Transition Of Acute Kidney Injury Research Articles

Epidemiology, risk factors, outcomes, and role of Serpin A3 as a biomarker for transition of acute kidney injury to chronic kidney disease in critically ill patients

BackgroundSeveral studies have suggested a causal link between acute kidney injury and the consequent development of chronic kidney disease. The severity, frequency, and duration of acute injury are key factors in this process.AimsThis study aimed to determine the epidemiology and outcomes of AKI to CKD transition in critically ill adult patients and to study the role of Serpin-A3 in the early recognition of AKI to CKD transition.MethodsIn this prospective observational study, a total of 252 patients attending Assiut University Hospitals Critical Care Unit and developed AKI during their stay were recruited. Serum and urinary Serpin A3 were measured by ELISA Kit. Complete blood picture, kidney function tests, urine analysis, serum electrolytes (serum sodium, potassium, calcium, phosphorus, and magnesium), liver function test, coagulation profile, C-reactive protein, 24-h urinary protein or urinary albumin/creatinine ratio, abdominal ultrasound were assessed for all the recruited participants. Follow-up was done for three consecutive months and after 3 months using serum creatinine, BUN, and serum potassium.ResultsIt was found that old age is a risk factor for CKD following AKI, i.e., with 1-year increase in the patient’s age, there was 3% increase in the chance of transition. Significant association was found between rate of comorbidity and transition status. Also, cases with either infection or IV radio contrast exposure were 2.8 and 6.5 times more liable for transition. Cases with transition in this study had significantly higher renal function parameters. Higher median levels of Serpin A3 either serum or urinary was reported in transition patients. Improvement was reported in two-third of those without transition, and higher mortality rate was recorded in those without transition.ConclusionThe frequency of transition was 20%. Older age, male gender, cardiac and CVS disease, the presence of infection, higher BUN and creatinine level, higher median K and PO4 levels, and higher median levels of Serpin A3 are risk factors for transition from AKI to CKD.

GSDMD and GSDME synergy in the transition of acute kidney injury to chronic kidney disease.

Acute kidney injury (AKI) could progress to chronic kidney disease (CKD) and the AKI-CKD transition has major clinical significance. A growing body of evidence has unveiled the role of pyroptosis in kidney injury. We postulate that GSDMD and GSDME exert cumulative effects on the AKI-CKD transition by modulating different cellular responses. We established an AKI-CKD transition model induced by folic acid in wildtype (WT), Gsdmd-/-, Gsdme-/-, and Gsdmd-/-Gsdme-/- mice. Tubular injury, renal fibrosis and inflammatory responses were evaluated. In vitro studies were conducted to investigate the interplay among tubular cells, neutrophils, and macrophages. Double deletion of Gsdmd and Gsdme conferred heightened protection against AKI, mitigating inflammatory responses, including the formation of neutrophil extracellular traps (NETs), macrophage polarization and differentiation, and ultimately renal fibrosis, compared with wildtype mice and mice with single deletion of either Gsdmd or Gsdme. Gsdme, but not Gsdmd deficiency, shielded tubular cells from pyroptosis. GSDME-dependent tubular cell death stimulated NETs formation and prompted macrophage polarization towards a pro-inflammatory phenotype. Gsdmd deficiency suppressed NETs formation and subsequently hindered NETs-induced macrophage-to-myofibroblast transition (MMT). GSDMD and GSDME collaborate to contribute to AKI and subsequent renal fibrosis induced by folic acid. Synchronous inhibition of GSDMD and GSDME could be an innovative therapeutic strategy for mitigating the AKI-CKD transition.

Human proximal tubular epithelial cell-derived small extracellular vesicles mediate synchronized tubular ferroptosis in hypoxic kidney injury

