Kidney ischemic preconditioning

Dexmedetomidine preconditioning reduces ischaemia-reperfusion injury in equine model of large colon volvulus

BACKGROUND

Large colon volvulus is a cause of colic in horses with high morbidity and mortality when not promptly treated. More treatment options are needed to improve the outcome of these cases by protecting against the damage caused by ischaemia and reperfusion injury.

OBJECTIVES

To determine the effect of preconditioning with dexmedetomidine prior to induction of ischaemia-reperfusion (IR) injury in a large colon volvulus model in the horse.

STUDY DESIGN

Randomised blinded in vivo experiments.

METHODS

Horses received either a dexmedetomidine (DEX) or saline (CON) constant rate infusion (CRI) immediately following induction of anaesthesia. Venous, arterial, and transmural occlusion of a section of the large colon was performed for 3 h, after which the ligatures and clamps were removed to allow for reperfusion for 3 h. Biopsies of the large colon were taken at baseline, 1 and 3 h of ischaemia, and at 1 and 3 h of reperfusion.

RESULTS

The severity of crypt epithelial loss (DEX = 2.1 [0.8-2.8], CON = 3.1 [2.5-4], p = 0.03) and mucosal haemorrhage was decreased (DEX = 2.1 [1.3-3], CON = 3.5 [2.5-4], p = 0.03) in group DEX compared to group CON when graded on a scale of 0-4. Crypt length remained longer (DEX = 369.5 ± 91.7 μm, CON = 238.5 ± 72.6 μm, p = 0.02) and interstitium to crypt (I:C) ratio remained lower (DEX = 1.4 (1-1.7), CON = 2.6 [1.8-5.9], p = 0.03) in group DEX compared to group CON during reperfusion.

MAIN LIMITATIONS

Clinical applicability of pharmacologic preconditioning is limited.

CONCLUSION

Preconditioning with a dexmedetomidine CRI prior to IR injury demonstrated a protective effect histologically on the large colon in the horse. Further investigation into postconditioning with dexmedetomidine is warranted as a possible intervention in colic cases suspected of being large colon volvulus.

The Dual-specificity Phosphatase 3 (DUSP3): A Potential Target Against Renal Ischemia/Reperfusion Injury

Renal ischemia/reperfusion (I/R) injury is a common clinical challenge faced by clinicians in kidney transplantation. I/R is the leading cause of acute kidney injury, and it occurs when blood flow to the kidney is interrupted and subsequently restored. I/R impairs renal function in both short and long terms. Renal ischemic preconditioning refers to all maneuvers intended to prevent or attenuate ischemic damage. In this context, the present review focuses on the dual-specificity phosphatase 3 (DUSP3), also known as vaccinia H1-related phosphatase, an uncommon regulator of mitogen-activated protein kinase (MAPK) phosphorylation. DUSP3 has different biological functions: (1) it acts as a tumor modulator and (2) it is involved in the regulation of immune response, thrombosis, hemostasis, angiogenesis, and genomic stability. These functions occur either through MAPK-dependent or MAPK-independent mechanisms. DUSP3 genetic deletion dampens kidney damage and inflammation caused by I/R in mice, suggesting DUSP3 as a potential target for preventing renal I/R injury. Here, we discuss the putative role of DUSP3 in ischemic preconditioning and the potential mechanisms of such an attenuated inflammatory response via improved kidney perfusion and adequate innate immune response.

Energy depletion by cell proliferation sensitizes the kidney epithelial cells to injury

Acute kidney injury activates both proliferative and antiproliferative pathways, the consequences of which are not fully elucidated. If an initial proliferation of the renal epithelium is necessary for the successful repair, the persistence of proliferation markers is associated with the occurrence of chronic kidney disease. We hypothesized that proliferation in stress conditions impacts cell viability and renal outcomes. We found that proliferation is associated with cell death after various stresses in kidney cells. In vitro, the ATP/ADP ratio oscillates reproducibly throughout the cell cycle, and cell proliferation is associated with a decreased intracellular ATP/ADP ratio. In vivo, transcriptomic data from transplanted kidneys revealed that proliferation was strongly associated with a decrease in the expression of the mitochondria-encoded genes of the oxidative phosphorylation pathway, but not of the nucleus-encoded ones. These observations suggest that mitochondrial function is a limiting factor for energy production in proliferative kidney cells after injury. The association of increased proliferation and decreased mitochondrial function was indeed associated with poor renal outcomes. In summary, proliferation is an energy-demanding process impairing the cellular ability to cope with an injury, highlighting proliferative repair and metabolic recovery as indispensable and interdependent features for successful kidney repair.NEW & NOTEWORTHY ATP depletion is a hallmark of acute kidney injury. Proliferation is instrumental to kidney repair. We show that ATP levels vary during the cell cycle and that proliferation sensitizes renal epithelial cells to superimposed injuries in vitro. More proliferation and less energy production by the mitochondria are associated with adverse outcomes in injured kidney allografts. This suggests that controlling the timing of kidney repair might be beneficial to mitigate the extent of acute kidney injury.

