Remote ischemic preconditioning for kidney protection: GSK3β-centric insights into the mechanism of action

NRF2 in kidney physiology and disease

The role of NRF2 in kidney biology has received considerable interest over the past decade. NRF2 transcriptionally controls genes responsible for cellular protection against oxidative and electrophilic stress and has anti-inflammatory functions. NRF2 is expressed throughout the kidney and plays a role in salt and water handling. In disease, animal studies show that NRF2 protects against tubulointerstitial damage and reduces interstitial fibrosis and tubular atrophy, and may slow progression of polycystic kidney disease. However, the role of NRF2 in proteinuric glomerular diseases is controversial. Although the NRF2 inducer, bardoxolone methyl (CDDO-Me), increases glomerular filtration rate in humans, it has not been shown to slow disease progression in diabetic kidney disease and Alport syndrome. Furthermore, bardoxolone methyl was associated with negative effects on fluid retention, proteinuria, and blood pressure. Several animal studies replicate findings of worsened proteinuria and a more rapid progression of kidney disease, although considerable controversy exists. It is clear that further study is needed to better understand the effects of NRF2 in the kidney. This review summarizes the available data to clarify the promise and risks associated with targeting NRF2 activity in the kidney.

Limonin, a natural ERK2 agonist, protects against ischemic acute kidney injury

Acute kidney injury (AKI) is a refractory clinical syndrome with limited effective treatments. Amid AKI, activation of the extracellular signal-regulated kinase (ERK) cascade plays a critical role in promoting kidney repair and regeneration. However, a mature ERK agonist in treating kidney disease remains lacking. This study identified limonin, a member of the class of compounds known as furanolactones, as a natural ERK2 activator. Employing a multidisciplinary approach, we systemically dissected how limonin mitigates AKI. Compared to vehicles, pretreatment of limonin significantly preserved kidney functions after ischemic AKI. We revealed that ERK2 is a significant protein linked to the limonin's active binding sites through structural analysis. The molecular docking study showed a high binding affinity between limonin and ERK2, which was confirmed by the cellular thermal shift assay and microscale thermophoresis. Mechanistically, we further validated that limonin promoted tubular cell proliferation and reduced cell apoptosis after AKI by activating ERK signaling pathway in vivo. In vitro and ex vivo, blockade of ERK abolished limonin's capacity of preventing tubular cell death under hypoxia stress. Our results indicated that limonin is a novel ERK2 activator with strong translational potential in preventing or mitigating AKI.

Beyond its Psychiatric Use: The Benefits of Low-dose Lithium Supplementation

Lithium is most well-known for its mood-stabilizing effects in the treatment of bipolar disorder. Due to its narrow therapeutic window (0.5-1.2 mM serum concentration), there is a stigma associated with lithium treatment and the adverse effects that can occur at therapeutic doses. However, several studies have indicated that doses of lithium under the predetermined therapeutic dose used in bipolar disorder treatment may have beneficial effects not only in the brain but across the body. Currently, literature shows that low-dose lithium (≤0.5 mM) may be beneficial for cardiovascular, musculoskeletal, metabolic, and cognitive function, as well as inflammatory and antioxidant processes of the aging body. There is also some evidence of low-dose lithium exerting a similar and sometimes synergistic effect on these systems. This review summarizes these findings with a focus on low-dose lithium's potential benefits on the aging process and age-related diseases of these systems, such as cardiovascular disease, osteoporosis, sarcopenia, obesity and type 2 diabetes, Alzheimer's disease, and the chronic low-grade inflammatory state known as inflammaging. Although lithium's actions have been widely studied in the brain, the study of the potential benefits of lithium, particularly at a low dose, is still relatively novel. Therefore, this review aims to provide possible mechanistic insights for future research in this field.

PLK2 targets GSK3β to protect against cisplatin-induced acute kidney injury

Cisplatin-induced acute kidney injury (AKI), which is accompanied by a rapid decline in renal function and a high risk of death, is a complex critical illness with no effective or specific treatment. Polo-like kinase 2 (PLK2), a serine/threonine kinase, is involved in the progression of multiple diseases, including cancers, cardiac fibrosis, diabetic nephropathy, etc. Here, by integrating two Gene Expression Omnibus (GEO) datasets of cisplatin-induced AKI animal models, we identified PLK2 as a significantly up-regulated gene in AKI renal tissues, which was then verified in different AKI animal models and cell models. Suppressing PLK2 using siRNAs or inhibitors could enhance cisplatin-induced AKI by inducing severe apoptosis and oxidative stress damage, while enforced PLK2 expression could prevent renal dysfunction induced by cisplatin. We further discovered that PLK2 might phosphorylate glycogen synthase kinase 3β (GSK3β) in the pathogenesis of AKI. In conclusion, our results show that PLK2 play a protective role in cisplatin-induced AKI and may be a new protective target of cisplatin nephrotoxicity.

