had fewer ICU-free days (17 (7, 21) vs. 24 (17, 26), p < 0.001) and higher ICU complexity (52.8 vs. 22.9%, p = 0.002) than transient AKI, even after exclusion of patients with early mortality. AKI phenotypes incorporating temporal and severity data correlate with unique survival (range 4.4-21.6%) and ICU-free days (range of 15-25 days) CONCLUSIONS: The outcome of septic children with AKI changes by clinical phenotype. Our findings underscore the importance of prognostic enrichment in sepsis and AKI for the purpose of trial design and patient management.

IMPACT

Although AKI occurs commonly in patients with sepsis (S-AKI), outcomes for children with S-AKI varies based on the severity and timing of the AKI. Existing S-AKI pediatric data utilize a broad singular definition of kidney injury. Increasing the precision of AKI classification results in a new understanding of how S-AKI associates with patient outcome. A refined classification of S-AKI identifies subgroups of children, making possible a targeted and a personalized medicine approach to S-AKI study and management.

Post-operative renal failure management in mechanical circulatory support patients

Acute kidney injury (AKI) occurs commonly in patients requiring mechanical circulatory support (MCS) after cardiothoracic surgery. The prognostic implications of AKI in this patient group relate closely to the pathophysiology and risk factors associated with the underlying disease; pre-operative, intra-operative, and post-operative variables; hemodynamic factors; and type of support device used. General approaches to AKI management, including prevention strategies, medical management, and hemodynamic support, are also applicable in patients requiring MCS. Approaches to renal replacement therapy vary depend on patient factors, device-specific factors, and local preferences and experience. In this invited narrative review, we discuss the pathophysiology, risk factors, and prognostic implications of AKI in post-operative adult patients following institution of MCS. Management strategies for AKI are presented with a focus on those supported with either extracorporeal membrane oxygenation or a ventricular assist device.

[Evaluation of the microcirculation in critically ill patients : Relevance, practical possibilities and scientific evidence]

Für die Aufrechterhaltung der Organdurchblutung ist eine intakte Makro- und Mikrozirkulation essentiell. Sowohl das wachsende Verständnis um die Bedeutung der Mikrozirkulation im Organversagen als auch die Möglichkeit, diese zu visualisieren, lenken die Aufmerksamkeit der Intensivmedizin auf die mikrovaskuläre Endstrombahn. Als Surrogat-Parameter sind die Rekapillarisierungszeit, der „mottling score“ und die Messung des Serum-Laktats bereits lange in der klinischen Praxis etabliert. Neuere Studien messen der Echtzeit-Darstellung der sublingualen Mikrozirkulation mittels Intravital-Videomikroskopie eine immer größere Bedeutung bei. Verschiedene Studien unterstreichen hierbei die Mikrozirkulation als prognostischen Parameter. Darüber hinaus ermöglicht die Erhebung von objektivierbaren Messwerten, diese in der Zukunft zur individuellen Therapiesteuerung weitergehend zu untersuchen.

Single-cell RNA sequencing analysis of human kidney reveals the presence of ACE2 receptor: A potential pathway of COVID-19 infection

BACKGROUND

A novel coronavirus called SARS-Cov-2, which shared 82% similarity of genome sequence with SARS-CoV, was found in Wuhan in late December of 2019, causing an epidemic outbreak of novel coronavirus-induced pneumonia with dramatically increasing number of cases. Several organs are vulnerable to COVID-19 infection. Acute kidney injury (AKI) was reported in parts of case-studies reporting characteristics of COVID-19 patients. This study aimed at analyzing the potential route of SARS-Cov-2 entry and mechanism at cellular level.

METHOD

Single-cell RNA sequencing (scRNA-seq) technology was used to obtain evidence of potential route and ACE2 expressing cell in renal system for underlying pathogenesis of kidney injury caused by COVID-19. The whole process was performed under R with Seurat packages. Canonical marker genes were used to annotate different types of cells.

RESULTS

Ten different clusters were identified and ACE2 was mainly expressed in proximal tubule and glomerular parietal epithelial cells. From Gene Ontology (GO) & KEGG enrichment analysis, imbalance of ACE2 expression, renin-angiotensin system (RAS) activation, and neutrophil-related processes were the main issue of COVID-19 leading kidney injury.