Pretreatment with remote ischemic conditioning attenuates testicular damage after testicular ischemia and reperfusion injury in rats

Testicular torsion is a urological emergency. However, surgical detorsion of the torsed spermatic cord can cause testicular reperfusion injury. Although remote ischemic preconditioning (RIPC) has been convincingly shown to protect organs against ischemia/reperfusion (I/R) injury, little is known regarding the effect of RIPC on testicular torsion/detorsion-induced reperfusion injury. Therefore, we aimed to evaluate the effect of RIPC on testes after testicular I/R injury in a rat model in vivo. Male Sprague-Dawley rats were randomly classified into 4 groups: sham-operated (sham), testicular I/R (TI/R), or remote liver (RIPC liver) and limb (RIPC limb) ischemic preconditioning groups. Testis I/R was induced by 3 h of right spermatic cord torsion (720° clockwise), and reperfusion was allowed for 3 hours. In the RIPC group, four cycles of 5 min of ischemia and 5 min of reperfusion were completed 30 min prior to testicular torsion. The ERK1/2 inhibitor U0126 was administered intravenously at the beginning of reperfusion (1 mg/kg). The testes were taken for the oxidative stress evaluations, histology, apoptosis, immunohistochemical and western blotting analysis. Remote liver and limb ischemic preconditioning attenuated ipsilateral and contralateral testicular damage after testicular I/R injury. For example. RIPC reduced testicular swelling and oxidative stress, lessened structural damage, and inhibited the testicular inflammatory response and apoptosis. Furthermore, RIPC treatment enhanced testicular ERK1/2 phosphorylation postI/R. Inhibition of ERK1/2 activity using U0126 eliminated the protection offered by RIPC. Our data demonstrate for the first time that RIPC protects testes against testicular I/R injury via activation of the ERK1/2 signaling pathway.

Nitric Oxide in Cardiac Surgery: A Review Article

Perioperative organ injury remains a medical, social and economic problem in cardiac surgery. Patients with postoperative organ dysfunction have increases in morbidity, length of stay, long-term mortality, treatment costs and rehabilitation time. Currently, there are no pharmaceutical technologies or non-pharmacological interventions that can mitigate the continuum of multiple organ dysfunction and improve the outcomes of cardiac surgery. It is essential to identify agents that trigger or mediate an organ-protective phenotype during cardiac surgery. The authors highlight nitric oxide (NO) ability to act as an agent for perioperative protection of organs and tissues, especially in the heart-kidney axis. NO has been delivered in clinical practice at an acceptable cost, and the side effects of its use are known, predictable, reversible and relatively rare. This review presents basic data, physiological research and literature on the clinical application of NO in cardiac surgery. Results support the use of NO as a safe and promising approach in perioperative patient management. Further clinical research is required to define the role of NO as an adjunct therapy that can improve outcomes in cardiac surgery. Clinicians also have to identify cohorts of responders for perioperative NO therapy and the optimal modes for this technology.

Radiotherapy Advances in Renal Disease-Focus on Renal Ischemic Preconditioning

Ionizing irradiation is widely applied as a fundamental therapeutic treatment in several diseases. Acute kidney injury (AKI) represents a global public health problem with major morbidity and mortality. Renal ischemia/reperfusion (I/R) is the main cause of AKI. I/R injury occurs when blood flow to the kidney is transiently interrupted and then restored. Such an ischemic insult significantly impairs renal function in the short and long terms. Renal ischemic preconditioning (IPC) corresponds to the maneuvers intended to prevent or attenuate the ischemic damage. In murine models, irradiation-induced preconditioning (IP) renders the renal parenchyma resistant to subsequent damage by activating defense pathways involved in oxidative stress, angiogenesis, and inflammation. Before envisioning translational applications in patients, safe irradiation modalities, including timing, dosage, and fractionation, need to be defined.

P2X7 Receptors in Astrocytes: A Switch for Ischemic Tolerance

A sub-lethal ischemic episode (preconditioning [PC]) protects neurons against a subsequent lethal ischemic injury. This phenomenon is known as ischemic tolerance. PC itself does not cause brain damage, but affects glial responses, especially astrocytes, and transforms them into an ischemia-resistant phenotype. P2X7 receptors (P2X7Rs) in astrocytes play essential roles in PC. Although P2X7Rs trigger inflammatory and toxic responses, PC-induced P2X7Rs in astrocytes function as a switch to protect the brain against ischemia. In this review, we focus on P2X7Rs and summarize recent developments on how astrocytes control P2X7Rs and what molecular mechanisms they use to induce ischemic tolerance.

Value of T2 Mapping in the Dynamic Evaluation of Renal Ischemia-Reperfusion Injury

OBJECTIVE

To explore the value of T2 mapping in the dynamic quantitative evaluation of renal ischemia- reperfusion injury (IRI).

