Renal ischemic injury results in permanent damage to peritubular capillaries and influences long-term function

Inhibition of RIPK1 or RIPK3 kinase activity post ischemia-reperfusion reduces the development of chronic kidney injury

Ischemia-reperfusion injury (IRI) occurs when the blood supply to an organ is temporarily reduced and then restored. Kidney IRI is a form of acute kidney injury (AKI), which often progresses to kidney fibrosis. Necroptosis is a regulated necrosis pathway that has been implicated in kidney IRI. Necroptotic cell death involves the recruitment of the RIPK1 and RIPK3 kinases and the activation of the terminal effector, the mixed lineage kinase domain-like (MLKL) pseudokinase. Phosphorylated MLKL causes cell death by plasma membrane rupture, driving 'necroinflammation'. Owing to their apical role in the pathway, RIPK1 and RIPK3 have been implicated in the development of kidney fibrosis. Here, we used a mouse model of unilateral kidney IRI to assess whether the inhibition of RIPK1 or RIPK3 kinase activity reduces AKI and the progression to kidney fibrosis. Mice treated with the RIPK1 inhibitor Nec-1s, either before or after IR, showed reduced kidney injury at 24 hr compared with controls, whereas no protection was offered by the RIPK3 inhibitor GSK´872. In contrast, treatment with either inhibitor from days 3 to 9 post-IR reduced the degree of kidney fibrosis at day 28. These findings further support the role of necroptosis in IRI and provide important validation for the contribution of both RIPK1 and RIPK3 catalytic activities in the progression of kidney fibrosis. Targeting the necroptosis pathway could be a promising therapeutic strategy to mitigate kidney disease following IR.

Unraveling Ferroptosis: A New Frontier in Combating Renal Fibrosis and CKD Progression

Chronic kidney disease (CKD) is a global health concern caused by conditions such as hypertension, diabetes, hyperlipidemia, and chronic nephritis, leading to structural and functional kidney injury. Kidney fibrosis is a common outcome of CKD progression, with abnormal fatty acid oxidation (FAO) disrupting renal energy homeostasis and leading to functional impairments. This results in maladaptive repair mechanisms and the secretion of profibrotic factors, and exacerbates renal fibrosis. Understanding the molecular mechanisms of renal fibrosis is crucial for delaying CKD progression. Ferroptosis is a type of discovered an iron-dependent lipid peroxidation-regulated cell death. Notably, Ferroptosis contributes to tissue and organ fibrosis, which is correlated with the degree of renal fibrosis. This study aims to clarify the complex mechanisms of ferroptosis in renal parenchymal cells and explore how ferroptosis intervention may help alleviate renal fibrosis, particularly by addressing the gap in CKD mechanisms related to abnormal lipid metabolism under the ferroptosis context. The goal is to provide a new theoretical basis for clinically delaying CKD progression.

Role of mitochondria in reno-cardiac diseases: A study of bioenergetics, biogenesis, and GSH signaling in disease transition

Acute kidney injury (AKI) and chronic kidney disease (CKD) are global health burdens with rising prevalence. Their bidirectional relationship with cardiovascular dysfunction, manifesting as cardio-renal syndromes (CRS) types 3 and 4, underscores the interconnectedness and interdependence of these vital organ systems. Both the kidney and the heart are critically reliant on mitochondrial function. This organelle is currently recognized as a hub in signaling pathways, with emphasis on the redox regulation mediated by glutathione (GSH). Mitochondrial dysfunction, including impaired bioenergetics, redox, and biogenesis pathways, are central to the progression of AKI to CKD and the development of CRS type 3 and 4. This review delves into the metabolic reprogramming and mitochondrial redox signaling and biogenesis alterations in AKI, CKD, and CRS. We examine the pathophysiological mechanisms involving GSH redox signaling and the AMP-activated protein kinase (AMPK)-sirtuin (SIRT)1/3-peroxisome proliferator-activated receptor-gamma coactivator (PGC-1α) axis in these conditions. Additionally, we explore the therapeutic potential of GSH synthesis inducers in mitigating these mitochondrial dysfunctions, as well as their effects on inflammation and the progression of CKD and CRS types 3 and 4.

Alterations to peritubular capillary structure in a rat model of kidney interstitial fibrosis: Implications for oxygen diffusion

Fibrosis and loss of functional capillary surface area may contribute to renal tissue hypoxia in a range of kidney diseases. However, there is limited quantitative information on the impact of kidney disease on the barriers to oxygen diffusion from cortical peritubular capillaries (PTCs) to kidney epithelial tubules. Here, we used stereological methods to quantify changes in total cortical PTC length and surface area, PTC length and surface densities, and diffusion distances between PTCs and kidney tubules in adenine-induced kidney injury. After 7 days of oral gavage of adenine (100 mg), plasma creatinine was 3.5-fold greater than in vehicle-treated rats, while total kidney weight was 83% greater. The total length of PTCs was similar in adenine-treated (1.47 ± 0.23 km (mean ± standard deviation)) to vehicle-treated (1.24 ± 0.24 km) rats, as was the surface density of PTCs (0.025 ± 0.002 vs. 0.024 ± 0.004 μm2/μm3). The total surface area of PTCs was 69% greater in adenine-treated than vehicle-treated rats. However, the length density of PTCs was 28% less in adenine-treated than vehicle-treated rats. Diffusion distances, from PTCs to the basal membrane of the nearest renal tubule (108%), and to the mid-point of the cytoplasmic height of the nearest tubular epithelial cell (57%), were markedly increased. These findings indicate that, in adenine-induced kidney injury, expansion of the renal cortical interstitium increases the distance required for diffusion of oxygen from PTCs to tubules, rendering the kidney cortex susceptible to hypoxia.

Heme-induced loss of renovascular endothelial protein C receptor promotes chronic kidney disease in sickle mice

ABSTRACT

Chronic kidney disease (CKD) is a major contributor to morbidity and mortality in sickle cell disease (SCD). Anemia, induced by chronic persistent hemolysis, is associated with the progressive deterioration of renal health, resulting in CKD. Moreover, patients with SCD experience acute kidney injury (AKI), a risk factor for CKD, often during vaso-occlusive crisis associated with acute intravascular hemolysis. However, the mechanisms of hemolysis-driven pathogenesis of the AKI-to-CKD transition in SCD remain elusive. Here, we investigated the role of increased renovascular rarefaction and the resulting substantial loss of the vascular endothelial protein C receptor (EPCR) in the progressive deterioration of renal function in transgenic SCD mice. Multiple hemolytic events raised circulating levels of soluble EPCR (sEPCR), indicating loss of EPCR from the cell surface. Using bone marrow transplantation and super-resolution ultrasound imaging, we demonstrated that SCD mice overexpressing EPCR were protective against heme-induced CKD development. In a cohort of patients with SCD, plasma sEPCR was significantly higher in individuals with CKD than in those without CKD. This study concludes that multiple hemolytic events may trigger CKD in SCD through the gradual loss of renovascular EPCR. Thus, the restoration of EPCR may be a therapeutic target, and plasma sEPCR can be developed as a prognostic marker for sickle CKD.

Adverse effects of acute tubular injury on the glomerulus: contributing factors and mechanisms

The intricate relationship between tubular injury and glomerular dysfunction in kidney diseases has been a subject of extensive research. While the impact of glomerular injury on downstream tubules has been well-studied, the reverse influence of tubular injury on the glomerulus remains less explored. This paper provides a comprehensive review of recent advances in the field, focusing on key pathways and players implicated in the pathogenesis of tubular injury on glomerular dysfunction. Anatomical and physiological evidence supports the possibility of crosstalk from the tubule to the glomerulus, whereby various mechanisms contribute to glomerular injury following tubular injury. These mechanisms include tubular backleak, dysfunctional tubuloglomerular feedback, capillary rarefaction, atubular glomeruli, and the secretion of factors from damaged tubular epithelial cells. Clinical evidence further supports the association between even mild or recovered acute kidney injury and an increased risk of chronic kidney disease, including glomerular diseases. We also discuss potential therapeutic interventions aimed at mitigating acute tubular injury, thereby reducing the detrimental effects on glomerular function. By unraveling the complex interplay from tubular injury to glomerular dysfunction, we aim to provide insights that can enhance clinical management strategies and improve outcomes for patients with kidney disease.

Impact of a Single Dose of Alpha-1-Antitrypsin in a Rat Model of Bilateral Kidney Ischemia Reperfusion Injury

INTRODUCTION

Renal ischemia reperfusion injury is a major cause of perioperative acute kidney injury. Alpha-1-antitrypsin (AAT), a protease inhibitor, might improve outcomes by reducing inflammation and apoptosis. We investigated the effects of a single intravenous dose of AAT immediately before ischemia in a rat bilateral renal clamping model.

