Ischemia-reperfusion Acute Kidney Injury Research Articles

Hyperbaric Oxygen Reduces Oxidative Stress Impairment and DNA Damage and Simultaneously Increases HIF-1α in Ischemia-Reperfusion Acute Kidney Injury.

The central exacerbating factor in the pathophysiology of ischemic-reperfusion acute kidney injury (AKI) is oxidative stress. Lipid peroxidation and DNA damage in ischemia are accompanied by the formation of 3-nitrotyrosine, a biomarker for oxidative damage. DNA double-strand breaks (DSBs) may also be a result of postischemic AKI. γH2AX(S139) histone has been identified as a potentially useful biomarker of DNA DSBs. On the other hand, hypoxia-inducible factor (HIF) is the "master switch" for hypoxic adaptation in cells and tissues. The aim of this research was to evaluate the influence of hyperbaric oxygen (HBO) preconditioning on antioxidant capacity estimated by FRAP (ferric reducing antioxidant power) and ABTS (2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid)) assay, as well as on oxidative stress parameter 3-nitrotyrosine, and to assess its effects on γH2AX(S139), HIF-1α, and nuclear factor-κB (NF-κB) expression, in an experimental model of postischemic AKI induced in spontaneously hypertensive rats. The animals were divided randomly into three experimental groups: sham-operated rats (SHAM, n = 6), rats with induced postischemic AKI (AKI, n = 6), and group exposed to HBO preconditioning before AKI induction (AKI + HBO, n = 6). A significant improvement in the estimated glomerular filtration rate, eGFR, in AKI + HBO group (p < 0.05 vs. AKI group) was accompanied with a significant increase in plasma antioxidant capacity estimated by FRAP (p < 0.05 vs. SHAM group) and a reduced immunohistochemical expression of 3-nitrotyrosine and γH2AX(S139). Also, HBO pretreatment significantly increased HIF-1α expression (p < 0.001 vs. AKI group), estimated by Western blot and immunohistochemical analysis in kidney tissue, and decreased immunohistochemical NF-κB renal expression (p < 0.01). Taking all of these results together, we may conclude that HBO preconditioning has beneficial effects on acute kidney injury induced in spontaneously hypertensive rats.

Tolerogenic CD11c+dendritic cells regulate CD4+Tregs in replacing delayed ischemic preconditioning to alleviate ischemia-reperfusion acute kidney injury.

Ischemia-reperfusion injury (IRI) is one of the primary clinical causes of acute kidney injury (AKI). The key to IRI lies in immune-inflammatory damage, where dendritic cells (DCs) play a central role in eliciting immune responses within the context of inflammation induced by ischemia-reperfusion. Our previous study has confirmed that delayed ischemic preconditioning (DIPC) can reduce the kidney injury by mediating DCs to regulate T-cells. However, the clinical feasibility of DIPC is limited, as pre-clamping of the renal artery is not applicable for the prevention and treatment of ischemia-reperfusion acute kidney injury (I/R-AKI) in clinical patients. Therefore, the infusion of DCs as a substitute for DIPC presents a more viable strategy for preventing renal IRI. In this study, we further evaluated the impact and mechanism of infused tolerogenic CD11c+DCs on the kidneys following IRI by isolating bone marrow-derived dendritic cells and establishing an I/R-AKI model after pre-infusion of DCs. Renal function was significantly improved in the I/R-AKI mouse model after pre-infused with CD11c+DCs. The pro-inflammatory response and oxidative damage were reduced, and the levels of T helper 2 (Th2) cells and related anti-inflammatory cytokines were increased, which was associated with the reduction of autologous DCs maturation mediated by CD11c+DCs and the increase of regulatory T-cells (Tregs). Next, knocking out CD11c+DCs, we found that the reduced immune protection of tolerogenic CD11c+DCs reinfusion was related to the absence of own DCs. Together, pre-infusion of tolerogenic CD11c+DCs can replace the regulatory of DIPC on DCs and T-cells to alleviate I/R-AKI. DC vaccine is expected to be a novel avenue to prevent and treat I/R-AKI.