Therapeutic Targeting of GSK3β-Regulated Nrf2 and NFκB Signaling Pathways by Salvianolic Acid A Ameliorates Peritoneal Fibrosis

Peritoneal fibrosis is a devastating complication in patients undergoing peritoneal dialysis, with no definite therapy yet available. Salvia miltiorrhiza and its major active component Salvianolic acid A (Sal A) have demonstrated a beneficial effect in myriad diseases. However, their effect on peritoneal fibrosis is unknown. In murine models of peritoneal dialysis, daily Sal A treatment substantially improved the peritoneal dialysis fluid (PDF) elicited peritoneal fibrosis, marked by thickening of the submesothelial compact zone, accumulation of extracellular matrix and increased expression of vimentin and PAI-1, concomitant with attenuation of GSK3β hyperactivity. This coincided with diminished nitrotyrosine in peritoneal tissues and increased Nrf2 nuclear translocation, entailing a lessened oxidative injury and reinforced Nrf2 antioxidant response. Meanwhile, inflammatory infiltration and maladaptive angiogenesis in peritoneal tissues provoked by PDF injury were also mitigated by Sal A, associated with a suppressed NFκB activation. Mechanistically, ectopic expression of the constitutively active GSK3β blunted the NFκB-suppressing and Nrf2-activating efficacy of Sal A in peritoneal mesothelial cells exposed to hypertonic dextrose, suggesting that GSK3β inhibition mediates the protective effect of Sal A. Collectively, our findings may open the avenue for developing a novel therapy based on Sal A for preventing peritoneal fibrosis in peritoneal dialysis.

The p38 MAPK/NF-κB pathway mediates GLT-1 up-regulation during cerebral ischemic preconditioning-induced brain ischemic tolerance in rats

Our previous finding suggests that p38 MAPK contributes to the GLT-1 upregulation during induction of brain ischemic tolerance by cerebral ischemic preconditioning (CIP), however, the underlying mechanism is still unclear. Here, we investigated the molecular mechanisms underlying the CIP-induced GLT-1 upregulation by using Western blotting, Co-immunoprecipitation (Co-IP), electrophoretic mobility shift assay (EMSA) and thionin staining in rat hippocampus CA1 subset. We found that application of BAY11-7082 (an inhibitor of NF-κB), or dihydrokainate (an inhibitor of GLT-1), or SB203580 (an inhibitor of p38 MAPK) could attenuate the CIP-induced neuronal protection in hippocampus CA1 region of rats. Moreover, CIP caused rapid activation of NF-κB, as evidenced by nuclear translocation of NF-κB p50 protein, which led to active p50/p65 dimer formation and increased DNA binding activity. GLT-1 was also increased after CIP. Pretreatment with BAY11-7082 blocked the CIP-induced GLT-1 upregulation. The above results suggest that NF-κB participates in GLT-1 up-regulation during the induction of brain ischemic tolerance by CIP. We also found that pretreatment with SB203580 caused significant reduction of NF-κB p50 protein in nucleus, NF-κB p50/p65 dimer nuclear translocation and DNA binding activity of NF-κB. Together, we conclude that p38 MAPK/NF-κB pathway participates in the mediation of GLT-1 up-regulation during the induction of brain ischemic tolerance induced by CIP.

Nature's marvels endowed in gaseous molecules I: Carbon monoxide and its physiological and therapeutic roles

Nature has endowed gaseous molecules such as O2, CO2, CO, NO, H2S, and N2 with critical and diverse roles in sustaining life, from supplying energy needed to power life and building blocks for life's physical structure to mediating and coordinating cellular functions. In this article, we give a brief introduction of the complex functions of the various gaseous molecules in life and then focus on carbon monoxide as a specific example of an endogenously produced signaling molecule to highlight the importance of this class of molecules. The past twenty years have seen much progress in understanding CO's mechanism(s) of action and pharmacological effects as well as in developing delivery methods for easy administration. One remarkable trait of CO is its pleiotropic effects that have few parallels, except perhaps its sister gaseous signaling molecules such as nitric oxide and hydrogen sulfide. This review will delve into the sophistication of CO-mediated signaling as well as its validated pharmacological functions and possible therapeutic applications.