Hypoxia is the key pathobiological trigger of tubular oxidative stress and cell death that drives the transition of acute kidney injury (AKI) to chronic kidney disease (CKD). The mitochondrial-rich proximal tubular epithelial cells (PTEC) are uniquely sensitive to hypoxia and thus, are pivotal in propagating the sustained tubular loss of AKI-to-CKD transition. Here, we examined the role of PTEC-derived small extracellular vesicles (sEV) in propagating the ‘wave of tubular death’.Ex vivo patient-derived PTEC were cultured under normoxia (21 % O2) and hypoxia (1 % O2) on Transwell inserts for isolation and analysis of sEV secreted from apical versus basolateral PTEC surfaces. Increased numbers of sEV were secreted from the apical surface of hypoxic PTEC compared with normoxic PTEC. No differences in basolateral sEV numbers were observed between culture conditions. Biological pathway analysis of hypoxic-apical sEV cargo identified distinct miRNAs linked with cellular injury pathways. In functional assays, hypoxic-apical sEV selectively induced ferroptotic cell death (↓glutathione peroxidase-4, ↑lipid peroxidation) in autologous PTEC compared with normoxic-apical sEV. The addition of ferroptosis inhibitors, ferrostatin-1 and baicalein, attenuated PTEC ferroptosis. RNAse A pretreatment of hypoxic-apical sEV also abrogated PTEC ferroptosis, demonstrating a role for sEV RNA in ferroptotic ‘wave of death’ signalling. In line with these in vitro findings, in situ immunolabelling of diagnostic kidney biopsies from AKI patients with clinical progression to CKD (AKI-to-CKD transition) showed evidence of ferroptosis propagation (increased numbers of ACSL4+ PTEC), while urine-derived sEV (usEV) from these ‘AKI-to-CKD transition’ patients triggered PTEC ferroptosis (↑lipid peroxidation) in functional studies.Our data establish PTEC-derived apical sEV and their intravesicular RNA as mediators of tubular lipid peroxidation and ferroptosis in hypoxic kidney injury. This concept of how tubular pathology is propagated from the initiating insult into a ‘wave of death’ provides novel therapeutic check-points for targeting AKI-to-CKD transition.

Xanthine oxidase/NADPH oxidase inhibition by hydralazine attenuates acute kidney injury and prevents the transition of acute kidney injury to chronic kidney disease

AimsThe enhancement of inflammation and reactive oxygen species leads to the damage of renal tubular cells in acute kidney injury (AKI), and the upregulation of inflammation increases the risk of AKI being converted into chronic kidney disease (CKD). Hydralazine has shown renoprotective effects in multiple kidney diseases and was shown to be a potent xanthine oxidase (XO) inhibitor. This study aimed to investigate the mechanisms of hydralazine in ischemia–reperfusion (I/R)-stimulated renal proximal tubular epithelial cells in vitro and in AKI animals in vivo. Main methodsThe effects of hydralazine in AKI-to-CKD transition were also evaluated. Human renal proximal tubular epithelial cells were stimulated by I/R conditions in vitro. To generate a mouse model of AKI, a right nephrectomy was performed, followed by left renal pedicle I/R using a small atraumatic clamp. Key findingsIn the in vitro part, hydralazine could protect renal proximal tubular epithelial cells against insults from the I/R injury through XO/NADPH oxidase inhibition. In the in vivo part, hydralazine preserved renal function in AKI mice and improved the AKI-to-CKD transition by decreasing renal glomerulosclerosis and fibrosis independently of blood pressure lowering. Furthermore, hydralazine exerted antioxidant, anti-inflammatory, and anti-fibrotic effects both in vitro and in vivo. SignificanceHydralazine, as a XO/NADPH oxidase inhibitor, could protect renal proximal tubular epithelial cells from the insults of I/R and prevent kidney damage in AKI and AKI-to-CKD. The above experimental studies strengthen the possibility of repurposing hydralazine as a potential renoprotective agent through its antioxidative mechanisms.

Association between NLRP3 rs10754558 and CARD8 rs2043211 Variants and Susceptibility to Chronic Kidney Disease.

Nod-like receptor protein 3 (NLRP3) is a multi-protein complex belonging to the innate immune system, whose activation by danger stimuli promotes inflammatory cell death. Evidence supports the crucial role of NLRP3 inflammasome activation in the transition of acute kidney injury to Chronic Kidney Disease (CKD), by promoting both inflammation and fibrotic processes. Variants of NLRP3 pathway-related genes, such as NLRP3 itself and CARD8, have been associated with susceptibility to different autoimmune and inflammatory diseases. In this study, we investigated for the first time the association of functional variants of NLRP3 pathway-related genes (NLRP3-rs10754558, CARD8-rs2043211), with a susceptibility to CKD. A cohort of kidney transplant recipients, dialysis and CKD stage 3-5 patients (303 cases) and a cohort of elderly controls (85 subjects) were genotyped for the variants of interest and compared by using logistic regression analyses. Our analysis showed a significantly higher G allele frequency of the NLRP3 variant (67.3%) and T allele of the CARD8 variant (70.8%) among cases, compared with the control sample (35.9 and 31.2%, respectively). Logistic regressions showed significant associations (p < 0.001) between NLRP3 and CARD8 variants and cases. Our results suggest that the NLRP3 rs10754558 and CARD8 rs2043211 variants could be associated with a susceptibility to CKD.