Circ DENND4C inhibits pyroptosis and alleviates ischemia-reperfusion acute kidney injury by exosomes secreted from human urine-derived stem cells

Acute kidney injury (AKI) is a disease characterised by acute onset, high mortality, and poor prognosis, and is mainly caused by ischemia-reperfusion (I/R). Human urine-derived stem cells (USCs) exhibit antioxidant, anti-inflammatory, and anti-apoptotic cytoprotective effects. Previously, we found that exosomes from USCs had the ability to inhibit apoptosis and protect kidneys from I/R injury. This study aimed to investigate the role of USC-derived exosomes (USC-Exos) in reducing pyroptosis and alleviating I/R-AKI. Models of HK-2 cells hypoxia-reoxygenation (H/R) and I/R kidney injury was established in Sprague Dawley rats to simulate AKI in vitro and in vivo. USC-Exos were isolated using ultracentrifugation and identified via electron microscopy and western blotting. USC-Exos were co-cultured with HK-2 cells and injected into rats via the tail vein. The expression of pyroptosis-related molecules (GSDMD, caspase-1, and NLRP-3) was verified using PCR and western blotting. Changes in renal function were reflected in the serum creatinine, urea, and cystatin C levels. The degree of renal injury was determined using haematoxylin and eosin and immunohistochemical staining. The levels of IL-1β and IL-18 were detected using enzyme-linked immunosorbent assay (ELISA) to verify the role of USC-Exos in pyroptosis. Differentially expressed circRNAs in I/R rat kidneys were screened by transcriptome sequencing, and a dual-luciferase experiment was used to verify the interaction between upstream and downstream molecules. Ischemia-reperfusion resulted in significantly impaired renal function and expression of pyroptosis molecules, and significantly increased concentrations of inflammatory factors. These effects were reversed by injecting USC-Exos. Circ DENND4C was the most significantly decreased circRNA in I/R rat renal tissue, and knock-down of circ DENND4C can aggravate AKI in vivo and in vitro. DAVID(http://david.abcc.ncifcrf.gov) website showed that miR 138-5p/FOXO3a is a potential downstream target of circ DENND4C. Knock-down of circ DENND4C in HK-2 cells resulted in increased expression of miR 138-5p and increased miR 138-5p can reverse the regulation of FOXO3a. Dual-luciferase assay verified the reverse interaction between circ DENND4C, miR 138-5p, and FOXO3a. Exosomes promote cell proliferation and inhibit the activation of NLR family pyrin domain containing 3 through the circ DENND4C/miR 138-5p/FOXO3a pathway, thereby reducing pyroptosis and AKI. Circ DENND4C may be a potential therapeutic target for AKI.

Sex as a biological variable in acute kidney injury.

The purpose of this review is to provide an overview of the preclinical and clinical studies investigating sex as a biological variable, as well as the impact of gender, on the development of and progression of acute kidney injury (AKI). Despite a matched degree of ischemia-reperfusion AKI based on measured glomerular filtration rates, male and female mice demonstrated important sex biases in cardiorenal outcomes (1). Although the 2012 Kidney Disease Improving Global Outcomes (KDIGO) Clinical Practice Guideline for AKI reported that female sex is associated with increased rates of hospital acquired AKI, subsequent meta-analyses do not show increased risk of AKI in women. Recent large scale, multicenter epidemiologic studies suggest males have higher rates of hospital acquired AKI. However, women have been consistently shown to have worse renal outcomes after AKI. There may be also be gender-based differences in presentation to care and management. Sex is an important biological variable in animal models of acute kidney injury. The impact of sex on AKI likely varies based on the etiology of AKI. Preclinical studies demonstrate the nuances of sex chromosomes, sex hormones and epigenetic factors on AKI, however these have not been well studied in humans. Gender may also impact processes of care, treatment and clinical outcomes related to AKI. The scientific rigor and reproducibility of translational studies benefit from the consideration of sex and gender.

Mesenchymal Stem Cells Delivered Locally to Ischemia-Reperfused Kidneys via Injectable Hyaluronic Acid Hydrogels Decrease Extracellular Matrix Remodeling 1 Month after Injury in Male Mice.

The translation of stem cell therapies has been hindered by low cell survival and retention rates. Injectable hydrogels enable the site-specific delivery of therapeutic cargo, including cells, to overcome these challenges. We hypothesized that delivery of mesenchymal stem cells (MSC) via shear-thinning and injectable hyaluronic acid (HA) hydrogels would mitigate renal damage following ischemia-reperfusion acute kidney injury. Acute kidney injury (AKI) was induced in mice by bilateral or unilateral ischemia-reperfusion kidney injury. Three days later, mice were treated with MSCs either suspended in media injected intravenously via the tail vein, or injected under the capsule of the left kidney, or MSCs suspended in HA injected under the capsule of the left kidney. Serial measurements of serum and urine biomarkers of renal function and injury, as well as transcutaneous glomerular filtration rate (tGFR) were performed. In vivo optical imaging showed that MSCs localized to both kidneys in a sustained manner after bilateral ischemia and remained within the ipsilateral treated kidney after unilateral ischemic AKI. One month after injury, MSC/HA treatment significantly reduced urinary NGAL compared to controls; it did not significantly reduce markers of fibrosis compared to untreated controls. An analysis of kidney proteomes revealed decreased extracellular matrix remodeling and high overlap with sham proteomes in MSC/HA-treated animals. Hydrogel-assisted MSC delivery shows promise as a therapeutic treatment following acute kidney injury.