Nrf-2 as a therapeutic target in acute kidney injury

Multifaceted cellular pathways exhibit a crucial role in the preservation of homeostasis at the molecular, cellular, and organism levels. One of the most important of these protective cascades is Nuclear factor E2-related factor (Nrf-2) that regulates the expression of several genes responsible for cellular detoxification, antioxidant function, anti-inflammation, drug/xenobiotic transportation, and stress-related factors. A growing body of evidence provides information regarding the protective role of Nrf-2 against a number of kidney diseases. Acute kidney injury (AKI) is a substantial clinical problem that causes a huge social burden. In the kidneys, Nrf-2 exerts a dynamic role in improving the injury triggered by inflammation and oxidative stress. Understanding of the exact molecular mechanisms underlying AKI is vital in order to determine the equilibrium between renal adaptation and malfunction and thus reduce disease progression. This review highlights the role of Nrf-2 targeting against AKI and provides evidence that targeting Nrf-2 to prevail oxidative damage and its consequences might exhibit protective effects in kidney diseases.

[Ischemia-reperfusion injury after kidney transplantation]

Ischemia-reperfusion injury is an inescapable phenomenon in kidney transplantation. It combines lesional processes of biochemical origin associated with oxydative stress and of immunological origin in connection with the recruitment and activation of innate immunity cells. Histological lesions associate acute tubular necrosis and interstitial œdema, which can progress to interstitial fibrosis. The extent of these lesions depends on donor characteristics (age, expanded criteria donor, etc.) and cold ischemia time. In the short term, ischemia-reperfusion results in delayed recovery of graft function. Cold ischemia time also impacts long-term graft survival. Preclinical models, such as murine and porcine models, have furthered understanding of the pathophysiological mechanisms of ischemia-reperfusion injury. Due to its renal anatomical proximity to humans, the porcine model is relevant to assessment of the molecules administered to a donor or recipient, and also of additives to preservation solutions. Different donor resuscitation and graft perfusion strategies can be studied. In humans, prevention of ischemia-reperfusion injury is a research subject as concerns donor conditioning, additive molecules in preservation solutions, graft reperfusion modalities and choice of the molecules administered to the recipient. Pending significant advances in research, the goal is to achieve the shortest possible cold ischemia time.

Therapeutic strategies for ischemia reperfusion injury in emergency medicine

Ischemia reperfusion (IR) injury occurs when blood supply, perfusion, and concomitant reoxygenation is restored to an organ or area following an initial poor blood supply after a critical time period. Ischemia reperfusion injury contributes to mortality and morbidity in many pathological conditions in emergency medicine clinical practice, including trauma, ischemic stroke, myocardial infarction, and post‐cardiac arrest syndrome. The process of IR is multifactorial, and its pathogenesis involves several mechanisms. Reactive oxygen species are considered key molecules in reperfusion injury due to their potent oxidizing and reducing effects that directly damage cellular membranes by lipid peroxidation. In general, IR injury to an individual organ causes various pro‐inflammatory mediators to be released, which could then induce inflammation in remote organs, thereby possibly advancing the dysfunction of multiple organs. In this review, we summarize IR injury in emergency medicine. Potential therapies include pharmacological treatment, ischemic preconditioning, and the use of medical gases or vitamin therapy, which could significantly help experts develop strategies to inhibit IR injury.

Fundc1-dependent mitophagy is obligatory to ischemic preconditioning-conferred renoprotection in ischemic AKI via suppression of Drp1-mediated mitochondrial fission

FUN14 domain-containing protein 1 (Fundc1)-dependent mitophagy, mainly activated by ischemic/hypoxic preconditioning, benefits acute myocardial reperfusion injury and chronic metabolic syndrome via sustaining mitochondrial homeostasis. Mitochondrial fission plays a pathogenic role in ischemic acute kidney injury (AKI) through perturbation of mitochondrial quality and activation of mitochondrial apoptosis. The aim of our study was to explore the role of Fundc1 mitophagy in ischemia preconditioning (IPC)-mediated renoprotection. Proximal tubule-specific Fundc1 knockout (Fundc1^PTKO) mice were subjected to ischemia reperfusion injury (IRI) and IPC prior to assessment of renal function, mitophagy, mitochondrial quality control, and Drp1-related mitochondrial fission. Following exposure to IPC, Fundc1 mitophagy was activated through post-transcriptional phosphorylation at Ser17. Interestingly, IRI-mediated renal injury, inflammation, and tubule cell death were mitigated by IPC whereas proximal tubule-specific Fundc1 knockout (Fundc1PTKO) mice abolished IPC-offered renoprotection. Mechanistically, IRI-evoked mitochondrial damage was improved by IPC whereas Fundc1 deficiency provoked mitochondrial abnormality, manifested by impaired mitochondrial quality and hyperactivated Drp1-dependent mitochondrial fission. Interestingly, Fundc1 deficiency-associated mitochondrial dysfunction was reversed by pharmacological inhibition of mitochondrial fission. In vivo, Fundc1 deletion-caused renal injury, severe pro-inflammatory response, and tubule cell death could be nullified by way of knockout Drp1 on Fundc1PTKO background. Finally, we also revealed that IPC triggered Fundc1 mitophagy activation through UNC-51-like kinase 1 (Ulk1) and Ulk1 ablation interrupted IPC-mediated Fundc1 activation and thus attenuated IPC-induced renoprotection. Fundc1 mitophagy, primarily driven by IPC, confers resistance to AKI through reconciliation of mitochondrial fission, implicating the therapeutic potential of targeting mitochondrial homeostasis for AKI.