METHODS

Both renal pedicles of male Sprague-Dawley rats were clamped (45 min). Plasma and renal tissue were collected at 3 h, 24 h, and 7 d. Intravenous AAT (60 mg/kg) was administered 5 min before clamping. Controls received saline. Shams underwent surgery without clamping or injection. Kidney function was assessed by plasma creatinine; injury by aspartate aminotransferase, heart-type-fatty-acid-binding-protein, and histopathology. Renal gene expression of tumor necrosis factor α, interleukin (IL)-6, heat shock protein 70, Chemokine (C-X-C motif) ligand 2, cyclo-oxygenase 2, endothelin-1, IL-10, heme oxygenase 1, B-cell lymphoma 2, and bcl-2-like protein 4 were determined by quantitative reverse transcriptase polymerase chain reaction.

RESULTS

None of the 3 h and 24 h end points were different between Control and AAT. In Sham, survival was 100% (6/6), 33% in Control (2/6), and 83% (5/6) in AAT (overall log-rank 0.03). At 7 d, plasma creatinine was lower with higher glomerular filtration rate in surviving AAT treated animals compared to Control (P < 0.001, P 0.03, respectively). These also had lower tumor necrosis factor α and IL-6 gene expression (P 0.001, P < 0.001, respectively).

CONCLUSIONS

These data suggest that a single intravenous dose of AAT immediately before ischemia might affect proinflammatory gene expression, glomerular filtration rate and animal survival at 1 wk after reperfusion despite an absence of improvement in early renal function and injury. These findings deserve further investigating in sufficiently powered studies including both sexes.

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

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

miR-486-5p protects against rat ischemic kidney injury and prevents the transition to chronic kidney disease and vascular dysfunction

AIM

Acute kidney injury (AKI) increases the risk for progressive chronic kidney disease (CKD). MicroRNA (miR)-486-5p protects against kidney ischemia-reperfusion (IR) injury in mice, although its long-term effects on the vasculature and development of CKD are unknown. We studied whether miR-486-5p would prevent the AKI to CKD transition in rat, and affect vascular function.

METHODS

Adult male rats were subjected to bilateral kidney IR followed by i.v. injection of liposomal-packaged miR-486-5p (0.5 mg/kg). Kidney function and histologic injury were assessed after 24 h and 10 weeks. Kidney endothelial protein levels were measured by immunoblot and immunofluorescence, and mesenteric artery reactivity was determined by wire myography.

RESULTS

In rats with IR, miR-486-5p blocked kidney endothelial cell increases in intercellular adhesion molecule-1 (ICAM-1), reduced neutrophil infiltration and histologic injury, and normalized plasma creatinine (P<0.001). However, miR-486-5p attenuated IR-induced kidney endothelial nitric oxide synthase (eNOS) expression (P<0.05). At 10 weeks, kidneys from rats with IR alone had decreased peritubular capillary density and increased interstitial collagen deposition (P<0.0001), and mesenteric arteries showed impaired endothelium-dependent vasorelaxation (P<0.001). These changes were inhibited by miR-486-5p. Delayed miR-486-5p administration (96 h, 3 weeks after IR) had no impact on kidney fibrosis, capillary density, or endothelial function.

CONCLUSION

In rats, administration of miR-486-5p early after kidney IR prevents injury, and protects against CKD development and systemic endothelial dysfunction. These protective effects are associated with inhibition of endothelial ICAM-1 and occur despite reduction in eNOS. miR-486-5p holds promise for the prevention of ischemic AKI and its complications.

Preoperative fasting glucose value can predict acute kidney injury in non-cardiac surgical patients without diabetes but not in patients with diabetes

BACKGROUND

Postoperative acute kidney injury (AKI) is a common and costly complication after non-cardiac surgery. Patients with or without diabetes could develop hyperglycemia before surgery, and preoperative hyperglycemia was closely associated with postoperative poor outcomes, but the association between preoperative fasting blood glucose level and postoperative AKI is still unclear.

METHODS

Data from patients undergoing non-cardiac surgery in Chongqing University Cancer Hospital from January 1, 2017, to May 31, 2023, were collected, preoperative glucose value and perioperative variables were extracted, the primary exposure of interest was preoperative glucose value, and the outcome was postoperative AKI.

RESULTS

Data from 39,986 patients were included in the final analysis, 741(1.9%) patients developed AKI, 134(5.6%) in the cohort with DM, and 607(1.6%) in the cohort without DM(OR 1.312, 95% CI 1.028-1.675, P = 0.029). A significant non-linear association between preoperative glucose and AKI exists in the cohort without DM after covariable adjustment (P = 0.000), and every 1 mmol/L increment of preoperative glucose level increased OR by 15% (adjusted OR 1.150, 95% CI 1.078-1.227, P = 0.000), the optimal cut-point of preoperative fasting glucose level to predict AKI was 5.39 mmol/L (adjusted OR 1.802, 95%CI 1.513-2.146, P = 0.000). However, in the cohort with DM, the relation between preoperative glucose and postoperative AKI was not significant after adjusting by covariables (P = 0.437). No significance exists between both cohorts in the risk of AKI over the range of preoperative glucose values.

CONCLUSION

A preoperative fasting glucose value of 5.39 mmol/L can predict postoperative acute kidney injury after non-cardiac surgery in patients without diagnosed diabetes, but it is not related to AKI in patients with the diagnosis.

Serum Nostrin-A risk factor of death, kidney replacement therapy and acute kidney disease in acute kidney injury

BACKGROUND

The prediction of Acute Kidney Injury (AKI)-related outcomes remains challenging. Persistent kidney excretory dysfunction for longer than 7 days has been defined as Acute Kidney Disease (AKD). In this study, we prospectively quantified serum Nostrin, an essential regulator of endothelial NO metabolism, in hospitalized patients with AKI.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

In-hospital subjects with AKI of various etiology were identified through the in-hospital AKI alert system of the Brandenburg University Hospital. Serum Nostrin, and serum NGAL and KIM-1 were measured within a maximum of 48 hours from the timepoint of initial diagnosis of AKI. The following endpoints were defined: in-hospital death, need of kidney replacement therapy (KRT), recovery of kidney function (ROKF) until discharge.

RESULTS

AKI patients had significantly higher serum Nostrin levels compared to Controls. The level of serum Nostrin increased significantly with the severity of AKI. Within the group of AKI patients (n = 150) the in-hospital mortality was 16.7%, KRT was performed in 39.3%, no ROKF occurred in 28%. Patients who required KRT had significantly higher levels of serum Nostrin compared to patients who did not require KRT. Significantly higher levels of serum Nostrin were also detected in AKI patients without ROKF compared to patients with ROKF. In addition, low serum Nostrin levels at the timepoint of AKI diagnosis were predictive of in-hospital survival. For comparison, the serum concentrations of NGAL and KIM-1 were determined in parallel to the Nostrin concentrations and the results confirm the prognostic properties of serum Nostrin in AKI.

CONCLUSIONS

The current study suggests serum Nostrin as novel biomarker of AKI-associated mortality, KRT and Acute Kidney Disease.

Effects of Beraprost with or without NOS Inhibition on Plasma Aldosterone and Hemodynamics in Healthy Cats

OBJECTIVES

The aim of the study was to evaluate the hemodynamic and RA system effects of the oral administration of the clinical dose of beraprost for feline CKD in healthy cats, and also to examine whether NOS inhibition reversed them.

METHODS

A placebo-controlled pharmacological sequential design study was carried out to assess the plasma aldosterone and renin concentrations (PAC and PRC), blood pressure, heart rate, and exploratorily to estimate renal plasma flow (RPF) and renal vascular resistance (RVR) with simplified methods.

RESULTS

Beraprost reduced PAC when compared to the placebo (p < 0.05); this was reversed when NOS inhibitor NG-nitro-L-arginine methyl ester (L-NAME) was added to the beraprost treatment (p < 0.01). No differences in the PRC or hemodynamic parameters were detected between beraprost and the placebo. The correlation ratios (η2) showed opposite relationships between beraprost and the added L-NAME effects on PAC, mean blood pressure (MBP), heart rate, estimated RPF (p < 0.001), estimated RVR (p < 0.01), and PRC (p < 0.05).

CONCLUSIONS

In healthy cats, the clinical dose of beraprost suppresses PAC, which can be reversed by the inhibition of NOS.

Specific knockout of macrophage SHP2 promotes macrophage M2 polarization and alleviates renal ischemia-reperfusion injury

To investigate the effect of specific knockout of SHP2 in mononuclear macrophages on renal ischemia-reperfusion injury and its molecular mechanism. The structural, functional, and pathological changes in the mouse kidney were detected by ultrasound testing. The relative fluorescence intensity of α-SMA, Col1, Col3, and Vim was measured by immunofluorescence staining, and ELISA was performed to detect the concentrations of blood urea nitrogen (BUN), creatinine (Crea), and uric acid (UA). The relative protein expressions of relevant proteins in the mouse kidney tissue were detected by western blotting. Specific knockout of SHP2 could improve both renal function and structure, reduce the relative fluorescence intensity of α-SMA, Col1, Col3 and Vim, lower the concentrations of BUN, Crea, and UA and the expressions of TNF-α, IFNγ, p-NFκB, and p-MyD88, and increase the expressions of p-MerTK, p-FAK, p-PI3K, and p-IκB. The above results illustrate that specific knockdown of macrophage SHP2 promotes macrophage M2 polarization and alleviates renal ischemia-reperfusion injury. The above results illustrate that specific knockdown of macrophage SHP2 promotes macrophage M2 polarization and attenuatesll renal ischemia-reperfusion injury. Specific knockout of macrophage SHP2 promotes macrophage M2 polarization and alleviates renal ischemia-reperfusion injury.