Self-oriented ferritin nanocages mitigate iron overload-induced oxidative stress for acute kidney injury

Iron overload-induced oxidative injury of renal tubular epithelial cells plays crucial roles in the pathogenesis of ischemia–reperfusion acute kidney injury (IR-AKI). Curcumin is a polyphenolic compound that can effectively scavenge free radicals, but its poor water solubility and renal distribution restrict its application. Although nanotechnology helps to improve this situation by enabling solubility and renal accumulation, the headstream of oxidative injury, iron overload, has not been reverted. Ferritin (Fer) is a well-known iron storage protein with a favorable particle size for renal filtration that can potently transport excess iron into its core to prevent further oxidative damage. In this regard, ferritin nanocages loaded with curcumin (FNC/Cur) were prepared. It is worth noting that ferritin nanocage-based proteins showed a significant self-orientation capability into injured kidneys at 4 h. After kidney aggregation, glomerular filtration and renal tubular reabsorption, FNC/Cur finally internalized by the target cells (renal tubular epithelial cells) under the mediation of transferrin receptor-1 (TfR1). Once internalized, FNC/Cur released curcumin to reduce excess reactive oxygen species (ROS) with the help of lysosomal acidic environment and protease-rich environment. At the same time, the dissembled FNC or their released heavy chain are able to bind lysosomal redox-active iron for a period of time, thereby temporarily protect against iron-mediated oxidation. As a result, FNC/Cur represents a potential kidney-targeted nanoplatform for synergistic treatment of IR-AKI.

TIGIT mediates experimental ischemia reperfusion and nephrotoxic acute kidney injury in mice

Abstract Background: We unexpectedly found upregulated expression of T cell immunoreceptor with Ig and ITIM domains (TIGIT) on kidney CD4 T cells after ischemia reperfusion (IR) using RNA-Seq. However, TIGIT role in kidney T cells and during acute kidney injury (AKI) is poorly understood. Methods: Effect of TIGIT on murine kidney T cells was assessed at baseline and after IR injury by flow cytometry and single cell RNA sequencing (scRNA-Seq). B6 wild type (WT) and TIGIT knockout (KO) mice were subjected to IR and cisplatin-induced AKI. TIGIT expression was assessed in AKI patients using the Kidney Precision Medicine Project (KPMP) scRNA-Seq dataset. Results: We found increased kidney CD4+TIGIT+ central memory (10.0±2.3 vs 0.9±0.1%, p=0.001) cells compared to CD4+TIGIT− cells in WT mice. TIGIT KO mice had reduced serum creatinine (SCr) after IR (24h Scr, 1.1±0.2 vs 2.7±0.1 mg/dL; p≤0.001) and cisplatin (72h Scr, 0.8±0.1 vs 1.4±0.1 mg/dL; p=0.0002) injury compared to WT mice. TIGIT KO kidneys had reduced necrotic tubules in outer medulla after IR (48.8±4.7% vs 73.0±1.5%; p=0.001) and cisplatin (11.5±3.0% vs 31.3±4.0%; p=0.008) injury than WT kidneys. Gene set enrichment analysis of scRNA-Seq data showed enrichment of inflammatory genes in Th17 cells from WT kidney and oxidative phosphorylation and mTORC1 signaling genes in TIGIT KO kidney. Human KPMP data demonstrated significant TIGITexpression in kidney T/NK cells from AKI patients compared to controls (p≤0.0001). Conclusions: TIGIT mediates both IR and nephrotoxic AKI in mice and its expression increases in kidney T cells from AKI patients. TIGIT is a promising novel therapeutic target for AKI, and also relevant due to increasing efforts to develop TIGIT blockade to treat cancers. American Society of Nephrology, Johns Hopkins University Ed Kraus Award, National Kidney Foundation of Maryland and Delaware

Complement C3 mediates podocyte injury through TLR4/NFΚB-P65 signaling during ischemia–reperfusion acute kidney injury and post-injury fibrosis

BackgroundThe aim of this study was to explore the mechanism of complement C3a mediating podocyte injury during ischemia–reperfusion acute kidney injury (IR-AKI) and post-injury fibrosis.MethodsRenal artery clamping was used to establish IR-AKI and post-injury fibrosis model. HE and Masson staining were performed to observe renal fibrosis. The protein abundance levels were measured along with inflammatory markers, renal complement C3. Podocytes were treated with C3a with or without Toll-like receptor 4(TLR4) inhibitor. The effects of TLR4 up-regulation by TLR4 plasmids were examined.ResultsC3−/− resulted in amelioration of renal dysfunction by reducing podocyte damage and renal fibrosis. Immunoblot with renal tissue homogenates from IR-AKI mice revealed that C3−/− decreased TLR4/Nuclear Factor-κB (NFκB)-P65.ConclusionOur results indicate that modulating C3/TLR4/NFκB-P65 signaling pathway is a novel therapeutic target for the IR-AKI and post-injury fibrosis.Graphical

Reactive Oxygen Species- and Cell-Free DNA-Scavenging Mn3O4 Nanozymes for Acute Kidney Injury Therapy.