Impact of Arteriovenous fistula creation on estimated glomerular filtration rate decline in Predialysis patients

BACKGROUND

Arteriovenous fistula (AVF) is the vascular access of choice for patients on hemodialysis. Recent evidence suggests that AVF creation may slow estimated glomerular filtration rate (eGFR) decline. The study objective was to assess the impact of the AVF creation on eGFR decline, after controlling for key confounding factors.

METHODS

This retrospective cohort study included adult patients followed in a single-center predialysis clinic between 1999 and 2016. Patients with a patent AVF were followed up to 2 years pre- and post-AVF creation. Estimated GFR trajectory was reported using linear mixed models adjusted for demographic characteristics, comorbidities and use of renin-angiotensin-aldosterone blockade.

RESULTS

A total of 146 patients were studied with a median age 68.7 (60.5-75.4) years and a median eGFR at time of AVF creation of 12.8 (11.3-13.9) mL/min/1.73m2. The crude annual eGFR decline rates were - 3.60 ± 4.00 mL/min/1.73 m2 pre- and - 2.28 ± 3.56 mL/min/1.73 m2 post-AVF, resulting in a mean difference of 1.28 mL/min/1.73 m2 (95% CI 0.49, 2.07). In a mixed effect linear regression model, monthly eGFR decline was - 0.63 (95% CI -0.81, - 0.46; p <  0.001) mL/min/1.73m2/month. The period after AVF creation was associated with a relatively higher eGFR (β 0.94, 95% CI 0.61-1.26, p <  0.001). There was a significant association between follow-up time and the period pre/post AVF (β 0.19, 95% CI 0.16, 0.22; p <  0.001) such that eGFR decline was more attenuated each month after AVF creation.

CONCLUSIONS

In this cohort, AVF creation was associated with a significant reduction of eGFR decline. Further prospective studies are needed to confirm this association.

SGK1 Attenuates Oxidative Stress-Induced Renal Tubular Epithelial Cell Injury by Regulating Mitochondrial Function

Mitochondrial dysfunction has been implicated in the early stages or progression of many renal diseases. Improving mitochondrial function and homeostasis has the potential to protect renal function. Serum- and glucocorticoid-induced kinase 1 (SGK1) is known to regulate various cellular processes, including cell survival. In this study, we intend to demonstrate the effect and molecular mechanisms of SGK1 in renal tubular cells upon oxidative stress injury and to determine whether regulation of mitochondrial function is implicated in this process. HK-2 cells were exposed to H₂O₂, and cell viability and apoptosis were dynamically detected by the CCK-8 assay and annexin-V/PI staining. The concentrations of cellular reactive oxygen species (ROS) and adenosine triphosphate (ATP) and the expression of the SGK1/GSK3β/PGC-1α signaling pathway were analyzed by flow cytometry or western blot. In addition, shRNA targeting SGK1 and SB216763 were added into the culture medium before H₂O₂ exposure to downregulate SGK1 and GSK3β, respectively. Cell viability and mitochondrial functions, including mitochondrial membrane potential (Δψm), Cytochrome C release, mtDNA copy number, and mitochondrial biogenesis, were examined. Protein levels and SGK1 activation were significantly stimulated by H₂O₂ exposure. HK-2 cells with SGK1 inhibition were much more sensitive to H₂O₂-induced oxidative stress injury than control group cells, as they exhibited increased apoptotic cell death and mitochondrial dysfunction involving the deterioration of cellular ATP production, ROS accumulation, mitochondrial membrane potential reduction, and release of Cytochrome C into the cytoplasm. Studies on SGK1 knockdown also indicated that SGK1 is required for the induction of proteins associated with mitochondrial biogenesis, including PGC-1α, NRF-1, and TFAM. Moreover, the deleterious effects of SGK1 suppression on cell apoptosis and mitochondrial function, including mitochondrial biogenesis, were related to the phosphorylation of GSK3β and partially reversed by SB216763 treatment. H₂O₂ leads to SGK1 overexpression in HK-2 cells, which protects human renal tubule cells from oxidative stress injury by improving mitochondrial function and inactivating GSK3β.