The role of epigenetic modifi - cation and the possibility of epigenetic therapy in the transition of acute kidney injury to chronic kidney disease

Acute kidney injury (AKI) is a clinically common and life-threatening disease. AKI has become a global problem for human health due to its high prevalence, increased risk of complications, high mortality and high medical costs. Initially, researchers believed that the kidneys had an eff ective ability to regenerate and recover, but studies over the past 20 years have shown that it’s rarely true when we speak about the damage caused by AKI. Even when serum creatinine levels return to baseline, structural damage to the kidneys persists for a long time, leading to the development of chronic kidney disease (CKD). The mechanism for the transition of AKI to CKD has not been fully established. Epigenetic changes, such as histone modifi cation, DNA methylation, and noncoding RNAs, can play an important role in this process as regulators of gene expression. Epigenetic modifi cations are induced by hypoxia, which promotes the gene expression associated with infl ammatory factors and collagen secretion. This review discusses in detail the role of epigenetic modifi cations in the progression of AKI to CKD, the diagnostic value of biomarkers of epigenetic modifi cations in the chronic outcome of AKI, and the potential role of infl uencing epigenetic modifi cations that inhibit the transition of AKI to CKD and improve disease prognosis.

TNF or EGFR inhibition equally block AKI-to-CKD transition: opportunities for etanercept treatment.

Inflammation is a key driver of the transition of acute kidney injury to progressive fibrosis and chronic kidney disease (AKI-to-CKD transition). Blocking a-disintegrin-and-metalloprotease-17 (ADAM17)-dependent ectodomain shedding, in particular of epidermal growth factor receptor (EGFR) ligands and of the type 1 inflammatory cytokine tumor necrosis factor (TNF), reduces pro-inflammatory and pro-fibrotic responses after ischemic AKI or unilateral ureteral obstruction (UUO), a classical fibrosis model. Metalloprotease or EGFR inhibition show significant undesirable side effects in humans. In retrospective studies anti-TNF biologics reduce the incidence and progression of CKD in humans. Whether TNF has a role in AKI-to-CKD transition and how TNF inhibition compares to EGFR inhibition is largely unknown. Mice were subjected to bilateral renal ischemia-reperfusion injury or unilateral ureteral obstruction. Kidneys were analyzed by histology, immunohistochemistry, qPCR, western blot, mass cytometry, scRNA sequencing, and cytokine profiling. Here we show that TNF or EGFR inhibition reduce AKI-to-CKD transition and fibrosis equally by about 25%, while combination has no additional effect. EGFR inhibition reduced kidney TNF expression by about 50% largely by reducing accumulation of TNF expressing immune cells in the kidney early after AKI, while TNF inhibition did not affect EGFR activation or immune cell accumulation. Using scRNAseq data we show that TNF is predominantly expressed by immune cells in AKI but not in proximal tubule cells (PTC), and PTC-TNF knockout did not affect AKI-to-CKD transition in UUO. Thus, the anti-inflammatory and anti-fibrotic effects of the anti-TNF biologic etanercept in AKI-to-CKD transition rely on blocking TNF that is released from immune cells recruited or accumulating in response to PTC-EGFR signals. Short-term anti-TNF biologics during or after AKI could be helpful in the prevention of AKI-to-CKD transition.

Fatty acid amide hydrolase (FAAH) inhibition mitigates TGF‐β1‐induced fibrogenesis via the anandamide‐COX‐2‐dependent pathway