Mitochondrial Signaling, the Mechanisms of AKI-to-CKD Transition and Potential Treatment Targets

Acute kidney injury (AKI) is increasing in prevalence and causes a global health burden. AKI is associated with significant mortality and can subsequently develop into chronic kidney disease (CKD). The kidney is one of the most energy-demanding organs in the human body and has a role in active solute transport, maintenance of electrochemical gradients, and regulation of fluid balance. Renal proximal tubular cells (PTCs) are the primary segment to reabsorb and secrete various solutes and take part in AKI initiation. Mitochondria, which are enriched in PTCs, are the main source of adenosine triphosphate (ATP) in cells as generated through oxidative phosphorylation. Mitochondrial dysfunction may result in reactive oxygen species (ROS) production, impaired biogenesis, oxidative stress multiplication, and ultimately leading to cell death. Even though mitochondrial damage and malfunction have been observed in both human kidney disease and animal models of AKI and CKD, the mechanism of mitochondrial signaling in PTC for AKI-to-CKD transition remains unknown. We review the recent findings of the development of AKI-to-CKD transition with a focus on mitochondrial disorders in PTCs. We propose that mitochondrial signaling is a key mechanism of the progression of AKI to CKD and potential targeting for treatment.

Effects of Low-Osmolar Contrast Media on Long-Term Renal Impairment After Coronary Angiography: Iohexol Versus Iopromide

To investigate the long-term effects of 2 commonly used low-osmolar contrast media, iohexol and iopromide, on renal function and survival in patients who underwent coronary angiography. A total of 14,141 cardiology patients from 2006 to 2013 were recruited, of whom 1,793 patients (679 patients on iohexol and 1,114 on iopromide) were evaluated for long-term renal impairment and 5,410 patients (1,679 patients on iohexol and 3,731 on iopromide) were admitted for survival analyses spanning as long as 15 years. Univariate and multivariate logistic regression were used to explore the risk factors for long-term renal impairment. Cox proportional hazard regression was used to investigate the risk factors affecting survival. Propensity score matching and inverse probability of treatment weighting were applied to balance the baseline clinical characteristics. Patients receiving iohexol demonstrated a greater occurrence of renal impairment compared with those who received iopromide. Such difference remained consistent both before and after propensity score matching or inverse probability of treatment weighting, with a statistical significance of p <0.05. Among clinical variables, receiving contrast-enhanced contrast tomography/magnetic resonance imaging during follow-up, antihypertensive medication usage, presence of proteinuria, and anemia were identified as risk factors for long-term renal impairment (p = 0.041, 0.049, 0.006, and 0.029, respectively). During survival analyses, the difference was insignificant after propensity score matching and inverse probability of treatment weighting. In conclusion, administration of iohexol was more likely to induce long-term renal impairment than iopromide, particularly among patients diagnosed with anemia and proteinuria and those taking antihypertensive medication and with additional contrast exposure. The all-cause mortality, however, showed no significant difference between iohexol and iopromide administration.

A gradient model of renal ischemia reperfusion injury to investigate renal interstitial fibrosis

Background: The progression from acute kidney injury to chronic kidney disease poses a significant health challenge. Nonetheless, a constraint in existing animal models of renal ischemia/reperfusion (I/R) injury is the necessity for a severe injury, almost reaching a life-threatening level, to trigger the subsequent onset of renal fibrosis. Hence, we explored an adapted gradient approach to induce I/R injury, aiming to promote the progression of renal fibrosis while preserving the overall normal functioning of the kidney. Methods: In each group, 6-8 male C57BL/6 mice were used for model construction, with all undergoing sodium pentobarbital anesthesia and left kidney removal. Subsequently, a silk thread was passed beneath the lower renal branch, elevating the right kidney under a 20-g weight's tension via a pulley system for durations of 30, 40, or 60 min. Afterwards, we lowered the kidney, sutured the wound, and administered intraperitoneal saline. Mice in different groups were euthanized following reperfusion for 1, 3, 7, or 28 days. Results: We observed a complete cessation of blood flow in the lower pole, while an incomplete cessation in the upper pole in the elevated kidney. Significant renal impairment was evident on day 1 with a 60min ischemic period (187.0 ± 65.3 vs 17.9 ± 4.8 μmol/L serum creatinine in normal; p < .001), but not with 30 or 40min. On day 1, tubular necrosis and hyaline cast formation was evident in both lower and upper poles. On day 3, renal function returned to normal and remained normal through day 28. Histologic damage resolved in the upper pole over days 3 to 7, resulting in normal histology on day 28. By contrast, there was sustained tubular damage tubular in the lower pole on days 3 and 7, which failed to resolve and led to significant renal fibrosis by day 28. Conclusion: We created a model demonstrating clinically "silent" renal fibrosis.

Reconfiguration and loss of peritubular capillaries in chronic kidney disease

Functional and structural alterations of peritubular capillaries (PTCs) are a major determinant of chronic kidney disease (CKD). Using a software-based algorithm for semiautomatic segmentation and morphometric quantification, this study analyzes alterations of PTC shape associated with chronic tubulointerstitial injury in three mouse models and in human biopsies. In normal kidney tissue PTC shape was predominantly elongated, whereas the majority of PTCs associated with chronic tubulointerstitial injury had a rounder shape. This was reflected by significantly reduced PTC luminal area, perimeter and diameters as well as by significantly increased circularity and roundness. These morphological alterations were consistent in all mouse models and human kidney biopsies. The mean circularity of PTCs correlated significantly with categorized glomerular filtration rates and the degree of interstitial fibrosis and tubular atrophy (IFTA) and classified the presence of CKD or IFTA. 3D reconstruction of renal capillaries revealed not only a significant reduction, but more importantly a substantial simplification and reconfiguration of the renal microvasculature in mice with chronic tubulointerstitial injury. Computational modelling predicted that round PTCs can deliver oxygen more homogeneously to the surrounding tissue. Our findings indicate that alterations of PTC shape represent a common and uniform reaction to chronic tubulointerstitial injury independent of the underlying kidney disease.

The AKI-to-CKD Transition: The Role of Uremic Toxins

After acute kidney injury (AKI), renal function continues to deteriorate in some patients. In a pro-inflammatory and profibrotic environment, the proximal tubules are subject to maladaptive repair. In the AKI-to-CKD transition, impaired recovery from AKI reduces tubular and glomerular filtration and leads to chronic kidney disease (CKD). Reduced kidney secretion capacity is characterized by the plasma accumulation of biologically active molecules, referred to as uremic toxins (UTs). These toxins have a role in the development of neurological, cardiovascular, bone, and renal complications of CKD. However, UTs might also cause CKD as well as be the consequence. Recent studies have shown that these molecules accumulate early in AKI and contribute to the establishment of this pro-inflammatory and profibrotic environment in the kidney. The objective of the present work was to review the mechanisms of UT toxicity that potentially contribute to the AKI-to-CKD transition in each renal compartment.

Dynamics of necroptosis in kidney ischemia-reperfusion injury

Necroptosis, a pathway of regulated necrosis, involves recruitment and activation of RIPK1, RIPK3 and MLKL, leading to cell membrane rupture, cell death and release of intracellular contents causing further injury and inflammation. Necroptosis is believed to play an important role in the pathogenesis of kidney ischemia-reperfusion injury (IRI). However, the dynamics of necroptosis in kidney IRI is poorly understood, in part due to difficulties in detecting phosphorylated MLKL (pMLKL), the executioner of the necroptosis pathway. Here, we investigated the temporal and spatial activation of necroptosis in a mouse model of unilateral warm kidney IRI, using a robust method to stain pMLKL. We identified the period 3-12 hrs after reperfusion as a critical phase for the activation of necroptosis in proximal tubular cells. After 12 hrs, the predominant pattern of pMLKL staining shifted from cytoplasmic to membrane, indicating progression to the terminal phase of necroptotic cell death. Mlkl-ko mice exhibited reduced kidney inflammation at 12 hrs and lower serum creatinine and tubular injury at 24 hrs compared to wild-type littermates. Interestingly, we observed increased apoptosis in the injured kidneys of Mlkl-ko mice, suggesting a relationship between necroptosis and apoptosis in kidney IRI. Together, our findings confirm the role of necroptosis and necroinflammation in kidney IRI, and identify the first 3 hrs following reperfusion as a potential window for targeted treatments.