Additional effects of erythropoietin pretreatment, ischemic preconditioning, and N-acetylcysteine posttreatment in rat kidney reperfusion injury

Background/aim

Since the nature of ischemia/reperfusion (IR)-induced tissue damage is multifactorial and complex, in the current study, the effects of multiple treatment strategies via concomitant administration of erythropoietin (EPO) and N-acetylcysteine (NAC) with an ischemic preconditioning (IPC) regimen on renal IR injury were examined.

Materials and methods

Thirty male Wistar rats were subjected to bilateral occlusion of the renal pedicles for 50 min followed by reperfusion. EPO (1000 IU/kg) was administered for 3 days, as well as IPC before the IR and NAC (150 mg/kg) administration for 4 days after IR. The animals were randomly allocated into 6 groups (n = 5): sham, IR, EPO+IR, IPC+IR, NAC+IR, and EPO+IPC+NAC+IR. Kidney tissues and blood samples were obtained for oxidative stress, proinflammatory cytokines, and renal functional evaluations.

Results

IR caused significant inflammatory response, oxidative stress, and reduced renal function. Treatment with EPO, IPC, and NAC or a combination of two of them attenuated renal dysfunction and reduced the oxidative stress and inflammatory markers. Rats treated with the combination of EPO, IPC, and NAC showed a higher degree of protection compared to the other groups.

Conclusion

These results showed that concomitant administration of EPO and IPC along with posttreatment NAC may have additive beneficial effects on kidney IR injury during IR-induced acute renal failure.

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.

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AKI to CKD transition involves sustained GSK3β overactivation and impaired Nrf2 response in injured renal tubules.

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Microdose lithium rectifies GSK3β overactivity in the kidney, reinstates Nrf2 response and hinders AKI to CKD transition.

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GSK3β-mediated Keap1-independent regulation of Nrf2 is a novel therapeutic target for modifying long-term sequelae of AKI.

Inhibition of glycogen synthase kinase-3β is involved in cardioprotection by α7nAChR agonist and limb remote ischemic postconditionings

The present study was designed to determine whether glycogen synthase kinase-3β (GSK-3β) was involved in the cardioprotection by α7 nicotinic acetylcholine receptor (α7nAChR) agonist and limb remote ischemic postconditionings. Forty male Sprague-Dawley rats were randomly divided equally into control (C), α7nAChR agonist postconditioning (P), limb remote ischemic postconditioning (L), combined α7nAChR agonist and limb remote ischemic postconditioning (P+L) groups. At the end of experiment, serum cTnI, creatine kinase-MB (CK-MB), tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), high mobility group protein (HMGB1) and interleukin-10 (IL-10) levels were measured; infarct size (IS), myocardial expressions of GSK-3β, p-GSK-3β (Ser9), nuclear factor-κB (NF-κB) and p-NF-κB (Ser536) in the ischemic area were assessed. The results showed that compared with group C, IS, serum cTnI and CK-MB levels obviously decreased in groups P, L and P+L. Compared with groups P and L, IS, serum cTnI and CK-MB levels significantly decreased in group P+L. Compared with group C, serum TNF-α, IL-6 and HMGB1 levels, and myocardial expression of p-NF-κBp65 (Ser536) evidently decreased, and myocardial expression of p-GSK-3β (Ser9) obviously increased in groups P, L and P+L. Compared with group P, serum TNF-α, IL-6 and HMGB1 levels and myocardial expression of p-NF-κBp65 (Ser536) significantly increased, and myocardial expression of p-GSK-3β (Ser9) evidently decreased in group L. Compared with group L, serum TNF-α, IL-6, HMGB1 levels, and myocardial expression of p-NF-κBp65 (Ser536) significantly decreased, and myocardial expression of p-GSK-3β (Ser9) obviously increased in group P+L. In conclusion, our findings indicate that inhibition of GSK-3β to decrease NF-κB transcription is one of cardioprotective mechanisms of α7nAChR agonist and limb remote ischemic postconditionings by anti-inflammation, but improved cardioprotection by combined two interventions is not completely attributable to an enhanced anti-inflammatory mechanism.