Chronic proximal tubular injury with subsequent fibrosis is the key factor in the transition of acute kidney injury (AKI) to chronic kidney disease (CKD). An increasing body of evidence has shown that endocannabinoids such as anandamide (AEA) and 2‐arachidonoylglycerol (2AG) and their cannabinoid receptors (CBs) play important roles in renal diseases. It remains unclear whether substrates or metabolites of AEA‐metabolizing enzyme FAAH participate in fibrogenesis of kidneys. Though AEA binds the CB1 receptor with high binding affinity, its in vivo pharmacological effects mediated by cannabinoid receptors are of short duration. Likely, active metabolites produced from the rapid catabolism of AEA exert physiological actions. We have previously showed that inhibition of FAAH protects against TGF‐β1‐induced damages via actions independent of CBs in renal tubular cells. Therefore, our aims are to study the effects of downstream metabolites derived from FAAH as well as AEA‐ cyclooxygenase‐2 (COX‐2) pathways on TGF‐β1‐induced renal fibrogenesis. To produce the AKI to CKD transition model, male wild type (WT) C57BL6 and Faah−/− mice were subjected to post ischemia‐reperfusion injury (PIR) by unilateral kidney ischemia‐reperfusion and contralateral nephrectomy 10 days after ischemia‐reperfusion. Our previous studies showed that Faah−/− mice protected against PIR‐induced renal fibrogenesis. Here, LC‐MS/MS assay demonstrated that PIR‐injured WT mice had a significant downregulation of renal AEA level, which was blocked in Faah−/−‐PIR mice (68% reduction in WT‐PIR versus 12% in Faah−/−‐PIR mice compared with WT‐sham group, p&lt;0.001), whereas 2AG showed no difference between WT‐PIR and Faah−/−‐PIR mice (1.2‐fold versus 1.1‐fold increase, p&gt;0.9). In addition, Faah−/− mice did not show difference in the levels of arachidonic acid (AA) (1.13‐fold to WT‐sham, p=0.25), the downstream metabolites of FAAH. Our previous in vitro studies showed that TGF‐β1‐induced profibrotic effects in HK‐2 cells (human kidney proximal tubular epithelial cells) were abolished after the treatment of FAAH inhibitor (PF‐04457845, PF, 1μM) in a CB2‐independent manner. In the current study, blockage of AEA‐COX‐2 derived prostamides pathway by a substrate‐selective COX‐2 inhibitor (LM‐4131, 300nM) reversed the decreased level of a profibrotic marker α‐smooth muscle actin (α‐SMA) caused by PF (1.9‐fold in TGF‐β1, 0.83‐fold in PF+TGF‐β1 and 2.88‐fold in PF+LM‐4131+TGF‐β1 compared to the control group, p&lt;0.0001). Further, supplement of AA did not reverse the protection of FAAH inhibition against TGF‐β1‐induced expression of α‐SMA (2.53‐fold in TGF‐β1, 0.62‐fold in PF+TGF‐β1 versus 0.48‐fold in AA+PF+TGF‐β1 compared to the control group, p&gt;0.99). The AEA‐COX‐2 metabolite, prostamide E2 mimicked the protective effect of FAAH inhibition against TGF‐β1‐induced α‐SMA expression (2.17‐fold in TGF‐β1 vs. 0.9‐fold in prostamide E2 +TGF‐β1 compared to the control group, p&lt;0.0001). Overall, the present study suggests that inactivation of FAAH augments the actions of downstream metabolites of AEA‐COX‐2, which mediates the protection against TGF‐β1‐induced renal fibrogenesis.

Serial Intravital 2‐photon Imaging Deciphers in Vivo Renal Myofibroblast Dynamics at the Fork of Acute Kidney Injury‐induced Tubular Repair and Nephron Loss

Myofibroblasts were suggested to play a pivotal role in the transition of acute kidney injury (AKI) to chronic kidney disease, by engaging in progressive and self‐perpetuating tubulointerstitial fibrosis. Wound healing from AKI gives rise to myofibroblast‐activation from renal interstitial PDGFRβ‐cells. In this study, we exploited a novel model of partial ischemia reperfusion injury (IRI), to track dynamic PDGFRbeta‐cell interactions with injured and non‐injured tissue over time and addressed the question if and how myofibroblast‐derived renal interstitial fibrosis may progress and deteriorate non‐injured renal tissue after AKI.PDGFRβ‐CreERT2‐Salsa6F reporter mice identified PDGFRβ‐cells by tdTomato expression. IRI was performed by unilateral occlusion of only one branch of the left renal artery for 21 min, resulting in half of the left kidney being ischemic, while the other half remained non‐ischemic. This was followed by abdominal imaging window implantation for serial imaging of the same kidney cells in border areas for 2 to 3 weeks (N=5). To test for myofibroblast differentiation, we performed ex vivo staining for αSMA on the same tissue regions as previously imaged in vivo.IRI‐induced necrotic tubular cell death, as detected in vivo by Propidium Iodide (PI)‐staining, was only observed on day 0 (D0) post IRI. Proximal tubules (PTs) with intermediate necrotic injury (mean ± SD) (21±15% dead cells of total cell number per segment) underwent successful self‐repair within 7 days through dedifferentiation as indicated by shedding of the apical membrane (peaking at D2), followed by the temporal flattening of the epithelium. In highly injured PT segments (39±15% cell death), dedifferentiation was followed by epithelial vacuolization (starting at D4/D7), resulting in failed repair in 35% of the cases as indicated by collapsed and karyolitic tubules evident between D7 and D14.Tubule injury initiated pronounced PDGFRβ‐cell recruitment, which resulted in remarked enclosure of the remodeling epithelium. Thus, PDGFRβ‐cell recruitment peaked at D4, and D7 with a maximum coverage of PT cell surface of 29±6% and 44±14% for surviving tubules of initially low and high necrotic injury, respectively. In non‐surviving tubules, PDGFRβ‐cell recruitment peaked D7 with 63±18% of the remodeling PT cells covered. Ex vivo stainings for αSMA confirmed PDGFRβ‐cell differentiation to myofibroblasts. Importantly, regardless of respective tubule faith, PDGFRβ‐cell accumulation resolved over the period from D7‐D14/21 and did not progress towards non‐injured tubules. Further, ex vivo stainings at D14/21 indicated αSMA‐negativity of persistent and previously injury‐interacting PDGFRβ‐cells, indicating the reversibility of myofibroblast differentiation.Our data indicate locally restricted, injury‐dependent and reversible PDGFRβ‐cell accumulation and myofibroblast‐differentiation in ischemic tissue regions. There is no indication for the existence of self‐perpetuating interstitial fibrosis and deterioration of healthy nephrons. Furthermore, our data indicates the reversibility of myofibroblast‐differentiation upon completed repair programs.