Reactive oxygen species (ROS) scavenging therapy toward acute kidney injury (AKI) is promising, but no effective ROS scavenging drug has been developed yet. Moreover, cell-free DNA (cfDNA) is also involved in AKI, but the corresponding therapies have not been well developed. To tackle these challenges, Mn3O4 nanoflowers (Nfs) possessing both ROS and cfDNA scavenging activities were developed for better AKI protection as follows. First, Mn3O4 Nfs could protect HK2 cells through cascade ROS scavenging (dismutating ·O2- into H2O2 by superoxide dismutase-like activity and then decomposing H2O2 by catalase-like activity). Second, Mn3O4 Nfs could efficiently adsorb cfDNA and then decrease the inflammation caused by cfDNA. Combined, remarkable therapeutic efficacy was achieved in both cisplatin-induced and ischemia-reperfusion AKI murine models. Furthermore, Mn3O4 Nfs could be used for the T1-MRI real-time imaging of AKI. This study not only offered a promising treatment for AKI but also showed the translational potential of nanozymes.

MiR-6918-5p prevents renal tubular cell apoptosis by targeting MBD2 in ischemia/reperfusion-induced AKI

AimsAlthough previous studies reported that miRNAs are involved in the progression of acute kidney injury (AKI), their exact function and mechanism in ischemic AKI remains largely unknown. This study aims to define the role of miR-6918-5p in ischemia-reperfusion AKI. Materials and methodsThe renal arteries of C57BL/6J mice were clamped to establish a model of ischemia-reperfusion renal injury. BUMPT cells were added with Antimycin A and calcium ionophore to establish a model of ATP depletion in vitro. Cell apoptosis was detected by CCK8, flow cytometry and western blot, while HE staining and TUNEL staining were used to assess the degree of kidney damage. Key findingsWe suppressed mmu_miR-6918-5p by ischemic injury in vitro and in vivo. We found that ischemia-reperfusion (I/R)-induced renal tubular cell apoptosis and the expression of cleaved caspase3 were enhanced by the inhibitor of mmu_miR-6918-5p; this effect was attenuated by an mmu_miR-6918-5p mimic. Mechanistically, mmu_miR-6918-5p binds to the 3′ UTR region of MBD2 and represses its expression. The mmu_miR-6918-5p mimic alleviated the ischemic AKI by targeting MBD2. Conversely, the inhibitor of mmu_miR-6918-5p enhanced the ischemic AKI; this was diminished by MBD2-KO. SignificanceMmu_miR-6918-5p protected against the development of ischemic AKI by targeting MBD2.

Identification of biomarkers, immune infiltration landscape, and treatment targets of ischemia–reperfusion acute kidney injury at an early stage by bioinformatics methods

BackgroundMechanisms underlying ischemia/reperfusion injury-acute kidney injury (IRI-AKI) are not fully elucidated. We conducted an integrative analysis of IRI-AKI by bioinformatics methods.MethodsWe screened gene expression profiles of the IRI-AKI at early phase from the Gene Expression Omnibus (GEO) database. Differentially expressed genes (DEGs) were identified and enrichment pathways were conducted based on gene ontology (GO), Kyoto Encyclopedia of Genes and Genomes (KEGG) database, and Gene set enrichment analysis (GSEA). Immune cell infiltration analysis was performed to reveal the change of the microenvironment cell types. We constructed protein–protein interaction (PPI), and Cytoscape with plug-ins to find hub genes and modules. We performed robust rank aggregation (RRA) to combine DEGs and analyzed the target genes for miRNA/transcription factor (TF) and drug-gene interaction networks.ResultsA total of 239 and 384 DEGs were identified in GSE87024 and GSE34351 separately, with the 73 common DEGs. Enrichment analysis revealed that the significant pathways involve mitogen-activated protein kinase (MAPK) signaling, interleukin-17, and tumor necrosis factor (TNF) signaling pathway, etc. RRA analysis detected a total of 27 common DEGs. Immune cell infiltration analysis showed the plasma cells reduced and T cells increased in IRI-AKI. We identified JUN, ATF3, FOS, EGR1, HMOX1, DDIT3, JUNB, NFKBIZ, PPP1R15A, CXCL1, ATF4, and HSPA1B as hub genes. The target genes interacted with 23 miRNAs and 116 drugs or molecular compounds such as curcumin, staurosporine, and deferoxamine.ConclusionOur study first focused on the early IRI-AKI adopting RRA analysis to combine DEGs in different datasets. We identified significant biomarkers and crucial pathways involved in IRI-AKI and first construct the immune landscape and detected the potential therapeutic targets of the IRI-AKI by drug-gene network.