Association between vascular access creation and deceleration of estimated glomerular filtration rate decline in late-stage chronic kidney disease patients transitioning to end-stage renal disease

Background

Prior studies have suggested that arteriovenous fistula (AVF) or graft (AVG) creation may be associated with slowing of estimated glomerular filtration rate (eGFR) decline. It is unclear if this is attributable to the physiological benefits of a mature access on systemic circulation versus confounding factors.

Methods

We examined a nationwide cohort of 3026 US veterans with advanced chronic kidney disease (CKD) transitioning to dialysis between 2007 and 2011 who had a pre-dialysis AVF/AVG and had at least three outpatient eGFR measurements both before and after AVF/AVG creation. Slopes of eGFR were estimated using mixed-effects models adjusted for fixed and time-dependent confounders, and compared separately for the pre- and post-AVF/AVG period overall and in patients stratified by AVF/AVG maturation. In all, 3514 patients without AVF/AVG who started dialysis with a catheter served as comparators, using an arbitrary 6-month index date before dialysis initiation to assess change in eGFR slopes.

Results

Of the 3026 patients with AVF/AVG (mean age 67 years, 98% male, 75% diabetic), 71% had a mature AVF/AVG at dialysis initiation. eGFR decline accelerated in the last 6 months prior to dialysis in patients with a catheter (median, from -6.0 to -16.3 mL/min/1.73 m2/year, P < 0.001), while a significant deceleration of eGFR decline was seen after vascular access creation in those with AVF/AVG (median, from -5.6 to -4.1 mL/min/1.73 m2/year, P < 0.001). Findings were independent of AVF/AVG maturation status and were robust in adjusted models.

Conclusions

The creation of pre-dialysis AVF/AVG appears to be associated with eGFR slope deceleration and, consequently, may delay the onset of dialysis initiation in advanced CKD patients.

Remote Ischemic Preconditioning has a Cardioprotective Effect in Children in the Early Postoperative Phase: A Meta-Analysis of Randomized Controlled Trials

In this updated meta-analysis, we assessed the cardioprotective effect of remote ischemic preconditioning (RIPC) in pediatric patients undergoing congenital heart surgery. A total of 9 randomized controlled trials (RCTs) involving 793 pediatric patients under 18 years old were identified. RIPC obviously reduced the release of troponin I at 6 h after surgery [standard mean difference (SMD) -0.59, 95% confidence interval (CI) -1.14 to -0.04; p = 0.03], mitigated the inotropic scores within 4-6 h (SMD -0.43, 95% CI -0.72 to -0.14; p = 0.004) and within 12 h (SMD -0.26, 95% CI -0.50 to -0.02; p = 0.03) and shortened the ventilator support time (SMD -0.28, 95% CI -0.49 to -0.07; p = 0.01) as well as the duration of intensive care unit (ICU) stay (SMD -0.21, 95% CI -0.35 to -0.06; p = 0.004). Our meta-analysis determined that RIPC had cardioprotective effects in the early postoperative phase. Additional RCTs focused on the cardiac benefits from RIPC in pediatric patients are warranted.

Ischemic preconditioning attenuates ischemia/reperfusion-induced kidney injury by activating autophagy via the SGK1 signaling pathway

Ischemic preconditioning (IPC) has a strong renoprotective effect during renal ischemia/reperfusion (I/R) injury that is thought to relate to autophagy. However, the role of autophagy during IPC-afforded renoprotection and the precise mechanisms involved are unknown. In this study, an in vitro hypoxia/reoxygenation (H/R) model was established in which oxygen and glucose deprivation (OGD) was applied to renal cells for 15 h followed by reoxygenation under normal conditions for 30 min, 2 h or 6 h; transient OGD and subsequent reoxygenation were implemented before prolonged H/R injury to achieve hypoxic preconditioning (HPC). 3-Methyladenine (3-MA) was used to inhibit autophagy. In a renal I/R injury model, rats were subjected to 40 min of renal ischemia followed by 6 h, 12 h or 24 h of reperfusion. IPC was produced by four cycles of ischemia (8 min each) followed by 5 min of reperfusion prior to sustained ischemia. We found that IPC increased LC3II and Beclin-1 levels and decreased SQSTM/p62 and cleaved caspase-3 levels in a time-dependent manner during renal I/R injury, as well as increased the number of intracellular double-membrane vesicles in injured renal cells. IPC-induced renal protection was efficiently attenuated by pretreatment with 5 mM 3-MA. Pretreatment with IPC also dynamically affected the expression of SGK1/FOXO3a/HIF-1α signaling components. Moreover, knocking down SGK1 expression significantly downregulated phosphorylated-FOXO3a (p-FOXO3a)/FOXO3 and HIF-1α, suppressed LC3II and Beclin-1 levels, increased SQSTM/p62 and cleaved caspase-3 levels, and abolished the protective effect of IPC against I/R-induced renal damage. SGK1 overexpression efficiently increased p-FOXO3a/FOXO3 and HIF-1α levels, promoted the autophagy flux and enhanced the protective effect mediated by HPC. Furthermore, FOXO3a overexpression decreased HIF-1α protein levels, inhibited HIF-1α transcriptional activity and reduced the protective effect of IPC. Our study indicates that IPC can ameliorate renal I/R injury by promoting autophagy through the SGK1 pathway.