Association between fibrosis-related gene polymorphism and long-term allograft outcome in renal transplant recipients

BACKGROUND

Renal allograft fibrosis is one of characteristic causes of long-term renal function loss. The purpose of our study is to investigate the association between fibrosis-related genes single nucleotide polymorphism (SNPs) and kidney function in 5 years after kidney transplantation.

METHODS

A total of 143 recipients were eligible for screening with 5-year follow-up information and SNP sequencing information from blood samples were included in this study. Minor Allele Frequency (MAF) and Hardy-Weinberg Equilibrium (HWE) analysis was conducted to identify tagger single-nucleotide polymorphisms (SNPs) and haplotypes. SNPs associated with the fifth year chronic kidney disease (CKD) staging were screened by SPSS and the "SNPassoc" package in RStudio and used for subsequent prediction model construction.

RESULTS

A total of 275 renal transplant-related SNPs identified after target sequencing analysis. 64 Tagger SNPs were selected, and two SNPs (rs13969 and rs243849) were statistically significant for stage of CKD in 5 years. Finally, a model based on Gender, Age, rs1396, and rs243849 was constructed by multivariate linear regression analysis. Additionally, this model has a good performance in predicting uremia five years after kidney transplantation.

CONCLUSION

Two SNPs (rs13969 and rs243849) were identified to be significantly associated with long-term renal allograft function. Based on this, a prediction model for long-term allograft function was established containing Gender, Age, rs1396, and rs243849. However, an independent cohort should be enrolled to validate the predicting performance.

Anemia and Hypoxia Impact on Chronic Kidney Disease Onset and Progression: Review and Updates

Chronic kidney disease (CKD) is caused by hypoxia in the renal tissue, leading to inflammation and increased migration of pathogenic cells. Studies showed that leukocytes directly sense hypoxia and respond by initiating gene transcription, encoding the 2-integrin adhesion molecules. Moreover, other mechanisms participate in hypoxia, including anemia. CKD-associated anemia is common, which induces and worsens hypoxia, contributing to CKD progression. Anemia correction can slow CKD progression, but it should be cautiously approached. In this comprehensive review, the underlying pathophysiology mechanisms and the impact of renal tissue hypoxia and anemia in CKD onset and progression will be reviewed and discussed in detail. Searching for the latest updates in PubMed Central, Medline, PubMed database, Google Scholar, and Google search engines were conducted for original studies, including cross-sectional studies, cohort studies, clinical trials, and review articles using different keywords, phrases, and texts such as "CKD progression, anemia in CKD, CKD, anemia effect on CKD progression, anemia effect on CKD progression, and hypoxia and CKD progression". Kidney tissue hypoxia and anemia have an impact on CKD onset and progression. Hypoxia causes nephron cell death, enhancing fibrosis by increasing interstitium protein deposition, inflammatory cell activation, and apoptosis. Severe anemia correction improves life quality and may delay CKD progression. Detection and avoidance of the risk factors of hypoxia prevent recurrent acute kidney injury (AKI) and reduce the CKD rate. A better understanding of kidney hypoxia would prevent AKI and CKD and lead to new therapeutic strategies.

Tubulovascular protection from protease-activated receptor-1 depletion during AKI-to-CKD transition

BACKGROUND

Thromboembolic events are prevalent in chronic kidney disease (CKD) patients due to increased thrombin generation leading to a hypercoagulable state. We previously demonstrated that inhibition of protease-activated receptor-1 (PAR-1) by vorapaxar reduces kidney fibrosis.

METHODS

We used an animal model of unilateral ischemia-reperfusion injury-induced CKD to explore the tubulovascular crosstalk mechanisms of PAR-1 in acute kidney injury (AKI)-to-CKD transition.

RESULTS

During the early phase of AKI, PAR-1-deficient mice exhibited reduced kidney inflammation, vascular injury, and preserved endothelial integrity and capillary permeability. During the transition phase to CKD, PAR-1 deficiency preserved kidney function and diminished tubulointerstitial fibrosis via downregulated transforming growth factor-β/Smad signaling. Maladaptive repair in the microvasculature after AKI further exacerbated focal hypoxia with capillary rarefaction, which was rescued by stabilization of hypoxia-inducible factor and increased tubular vascular endothelial growth factor A in PAR-1-deficient mice. Chronic inflammation was also prevented with reduced kidney infiltration by both M1- and M2-polarized macrophages. In thrombin-induced human dermal microvascular endothelial cells (HDMECs), PAR-1 mediated vascular injury through activation of NF-κB and ERK MAPK pathways. Gene silencing of PAR-1 exerted microvascular protection via a tubulovascular crosstalk mechanism during hypoxia in HDMECs. Finally, pharmacologic blockade of PAR-1 with vorapaxar improved kidney morphology, promoted vascular regenerative capacity, and reduced inflammation and fibrosis depending on the time of initiation.

CONCLUSIONS

Our findings elucidate a detrimental role of PAR-1 in vascular dysfunction and profibrotic responses upon tissue injury during AKI-to-CKD transition and provide an attractive therapeutic strategy for post-injury repair in AKI.

Precision management of acute kidney injury in the intensive care unit: current state of the art

Acute kidney injury (AKI) is a prototypical example of a common syndrome in critical illness defined by consensus. The consensus definition for AKI, traditionally defined using only serum creatinine and urine output, was needed to standardize the description for epidemiology and to harmonize eligibility for clinical trials. However, AKI is not a simple disease, but rather a complex and multi-factorial syndrome characterized by a wide spectrum of pathobiology. AKI is now recognized to be comprised of numerous sub-phenotypes that can be discriminated through shared features such as etiology, prognosis, or common pathobiological mechanisms of injury and damage. The characterization of sub-phenotypes can serve to enable prognostic enrichment (i.e., identify subsets of patients more likely to share an outcome of interest) and predictive enrichment (identify subsets of patients more likely to respond favorably to a given therapy). Existing and emerging biomarkers will aid in discriminating sub-phenotypes of AKI, facilitate expansion of diagnostic criteria, and be leveraged to realize personalized approaches to management, particularly for recognizing treatment-responsive mechanisms (i.e., endotypes) and targets for intervention (i.e., treatable traits). Specific biomarkers (e.g., serum renin; olfactomedin 4 (OLFM4); interleukin (IL)-9) may further enable identification of pathobiological mechanisms to serve as treatment targets. However, even non-specific biomarkers of kidney injury (e.g., neutrophil gelatinase-associated lipocalin, NGAL; [tissue inhibitor of metalloproteinases 2, TIMP2]·[insulin like growth factor binding protein 7, IGFBP7]; kidney injury molecule 1, KIM-1) can direct greater precision management for specific sub-phenotypes of AKI. This review will summarize these evolving concepts and recent innovations in precision medicine approaches to the syndrome of AKI in critical illness, along with providing examples of how they can be leveraged to guide patient care.

Recovery after AKI: Effects on outcomes over 15 years

PURPOSE

To examine the effect of kidney recovery on mortality, dialysis and kidney transplantation up to 15 years after AKI.

MATERIALS AND METHODS

We studied 29,726 survivors of critical illness and compared these outcomes stratified by AKI and recovery status at hospital discharge. Kidney recovery was defined as a return of serum creatinine to ≤150% of baseline without dialysis prior to hospital discharge.

RESULTS

Overall AKI occurred in 59.2% in which two thirds developed stage 2-3 AKI. Recovery rate of AKI at hospital discharge was 80.8%. Patients who did not recover experienced the worst 15-year mortality compared to those who recovered and those without AKI (57.8% vs 45.2% vs 30.3%, p < 0.001). This pattern was also found in subgroups of patients with suspected sepsis-associated (57.1% vs 47.9% vs 36.5%, p < 0.001) and cardiac surgery-associated AKI (60.1% vs 41.8% vs 25.9%, p < 0.001). The rates of dialysis and transplantation at 15 years were low and not associated with recovery status.

CONCLUSIONS

Recovery of AKI in critically ill patients at hospital discharge had an effect on long-term mortality for up to 15 years. These results have implications for acute care, follow-up and choice of endpoints for clinical trials.

Longitudinal tracking of acute kidney injury reveals injury propagation along the nephron

Acute kidney injury (AKI) is an important risk factor for chronic kidney disease (CKD), but the underlying mechanisms of failed tubule repair and AKI-CKD transition are incompletely understood. In this study, we aimed for dynamic tracking of tubule injury and remodeling to understand if focal injury upon AKI may spread over time. Here, we present a model of AKI, in which we rendered only half of the kidney ischemic. Using serial intravital 2-photon microscopy and genetic identification of cycling cells, we tracked dynamic tissue remodeling in post- and non-ischemic kidney regions simultaneously and over 3 weeks. Spatial and temporal analysis of cycling cells relative to initial necrotic cell death demonstrated pronounced injury propagation and expansion into non-necrotic tissue regions, which predicted tubule atrophy with epithelial VCAM1 expression. In summary, our longitudinal analyses of tubule injury, remodeling, and fate provide important insights into AKI pathology.