CONCLUSION

Our study provided the cellular evidence that SARS-Cov-2 invaded human kidney tissue via proximal convoluted tubule, proximal tubule, proximal straight tubule cells, and glomerular parietal cells by means of ACE2-related pathway and used their cellular protease TMPRSS2 for priming.

Adenosine kinase inhibition attenuates ischemia reperfusion-induced acute kidney injury

Acute kidney injury (AKI) has a high morbidity and mortality, and there is no targeted treatment yet. One of the main causes of AKI is ischemia-reperfusion (IR). Increased release of adenosine under stress and hypoxia exerts anti-inflammatory and antioxidant effects. Adenosine kinase (ADK) is an important enzyme that eliminates adenosine in cells, and can maintain low adenosine concentration in cells. Our previous studies have shown that pretreatment of adenosine kinase inhibitor ABT-702 could markedly attenuate cisplatin-induced nephrotoxicity both in vivo and in vitro. This study is designed to investigate the effect of ADK inhibition on IR-induced AKI. The results showed that ADK expression was positively correlated with the degree of renal tubular injury, which suggested that the degree of ADK inhibition reflected the severity of acute tubular necrosis. In vivo, ADK inhibitor could reduce IR-induced renal injury, which might play a protective role by increasing tissue adenosine level, inhibiting oxidative stress, and reducing cell apoptosis. In HK2 cells, cobaltous dichloride (CoCl₂) increased the level of oxidative stress, up-regulated the production of pro-inflammatory factor, and induced apoptosis, ADK inhibition could alleviate the above damaging effects. Moreover, the anti-apoptotic effect exerted by ADK inhibition was independent of inosine. In summary, our results support the idea that ADK inhibition has protective effects on IR-induced AKI. Adenosine kinase inhibition might provide a new target for AKI prevention and treatment.

Recent advances in acute kidney injury and its consequences and impact on chronic kidney disease

PURPOSE OF REVIEW

Acute kidney injury (AKI) remains a major unmet medical need and associates with high morbidity, mortality, and healthcare costs. Among survivors, long-term outcomes of AKI can include development of chronic kidney disease (CKD) or progression of preexisting CKD. In this review, we focus on ongoing efforts by the AKI community to understand the human AKI to CKD continuum, with an emphasis on the cellular stress responses that underlie AKI and the maladaptive responses that persist in the acute-to-chronic phase. The emphasis is on work that has been published in the past year in this rapidly expanding field.

RECENT FINDINGS

Recent studies in preclinical models highlight the importance of mitochondrial dysfunction, cell death, and inflammation on the underlying pathogenesis of AKI. These pathogenic mechanisms can resolve with adaptive kidney repair but persist in maladaptive repair that leads to progressive chronic disease. The complexity and interconnections of these pathways involve cross-talk between the tubular epithelium, endothelium, and interstitial compartments.

SUMMARY

Approaches which lessen or counteract these cellular responses represent novel strategies to prevent AKI and stop or slow down the progression to CKD.

Probing renal blood volume with magnetic resonance imaging

Damage to the kidney substantially reduces life expectancy. Renal tissue hypoperfusion and hypoxia are key elements in the pathophysiology of acute kidney injury and its progression to chronic kidney disease. In vivo assessment of renal haemodynamics and tissue oxygenation remains a challenge. Blood oxygenation level-dependent (BOLD) magnetic resonance imaging (MRI) is sensitive to changes in the effective transversal relaxation time (T₂ *) in vivo, and is non-invasive and indicative of renal tissue oxygenation. However, the renal T₂ * to tissue pO₂ relationship is not governed exclusively by renal blood oxygenation, but is affected by physiological confounders with alterations in renal blood volume fraction (BVf) being of particular relevance. To decipher this interference probing renal BVf is essential for the pursuit of renal MR oximetry. Superparamagnetic iron oxide nanoparticle (USPIO) preparations can be used as MRI visible blood pool markers for detailing alterations in BVf. This review promotes the opportunities of MRI-based assessment of renal BVf. Following an outline on the specifics of renal oxygenation and perfusion, changes in renal BVf upon interventions and their potential impact on renal T₂ * are discussed. We also describe the basic principles of renal BVf assessment using ferumoxytol-enhanced MRI in the equilibrium concentration regimen. We demonstrate that ferumoxytol does not alter control of renal haemodynamics and oxygenation. Preclinical applications of ferumoxytol enhanced renal MRI as well as considerations for its clinical implementation for examining renal BVf changes are provided alongside practical considerations. Finally, we explore the future directions of MRI-based assessment of renal BVf.