A partnership with the proteasome; the destructive nature of GSK3

Glycogen Synthase Kinase-3 (GSK3) was originally reported as a key enzyme of glucose homeostasis through regulation of the rate of glycogen synthesis. It has subsequently been found to influence most cellular processes, including growth, differentiation and death, as part of its role in modulating response to hormonal, nutritional and cellular stress stimuli. More than 100 protein targets for GSK3 have been proposed although only a small fraction of these have been convincingly validated in physiological cell systems. The effects of GSK3 phosphorylation on substrates include alteration of enzyme activity, protein localisation, protein:protein interaction and protein stability. This latter form of regulation of GSK3 substrates is the focus of this review. There is an ever-growing list of GSK3 substrates that upon phosphorylation are targeted to the beta-transducin repeat containing protein (β-TrCP), thereby allowing ubiquitination of bound protein by cullin-1 and so initiating destruction at the proteasome. We propose the existence of a GSK3-β-TrCP ‘destruction hit-list’ that allows co-ordinated removal (or stabilisation) of a set of proteins with a common physiological purpose, through control of GSK3. We identify 29 proteins where there is relatively strong evidence for regulation by a GSK3-β-TrCP axis and note common features of regulation and pathophysiology. Furthermore, we assess the potential of pre-phosphorylation (priming) of these targets (normally a prerequisite for GSK3 recognition) to provide a second layer of regulation delineated by the priming kinase that allows GSK3 to mark them for destruction. Finally, we discuss whether this knowledge improves options for therapeutic intervention.

Renal Tubular Cell-Derived Extracellular Vesicles Accelerate the Recovery of Established Renal Ischemia Reperfusion Injury

Ischemic renal injury is a complex syndrome; multiple cellular abnormalities cause accelerating cycles of inflammation, cellular damage, and sustained local ischemia. There is no single therapy that effectively resolves the renal damage after ischemia. However, infusions of normal adult rat renal cells have been a successful therapy in several rat renal failure models. The sustained broad renal benefit achieved by relatively few donor cells led to the hypothesis that extracellular vesicles (EV, largely exosomes) derived from these cells are the therapeutic effector in situ We now show that EV from adult rat renal tubular cells significantly improved renal function when administered intravenously 24 and 48 hours after renal ischemia in rats. Additionally, EV treatment significantly improved renal tubular damage, 4-hydroxynanoneal adduct formation, neutrophil infiltration, fibrosis, and microvascular pruning. EV therapy also markedly reduced the large renal transcriptome drift observed after ischemia. These data show the potential utility of EV to limit severe renal ischemic injury after the occurrence.

Rescue therapy with Tanshinone IIA hinders transition of acute kidney injury to chronic kidney disease via targeting GSK3β

Acute kidney injury (AKI) remains challenging for clinical practice and poses a risk of developing progressive chronic kidney disease (CKD) with no definitive treatment available yet. Tanshinone IIA, an active ingredient of Chinese herbal Salvia miltiorrhiza, has been widely used in Asia for the remarkable organoprotective activities. Its effect on established AKI, however, remains unknown. In mice with folic acid-induced AKI, delayed treatment with Tanshinone IIA, commenced early or late after injury, diminished renal expression of kidney injury markers, reduced apoptosis and improved kidney dysfunction, concomitant with mitigated histologic signs of AKI to CKD transition, including interstitial fibrosis and tubular atrophy, and with an ameliorated inflammatory infiltration in tubulointerstitium and a favored M2-skewed macrophage polarization. Mechanistically, Tanshinone IIA blunted glycogen synthase kinase (GSK)3β overactivity and hyperactivation of its downstream mitogen-activated protein kinases that are centrally implicated in renal fibrogenesis and inflammation. Inhibition of GSK3β is likely a key mechanism mediating the therapeutic activity of Tanshinone IIA, because sodium nitroprusside, a GSK3β activator, largely offset its renoprotective effect. In confirmatory studies, rescue treatment with Tanshinone IIA likewise ameliorated ischemia/reperfusion-induced kidney destruction in mice. Our data suggest that Tanshinone IIA represents a valuable treatment that improves post-AKI kidney salvage via targeting GSK3β.