Traumatic injuries to the renal blood vessels and in-hospital renal complications in patients with penetrating or blunt trauma

Background

Traumatic injuries to renal blood vessels (IRBV) can have significant consequences for patients, impacting their mortality, morbidity, and quality of life.

Objective

This study aimed to compare trauma types and injury characteristics, vital signs, and outcomes in patients with and without IRBV (nIRBV) and examine whether IRBV and pre-existing renal dysfunction affected the likelihood of in-hospital renal complications (iHRC).

Materials and Methods

After identifying penetrating and blunt trauma victims with IRBV in the National Trauma Data Bank, patient demographics, injury-related variables, treatment outcomes, and deaths under care were analyzed and compared.

Results

Of the 994,184 trauma victims, 610 (0.6%) experienced IRBV. Victims in the IRBV group (IRBVG) had a significantly higher frequency of penetrating injuries (19.5% vs. 9.2%, P < 0.001) and higher injury severity score (ISS ≥25, 61.5% vs. 6.7%). Most injuries in both groups were unintentional, although a higher frequency of assault was noted in the IRBVG. The incidence of iHRC was higher in the IRBVG (6.6%) than in the nIRBVG (0.4%; P < 0.001). The IRBV {OR = 3.5 [95% CI = (2.4-5.0)]}, preexisting renal disorders {OR = 2.5 [95% CI = (2.1-2.9)]}, and in-hospital cardiac arrest {OR = 8.6 [95% CI = (7.7-9.5)]} were found to be among the factors associated with a higher risk of iHRC.

Conclusions

IRBV and pre-existing renal disorders considerably increased the risk of developing iHRC. Due to the long- and short-term consequences of associated cardiovascular, renal, and hemodynamic complications, victims of IRBV require specialized renal management and close monitoring.

Long-Term Effects of Severe Burns on the Kidneys: Research Advances and Potential Therapeutic Approaches

Burns are a seriously underestimated form of trauma that not only damage the skin system but also cause various complications, such as acute kidney injury (AKI). Recent clinical studies have shown that the proportion of chronic kidney diseases (CKD) in burn patients after discharge is significantly higher than that in the general population, but the mechanism behind this is controversial. The traditional view is that CKD is associated with hypoperfusion, AKI, sepsis, and drugs administered in the early stages of burns. However, recent studies have shown that burns can cause long-term immune dysfunction, which is a high-risk factor for CKD. This suggests that burns affect the kidneys more than previously recognized. In other words, severe burns are not only an acute injury but also a chronic disease. Neglecting to study long-term kidney function in burn patients also results in a lack of preventive and therapeutic methods being developed. Furthermore, stem cells and their exosomes have shown excellent comprehensive therapeutic properties in the prevention and treatment of CKD, making them increasingly the focus of research attention. Their engineering strategy further improved the therapeutic performance. This review will focus on the research advances in burns on the development of CKD, illustrating the possible mechanism of burn-induced CKD and introducing potential biological treatment options and their engineering strategies.

High-throughput image analysis with deep learning captures heterogeneity and spatial relationships after kidney injury

Recovery from acute kidney injury can vary widely in patients and in animal models. Immunofluorescence staining can provide spatial information about heterogeneous injury responses, but often only a fraction of stained tissue is analyzed. Deep learning can expand analysis to larger areas and sample numbers by substituting for time-intensive manual or semi-automated quantification techniques. Here we report one approach to leverage deep learning tools to quantify heterogenous responses to kidney injury that can be deployed without specialized equipment or programming expertise. We first demonstrated that deep learning models generated from small training sets accurately identified a range of stains and structures with performance similar to that of trained human observers. We then showed this approach accurately tracks the evolution of folic acid induced kidney injury in mice and highlights spatially clustered tubules that fail to repair. We then demonstrated that this approach captures the variation in recovery across a robust sample of kidneys after ischemic injury. Finally, we showed markers of failed repair after ischemic injury were correlated both spatially within and between animals and that failed repair was inversely correlated with peritubular capillary density. Combined, we demonstrate the utility and versatility of our approach to capture spatially heterogenous responses to kidney injury.

Lineage Tracing and Single-Nucleus Multiomics Reveal Novel Features of Adaptive and Maladaptive Repair after Acute Kidney Injury

SIGNIFICANCE STATEMENT

Understanding the mechanisms underlying adaptive and maladaptive renal repair after AKI and their long-term consequences is critical to kidney health. The authors used lineage tracing of cycling cells and single-nucleus multiomics (profiling transcriptome and chromatin accessibility) after AKI. They demonstrated that AKI triggers a cell-cycle response in most epithelial and nonepithelial kidney cell types. They also showed that maladaptive proinflammatory proximal tubule cells (PTCs) persist until 6 months post-AKI, although they decreased in abundance over time, in part, through cell death. Single-nucleus multiomics of lineage-traced cells revealed regulatory features of adaptive and maladaptive repair. These included activation of cell state-specific transcription factors and cis-regulatory elements, and effects in PTCs even after adaptive repair, weeks after the injury event.

BACKGROUND

AKI triggers a proliferative response as part of an intrinsic cellular repair program, which can lead to adaptive renal repair, restoring kidney structure and function, or maladaptive repair with the persistence of injured proximal tubule cells (PTCs) and an altered kidney structure. However, the cellular and molecular understanding of these repair programs is limited.

METHODS

To examine chromatin and transcriptional responses in the same cell upon ischemia-reperfusion injury (IRI), we combined genetic fate mapping of cycling ( Ki67+ ) cells labeled early after IRI with single-nucleus multiomics-profiling transcriptome and chromatin accessibility in the same nucleus-and generated a dataset of 83,315 nuclei.

RESULTS

AKI triggered a broad cell cycle response preceded by cell type-specific and global transcriptional changes in the nephron, the collecting and vascular systems, and stromal and immune cell types. We observed a heterogeneous population of maladaptive PTCs throughout proximal tubule segments 6 months post-AKI, with a marked loss of maladaptive cells from 4 weeks to 6 months. Gene expression and chromatin accessibility profiling in the same nuclei highlighted differences between adaptive and maladaptive PTCs in the activity of cis-regulatory elements and transcription factors, accompanied by corresponding changes in target gene expression. Adaptive repair was associated with reduced expression of genes encoding transmembrane transport proteins essential to kidney function.

CONCLUSIONS

Analysis of genome organization and gene activity with single-cell resolution using lineage tracing and single-nucleus multiomics offers new insight into the regulation of renal injury repair. Weeks to months after mild-to-moderate IRI, maladaptive PTCs persist with an aberrant epigenetic landscape, and PTCs exhibit an altered transcriptional profile even following adaptive repair.

Long-term outcomes after severe acute kidney injury in critically ill patients: the SALTO study

BACKGROUND

The extent of the consequences of an episode of severe acute kidney injury (AKI) on long-term outcome of critically ill patients remain debated. We conducted a prospective follow-up of patients included in a large multicenter clinical trial of renal replacement therapy (RRT) initiation strategy during severe AKI (the Artificial Kidney Initiation in Kidney Injury, AKIKI) to investigate long-term survival, renal outcome and health related quality of life (HRQOL). We also assessed the influence of RRT initiation strategy on these outcomes.

RESULTS

Follow-up of patients extended from 60 days to a median of 3.35 years [interquartile range (IQR), 1.89 to 4.09] after the end of initial study. Of the 619 patients included in the AKIKI trial, 316 survived after 60 days. The overall survival rate at 3 years from inclusion was 39.4% (95% CI 35.4 to 43.4). A total of 46 patients (on the 175 with available data on long-term kidney function) experienced worsening of renal function (WRF) at the time of follow-up [overall incidence of 26%, cumulative incidence at 4 years: 20.6% (CI 95% 13.0 to 28.3)]. Fifteen patients required chronic dialysis (5% of patients who survived after day 90). Among the 226 long-term survivors, 80 (35%) answered the EQ-5D questionnaire. The median index value reported was 0.67 (IQR 0.40 to 1.00) indicating a noticeable alteration of quality of life. Initiation strategy for RRT had no effect on any long-term outcome.

CONCLUSION

Severe AKI in critically ill patients was associated with a high proportion of death within the first 2 months but less so during long-term follow-up. A quarter of long-term survivors experienced a WRF and suffered from a noticeable impairment of quality of life. Renal replacement therapy initiation strategy was not associated with mortality outcome.