Single Cell Dissection of Epithelial-Immune Cellular Interplay in Acute Kidney Injury Microenvironment.

BackgroundUnderstanding the acute kidney injury (AKI) microenvironment changes and the complex cellular interaction is essential to elucidate the mechanisms and develop new targeted therapies for AKI.MethodsWe employed unbiased single-cell RNA sequencing to systematically resolve the cellular atlas of kidney tissue samples from mice at 1, 2 and 3 days after ischemia-reperfusion AKI and healthy control. The single-cell transcriptome findings were validated using multiplex immunostaining, western blotting, and functional experiments.ResultsWe constructed a systematic single-cell transcriptome atlas covering different AKI timepoints with immune cell infiltration increasing with AKI progression. Three new proximal tubule cells (PTCs) subtypes (PTC-S1-new/PTC-S2-new/PTC-S3-new) were identified, with upregulation of injury and repair-regulated signatures such as Sox9, Vcam1, Egr1, and Klf6 while with downregulation of metabolism. PTC-S1-new exhibited pro-inflammatory and pro-fibrotic signature compared to normal PTC, and trajectory analysis revealed that proliferating PTCs were the precursor cell of PTC-S1-new, and part of PTC-S1-new cells may turn into PTC-injured and then become fibrotic. Cellular interaction analysis revealed that PTC-S1-new and PTC-injured interacted closely with infiltrating immune cells through CXCL and TNF signaling pathways. Immunostaining validated that injured PTCs expressed a high level of TNFRSF1A and Kim-1, and functional experiments revealed that the exogenous addition of TNF-α promoted kidney inflammation, dramatic injury, and specific depletion of TNFRSF1A would abrogate the injury.ConclusionsThe single-cell profiling of AKI microenvironment provides new insight for the deep understanding of molecular changes of AKI, and elucidates the mechanisms and developing new targeted therapies for AKI.

Analysis of microRNA Expression after Glutamine Intervention in Acute Renal Ischemia-Reperfusion Injury.

Background Ischemia-reperfusion acute kidney injury (I/R AKI) is a severe kidney disease with high mortality and morbidity. This study aimed to explore the protective mechanism of glutamine (GLN) against I/R AKI. MethodsThe I/R AKI rat model was established, and HE staining of kidney tissue and serum creatinine (SCr) and blood urea nitrogen (BUN) detection were performed. The miRNAs were sequenced by high throughput in rat kidney tissue samples. Differentially expressed miRNAs (DEmiRs) between the I/R group and I/R + GLN group were screened, and enrichment analysis for target genes of DEmiRs was performed. Meanwhile, human HK-2 cells were cultured, and an I/R model was established to verify the expression of DEmiRs. Results Compared with the I/R group, the SCr and BUN levels at each time point were lower in the I/R + GLN group. Vacuolar degeneration of renal tubules in the I/R + GLN group was significantly reduced. In the 104 DEmiRs, we selected miR-132-5p, miR-205, and miR-615 as key miRNAs. KEGG analysis showed that the Notch signaling pathway, PI3K-Akt signaling pathway, and cGMP signaling pathway were mainly related to the GLN against I/R. qRT-PCR verified the downregulation of miR-205 in the I/R group, compared to the sham and I/R + GLN group. The I/R model was established with HK-2 cells, and the expression of miR-132-5p and miR-205 was decreased. Conclusion GLN reduced I/R-induced AKI. There were significant differences between miRNAs expression in I/R after GLN treatment. The process of GLN against I/R-induced AKI may be related to the Notch and PI3K-Akt signaling pathway.

Xiaoyu Xiezhuo Drink Protects against Ischemia-Reperfusion Acute Kidney Injury in Aged Mice through Inhibiting the TGF-β1/Smad3 and HIF1 Signaling Pathways.