Endothelin-1 Mediates the Systemic and Renal Hemodynamic Effects of GPR81 Activation

Supplemental Digital Content is available in the text.

GPR81 (G-protein-coupled receptor 81) is highly expressed in adipocytes, and activation by the endogenous ligand lactate inhibits lipolysis. GPR81 is also expressed in the heart, liver, and kidney, but roles in nonadipose tissues are poorly defined. GPR81 agonists, developed to improve blood lipid profile, might also provide insights into GPR81 physiology. Here, we assessed the blood pressure and renal hemodynamic responses to the GPR81 agonist, AZ′5538. In male wild-type mice, intravenous AZ′5538 infusion caused a rapid and sustained increase in systolic and diastolic blood pressure. Renal artery blood flow, intrarenal tissue perfusion, and glomerular filtration rate were all significantly reduced. AZ′5538 had no effect on blood pressure or renal hemodynamics in Gpr81^−/− mice. Gpr81 mRNA was expressed in renal artery vascular smooth muscle, in the afferent arteriole, in glomerular and medullary perivascular cells, and in pericyte-like cells isolated from kidney. Intravenous AZ′5538 increased plasma ET-1 (endothelin 1), and pretreatment with BQ123 (endothelin-A receptor antagonist) prevented the pressor effects of GPR81 activation, whereas BQ788 (endothelin-B receptor antagonist) did not. Renal ischemia-reperfusion injury, which increases renal extracellular lactate, increased the renal expression of genes encoding ET-1, KIM-1 (Kidney Injury Molecule 1), collagen type 1-α1, TNF-α (tumor necrosis factor-α), and F4/80 in wild-type mice but not in Gpr81^−/− mice. In summary, activation of GPR81 in vascular smooth muscle and perivascular cells regulates renal hemodynamics, mediated by release of the potent vasoconstrictor ET-1. This suggests that lactate may be a paracrine regulator of renal blood flow, particularly relevant when extracellular lactate is high as occurs during ischemic renal disease.

Diffusion-weighted Renal MRI at 9.4 Tesla Using RARE to Improve Anatomical Integrity

Diffusion-weighted magnetic resonance imaging (DWI) is a non-invasive imaging technique sensitive to tissue water movement. By enabling a discrimination between tissue properties without the need of contrast agent administration, DWI is invaluable for probing tissue microstructure in kidney diseases. DWI studies commonly make use of single-shot Echo-Planar Imaging (ss-EPI) techniques that are prone to suffering from geometric distortion. The goal of the present study was to develop a robust DWI technique tailored for preclinical magnetic resonance imaging (MRI) studies that is free of distortion and sensitive to detect microstructural changes. Since fast spin-echo imaging techniques are less susceptible to B₀ inhomogeneity related image distortions, we introduced a diffusion sensitization to a split-echo Rapid Acquisition with Relaxation Enhancement (RARE) technique for high field preclinical DWI at 9.4 T. Validation studies in standard liquids provided diffusion coefficients consistent with reported values from the literature. Split-echo RARE outperformed conventional ss-EPI, with ss-EPI showing a 3.5-times larger border displacement (2.60 vs. 0.75) and a 60% higher intra-subject variability (cortex = 74%, outer medulla = 62% and inner medulla = 44%). The anatomical integrity provided by the split-echo RARE DWI technique is an essential component of parametric imaging on the way towards robust renal tissue characterization, especially during kidney disease.

Long-term outcomes in mouse models of ischemia-reperfusion-induced acute kidney injury

Severe acute kidney injury has a high mortality and is a risk factor for progressive chronic kidney disease. None of the potential therapies that have been identified in preclinical studies have successfully improved clinical outcomes. This failure is partly because animal models rarely reflect the complexity of human disease: most preclinical studies are short term and are commonly performed in healthy, young, male mice. Therapies that are effective in preclinical models that share common clinical features seen in patients with acute kidney injury, including genetic diversity, different sexes, and comorbidities, and evaluate long-term outcomes are more likely to predict success in the clinic. Here, we evaluated susceptibility to chronic kidney disease after ischemia-reperfusion injury with delayed nephrectomy by monitoring long-term functional and histological responses to injury. We defined conditions required to induce long-term postinjury renal dysfunction and fibrosis without increased mortality in a reproducible way and evaluate effect of mouse strains, sexes, and preexisting diabetes on these responses.