MATERIALS AND METHODS

Forty-eight healthy New Zealand rabbits were randomly divided into IRI group (n = 40) and control group (n = 8). Rabbits in the IRI group underwent left renal artery clamping for 60 minutes. Rabbits underwent MRI examinations (T2WI and T2 mapping) before and 1, 12, 24, and 48 hours after IRI. The inter-observer and intra-observer reproducibility of the T2 values were assessed using the intraclass correlation coefficient (ICC) with 95% confidence interval (CI). Correlations between the T2 value of the renal outer medulla and injury scores were assessed by Spearman correlation analysis. The repeated measures analysis of variance was used to compare the differences in T2 values of the IRI and control group across the different time points.

RESULTS

Both of the intra-observer (ICC = 0.97, 95% CI 0.95-0.99) and inter-observer reproducibility (ICC = 0.92, 95% CI 0.86-0.96) were excellent for T2 values. The T2 value of the renal outer medulla was moderately positive correlated with tubular epithelial edema (ρ = 0.686, p < 0.001). In IRI group, T2 values of the renal outer medulla were increase at 1 h after IRI (p = 0.001) and were decrease from 1 h to 12 h (p = 0.002). At 1 h after IRI, the T2 values of the renal outer medulla for the IRI group were higher than those for the control group (p < 0.001).

CONCLUSION

T2 mapping can reflect the dynamic changes of renal parenchyma in an animal model of IRI and be used to assess the early renal IRI.

Sex Differences in Acute Kidney Injury

Female sex confers renoprotection in chronic progressive kidney disease. It is less well recognized that sexual dimorphism also is evident in the development of ischemic and nephrotoxic acute kidney injury (AKI). Animal studies consistently have shown that female sex protects against the development of renal injury in experimental models of ischemic AKI. However, the consensus opinion is that in human beings, female sex is an independent risk factor for AKI. Based on a systematic review of experimental and clinical literature, we present data to support the conclusion that, contrary to consensus opinion, it is male sex, not female sex, that is associated with the development of AKI.

Hypoxic preconditioning in renal ischaemia-reperfusion injury: a review in pre-clinical models

Ischaemia-reperfusion injury (IRI) is a major cause of acute kidney injury (AKI) and chronic kidney disease, which consists of cellular damage and renal dysfunction. AKI is a major complication that is of particular concern after cardiac surgery and to a lesser degree following organ transplantation in the immediate post-transplantation period, leading to delayed graft function. Because effective therapies are still unavailable, several recent studies have explored the potential benefit of hypoxic preconditioning (HPC) on IRI. HPC refers to the acquisition of increased organ tolerance to subsequent ischaemic or severe hypoxic injury, and experimental evidences suggest a potential benefit of HPC. There are three experimental forms of HPC, and, for better clarity, we named them as follows: physical HPC, HPC via treated-cell administration and stabilised hypoxia-inducible factor (HIF)-1α HPC, or mimicked HPC. The purpose of this review is to present the latest developments in the literature on HPC in the context of renal IRI in pre-clinical models. The data we compiled suggest that preconditional activation of hypoxia pathways protects against renal IRI, suggesting that HPC could be used in the treatment of renal IRI in transplantation.

PPARγ in Ischemia-Reperfusion Injury: Overview of the Biology and Therapy

Ischemia-reperfusion injury (IRI) is a complex pathophysiological process that is often characterized as a blood circulation disorder caused due to various factors (such as traumatic shock, surgery, organ transplantation, burn, and thrombus). Severe metabolic dysregulation and tissue structure destruction are observed upon restoration of blood flow to the ischemic tissue. Theoretically, IRI can occur in various tissues and organs, including the kidney, liver, myocardium, and brain, among others. The advances made in research regarding restoring tissue perfusion in ischemic areas have been inadequate with regard to decreasing the mortality and infarct size associated with IRI. Hence, the clinical treatment of patients with severe IRI remains a thorny issue. Peroxisome proliferator-activated receptor γ (PPARγ) is a member of a superfamily of nuclear transcription factors activated by agonists and is a promising therapeutic target for ameliorating IRI. Therefore, this review focuses on the role of PPARγ in IRI. The protective effects of PPARγ, such as attenuating oxidative stress, inhibiting inflammatory responses, and antagonizing apoptosis, are described, envisaging certain therapeutic perspectives.

Metabolically active and polyploid renal tissues rely on graded cytoprotection to drive developmental and homeostatic stress resilience

Body tissues are frequently exposed to stress, from toxic byproducts generated during cellular metabolism through to infection or wounding. Although it is well-established that tissues respond to exogenous injury by rapidly upregulating cytoprotective machinery, how energetically demanding tissues - vulnerable to persistent endogenous insult - withstand stress is poorly understood. Here, we show that the cytoprotective factors Nrf2 and Gadd45 act within a specific renal cell subtype, the energetically and biosynthetically active 'principal' cells, to drive stress resilience during Drosophila renal development and homeostasis. Renal tubules lacking Gadd45 exhibit striking morphogenetic defects (with cell death, inflammatory infiltration and reduced ploidy) and accumulate significant DNA damage in post-embryonic life. In parallel, the transcription factor Nrf2 is active during periods of intense renal physiological activity, where it protects metabolically active renal cells from oxidative damage. Despite its constitutive nature, renal cytoprotective activity must be precisely balanced and sustained at modest sub-injury levels; indeed, further experimental elevation dramatically perturbs renal development and function. We suggest that tissues requiring long-term protection must employ restrained cytoprotective activity, whereas higher levels might only be beneficial if activated transiently pre-emptive to exogenous insult.