Sepsis-associated acute kidney injury: consensus report of the 28th Acute Disease Quality Initiative workgroup

Sepsis-associated acute kidney injury (SA-AKI) is common in critically ill patients and is strongly associated with adverse outcomes, including an increased risk of chronic kidney disease, cardiovascular events and death. The pathophysiology of SA-AKI remains elusive, although microcirculatory dysfunction, cellular metabolic reprogramming and dysregulated inflammatory responses have been implicated in preclinical studies. SA-AKI is best defined as the occurrence of AKI within 7 days of sepsis onset (diagnosed according to Kidney Disease Improving Global Outcome criteria and Sepsis 3 criteria, respectively). Improving outcomes in SA-AKI is challenging, as patients can present with either clinical or subclinical AKI. Early identification of patients at risk of AKI, or at risk of progressing to severe and/or persistent AKI, is crucial to the timely initiation of adequate supportive measures, including limiting further insults to the kidney. Accordingly, the discovery of biomarkers associated with AKI that can aid in early diagnosis is an area of intensive investigation. Additionally, high-quality evidence on best-practice care of patients with AKI, sepsis and SA-AKI has continued to accrue. Although specific therapeutic options are limited, several clinical trials have evaluated the use of care bundles and extracorporeal techniques as potential therapeutic approaches. Here we provide graded recommendations for managing SA-AKI and highlight priorities for future research.

Single-cell transcriptome analysis of a rat model of bilateral renal ischemia-reperfusion injury

Ischemia-reperfusion injury (IRI) causes massive tissue damage. Renal IRI is the most common type of acute renal injury, and the defects caused by it may progress to chronic kidney disease (CKD). Rodent models of renal IRI, with various patterns, have been used to study the treatment of human kidney injury. A rat model of bilateral IRI, in which the bilateral kidney blood vessels are clamped for 60 min, is widely used, inducing both acute and chronic kidney disease. However, the molecular mechanisms underlying the effects of bilateral IRI on kidney cells have not yet been fully elucidated. This study aimed to perform a whole-transcriptome analysis of the IRI kidney using single-cell RNA sequencing. We found renal parenchymal cells, including those from the proximal tubule, the loop of Henle, and distal tubules, to be damaged by IRI. In addition, we observed significant changes in macrophage population. Our study delineated the detailed cellular and molecular changes that occur in the rat model of bilateral IRI. Collectively, our data and analyses provided a foundation for understanding IRI-related kidney diseases in rat models.

Acute kidney injury increases risk of kidney stones-a retrospective propensity score matched cohort study

BACKGROUND

Acute kidney injury (AKI) is common. An episode of AKI may modify the risk of developing kidney stones by potential long-term effects on urine composition. We aimed to investigate the association between AKI and the risk of kidney stone presentations.

METHODS

The retrospective cohort study used patient data (1 January 2008-31 December 2017), from an Australian Local Health District, which included AKI diagnosis, demographics, comorbidities and kidney stone admissions. Time-varying Cox proportional hazards and propensity-matched analysis were used to determine the impact of AKI on the risk of kidney stones. To address possible population inhomogeneity in comparisons between no AKI and hospitalized AKI, sub-group analysis was done comparing inpatient and outpatient AKI versus no AKI, to assess consistency of association with future stones. Sensitivity analysis was undertaken to capture the impact of a known AKI status and AKI severity.

RESULTS

Out of 137 635 patients, 23 001 (17%) had an AKI diagnosis and 2295 (2%) had kidney stone presentations. In the unadjusted analysis, AKI was associated with kidney stones, with AKI used as a time-varying exposure, [hazard ratio (HR) 1.32, 95% confidence interval (CI) 1.16-1.50)]. Both inpatient-AKI (HR 1.19, 95% CI 1.01-1.39) and outpatient-AKI (HR 1.59, 95% CI 1.30-1.94) were significantly associated with future stones compared to no AKI subjects. This association persisted in the adjusted analysis (HR 1.45, 95% CI 1.26-1.66), propensity-matched dataset (HR 1.67, 95% CI 1.40-1.99) and sensitivity analysis. There was a dose-response relationship with higher stages of AKI being associated with a greater risk of kidney stones.

CONCLUSIONS

In a large cohort of patients, AKI is associated with a greater risk of kidney stones, which increases with higher stages of AKI. This association should be examined in other cohorts and populations for verification.

Tubular epithelial cells-derived small extracellular vesicle-VEGF-A promotes peritubular capillary repair in ischemic kidney injury

Peritubular capillaries (PTCs) are closely related to renal tubules in structure and function, and both are pivotal regulators in the development and progression of acute kidney injury (AKI). However, the mechanisms that underlie the interaction between PTCs and tubules during AKI remain unclear. Here we explored a new mode of tubulovascular crosstalk mediated by small extracellular vesicles (sEV) after AKI. In response to renal ischemia/reperfusion (I/R) injury, endothelial proliferation of PTCs and tubular expression of vascular endothelial growth factor-A (VEGF-A) were increased, accompanied by a remarkable redistribution of cytoplasmic VEGF-A to the basolateral side of tubular cells. Meanwhile, the secretion mode of VEGF-A was converted in the injured tubular cells, which showed a much greater tendency to secrete VEGF-A via sEV other than the free form. Interestingly, tubular cell-derived VEGF-A-enriched sEV (sEV-VEGF-A) turned out to promote endothelial proliferation which was regulated by VEGF receptors 1 and 2. Furthermore, inhibition of renal sEV secretion by Rab27a knockdown resulted in a significant decrease in the proliferation of peritubular endothelial cells in vivo. Importantly, taking advantage of the newly recognized endogenous repair response of PTCs, exogenous supplementation of VEGF-A + sEV efficiently recused PTC rarefaction, improved renal perfusion, and halted the AKI to CKD transition. Taken together, our study uncovered a novel intrinsic repair response after AKI through renal tubule-PTC crosstalk via sEV-VEGF-A, which could be exploited as a promising therapeutic angiogenesis strategy in diseases with ischemia.

Prophylactic Treatment with Hydrogen Sulphide Can Prevent Renal Ischemia-Reperfusion Injury in L-NAME Induced Hypertensive Rats with Cisplatin-Induced Acute Renal Failure

(Background and Objectives): Renal ischemia perfusion injury is one of the major issues in kidney transplant. The aim of the study was to investigate the hypothesis that prophylactic treatment-with a hydrogen sulphide donor to an acute renal failure case of hypertensive rats-can minimize the ischemia reperfusion injury of the kidney which is beneficial for kidney transplant. To check this hypothesis, the present study was designed to investigate the effect of chronic administration of a hydrogen sulphide (H2S) donor and sodium hydrosulfide (NaHS) on nuclear factor kappa B (NF-kB) and inter cellular adhesion molecule-1 (ICAM-1) concentration in non-renal failure (NRF) and acute renal failure (ARF) rats in the ischemia-reperfusion injury (IRI) model of the kidney in both normotensive WKY and hypertensive rats (L-nitro arginine methyl ester (L-NAME-induced); (Materials and Methods): A total number of 48 Sprague-Dawley rats were recruited into eight groups each consisting of six animals. Each of these eight groups was used to measure systemic and renal parameters, H2S, antioxidant parameters in plasma, plasma concentration of NF-kB and ICAM-1 and renal cortical blood pressure. ARF was induced by single intraperitoneal (i.p.) cisplatin injection (5 mg/kg). Hypertension was induced by oral administration of L-NAME in drinking water for four weeks at 40 mg/kg/day. NaHS was administered (i.p) at 56 µmol/kg for five weeks while dL-propargylglycine (PAG), a H2S generation inhibitor, was administered as a single intra-peritoneal injection (50 mg/kg). An acute surgical experiment was performed for the induction of renal ischemia for 30 min by renal artery clamping followed by reperfusion for three hours; (Results): Chronic administration of NaHS attenuated the severity of ARF in both normotensive and hypertensive animals (L-NAME) along with lowering the blood pressure in hypertensive groups. NaHS improved the oxidative stress parameters such as total superoxide dismutase (T-SOD), glutathione (GSH) and reduced the malondialdehyde (MDA) concentration along with reduction of NF-kB and ICAM-1 following renal IRI; Conclusions: These findings demonstrate that H2S not only reduced the severity of cisplatin induced ARF but also reduced the severity of renal IRI by upregulating antioxidants along with decreased concentrations of NF-kB and ICAM-1 in normotensive and L-NAME induced hypertensive rats.

Resident macrophage subpopulations occupy distinct microenvironments in the kidney

The kidney contains a population of resident macrophages from birth that expands as it grows and forms a contiguous network throughout the tissue. Kidney-resident macrophages (KRMs) are important in homeostasis and the response to acute kidney injury. While the kidney contains many microenvironments, it is unknown whether KRMs are a heterogeneous population differentiated by function and location. We combined single-cell RNA-Seq (scRNA-Seq), spatial transcriptomics, flow cytometry, and immunofluorescence imaging to localize, characterize, and validate KRM populations during quiescence and following 19 minutes of bilateral ischemic kidney injury. scRNA-Seq and spatial transcriptomics revealed 7 distinct KRM subpopulations, which are organized into zones corresponding to regions of the nephron. Each subpopulation was identifiable by a unique transcriptomic signature, suggesting distinct functions. Specific protein markers were identified for 2 clusters, allowing analysis by flow cytometry or immunofluorescence imaging. Following injury, the original localization of each subpopulation was lost, either from changing locations or transcriptomic signatures. The original spatial distribution of KRMs was not fully restored for at least 28 days after injury. The change in KRM localization confirmed a long-hypothesized dysregulation of the local immune system following acute injury and may explain the increased risk for chronic kidney disease.