Angiotensin II type 2 receptor and angiotensin-converting enzyme 2 mediate ischemic renal injury in diabetic and non-diabetic rats

AIM

Depressor arm of the renin-angiotensin system (RAS) exerts reno-protective effects in chronic kidney diseases like diabetic nephropathy. However, same is still elusive under AKI and hyperglycaemia comorbidity. Hence, the present study delineates the role of angiotensin-II type 2 receptor (AT2R) and angiotensin-converting enzyme 2 (ACE2) in AKI under normal and hyperglycaemia condition.

METHODS

Non-diabetic (ND) and Streptozotocin-induced diabetes mellitus (DM) rats were subjected to ischemic renal injury (IRI). Rats underwent IRI were treated with an AT2R agonist, C21 (0.3 mg/kg/day, i.p.) or ACE2 activator, Dize, (5 mg/kg/day, p.o.) either alone or as combination therapy. Renal histopathology and immunohistochemistry, proximal tubular fraction isolation, ELISA, immunoblotting and qRT-PCR were performed for subsequent analysis.

KEY FINDINGS

Rats subjected to IRI displayed an increase in plasma ACE, AT1R, AT2R, Ang II, and reduction in ACE2, Ang-(1-7) expressions, with augmented renal inflammation and apoptosis. These changes were more prominent in diabetic rats with IRI. Co-administration of C21 and Dize augmented ACE2, Ang-(1-7), AT2R and MasR expressions, and attenuated tubular injury in both DM and ND rats.

CONCLUSION

We demonstrated that pharmacological activation of AT2R and ACE2 protects DM and ND rats from IRI by preventing oxidative stress, inflammation and apoptosis-mediated tubular damage.

Protocol for a prospective observational study on the association of variables obtained by contrast-enhanced ultrasonography and sepsis-associated acute kidney injury

INTRODUCTION

Sepsis commonly results in acute kidney injury (AKI), whereas about 50% of AKI cases are due to sepsis. Sepsis-associated acute kidney injury (SA-AKI) increases morbidity and mortality especially among critically ill patients. This study aims to monitor renal microcirculation perfusion during sepsis using contrast-enhanced ultrasonography (CEUS), and to explore whether CEUS is useful for predicting the development of SA-AKI.

METHODS AND ANALYSIS

This prospective observational study will enrol patients who were diagnosed with sepsis-3 definition. The total of septic or septic shock patients were stratified into AKI (including stages 1, 2 and 3) and non-AKI groups according to Kidney Disease Improving Global Outcomes criteria on days 0, 1, 2 and 7 after admission to the emergency intensive care unit, meanwhile, the CEUS technique will be performed to monitor renal microcirculation perfusion. A multivariable model including all CEUS variables were expected to create for predicting the development of AKI during sepsis. Ultrasonography results, demographic information, therapeutic interventions, survival outcomes, laboratory and other clinical datas will also be collected for further analysis.

ETHICS AND DISSEMINATION

The study protocol was approved on 2 August 2017 by the Ethics Committee of Sir Run Run Shaw Hospital (Zhejiang University Medical College) (approval number: 2016C91401). The results will be published in a peer-reviewed journal and shared with the worldwide medical community within 2 years after the start of the recruitment.

TRIAL REGISTRATION NUMBER

ISRCTN14728986.

Size and temporal-dependent efficacy of oltipraz-loaded PLGA nanoparticles for treatment of acute kidney injury and fibrosis

Acute kidney injury (AKI) is associated with high mortality and morbidity with no effective treatment available at present, which greatly escalates the risk of chronic kidney disease. Nanotechnology-based drug delivery for targeting renal tubules offers a new strategy for AKI treatment but remains challenging due to the glomerular filtration barrier. To tackle this challenge, here we demonstrate that poly (lactic-co-glycolic acid) (PLGA) nanoparticles (NPs) of 100 nm diameter could selectively accumulate in mouse injury kidneys in correlation to the degree of kidney injury and administration time during the initial phase of renal ischemia-reperfusion injury. The NPs were located in renal tubular epithelial cells confirmed by immunofluorescence, which is critical for the progression of AKI. Taking advantage of the high accumulation and renal tubule targeting of the PLGA NPs in the ischemia-reperfusion (IR) kidney, we designed PLGA NPs loaded with Oltipraz (PLGA-Oltipraz NPs) to treat IR-induced AKI and renal fibrosis. In vitro results showed that compared to free Oltipraz, PLGA-Oltipraz NPs displayed a higher antioxidation effect with improved cell viability, lower contents of malondialdehyde, and higher activity of superoxide dismutase. The therapeutic efficacy of PLGA-Oltipraz NPs was further investigated in vivo. Mice with AKI treated with PLGA-Oltipraz NPs exhibited significantly reduced tubular necrosis, less collagen deposition, and better renal function at the initial phase as well as improved renal fibrosis at the recovery phase. This study establishes a promising approach for AKI and fibrosis treatment with PLGA-Oltipraz NPs. It also reveals the importance of size-selective NPs and drug administration time window to nanotherpeutics.