LPS Preconditioning Attenuates Apoptosis Mechanism by Inhibiting NF-κB and Caspase-3 Activity: TLR4 Pre-activation in the Signaling Pathway of LPS-Induced Neuroprotection

Neuroinflammation, an inflammatory response within the nervous system, has been shown to be implicated in the progression of various neurodegenerative diseases. Recent in vivo studies showed that lipopolysaccharide (LPS) preconditioning provides neuroprotection by activating Toll-like receptor 4 (TLR4), one of the members for pattern recognition receptor (PRR) family that play critical role in host response to tissue injury, infection, and inflammation. Pre-exposure to low dose of LPS could confer a protective state against cellular apoptosis following subsequent stimulation with LPS at higher concentration, suggesting a role for TLR4 pre-activation in the signaling pathway of LPS-induced neuroprotection. However, the precise molecular mechanism associated with this protective effect is not well understood. In this article, we provide an overall review of the current state of our knowledge about LPS preconditioning in attenuating apoptosis mechanism and conferring neuroprotection via TLR4 signaling pathway.

Renal Dysfunction following Direct Current Cardioversion of Atrial Fibrillation: Incidence and Risk Factors

INTRODUCTION

Emerging data suggest that cardioversion for atrial fibrillation (AF) may be associated with acute kidney injury (AKI). However, limited data are available regarding the incidence and risk factors for AKI after direct current cardioversion (DCCV) of AF.

METHODS

All patients undergoing DCCV at Mayo Clinic between 2001 and 2012 for AF were prospectively enrolled in a database. All patients with serum creatinine (SCR) values pre- and post-cardioversion were reviewed for AKI, defined as a ≥25% decline in eGFR (estimated glomerular filtration rate) from baseline value within 7 days of the DCCV.

RESULTS

Of the 6,427 eligible patients, 1,256 (19.5%) patients had pre- and post-DCCV SCR available and formed the cohort under study. The mean age was 70.4 (SD 11.7) years, and 67.3% were male. During the study period, 131 (10.4%) patients suffered from AKI following DCCV. AKI was independently associated with inpatient status (OR 26.79; 95% CI 3.69-194.52), CHA2DS2-VASc score (OR 1.25; 95% CI 1.11-1.41), prior use of diuretics (OR 1.59; 95% CI 1.03-2.46), and absence of CKD (OR 1.61; 95% CI 1.04-2.49), and was independent of the success of the DCCV. None of the patients required acute dialysis during the study outcome period.

CONCLUSION

AKI following DCCV of AF is common, self-limited, and without the need for replacement therapies.

A Review of Donor Acute Kidney Injury and Posttransplant Outcomes

Although over 90 000 people are on the kidney transplant waitlist in the United States, some kidneys that are viable for transplantation are discarded. Transplant surgeons are more likely to discard deceased donors with acute kidney injury (AKI) versus without AKI (30% versus 18%). AKI is defined using changes in creatinine from baseline. Transplant surgeons can use DonorNet data, including admission, peak, and terminal serum creatinine, and biopsy data when available to differentiate kidneys with AKI from those with chronic injury. Although chronic kidney disease is associated with reduced graft survival, an abundance of literature has demonstrated similar graft survival for deceased donors with AKI versus donors without AKI. Donors with AKI are more likely to undergo delayed graft function but have similar long-term outcomes as donors without AKI. The mechanism for similar graft survival is unclear. Some hypothesized mechanisms include (1) ischemic preconditioning; (2) posttransplant and host factors playing a greater role in long-term survival than donor factors; and (3) selection bias of transplanting only relatively healthy donor kidneys with AKI. Existing literature suggests transplanting more donor kidneys with stage 1 and 2 AKI, and cautious utilization of stage 3 AKI donors, may increase the pool of viable kidneys. Doing so can reduce the number of people who die on the waitlist by over 500 every year.

Sequential Wnt Agonist Then Antagonist Treatment Accelerates Tissue Repair and Minimizes Fibrosis

Tissue fibrosis compromises organ function and occurs as a potential long-term outcome in response to acute tissue injuries. Currently, lack of mechanistic understanding prevents effective prevention and treatment of the progression from acute injury to fibrosis. Here, we combined quantitative experimental studies with a mouse kidney injury model and a computational approach to determine how the physiological consequences are determined by the severity of ischemia injury and to identify how to manipulate Wnt signaling to accelerate repair of ischemic tissue damage while minimizing fibrosis. The study reveals that memory of prior injury contributes to fibrosis progression and ischemic preconditioning reduces the risk of death but increases the risk of fibrosis. Furthermore, we validated the prediction that sequential combination therapy of initial treatment with a Wnt agonist followed by treatment with a Wnt antagonist can reduce both the risk of death and fibrosis in response to acute injuries.