From AKI to CKD: Maladaptive Repair and the Underlying Mechanisms

Acute kidney injury (AKI) is defined as a pathological condition in which the glomerular filtration rate decreases rapidly over a short period of time, resulting in changes in the physiological function and tissue structure of the kidney. An increasing amount of evidence indicates that there is an inseparable relationship between acute kidney injury and chronic kidney disease (CKD). With the progress in research in this area, researchers have found that the recovery of AKI may also result in the occurrence of CKD due to its own maladaptation and other potential mechanisms, which involve endothelial cell injury, inflammatory reactions, progression to fibrosis and other pathways that promote the progress of the disease. Based on these findings, this review summarizes the occurrence and potential mechanisms of maladaptive repair in the progression of AKI to CKD and explores possible treatment strategies in this process so as to provide a reference for the inhibition of the progression of AKI to CKD.

Suppression of NRF2 Activity by HIF-1α Promotes Fibrosis after Ischemic Acute Kidney Injury

Acute kidney injury (AKI) is a rapid decline in renal function and can occur after ischemia/reperfusion injury (IRI) to the tubular epithelia. The nuclear factor erythroid-2-related factor 2 (NRF2) pathway protects against AKI and AKI-to-chronic kidney disease (CKD) progression, but we previously demonstrated that severe IRI maladaptively reduced NRF2 activity in mice. To understand the mechanism of this response, we subjected C57BL/6J mice to unilateral kidney IRI with ischemia times that were titrated to induce mild to severe injury. Mild IRI increased NRF2 activity and was associated with renal recovery, whereas severe IRI decreased NRF2 activity and led to progressive CKD. Due to these effects of ischemia, we tested the hypothesis that hypoxia-inducible factor-1α (HIF-1α) mediates NRF2 activity. To mimic mild and severe ischemia, we activated HIF-1α in HK-2 cells in nutrient-replete or nutrient-deficient conditions. HIF-1α activation in nutrient-replete conditions enhanced NRF2 nuclear localization and activity. However, in nutrient-deficient conditions, HIF-1α activation suppressed NRF2 nuclear localization and activity. Nuclear localization was rescued with HIF-1α siRNA knockdown. Our results suggest that severe ischemic AKI leads to HIF-1α-mediated suppression of NRF2, leading to AKI-to-CKD progression.

Application of New Acute Kidney Injury Biomarkers

Kidney-related biomarkers can provide structural and functional information about different parts of the nephron. These biomarkers can be used to evaluate glomerular, tubular, or interstitial injury, inflammation, or repair, and glomerular or tubular function. Furthermore, biomarkers can improve the acute kidney injury diagnosis in various clinical conditions, including acute interstitial nephritis, acute tubular injury, hepatorenal and cardiorenal syndrome, ischemic and nephrotoxic acute kidney injury, and drug-induced acute kidney injury. Biomarkers might be used as an additional precision medicine tool in managing patients with acute kidney injury; they can help with clinical decision-making and impact patient outcomes. In this chapter, we reviewed the utility of biomarkers used in acute kidney injury.

Integrin receptor-binding nanofibrous peptide hydrogel for combined mesenchymal stem cell therapy and nitric oxide delivery in renal ischemia/reperfusion injury

Background

Mesenchymal-based therapy has been utilized as a practical approach in the treatment of renal ischemia/reperfusion (I/R) injury. However, low cell retention and survival in the ischemic site have remained challenging issues. To bridge this gap, the integrin receptor-binding RGD peptide-functionalized, s-nitroso-n-acetyl penicillamine (SNAP)-loaded hydrogel was used to transplant Wharton's jelly-mesenchymal stem cells (WJ-MSCs).

Methods

Apart from physicochemical and rheological characterizations that confirmed entangled interlocking β-sheets with nanofibrous morphology, real-time RT-PCR, ROS production, serum biomarker concentrations, and histopathological alterations were explored in a mouse model to assess the therapeutic efficacy of formulations in the treatment of renal I/R injury.

Results

The RGD-functionalized Fmoc-diphenylalanine (Fmoc-FF + Fmoc-RGD) hydrogel supported the spread and proliferation of WJ-MSCs in vivo. Notably, intralesional injection of nitric oxide donor combined with the embedded WJ-MSCs caused superior recovery of renal I/R injury compared to free WJ-MSCs alone in terms of histopathological scores and renal function indices. Compared to the I/R control group, oxidative stress and inducible nitric oxide synthase (iNOS) expression biomarkers showed a significant decline, whereas endothelial nitric oxide synthase (eNOS) and vascular endothelial growth factor (VEGF) expression exhibited a significant increment, indicating regeneration of the injured endothelial tissue.

Conclusion

The findings confirmed that the hydrogels containing WJ-MSCs and nitric oxide donors can promote the regeneration of renal I/R injuries by increasing angiogenic factors and cell engraftment.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-022-03045-1.

Chronic critical illness and post-intensive care syndrome: from pathophysiology to clinical challenges

Background

Post‐intensive care syndrome (PICS) encompasses physical, cognition, and mental impairments persisting after intensive care unit (ICU) discharge. Ultimately it significantly impacts the long‐term prognosis, both in functional outcomes and survival. Thus, survivors often develop permanent disabilities, consume a lot of healthcare resources, and may experience prolonged suffering. This review aims to present the multiple facets of the PICS, decipher its underlying mechanisms, and highlight future research directions.

Main text

This review abridges the translational data underlying the multiple facets of chronic critical illness (CCI) and PICS. We focus first on ICU-acquired weakness, a syndrome characterized by impaired contractility, muscle wasting, and persisting muscle atrophy during the recovery phase, which involves anabolic resistance, impaired capacity of regeneration, mitochondrial dysfunction, and abnormalities in calcium homeostasis. Second, we discuss the clinical relevance of post-ICU cognitive impairment and neuropsychological disability, its association with delirium during the ICU stay, and the putative role of low-grade long-lasting inflammation. Third, we describe the profound and persistent qualitative and quantitative alteration of the innate and adaptive response. Fourth, we discuss the biological mechanisms of the progression from acute to chronic kidney injury, opening the field for renoprotective strategies. Fifth, we report long-lasting pulmonary consequences of ARDS and prolonged mechanical ventilation. Finally, we discuss several specificities in children, including the influence of the child’s pre-ICU condition, development, and maturation.

Conclusions

Recent understandings of the biological substratum of the PICS’ distinct features highlight the need to rethink our patient trajectories in the long term. A better knowledge of this syndrome and precipitating factors is necessary to develop protocols and strategies to alleviate the CCI and PICS and ultimately improve patient recovery.

An update on the functional roles of long non‑coding RNAs in ischemic injury (Review)

Ischemic injuries result from ischemia and hypoxia in cells. Tissues and organs receive an insufficient supply of nutrients and accumulate metabolic waste, which leads to the development of inflammation, fibrosis and a series of other issues. Ischemic injuries in the brain, heart, kidneys, lungs and other organs can cause severe adverse effects. Acute renal ischemia induces acute renal failure, heart ischemia induces myocardial infarction and cerebral ischemia induces cerebrovascular accidents, leading to loss of movement, consciousness and possibly, life-threatening disabilities. Existing evidence suggests that long non-coding RNAs (lncRNAs) are regulatory sequences involved in transcription, post-transcription, epigenetic regulation and multiple physiological processes. lncRNAs have been shown to be differentially expressed following ischemic injury, with the severity of the ischemic injury being affected by the upregulation or downregulation of certain types of lncRNA. The present review article provides an extensive summary of the functional roles of lncRNAs in ischemic injury, with a focus on the brain, heart, kidneys and lungs. The present review mainly summarizes the functional roles of lncRNA MALAT1, lncRNA MEG3, lncRNA H19, lncRNA TUG1, lncRNA NEAT1, lncRNA AK139328 and lncRNA CAREL, among which lncRNA MALAT1, in particular, plays a crucial role in ischemic injury and is currently a hot research topic.