Associations between tricuspid annular plane systolic excursion to reflect right ventricular function and acute kidney injury in critically ill patients: a SICS-I sub-study

BACKGROUND

Acute kidney injury (AKI) occurs in up to 50% of all critically ill patients and hemodynamic abnormalities are assumed to contribute, but their nature and share is still unclear. We explored the associations between hemodynamic variables, including cardiac index and right ventricular function, and the occurrence of AKI in critically ill patients.

METHODS

In this prospective cohort study, we included all patients acutely admitted to an intensive care unit (ICU). Within 24 h after ICU admission clinical and hemodynamic variables were registered including ultrasonographic measurements of cardiac index and right ventricular function, assessed using tricuspid annular plane systolic excursion (TAPSE) and right ventricular systolic excursion (RV S'). Maximum AKI stage was assessed according to the KDIGO criteria during the first 72 h after admission. Multivariable logistic regression modeling was used including both known predictors and univariable significant predictors of AKI. Secondary outcomes were days alive outside ICU and 90-day mortality.

RESULTS

A total of 622 patients were included, of which 338 patients (54%) had at least AKI stage 1 within 72 h after ICU admission. In the final multivariate model higher age (OR 1.01, 95% CI 1.00-1.03, for each year), higher weight (OR 1.03 CI 1.02-1.04, for each kg), higher APACHE IV score (OR 1.02, CI 1.01-1.03, per point), lower mean arterial pressure (OR 1.02, CI 1.01-1.03, for each mmHg decrease) and lower TAPSE (OR 1.05, CI 1.02-1.09 per millimeter decrease) were all independent predictors for AKI in the final multivariate logistic regression model. Sepsis, cardiac index, RV S' and use of vasopressors were not significantly associated with AKI in our data. AKI patients had fewer days alive outside of ICU, and their mortality rate was significantly higher than those without AKI.

CONCLUSIONS

In our cohort of acutely admitted ICU patients, the incidence of AKI was 54%. Hemodynamic variables were significantly different between patients with and without AKI. A worse right ventricle function was associated with AKI in the final model, whereas cardiac index was not.

ADAMTS13 protects mice against renal ischemia-reperfusion injury by reducing inflammation and improving endothelial function

Acute kidney injury (AKI) is a serious condition without efficient therapeutic options. Recent studies have indicated that recombinant human a disintegrin and metalloprotease with thrombospondin motifs 13 (rhADAMTS13) provides protection against inflammation. Therefore, we hypothesized that ADAMTS13 might protect against AKI by reducing inflammation. Bilateral renal ischemia-reperfusion injury (I/R) was used as AKI models in this study. Prophylactic infusion of rhADAMTS13 was employed to investigate potential mechanisms of renal protection. Renal function, inflammation, and microvascular endothelial function were assessed after 24 h of reperfusion. Our results showed that I/R mice increased plasma von Willebrand factor levels but decreased ADAMTS13 expression. Administration of rhADAMTS13 to I/R mice recovered renal function, histological injury, and apoptosis. Renal inflammation was reduced by rhADAMTS13, accompanied with the downregulation of p38/extracellular signal-regulated protein kinase phosphorylation and cyclooxygenase-2 expression. rhADAMTS13 restored vasodilation in afferent arterioles in I/R mice. Furthermore, rhADAMTS13 treatment enhanced phosphorylation of Akt at Ser473 and eNOS at Ser1177. Administration of the Akt pathway inhibitor wortmannin reduced the protective effect of rhADAMTS13. Our conclusions are that treatment with rhADAMTS13 ameliorates renal I/R injury by reducing inflammation, tubular cell apoptosis, and improving microvascular endothelial dysfunction. rhADAMTS13 could be a promising strategy to treat AKI in clinical settings.