Parenterial iron sucrose-induced renal preconditioning: differential ferritin heavy and light chain expression in plasma, urine, and internal organs

Experimental data suggest that iron sucrose (FeS) injection, used either alone or in combination with other prooxidants, can induce "renal preconditioning," in part by upregulating cytoprotective ferritin levels. However, the rapidity, degree, composition (heavy vs. light chain), and renal ferritin changes after FeS administration in humans remain to be defined. To address these issues, healthy human volunteers (n = 9) and patients with stage 3-4 chronic kidney disease(n = 9) were injected once with FeS (120, 240, or 360 mg). Plasma ferritin was measured from 0 to 8 days postinjection as an overall index of ferritin generation. Urinary ferritin served as a "biomarker" of renal ferritin production. FeS induced rapid (≤2 h), dose-dependent, plasma ferritin increases in all study participants, peaking at approximately three to five times baseline within 24-48 h. Significant urinary ferritin increases (~3 times), without dose-dependent increases in albuminuria, neutrophil gelatinase-associated lipocalin, or N-acetyl-β-d-glucosaminidase excretion, were observed. Western blot analysis with ferritin heavy chain (Fhc)- and light chain (Flc)-specific antibodies demonstrated that FeS raised plasma Flc but not Fhc levels. Conversely, FeS increased both Fhc and Flc in urine. To assess sites of FeS-induced ferritin generation, organs from FeS-treated mice were probed for Fhc, Flc, and their mRNAs. FeS predominantly raised hepatic Flc. Conversely, marked Fhc and Flc elevations developed in the kidney and spleen. No cardiopulmonary ferritin increases occurred. Ferritin mRNAs remained unchanged throughout, implying posttranscriptional ferritin production. We conclude that FeS induces rapid, dramatic, and differential Fhc and Flc upregulation in organs. Renal Fhc and Flc increases, in the absence of nephrotoxicity, suggest potential FeS utility as a clinical renal "preconditioning" agent.

Clearance of damaged mitochondria via mitophagy is important to the protective effect of ischemic preconditioning in kidneys

Ischemic preconditioning (IPC) affords tissue protection in organs including kidneys; however, the underlying mechanism remains unclear. Here we demonstrate an important role of macroautophagy/autophagy (especially mitophagy) in the protective effect of IPC in kidneys. IPC induced autophagy in renal tubular cells in mice and suppressed subsequent renal ischemia-reperfusion injury (IRI). The protective effect of IPC was abolished by pharmacological inhibitors of autophagy and by the ablation of Atg7 from kidney proximal tubules. Pretreatment with BECN1/Beclin1 peptide induced autophagy and protected against IRI. These results suggest the dependence of IPC protection on renal autophagy. During IPC, the mitophagy regulator PINK1 (PTEN induced putative kinase 1) was activated. Both IPC and BECN1 peptide enhanced mitolysosome formation during renal IRI in mitophagy reporter mice, suggesting that IPC may protect kidneys by activating mitophagy. We further established an in vitro model of IPC by inducing ‘chemical ischemia’ in kidney proximal tubular cells with carbonyl cyanide 3-chlorophenylhydrazone (CCCP). Brief treatment with CCCP protected against subsequent injury in these cells and the protective effect was abrogated by autophagy inhibition. In vitro IPC increased mitophagosome formation, enhanced the delivery of mitophagosomes to lysosomes, and promoted the clearance of damaged mitochondria during subsequent CCCP treatment. IPC also suppressed mitochondrial depolarization, improved ATP production, and inhibited the generation of reactive oxygen species. Knockdown of Pink1 suppressed mitophagy and reduced the cytoprotective effect of IPC. Together, these results suggest that autophagy, especially mitophagy, plays an important role in the protective effect of IPC.

Abbreviations: ACTB: actin, beta; ATG: autophagy related; BNIP3: BCL2 interacting protein 3; BNIP3L/NIX: BCL2 interacting protein 3 like; BUN: blood urea nitrogen; CASP3: caspase 3; CCCP: carbonyl cyanide 3-chlorophenylhydrazone; COX4I1: cytochrome c oxidase subunit 4I1; COX8: cytochrome c oxidase subunit 8; DAPI: 4ʹ,6-diamidino-2-phenylindole; DNM1L: dynamin 1 like; EGFP: enhanced green fluorescent protein; EM: electron microscopy; ER: endoplasmic reticulum; FC: floxed control; FIS1: fission, mitochondrial 1; FUNDC1: FUN14 domain containing 1; H-E: hematoxylin-eosin; HIF1A: hypoxia inducible factor 1 subunit alpha; HSPD1: heat shock protein family D (Hsp60) member 1; IMMT/MIC60: inner membrane mitochondrial protein; IPC: ischemic preconditioning; I-R: ischemia-reperfusion; IRI: ischemia-reperfusion injury; JC-1: 5,5ʹ,6,6ʹ-tetrachloro-1,1ʹ,3,3ʹ-tetraethylbenzimidazolylcarbocyanine iodide; KO: knockout; MAP1LC3B/LC3B: microtubule associated protein 1 light chain 3 beta; mito-QC: mito-quality control; mRFP: monomeric red fluorescent protein; NAC: N-acetylcysteine; PINK1: PTEN induced putative kinase 1; PPIB: peptidylprolyl isomerase B; PRKN: parkin RBR E3 ubiquitin protein ligase; ROS: reactive oxygen species; RPTC: rat proximal tubular cells; SD: standard deviation; sIPC: simulated IPC; SQSTM1/p62: sequestosome 1; TOMM20: translocase of outer mitochondrial membrane 20; TUNEL: terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling

UCP2 protect the heart from myocardial ischemia/reperfusion injury via induction of mitochondrial autophagy

Uncoupling protein 2 (UCP2), located in the mitochondrial inner membrane, is a predominant isoform of UCP that expressed in the heart and other tissues of human and rodent tissues. Nevertheless, its functional role during myocardial ischemia/reperfusion (I/R) is not entirely understood. Ischemic preconditioning (IPC) remarkably improved postischemic functional recovery followed by reduced lactate dehydrogenase (LDH) release with simultaneous upregulation of UCP2 in perfused myocardium. We then investigated the role of UCP2 in IPC-afforded cardioprotective effects on myocardial I/R injury with adenovirus-mediated in vivo UCP2 overexpression (AdUCP2) and knockdown (AdshUCP2). IPC-induced protective effects were mimicked by UCP2 overexpression, while which were abolished with silencing UCP2. Mechanistically, UCP2 overexpression significantly reinforced I/R-induced mitochondrial autophagy (mitophagy), as measured by biochemical hallmarks of mitochondrial autophagy. Moreover, primary cardiomyocytes infected with AdUCP2 increased simulated ischemia/reperfusion (sI/R)-induced mitophagy and therefore reversed impaired mitochondrial function. Finally, suppression of mitophagy with mdivi-1 in cultured cardiomyocytes abolished UCP2-afforded protective effect on sI/R-induced mitochondrial dysfunction and cell death. Our data identify a critical role for UCP2 against myocardial I/R injury through preventing the mitochondrial dysfunction through reinforcing mitophagy. Our findings reveal novel mechanisms of UCP2 in the cardioprotective effects during myocardial I/R.

Remote ischemic conditioning in a rat model of testicular torsion: does it offer testicular protection?

BACKGROUND

Testicular torsion is a surgical emergency mainly affecting adolescent boys, with a relatively high rate of missed torsion and testicular loss secondary to delay in prompt diagnosis and surgical intervention. With ischemic reperfusion injury as its underlying culprit, testicular torsion may respond favorably to remote ischemic conditioning (RIC) where a non-privileged site (e.g. limb) is concurrently rendered ischemic to divert the cascade of reperfusion injury from the privileged organ (e.g. testicle), thus offering a protective effect in improving salvage. This mechanism is established for other organs, whereas it has not been evaluated for testis.

AIM

It was aimed to evaluate RIC in a rat model of testicular torsion as a proof of principle that, similar to what has been demonstrated in other organs, RIC does offer testicular protection.

STUDY DESIGN

This is an animal experimental study. Thirty Sprague-Dawley male rats were divided into control group (n = 15) and experimental group (n = 15). Non-survival surgeries of right-sided spermatic cord torsion (720° counter-clockwise twist) were performed for both the groups (45 min) followed by detorsion and reperfusion (5 min) and then orchiectomy. For the experiment group, an intervention of tail clamping to create RIC was applied 5 min after torsion, then unclamping 5 min before detorsion, followed by detorsion and reperfusion for 5 min and then orchiectomy. The testicles were histologically and immunologically examined using a hypoxia inducible factor (HIF-1α) ELISA Kit. The histological findings on ischemic changes, vascular congestion, and immunohistochemistry were quantified using previously described, validated grading systems.

RESULTS

DISCUSSION: This is the first study to demonstrate the concept of RIC in an animal model of testicular torsion. It is limited by the non-availability of similar studies to compare outcomes and by the caution of extrapolating animal studies on humans. It does lay grounds, however, to subsequent studies to further elaborate on this concept and its clinical applicability.

CONCLUSION

When RIC is applied in the experimental setting of testicular torsion, there is less evidence of hypoxic injury by histology and immunohistochemistry.