Opioids in Remote Ischemic Preconditioning-Induced Cardioprotection

Remote ischemic preconditioning (RIPC) is an intriguing process whereby transient regional ischemia and reperfusion episodes to remote tissues including skeletal, renal, mesenteric provide protection to the heart against sustained ischemia-reperfusion-induced injury. Clinically, this technique has been used in patients undergoing various surgical interventions including coronary artery bypass graft surgery, abdominal aortic aneurysm repair, percutaneous coronary intervention, and heart valve surgery. The endogenous opioid system is extensively expressed in the brain to modulate pain sensation. Besides the role of opioids in relieving pain, numerous researchers have found their critical involvement in evoking cardioprotective effects. Endogenous opioids including endorphins, enkephalins, and dynorphins are released during RIPC and are critically involved in mediating RIPC-induced cardioprotective effects. It has been suggested that during RIPC, the endogenous opioids may be released into the systemic circulation and may travel via bloodstream that act on the myocardial opioid receptors to induce cardioprotection. The present review describes the potential role of opioids in mediating RIPC-induced cardioprotection.

A differential impact of lithium on endothelium-dependent but not on endothelium-independent vessel relaxation

Lithium is drug for bipolar disorders with a narrow therapeutic window. Lithium was recently reported to prevent stroke and protect vascular endothelium but tends to accumulate particularly in the brain and kidney. Here, adverse effects are common; however mechanisms are still vaguely understood. If lithium could also negatively influence the endothelium is unclear. We hypothesize that at higher lithium levels, the effects on endothelium reverses--that lithium also impairs endothelial-dependent relaxation of blood vessels. Vessel grafts from de-nerved murine aortas and porcine middle cerebral arteries were preconditioned using media supplemented with lithium chloride or acetate (0.4-100 mmol/L). Native or following phenylephrine-induced vasoconstriction, the relaxation capacity of preconditioned vessels was assessed by isometric myography, using acetylcholine to test the endothelium-dependent or sodium nitroprusside to test the endothelium-independent vasorelaxation, respectively. At the 0.4 mmol/L lithium concentration, acetylcholine-induced endothelium-dependent vessel relaxation was slightly increased, however, diminished in a concentration-dependent manner in vessel grafts preconditioned with lithium at higher therapeutic and supratherapeutic concentrations (0.8-100 mmol/L). In contrast, endothelium-independent vasorelaxation remained unaltered in preconditioned vessel grafts at any lithium concentration tested. Lithium elicits opposing effects on endothelial functions representing a differential impact on the endothelium within the narrow therapeutic window. Lithium accumulation or overdose reduces endothelium-dependent but not endothelium-independent vasorelaxation. The differentially modified endothelium-dependent vascular response represents an additional mechanism contributing to therapeutic or adverse effects of lithium.

What we need to know about the effect of lithium on the kidney

Lithium has been a valuable treatment for bipolar affective disorders for decades. Clinical use of lithium, however, has been problematic due to its narrow therapeutic index and concerns for its toxicity in various organ systems. Renal side effects associated with lithium include polyuria, nephrogenic diabetes insipidus, proteinuria, distal renal tubular acidosis, and reduction in glomerular filtration rate. Histologically, chronic lithium nephrotoxicity is characterized by interstitial nephritis with microcyst formation and occasional focal segmental glomerulosclerosis. Nevertheless, this type of toxicity is uncommon, with the strongest risk factors being high serum levels of lithium and longer time on lithium therapy. In contrast, in experimental models of acute kidney injury and glomerular disease, lithium has antiproteinuric, kidney protective, and reparative effects. This paradox may be partially explained by lower lithium doses and short duration of therapy. While long-term exposure to higher psychiatric doses of lithium may be nephrotoxic, short-term low dose of lithium may be beneficial and ameliorate kidney and podocyte injury. Mechanistically, lithium targets glycogen synthase kinase-3β, a ubiquitously expressed serine/threonine protein kinase implicated in the processes of tissue injury, repair, and regeneration in multiple organ systems, including the kidney. Future studies are warranted to discover the exact "kidney-protective dose" of lithium and test the effects of low-dose lithium on acute and chronic kidney disease in humans.