Incidence and Transition of Acute Kidney Injury, Acute Kidney Disease to Chronic Kidney Disease after Acute Type A Aortic Dissection Surgery.

Acute kidney disease (AKD) is the persistence of renal injury between days 8 and 90 after an initial acute kidney injury (AKI). In this study, we aimed to explore the incidence of AKD, the association between AKD, and patient outcomes after acute type A aortic dissection (type A AAD) surgery. We identified 696 participants who underwent type A AAD surgery. Patients were categorized into stages 1 to 3 or 0 (non-AKD) AKD groups. Outcomes included major adverse kidney events (MAKEs), respiratory failure, all-cause readmission, and ischemic stroke from day 91 after operation. A total of 376 (54%) participants developed AKI, and 135/376 (35.9%) developed AKD. Moreover, 34/320 (10.6%) patients without AKI still developed AKD. Overall, 169/696 (24.3%) participants developed AKD. Patients with stages 2 and 3 AKD are associated with persisted declined renal function within 1 year. AKD was associated with a higher risk of MAKEs (hazard ratio (HR): 2.52, 95% confidence interval (CI) 1.90–3.33) and all-cause readmission (HR: 2.86, 95% CI: 2.10–3.89). Development of AKD with or without AKI is associated with a higher risk of MAKEs and hospitalization after acute aortic dissection surgery. Higher-stage AKD is associated with a trend of persistent decline in kidney function.

Cyclophilin D Promotes Acute, but Not Chronic, Kidney Injury in a Mouse Model of Aristolochic Acid Toxicity.

The plant-derived toxin, aristolochic acid (AA), is the cause of Chinese Herb Nephropathy and Balkan Nephropathy. Ingestion of high dose AA induces acute kidney injury, while chronic low dose ingestion leads to progressive kidney disease. Ingested AA is taken up by tubular epithelial cells of the kidney, leading to DNA damage and cell death. Cyclophilin D (CypD) participates in mitochondrial-dependent cell death, but whether this mechanism operates in acute or chronic AA-induced kidney injury is unknown. We addressed this question by exposing CypD-/- and wild type (WT) mice to acute high dose, or chronic low dose, AA. Administration of 5 mg/kg AA to WT mice induced acute kidney injury 3 days later, characterised by loss of kidney function, tubular cell damage and death, and neutrophil infiltration. All of these parameters were significantly reduced in CypD-/- mice. Chronic low dose (2 mg/kg AA) administration in WT mice resulted in chronic kidney disease with impaired renal function and renal fibrosis by day 28. However, CypD-/- mice were not protected from AA-induced chronic kidney disease. In conclusion, CypD facilitates AA-induced acute kidney damage, but CypD does not contribute to the transition of acute kidney injury to chronic kidney disease during ongoing AA exposure.