Human extracellular microvesicles from renal tubules reverse kidney ischemia-reperfusion injury in rats

Hypoxic acute kidney injury, a major unresolved problem, initiates, or aggravates, renal functional and structural decline. There is no treatment for hypoxic acute renal injury and its sequelae. We tested the hypothesis that human kidney tubular cells, or their extracellular vesicles (exosomes), prevent renal injury when infused intravenously 24 hours after 50 minutes of bilateral renal ischemia in Nude rats. Cells and their exosomes were from harvested human kidneys declined for transplantation. Injections of either cells or exosomes, given after 24 and 48 hours of reperfusion, preserved renal function and structure in both treatment groups. However, exosomes were superior to cells; and maintained renal vascular and epithelial networks, prevented renal oxidant stress, and apoptosis; and restrained activation of pro-inflammatory and pro-fibrogenic pathways. Exosomes worked in 24 hours, consistent with functional rather than regenerative activity. Comprehensive proteomic analysis identified 6152 renal proteins from all cellular compartments; and 628 were altered by ischemia at all cell levels, while 377 were significantly improved by exosome infusions. We conclude that renal damage from severe ischemia was broad, and human renal exosomes prevented most protein alterations. Thus, exosomes seem to acutely correct a critical and consequential abnormality during reperfusion. In their absence, renal structure and cells transition to a chronic state of fibrosis and extensive renal cell loss.

New roles of reactive astrocytes in the brain; an organizer of cerebral ischemia

The brain consists of neurons and much higher number of glial cells. They communicate each other, by which they control brain functions. The brain is highly vulnerable to several insults such as ischemia, but has a self-protective and self-repairing mechanisms against these. Ischemic tolerance or preconditioning is an endogenous neuroprotective phenomenon, where a mild non-lethal ischemic episode can induce resistance to a subsequent severe ischemic injury in the brain. Because of its neuroprotective effects against cerebral ischemia or stroke, ischemic tolerance has been widely studied. However, almost all studies have been performed from the viewpoint of neurons. Glial cells are structurally in close association with synapses. Recent studies have uncovered the active roles of astrocytes in modulating synaptic connectivity, such as synapse formation, elimination and maturation, during development or pathology. However, glia-mediated ischemic tolerance and/or neuronal repairing have received only limited attention. We and others have demonstrated that glial cells, especially astrocytes, play a pivotal role in regulation of induction of ischemic tolerance as well as repairing/remodeling of neuronal networks by phagocytosis. Here, we review our current understanding of (1) glial-mediated ischemic tolerance and (2) glia-mediated repairing/remodeling of the penumbra neuronal networks, and highlight their mechanisms as well as their potential benefits, problems, and therapeutic application.

Astrocytes and ischemic tolerance

A mild non-lethal ischemic episode can induce resistance to a subsequent severe ischemic injury in the brain. This phenomenon is termed ischemic tolerance or ischemic preconditioning, and is an endogenous mechanism that can provide robust neuroprotection. Because of its neuroprotective effects against cerebral ischemia or stroke, ischemic tolerance has been widely studied. However, almost all studies have been performed from the viewpoint of neurons. Accumulating evidence suggests that glial cells have various roles in regulation of brain function, including modulation of synaptic transmission, neuronal excitation, and neuronal structure. In addition, astrocytes are closely related to homeostasis, stability of brain function, and protection of neurons. However, glial cells have received only limited attention with regard to ischemic tolerance. Cross-ischemic preconditioning is a phenomenon whereby non-ischemic preconditioning such as mechanical, thermal, and chemical treatment can induce ischemic tolerance. Of these, chemical treatments that affect the immune system can strongly induce ischemic tolerance, suggesting that glial cells may have important roles in this process. Indeed, we and others have demonstrated that glial cells, especially astrocytes, play a pivotal role in the induction of ischemic tolerance. This glial-mediated ischemic tolerance provides a robust and long-lasting neuroprotection against ischemic injury. In this review, we discuss the mechanisms underlying glial-mediated ischemic tolerance, as well as its potential benefits, problems, and therapeutic application.

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.

The role of Toll-like receptor 4 (TLR4) in cardiac ischaemic-reperfusion injury, cardioprotection and preconditioning

Cardiac ischaemic-reperfusion injury (IRI) remains the primary cause of mortality throughout the developed world. Molecular mechanisms underlying IRI are complex and are often interlinked with each other driving a synergistic response. Toll-like receptor 4 (TLR4), an immunosurveillance receptor, is known to enhance tissue injury during IRI by enhancing the inflammatory response. The release of endogenous components during IRI bind onto TLR4 leading to the activation of multiple signalling kinases. Once this event occurs these proteins are defined as danger associated molecular patterns molecules (DAMPs) or alarmins. Examples include heat shock proteins, high mobility group box one (HMGB1) and extracellular matrix proteins, all of which are involved in IRI. However, literature in the last two decades suggests that transient stimulation of TLR4 may suppress IRI and thus improve cardiac recovery. Furthermore, it remains to be seen what role TLR4 plays during ischaemic-preconditioning where acute bouts of ischaemia, preceding a harmful bout of ischaemic-reperfusion, is cardioprotective. The other question which also needs to be considered is that if transient TLR4 signalling drives a preconditioning response then what are the ligands which drive this? Hence the second part of this review explores the possible TLR4 ligands which may promote cardioprotection against IRI.