Acute kidney injury (AKI) is responsible for significant mortality among hospitalized patients that is especially troubling aged people. An effective self-made Chinese medicine formula, Xiaoyu Xiezhuo Drink (XXD), displayed therapeutic effects on AKI. However, the compositions and underlying mechanisms of XXD remain to be elucidated. In this study, we used the ultra-high-performance liquid chromatography method coupled with hybrid triple quadrupole time-of-flight mass spectrometry (UHPLC-Q-TOF-MS) to investigate the chemical components in XXD. Then, the absorbable components of XXD were identified based on the five principles and inputted into the SwissTargetPrediction and STITCH databases to identify the drug targets. AKI-related targets were collected from the GenCLiP 3, GeneCards, and DisGeNET databases. The crossover genes of XXD and AKI were identified for functional enrichment analysis. The protein-protein interaction (PPI) network of crossover genes was constructed, followed by the identification of hub genes. Subsequently, the effects and potential mechanisms of XXD on AKI predicted by the network pharmacology and bioinformatics analyses were experimentally validated in ischemia-reperfusion (I/R) injury-induced AKI aged mouse models. A total of 122 components in XXD were obtained; among them, 58 components were found that could be absorbed in the blood. There were 800 potential drug targets predicted from the 58 absorbable components in AKI which shared 36 crossover genes with AKI-related targets. The results of functional enrichment analysis indicated that crossover genes mostly associated with the response to oxidative stress and the HIF1 signaling pathway. In the PPI network analysis, 12 hub genes were identified, including ALB, IL-6, TNF, TP53, VEGFA, PTGS2, TLR4, NOS3, EGFR, PPARG, HIF1A, and HMOX1. In AKI aged mice, XXD prominently alleviated I/R injury-induced renal dysfunction, abnormal renal pathological changes, and cellular senescence, inflammation, and oxidative damage with a reduction in the expression level of the inflammatory mediator, α-SMA, collagen-1, F4/80, TP53, VEGFA, PTGS2, TLR4, NOS3, EGFR, PPARG, HIF1A, ICAM-1, TGF-β1, Smad3, and p-Smad3 and an increase of nephridial tissue p-H3, Ki67, HMOX1, MMP-9, and Smad7 levels. In summary, our findings suggest that XXD has renoprotective effects against AKI in aged mice via inhibiting the TGF-β1/Smad3 and HIF1 signaling pathways.

Local direct thrombin inhibition preserves renal function by mitigating vascular damage and modulating pathophysiologic processes after onset of acute kidney injury

Objective : To determine if thrombin-inhibiting nanoparticles preserve renal function when administered after onset of ischemia-reperfusion acute kidney injury (AKI), and to determine physiologic mechanisms by which this occurs. Hypothesis AKI therapy remains mainly supportive, as recent clinical trials of promising therapeutic agents have failed to preserve renal function. It has been previously shown that delivery of direct thrombin inhibiting nanoparticles prior to onset of AKI in mice has successfully preserved renal function. We hypothesized that inhibition of thrombin clotting and inflammatory signaling with the use of a sustained locally acting nanoparticle formulation might both preserve renal vasculature and broadly modulate pathophysiologic processes that contribute to renal ischemia reperfusion injury even after its onset. Methods C57BL/6 mice underwent bilateral warm ischemia for 17 minutes at 37°C followed by reperfusion. Two hours after reperfusion, mice were injected with either direct thrombin-inhibiting (n=10) or control (n=12) perfluorocarbon nanoparticles (PFC NP). The treatment PFC NP contained ~ 13650 copies per nanoparticle of the direct thrombin inhibitor, PPACK (Proline-Phenylalanine-Arginine-Chloromethyl-Ketone). After 24 hours, blood and kidneys were collected for evaluation of BUN, inflammatory eicosanoids and cytokines, histological analysis of vascular damage, endothelial activation, and cellular infiltrates. Results : Mice treated after AKI with direct thrombin-inhibiting PPACK NP exhibited significantly improved kidney function at 24 hours versus the control group (BUN: 62.10±8.71mg/dL vs 110.96 ±6.21mg/dL, p=0.0002). Vascular integrity was preserved as evidenced by increased expression of CD31 in both cortex (4.28±0.62% vs 1.75±0.34%, p=0.0018) and medulla (3.24±0.38% vs 1.91±0.29%; p=0.0073). Additionally, the PPACK NP group demonstrated significantly less acute tubular necrosis (ATN), further mitigating vascular damage (ATN: 24.44±1.76% vs 37.00±4.96%, p=0.035). Treatment reduced red blood cell trapping and subsequent iron accumulation in both cortex (3.37±0.50% vs 5.34±0.42%, p=0.0083) and medulla (0.50%±0.10% vs 1.01%±0.12%, p=0.006). Inflammatory markers were also reduced in the PPACK NP group, including endothelial VCAM-1 (positive area in medulla 0.49±0.12% vs 1.41±0.60%, p=0.0073), ICAM-1 (positive area in medulla 3.07±0.51% vs 4.46±0.35%, p=0.030). and serum M-CSF and IL-6. Mast cell infiltration and prostaglandin D2 (PGD2) were also decreased. Conclusion Nanoparticle delivery of local thrombin inhibitors that have a known minimal effect on systemic clotting parameters successfully protects renal function by preserving renal vasculature, reducing ATN and iron accumulation, and broadly attenuating thrombin-induced inflammatory mechanisms even when delivered after onset of AKI.