Role of SIK1 in the transition of acute kidney injury into chronic kidney disease

BackgroundAcute kidney injury (AKI), with a high morbidity and mortality, is recognized as a risk factor for chronic kidney disease (CKD). AKI-CKD transition has been regarded as one of the most pressing unmet needs in renal diseases. Recently, studies have showed that salt inducible kinase 1 (SIK1) plays a role in epithelial-mesenchymal transition (EMT) and inflammation, which are the hallmarks of AKI-CKD transition. However, whether SIK1 is involved in AKI-CKD transition and by what mechanism it regulates AKI-CKD transition remains unknown.MethodsWe firstly detected the expression of SIK1 in kidney tissues of AKI patients and AKI mice by immunohistochemistry staining, and then we established Aristolochic acid (AA)-induced AKI-CKD transition model in C57BL/6 mice and HK2 cells. Subsequently, we performed immunohistochemistry staining, ELISA, real-time PCR, Western blot, immunofluorescence staining and Transwell assay to explore the role and underlying mechanism of SIK1 on AKI-CKD transition.ResultsThe expression of SIK1 was down-regulated in AKI patients, AKI mice, AA-induced AKI-CKD transition mice, and HK2 cells. Functional analysis revealed that overexpression of SIK1 alleviated AA-induced AKI-CKD transition and HK2 cells injury in vivo and in vitro. Mechanistically, we demonstrated that SIK1 mediated AA-induced AKI-CKD transition by regulating WNT/β-catenin signaling, the canonical pathway involved in EMT, inflammation and renal fibrosis. In addition, we discovered that inhibition of WNT/β-catenin pathway and its downstream transcription factor Twist1 ameliorated HK2 cells injury, delaying the progression of AKI-CKD transition.ConclusionsOur study demonstrated, for the first time, a protective role of SIK1 in AKI-CKD transition by regulating WNT/β-catenin signaling pathway and its downstream transcription factor Twist1, which will provide novel insights into the prevention and treatment AKI-CKD transition in the future.

Angiotensin II type 1a receptor loss ameliorates chronic tubulointerstitial damage after renal ischemia reperfusion

We investigate whether suppressing the activation of the angiotensin II type 1a receptor (AT1a) can ameliorate severe chronic tubulointerstitial damage (TID) after renal ischemia reperfusion (IR) using AT1a knockout homozygous (AT1a−/−) male mice. To induce severe chronic TID after renal IR, unilateral renal ischemia was performed via clamping of the right renal pedicle in both AT1a−/− and wild-type (AT1a+/+) mice for 45 min. While marked renal atrophy and severe TID at 70 days postischemia was induced in the AT1a+/+ mice, such a development was not provoked in the AT1a−/− mice. Although the AT1a+/+ mice were administered hydralazine to maintain the same systolic blood pressure (SBP) levels as the AT1a−/− mice with lower SBP levels, hydralazine did not reproduce the renoprotective effects observed in the AT1a−/− mice. Acute tubular injury at 3 days postischemia was similar between the AT1a−/− mice and the AT1a+/+ mice. From our investigations using IR kidneys at 3, 14, and 28 days postischemia, the multiple molecular mechanisms may be related to prevention of severe chronic TID postischemia in the AT1a−/− mice. In conclusion, inactivation of the AT1 receptor may be useful in preventing the transition of acute kidney injury to chronic kidney disease.

Inhibition of IRE1/JNK pathway in HK-2 cells subjected to hypoxia-reoxygenation attenuates mesangial cells-derived extracellular matrix production.

Endoplasmic reticulum (ER) stress and inflammatory responses play active roles in the transition of acute kidney injury (AKI) to chronic kidney disease (CKD). Inositol‐requiring enzyme 1 (IRE1) activates c‐Jun NH2‐terminal kinase (JNK) in ER stress. Tubular epithelial cells (TEC) are the main injury target and source of AKI inflammatory mediators. TEC injury may lead to glomerulosclerosis, however, the underlying mechanism remains unclear. Here, hypoxia/reoxygenation (H/R) HK‐2 cells were used as an AKI model. To determine the partial effects of TEC injury on the glomerulus, HK‐2 cells after H/R were co‐cultured with human renal mesangial cells (HRMC). H/R up‐regulated ER stress, IRE1/JNK pathway, IL‐6 and MCP‐1 in HK‐2 cells. Stimulation of HRMC with IL‐6 enhanced their proliferation and the expression of glomerulosclerosis‐associated fibronectin and collagen IV via signal transducer and activator of transcription 3 (STAT3) activation. Similar responses were observed in HRMC co‐cultured with HK‐2 cells after H/R. IRE1/JNK inhibition reversed these injury responses in HRMC. IRE1/JNK stable knock‐down in HK‐2 cells and shRNA‐mediated STAT3 depletion in HRMC confirmed their role in inflammation/glomerulosclerosis. These findings suggest that IRE1/JNK pathway mediates inflammation in TEC, affecting mesangial cells. The inhibition of this pathway could be a feasible approach to prevent AKI‐CKD transition.