Renal regeneration after acute kidney injury

Acute kidney injury is common and associated with negative renal and patient outcomes. The human kidney has a real but limited regeneration capacity. Understanding renal regeneration may allow us to manipulate this process and thus develop therapeutic weapons to improve patients' outcome. In the first part of this paper we discuss the clinical factors associated with renal recovery: baseline patient particularities, acute kidney injury characteristics and the medical approach taken in the short and long-term. In the second part, the cellular and molecular mechanisms underlying renal regeneration are explored. The immune system seems to have an important role, first promoting inflammation and then tissue healing. Other players, such as cellular senescence, mitochondrial dysfunction, renal haemodynamics and metabolic reprogramming also have a role in renal regeneration. We aim to develop a short review of renal regeneration, offering a holistic view of this process.

Microvascular rarefaction and hypertension in the impaired recovery and progression of kidney disease following AKI in preexisting CKD states

Acute kidney injury (AKI) is a major complication in hospitalized patients and is associated with elevated mortality rates. Numerous recent studies indicate that AKI also significantly increases the risk of chronic kidney disease (CKD), end-stage renal disease (ESRD), hypertension, cardiovascular disease, and mortality in those patients who survive AKI. Moreover, the risk of ESRD and mortality after AKI is substantially higher in patients with preexisting CKD. However, the underlying mechanisms by which AKI and CKD interact to promote ESRD remain poorly understood. The recently developed models that superimpose AKI on rodents with preexisting CKD have provided new insights into the pathogenic mechanisms mediating the deleterious interactions between AKI and CKD. These studies show that preexisting CKD impairs recovery from AKI and promotes the development of mechanisms of CKD progression. Specifically, preexisting CKD exacerbates microvascular rarefaction, failed tubular redifferentiation, disruption of cell cycle regulation, hypertension, and proteinuria after AKI. The purpose of this review is to discuss the potential mechanisms by which microvascular rarefaction and hypertension contribute to impaired recovery from AKI and the subsequent progression of renal disease in preexisting CKD states.

Renal failure in critically ill patients, beware of applying (central venous) pressure on the kidney

The central venous pressure (CVP) is traditionally used as a surrogate of intravascular volume. CVP measurements therefore are often applied at the bedside to guide fluid administration in postoperative and critically ill patients. Pursuing high CVP levels has recently been challenged. A high CVP might impede venous return to the heart and disturb microcirculatory blood flow which may cause tissue congestion and organ failure. By imposing an increased "afterload" on the kidney, an elevated CVP will particularly harm kidney hemodynamics and promote acute kidney injury (AKI) even in the absence of volume overload. Maintaining the lowest possible CVP should become routine to prevent and treat AKI, especially when associated with septic shock, cardiac surgery, mechanical ventilation, and intra-abdominal hypertension.

The angiotensin II/AT1 receptor pathway mediates malaria-induced acute kidney injury

Malaria-induced acute kidney injury (MAKI) is a life-threatening complication of severe malaria. Here, we investigated the potential role of the angiotensin II (Ang II)/AT1 receptor pathway in the development of MAKI. We used C57BL/6 mice infected by Plasmodium berghei ANKA (PbA-infected mice), a well-known murine model of severe malaria. The animals were treated with 20 mg/kg/day losartan, an antagonist of AT1 receptor, or captopril, an angiotensin-converting enzyme inhibitor. We observed an increase in the levels of plasma creatinine and blood urea nitrogen associated with a significant decrease in creatinine clearance, a marker of glomerular flow rate, and glomerular hypercellularity, indicating glomerular injury. PbA-infected mice also presented proteinuria and a high level of urinary γ-glutamyltransferase activity associated with an increase in collagen deposition and interstitial space, showing tubule-interstitial injury. PbA-infected mice were also found to have increased fractional excretion of sodium (FENa+) coupled with decreased cortical (Na++K+)ATPase activity. These injuries were associated with an increase in pro-inflammatory cytokines, such as tumor necrosis factor alpha, interleukin-6, interleukin-17, and interferon gamma, in the renal cortex of PbA-infected mice. All modifications of these structural, biochemical, and functional parameters observed in PbA-infected mice were avoided with simultaneous treatment with losartan or captopril. Our data allow us to postulate that the Ang II/AT1 receptor pathway mediates an increase in renal pro-inflammatory cytokines, which in turn leads to the glomerular and tubular injuries observed in MAKI.