Functional regulation of von Willebrand factor ameliorates acute ischemia-reperfusion kidney injury in mice

Acute kidney injury (AKI), an abrupt loss of renal function, is often seen in clinical settings and may become fatal. In addition to its hemostatic functions, von Willebrand factor (VWF) is known to play a role in cross-talk between inflammation and thrombosis. We hypothesized that VWF may be involved in the pathophysiology of AKI, major causes of which include insufficient renal circulation or inflammatory cell infiltration in the kidney. To test this hypothesis, we studied the role of VWF in AKI using a mouse model of acute ischemia-reperfusion (I/R) kidney injury. We analyzed renal function and blood flow in VWF-gene deleted (knock-out; KO) mice. The functional regulation of VWF by ADAMTS13 or a function-blocking anti-VWF antibody was also evaluated in this pathological condition. Greater renal blood flow and lower serum creatinine were observed after reperfusion in VWF-KO mice compared with wild-type (WT) mice. Histological analysis also revealed a significantly lower degree of tubular damage and neutrophil infiltration in kidney tissues of VWF-KO mice. Both human recombinant ADAMTS13 and a function-blocking anti-VWF antibody significantly improved renal blood flow, renal function and histological findings in WT mice. Our results indicate that VWF plays a role in the pathogenesis of AKI. Proper functional regulation of VWF may improve the microcirculation and vessel function in the kidney, suggesting a novel therapeutic option against AKI.

Determinants of preferential renal accumulation of synthetic polymers in acute kidney injury.

Acute kidney injury (AKI) is a major kidney disease associated with high mortality and morbidity. AKI may lead to chronic kidney disease and end-stage renal disease. Currently, the management of AKI is mainly focused on supportive treatments. Previous studies showed macromolecular delivery systems as a promising method to target AKI, but little is known about how physicochemical properties affect the renal accumulation of polymers in ischemia-reperfusion AKI. In this study, a panel of fluorescently labeled polymers with a range of molecular weights and net charge was synthesized by living radical polymerization. By testing biodistribution of the polymers in unilateral ischemia-reperfusion mouse model of AKI, the results showed that negatively charged and neutral polymers had the greatest potential for selectively accumulating in I/R kidneys. The polymers passed through glomerulus and were retained in proximal tubular cells for up to 24 h after injection. The results obtained in the unilateral model were validated in a bilateral ischemic-reperfusion model. This study demonstrates for the first time that polymers with specific physicochemical characteristics exhibit promising ability to accumulate in the injured AKI kidney, providing initial insights on their use as polymeric drug delivery systems in AKI.

The role of podocyte damage in the etiology of ischemia-reperfusion acute kidney injury and post-injury fibrosis

BackgroundTo establish a model of chronic renal fibrosis following acute kidney injury (AKI) in BALB/c mice and to observe the effect of AKI on podocyte injury and chronic fibrosis of the kidney. Additional aims included using the model to explore the role of podocyte injury in AKI and post-injury fibrosis.MethodsFifty BALB/C mice were randomly divided into control group (Ctr), sham group (sham), AKI 20 group (renal ischemia, 20 min reperfusion), AKI 30 group (renal ischemia, 30 min reperfusion) and AKI 40 group (renal ischemia, 40 min reperfusion). Mice serum and 24-h urine were collected on the 8th, 9th, 10th, 14th, and 28th days for urinary protein, serum creatinine (Scr) and blood urea nitrogen (BUN) analysis. HE staining, transmission electron microscopy (TEM), Masson staining, Q-PCR, Western Blot and immunohistochemistry were applied.ResultsSerum Scr and BUN levels across all AKI groups at the 9th day were significantly higher (P < 0.05) than controls, with higher reperfusion groups maintaining that increase up to 28 days (P < 0.05). Compared with Ctr group, the urinary protein of the AKI 40 group significantly rose on the 9th day (P < 0.05), normalizing immediately on the 10th day (P < 0.05). In contrast, the AKI 30 group rose significantly on the 14th day (P < 0.05) maintaining elevated levels for two weeks (P < 0.05). HE staining demonstrated ischemia-dependent renal tissue damage was aggravated in the mild to aggravated AKI groups. Mesangial proliferation, glomerulosclerosis, and tubulointerstitial pathology were also significantly increased in these groups (P < 0.05). Masson staining further showed that glomerular, renal tubular, and interstitial collagen were increased by ischemia in a time-dependent manner. Transmission EM additionally that podocytes of the mild to severe AKI groups displayed extensive fusion, exfoliation and GBM exposure. Synaptopodin, Nephrin, and CD2AP mRNA and protein expression demonstrated ischemic time-dependent decreases, while the TRPC6 was increased. There was a significant difference in the levels of Synaptopodin, Nephrin, CD2AP, and TRPC6 between the mild and severe AKI groups (P < 0.05).Conclusions1) During the AKI process mice podocyte injury, proteinuria and the subsequent progression into chronic renal fibrosis is observed.2) Podocyte injury may be one of the causes of ischemia-reperfusion acute kidney injury and post-injury fibrosis.