Impact of aging on transition of acute kidney injury to chronic kidney disease

Acute kidney injury (AKI) increases the risk of end stage renal disease among the elderly, but the precise underlying mechanism is unknown. We investigated the effects of aging on AKI-to-chronic kidney disease (CKD) transition, focusing on renal inflammation. Aged and young C57BL/6 mice were subjected to bilateral ischemia-reperfusion injury (IRI). Baseline proinflammatory cytokine levels of kidneys were elevated in aged mice. After IRI, aged mice also showed persistent M1 dominant inflammation, with increased proinflammatory cytokines during the recovery phase. Persistent M1 inflammation was associated with blunted activation of CSF-1/IRF4 signal for M1/M2 polarization, but in vitro macrophage polarization with cytokine stimulation was not different between young and aged mononuclear cells. The tubular expressions of cell cycle arrest markers increased in aged mice during recovery phase, and in vitro transwell experiments showed that mononuclear cells or M1 macrophages co-cultured with arrested proximal tubular cells at G1 phase significantly impaired M2 polarization, suggesting that prolonged G1 arrest might be involved in persistent M1 inflammation in aged mice. Finally, M1 dominant inflammation in aged mice resulted in fibrosis progression. Our data show that impaired M2 polarization partially driven by senescent tubule cells with cell-cycle arrest may lead to an accelerated progression to CKD in the elderly.

Incidence, Risk Factors, and Outcomes of Transition of Acute Kidney Injury to Chronic Kidney Disease in Cirrhosis: A Prospective Cohort Study.

Transition to chronic kidney disease (CKD) after an episode of acute kidney injury (AKI) is known in patients without cirrhosis. We studied the incidence and risk factors for development of CKD in patients with cirrhosis. Competing risk analysis was performed to identify risk factors for CKD development. Of 818 patients with cirrhosis (age, 50.4±11.8years; 84% males; Model for End-Stage Liver Disease [MELD], 19.9±9.9), 36% had AKI at enrollment, 27% had previous AKI, and 61% developed new episodes of AKI during the follow-up period. CKD developed in 269 (33%) patients. Serum cystatin C (CysC; subdistribution hazard ratio [SHR], 1.58; 1.07-2.33), episodes of previous AKI (SHR, 1.26; 1.02-1.56), and AKI stage at enrollment (no AKI [SHR, 1] vs. stage 1 [SHR, 3.28; 1.30-8.25] vs. stage 2 [SHR, 4.33; 1.76-10.66] vs. stage 3 [SHR, 4.5; 1.59-12.73]) were identified as baseline risk factors for CKD development. On time-varying competing risk analysis, MELD (SHR, 1.01; 1.00-1.03), number of AKI episodes (SHR, 1.25; 1.15-1.37), and CysC (SHR, 1.38; 1.01-1.89) predicted CKD development. Development of CKD was associated with higher risk of death. Reduction in glomerular filtration rate (GFR) not meeting CKD criteria was observed in 66% of patients with cirrhosis, more so in those with previous AKI episodes and a high CysC level and MELD score. Renal histology, available in 55 patients, showed tubulointerstitial injury in 86%, cholemic nephrosis in 29%, and glomerular changes in 38%. Conclusion: Almost two-thirds of patients with cirrhosis develop episodes of AKI and reduction in GFR; one-third progress to CKD, resulting in adverse outcomes. Higher MELD and CysC levels and number of AKI episodes predict development of CKD in patients with cirrhosis.

Transition of Acute Kidney Injury to Chronic Kidney Disease

Transition of Acute Kidney Injury to Chronic Kidney Disease

GSK3β-mediated Keap1-independent regulation of Nrf2 antioxidant response: A molecular rheostat of acute kidney injury to chronic kidney disease transition