Persistent vascular congestion in male spontaneously hypertensive rats contributes to delayed recovery of renal function following ischemia-reperfusion compared to females

Acute kidney injury (AKI) is a serious and frequent clinical complication with mortality rates up to 80%. Vascular congestion in the renal outer medulla occurs early after ischemia reperfusion (IR) injury, and congestion has been linked to worsened outcomes following IR. There is evidence implicating both male sex and preexisting hypertension as risk factors for poor outcomes following IR. The present study tested the hypothesis that male spontaneously hypertensive rats (SHR) have greater vascular congestion and impaired renal recovery following renal IR vs. female SHR and normotensive male Sprague-Dawley rats (SD). 13 wk old male and female SHR and SD were subjected to sham surgery or 30 minutes of warm bilateral ischemia followed by reperfusion. Rats were euthanized 24 hours or 7 days post-IR. IR increased renal injury in all groups vs. sham controls at 24 hours. At 7 days post-IR, injury remained elevated only in male SHR. Histological examination of SD and SHR kidneys 24 hours post-IR showed vascular congestion in males and females. Vascular congestion was sustained only in male SHR 7 days post-IR. To assess the role of vascular congestion on impaired recovery following IR, additional male and female SHR were pretreated with heparin (200 U/kg) prior to IR. Heparin pre-treatment reduced IR-induced congestion and improved renal function in male SHR 7 days post-IR. Interestingly, preventing increases in BP in male SHR did not alter sustained vascular congestion. Our data demonstrate that IR-induced vascular congestion is a major driving factor for impaired renal recovery in male SHR.

An Overview of the Cardiorenal Protective Mechanisms of SGLT2 Inhibitors

Sodium-glucose co-transporter 2 (SGLT2) inhibitors block glucose reabsorption in the renal proximal tubule, an insulin-independent mechanism that plays a critical role in glycemic regulation in diabetes. In addition to their glucose-lowering effects, SGLT2 inhibitors prevent both renal damage and the onset of chronic kidney disease and cardiovascular events, in particular heart failure with both reduced and preserved ejection fraction. These unexpected benefits prompted changes in treatment guidelines and scientific interest in the underlying mechanisms. Aside from the target effects of SGLT2 inhibition, a wide spectrum of beneficial actions is described for the kidney and the heart, even though the cardiac tissue does not express SGLT2 channels. Correction of cardiorenal risk factors, metabolic adjustments ameliorating myocardial substrate utilization, and optimization of ventricular loading conditions through effects on diuresis, natriuresis, and vascular function appear to be the main underlying mechanisms for the observed cardiorenal protection. Additional clinical advantages associated with using SGLT2 inhibitors are antifibrotic effects due to correction of inflammation and oxidative stress, modulation of mitochondrial function, and autophagy. Much research is required to understand the numerous and complex pathways involved in SGLT2 inhibition. This review summarizes the current known mechanisms of SGLT2-mediated cardiorenal protection.

In Vivo Ultrasound Localization Microscopy Imaging of the Kidney's Microvasculature With Block-Matching 3-D Denoising

Structural abnormalities and functional changes of renal microvascular networks play a significant pathophysiologic role in the occurrence of kidney diseases. Super-resolution ultrasound imaging has been successfully utilized to visualize the microvascular network and provide valuable diagnostic information. To prevent the burst of microbubbles, a lower mechanical index (MI) is generally used in ultrasound localization microscopy (ULM) imaging. However, high noise levels lead to incorrect signal localizations in relatively low-MI settings and deep tissue. In this study, we implemented a block-matching 3-D (BM3D) image-denoising method, after the application of singular value decomposition filtering, to further suppress the noise at various depths. The in vitro flow-phantom results show that the BM3D method helps the significant reduction of the error localizations, thus improving the localization accuracy. In vivo rhesus macaque experiments help conclude that the BM3D method improves the resolution more than other image-based denoising techniques, such as the nonlocal means method. The obtained clutter-filtered images with fewer incorrect localizations can enable robust ULM imaging, thus helping in establishing an effective diagnostic tool.

Protective Effect of Melatonin for Renal Ischemia-Reperfusion Injury: A Systematic Review and Meta-Analysis

Background: Renal ischemia-reperfusion (I/R) injury is one of the major causes related to acute kidney damage. Melatonin has been shown as a powerful antioxidant, with many animal experiments have been designed to evaluate the therapeutic effect of it to renal I/R injury.

Objectives: This systematic review aimed to assess the therapeutic effect of melatonin for renal I/R injury in animal models.

Methods and Results: The PubMed, Web of Science, Embase, and Science Direct were searched for animal experiments applying melatonin to treat renal I/R injury to February 2021. Thirty-one studies were included. The pooled analysis showed a greater reduction of blood urea nitrogen (BUN) (21 studies, weighted mean difference (WMD) = −30.00 [−42.09 to −17.91], p < 0.00001), and serum creatinine (SCr) (20 studies, WMD = −0.91 [−1.17 to −0.66], p < 0.00001) treated with melatonin. Subgroup analysis suggested that multiple administration could reduce the BUN compared with control. Malondialdehyde and myeloperoxidase were significantly reduced, meanwhile, melatonin significantly improved the activity of glutathione, as well as superoxide dismutase. The possible mechanism for melatonin to treat renal I/R injury is inhibiting endoplasmic reticulum stress, apoptosis, inflammation, autophagy, and fibrillation in AKI to chronic kidney disease.

Conclusions: From the available data of small animal studies, this systematic review demonstrated that melatonin could improve renal function and antioxidative effects to cure renal I/R injury through, then multiple administration of melatonin might be more appropriate. Nonetheless, extensive basic experiments are need to study the mechanism of melatonin, then well-designed randomized controlled trials to explore the protective effect of melatonin.

Risk factors and occurrence of chronic kidney disease following acute kidney injury in Children

Background

Chronic kidney disease (CKD) is an irreversible progressive condition with diverse etiologies among which acute kidney injury (AKI) is increasingly being recognized as an important one.

Methods

This was a prospective observational study of pediatric intensive care unit (PICU) patients admitted with different etiologies, at a tertiary care hospital for children in Kashmir India, between October 2018 and September 2020. AKI was defined as an increase in absolute serum creatinine (SCr) ≥0.3 mg/dL or by a percentage increase in SCr 50% and/or by a decrease in urine output to <0.5 mL/kg/h for >6 hours (h). Besides analysis of AKI and associated PICU mortality, post-AKI patients after discharge were kept on follow-up for complete 1 year.

Results

From 119 enrolled patients with AKI with no preexisting risk factors, 5.6% (n = 8/119) developed CKD. The AKI-associated mortality rate after 48 h of PICU stay was 13.4% (n = 16/119). At time of discharge from hospital, elevated blood pressure (BP) (n = 5/8) and subnephrotic proteinuria (n = 3/8) were the statistically significant sequels of AKI (P value <0.001) for progression to CKD. After 3 months of follow-up, elevated BP (n = 7/8) and subnephrotic proteinuria (n = 3/8) were significantly associated with progression to CKD at 1 year (P < 0.005).

Conclusions

Occurrence of CKD after an attack of AKI was not uncommon and the risk of long-term consequences in the form of hypertension, proteinuria, and CKD is significant, which may be much higher than observed. It is prudent that all post-AKI PICU discharged patients must be monitored for the long-term consequences of AKI.

Acute kidney injury and chronic kidney disease after liver transplant: A retrospective observational study

BACKGROUND AND RATIONALE

Chronic kidney disease remains an important risk factor for morbidity and mortality among LT recipients, but its exact incidence and risk factors are still unclear.

MATERIAL AND METHODS

We carried out a retrospective cohort study of consecutive adults who underwent liver transplant (January 2009-December 2018) and were followed (at least 6 months) at our institution. CKD was defined following the Kidney Disease: Improving Global Outcomes (KDIGO) 2012 Clinical Practice Guidelines. Long-term kidney function was classified into 4 groups: no CKD (eGFR, ≥60mL/min/1.73m²), mild CKD (eGFR, 30-59mL/min/1.73m²), severe CKD (eGFR, 15-29mL/min/1.73m²), and end-stage renal disease (ESRD).

RESULTS

We enrolled 410 patients followed for 53.2±32.6 months. 39 had CKD at baseline, and 95 developed de novo CKD over the observation period. There were 184 (44.9%) anti-HCV positive, 47 (11.5%) HBsAg positive, and 33 (8.1%) HBV/HDV positive recipients. Recipient risk factors for baseline CKD were advanced age (P=0.044), raised levels of serum uric acid (P<0.0001), and insulin dependent DM (P=0.0034). Early post-transplant AKI was common (n=95); logistic regression analysis found that baseline serum creatinine was an independent predictor of early post-LT AKI (P=0.0154). According to our Cox proportional hazards model, recipient risk factors for de novo CKD included aging (P<0.0001), early post-transplant AKI (P=0.007), and baseline serum creatinine (P=0.0002). At the end of follow-up, there were 116 LT recipients with CKD - 109 (93.9%) and 7 (6.1%) had stage 3 and advanced CKD, respectively. Only two of them are undergoing long-term dialysis.

CONCLUSION

The incidence of CKD was high in our cohort of LT recipients, but only a slight decline in kidney function over time was recorded. Prevention of post-transplant AKI will improve kidney function in the long run. We need more studies to analyze the function of kidneys among LT recipients over extended follow-ups and their impact on mortality.