Effects of Ischemic Preconditioning and Postconditioning in a Renal Ischemia-Reperfusion Injury Model: A Comparative Experimental Study in Rats

BackgroundIschemia-reperfusion injury is an unavoidable aspect of transplantation, as well as an important cause of acute kidney injury in clinical practice. Pre- and post-ischemic conditioning are strategies that may provide organs with resistance to major ischemic events. This study evaluates the effects of ischemic preconditioning and ischemic postconditioning, either separately or in combination, after an acute ischemia-reperfusion kidney injury. MethodsForty Wistar rats received isoflurane anesthesia and were randomized into 5 groups: 1. the sham group underwent laparotomy; 2. the control group underwent laparotomy and 30 minutes of renal ischemia followed by reperfusion; 3. the preconditioning group underwent laparotomy, ischemic preconditioning, and 30 minutes of renal ischemia followed by reperfusion; 4. the preconditioning and postconditioning group underwent laparotomy, ischemic preconditioning, 30 minutes of renal ischemia, and ischemic postconditioning followed by reperfusion; and 5. the postconditioning group underwent laparotomy, 30 minutes of renal ischemia, and ischemic postconditioning followed by reperfusion. Serum analyses of creatinine and neutrophil gelatinase-associated lipocalin (NGAL) were performed, and renal histology was examined 24 hours later. ResultsSevere tubular injury and increases in creatinine were observed in all groups except the sham group. The control group and all ischemic conditioning groups were no different in the degree of renal injury and values of NGAL and creatinine after the injury. ConclusionsIschemic preconditioning and ischemic postconditioning, together or separately, are unable to preserve kidney function or exert a protective effect against tubular cell injury after an acute ischemia-reperfusion kidney injury.

The effect of derivatives of sulfur-containing amino acids (ademetionine, taurine and glutathione) on survival of animals with acute kidney injury of various genesis

Aim. To study the nephroprotective effect of sulfur-containing amino acids (ademetionine, taurine and glutathione) on different models of acute kidney injury (AKI) by the integral index of the survival rate of animals.Materials and methods. The experiments were performed on 105 non-linear mature white laboratory rats and 35 mice. The drugs studied – ademetionine (Geptral, Abbott SpA, Italy) in the dose of 20 mg/kg, glutathione (TAD 600, Biomedica Foscama, Italy) in the dose of 30 mg/kg and taurine (Sigma-Aldrich, USA) in the dose of dose 100 mg/kg – were injected intraperitoneally 3-7 days before AKI modeling. Rhabdomyolysis-induced AKI was modeled by the intramuscular injection of 50 % glycerol solution in the dose of 10 ml/kg, toxic AKI – by the injection of gentamicin solution in the dose of 80 mg/kg and the subcutaneous injection of ethylene glycol in the dose of 10 ml/kg. Simulation of renal ischemia was performed under general anesthesia (ethaminal sodium, 40 mg/kg) by clamping of both renal pedicles for a period of 60 min, followed by reperfusion for 24 h.Results and discusion. The experimental results show a significant improvement in the survival of animals under the effect of the drugs of derivatives of sulfur-containing amino acids studied in conditions of various models of AKI. Ademetionine, taurine and glutathione reduced the lethality of animals on models of rhabdomyolytic, gentamicin, ischemia-reperfusion AKI. In conditions of ethylene glycol intoxication the highest nephroprotective activity by the survival criterion was shown by glutathione (57.1 % survival at 48 h after administration of ethylene glycol against 100 % of mortality in the control group (p &lt; 0.05).Conclusions. All derivatives of sulfur-containing amino acids studied (ademetionine, taurine and glutathione) exhibit the nephroprotective activity by the criterion of survival of animals on various models of AKI. Glutathione demonstrates the best survival of animals with acute kidney injury of various genesis, while ademetionine has the lowest survival.