Transition of acute kidney injury (AKI) to chronic kidney disease (CKD) represents an important cause of kidney failure. However, how AKI is transformed into CKD remains elusive. Following folic acid injury, mice developed AKI with ensuing CKD transition, featured by variable degrees of interstitial fibrosis and tubular cell atrophy and growth arrest. This lingering injury of renal tubules was associated with sustained oxidative stress that was concomitant with an impaired Nrf2 antioxidant defense, marked by mitigated Nrf2 nuclear accumulation and blunted induction of its target antioxidant enzymes, like heme oxygenase (HO)-1. Activation of the canonical Keap1/Nrf2 signaling, nevertheless, seems intact during CKD transition because Nrf2 in injured tubules remained activated and elevated in cytoplasm. Moreover, oxidative thiol modification and activation of Keap1, the cytoplasmic repressor of Nrf2, was barely associated with CKD transition. In contrast, glycogen synthase kinase (GSK)3β, a key modulator of the Keap1-independent Nrf2 regulation, was persistently overexpressed and hyperactive in injured tubules. Likewise, in patients who developed CKD following AKI due to diverse etiologies, like volume depletion and exposure to radiocontrast agents or aristolochic acid, sustained GSK3β overexpression was evident in renal tubules and coincided with oxidative damages, impaired Nrf2 nuclear accumulation and mitigated induction of antioxidant gene expression. Mechanistically, the Nrf2 response against oxidative insult was sabotaged in renal tubular cells expressing a constitutively active mutant of GSK3β, but reinforced by ectopic expression of dominant negative GSK3β in a Keap1-independent manner. In vivo in folic acid-injured mice, targeting GSK3β in renal tubules via conditional knockout or by weekly microdose lithium treatment reinstated Nrf2 antioxidant response in the kidney and hindered AKI to CKD transition. Ergo, our findings suggest that GSK3β-mediated Keap1-independent regulation of Nrf2 may serve as an actionable therapeutic target for modifying the long-term sequelae of AKI.

Metabolomic and biochemical characterization of a new model of the transition of acute kidney injury to chronic kidney disease induced by folic acid.

BackgroundRenal diseases represent a major public health problem. The demonstration that maladaptive repair of acute kidney injury (AKI) can lead to the development of chronic kidney disease (CKD) and end-stage renal disease has generated interest in studying the pathophysiological pathways involved. Animal models of AKI–CKD transition represent important tools to study this pathology. We hypothesized that the administration of multiple doses of folic acid (FA) would lead to a progressive loss of renal function that could be characterized through biochemical parameters, histological classification and nuclear magnetic resonance (NMR) profiling.MethodsWistar rats were divided into groups: the control group received a daily intraperitoneal (I.P.) injection of double-distilled water, the experimental group received a daily I.P. injection of FA (250 mg kg body weight−1). Disease was classified according to blood urea nitrogen level: mild (40–80 mg dL−1), moderate (100–200 mg dL−1) and severe (>200 mg dL−1). We analyzed through biochemical parameters, histological classification and NMR profiling.ResultsBiochemical markers, pro-inflammatory cytokines and kidney injury biomarkers differed significantly (P < 0.05) between control and experimental groups. Histology revealed that as damage progressed, the degree of tubular injury increased, and the inflammatory infiltrate was more evident. NMR metabolomics and chemometrics revealed differences in urinary metabolites associated with CKD progression. The main physiological pathways affected were those involved in energy production and amino-acid metabolism, together with organic osmolytes. These data suggest that multiple administrations of FA induce a reproducible model of the induction of CKD. This model could help to evaluate new strategies for nephroprotection that could be applied in the clinic.

Potential target-organ protection of mineralocorticoid receptor antagonist in acute kidney disease.

Acute kidney disease (AKD), the transition of acute kidney injury to chronic kidney disease, has major clinical significance. Whether mineralocorticoid receptor antagonist will afford target organ protection during this critical stage remains ill-defined. Using a population-based cohort database from January 1999 to July 2011, we identified 7252 AKD patients with hypertension, of whom 2255 were treated with mineralocorticoid receptor antagonist (user) and 4997 were treated by other antihypertensive medication (nonuser). Outcomes were all-cause mortality, major adverse cardiovascular events (MACE), and long-term dialysis dependence. With median 13.37 months of follow-up (IQR 30.53 months), users had a lower incidence of dialysis dependence than nonusers (138.3/1000 person-years vs. 267.2/1000 person-years). After matching users and nonusers (1 : 1) with mortality as a competing risk, Cox proportional hazards analyses showed that mineralocorticoid receptor antagonist therapy was associated with lower risk of dialysis dependence [subhazard ratio (sHR) = 0.83, 95% confidence interval (CI) 0.74-0.93, P = 0.001] but higher risk of hyperkalemia (sHR 1.15, 95% CI, 1.04-1.26, P = 0.005) compared with nonusers. Nonetheless, the risks for all-cause mortality [adjusted hazard ratio (aHR) 1.07, 95% CI 0.98-1.17, P = 0.109] and MACE (sHR 1.08, 95% CI 0.95-1.23, P = 0.210) were similar. Although carrying the risk of hyperkalemia, mineralocorticoid receptor antagonist therapy is associated with similar risk for incident MACE and death; however, with lower risk of long-term dialysis dependence. Our findings have the potential to provide target-organ protection insights in AKD patients with hypertension.