A nationwide survey of clinical characteristics, management, and outcomes of acute kidney injury (AKI) - patients with and without preexisting chronic kidney disease have different prognoses

Acute kidney injury (AKI) is a common complication in hospitalized patients. The International Society of Nephrology implemented the "0 by 25" initiative aimed at preventing deaths from treatable AKI worldwide by 2025 and conducted a global snapshot survey in 2014. We joined in the project and conducted this study to compare the epidemiology, risk factors, and prognosis between patients with pure AKI and those with acute-on-chronic kidney disease (ACKD). In this study, we prospectively collected demographic parameters and data on clinical characteristics, baseline comorbidities, management, and outcomes of 201 AKI patients in 18 hospitals in Taiwan from September 2014 to November 2014. The in-hospital mortality rate was 16%. AKI was mostly attributed to sepsis (52%). Multivariate logistic regression indicated that oliguria was a positive independent predictor of in-hospital mortality, whereas preexisting CKD and exposure to nephrotoxic agents were negative independent predictors. The prevalence of vasopressor use, intensive care unit care, and mortality were significantly higher in pure AKI patients than in ACKD patients. Moreover, serum creatinine (SCr) levels significantly increased within 7 days after AKI diagnosis in nonsurvivors but not in survivors in the pure AKI group. By contrast, SCr levels were persistently lower in nonsurvivors than in survivors in the ACKD group during the same period. We thus determined that the prognosis of ACKD patients differed from that of pure AKI patients. Considering the CKD history in the future AKI staging system may improve prognosis prediction.

Prolyl-hydroxylase inhibitor activating hypoxia-inducible transcription factors reduce levels of transplant arteriosclerosis in a murine aortic allograft model

OBJECTIVES

The development of transplant arteriosclerosis, the hallmark feature of heart transplant rejection, is associated with a chronic immune response and also influenced by an initial injury to the graft through ischaemia and reperfusion. Hypoxia-inducible transcription factor (HIF)-1 pathway signalling has a protective effect against ischaemia-reperfusion injury and has already been demonstrated to ameliorate allograft nephropathy in previous animal studies. Therefore, the aim of this study was to investigate the effect of stabilization of hypoxia-inducible transcription factors with a prolyl-hydroxylase domain (PHD) inhibitor on transplant arteriosclerosis in an experimental aortic allograft model.

METHODS

MHC-class I mismatched C.B10-H2(b)/LilMcdJ donor thoracic aortas were heterotopically transplanted into the abdominal aorta of BALB/c mice. Donor animals received a single dose of the PHD inhibitor 2-(1-chloro-4-hydroxyisoquinoline-3-carboxamido) acetate (ICA) (40 mg/kg) or vehicle i.p. 4 h before transplantation. Intragraft HIF accumulation after ICA treatment was detected by immunohistochemistry before and after cold ischaemia (n = 5). Grafts were harvested 30 days after transplantation and analysed by histology (n = 7) and immunofluorescence (n = 7). In addition, intragraft mRNA expression for cytokines, adhesion molecules and growth factors was determined on Day 14 (n = 7).

RESULTS

Donor preconditioning with ICA resulted in HIF accumulation in the aorta and induction of the HIF target genes vascular endothelial growth factor and transforming growth factor-beta. Vascular lesions were present in both experimental groups. However, there was significantly reduced intimal proliferation in preconditioned grafts when compared with vehicle controls [intimal proliferation 31.3 ± 8% (ICA) vs 55.3 ± 20% (control), P < 0.01]. In addition, experimental groups revealed a down-regulation of E-selectin (-57%) and MCP1 (-33%) expression after ICA pretreatment compared with controls, going along with decreased T-cell [1.4% CD4+ T-cell infiltration vs 8.4% (control) and 4.9% CD8+ T-cell infiltration vs 10.7% (control)], dendritic cell (0.6% dendritic cells infiltration vs 1.9% infiltration(control)] and macrophage infiltration [4.8% macrophages (ICA) vs 10.9% (control)] within vascular grafts.

CONCLUSIONS

These data of an animal transplant model show that the pharmaceutical activation of HIF with endogenous up-regulation of protective target genes leads to adaptation of the graft to low oxygen-saturation and hereby attenuates the development of transplant arteriosclerosis and allograft injury. Pharmaceutical inhibition of PHDs appears to be a very attractive strategy for organ preservation that deserves further clinical evaluation.

Maladaptive proximal tubule repair: cell cycle arrest

Acute kidney injury (AKI) leads to worsening of chronic kidney disease (CKD), and CKD predisposes to the clinical entity of AKI. The tubules of the kidney play a central role in the fibrotic response, which ultimately leads to progressive kidney disease. The cellular mechanisms responsible for the epidemiological association between AKI and CKD are complex. In order to unravel characteristics of this direct involvement of the tubules, in particular the proximal tubules, we established a model to specifically target injury to the proximal tubule using a genetic approach to express the simian diphtheria toxin (DT) receptor in the proximal tubule. A single administration of DT to the proximal tubule resulted in inflammation, reversible injury, and adaptive repair. By contrast, thrice repeated injury led to maladaptive repair with sustained tubule injury, vascular rarefaction, proliferation of interstitial myofibroblasts, interstitial fibrosis, and glomerular sclerosis. An important feature of the maladaptive repair process after severe injury is the development of cell cycle arrest in G2/M. There is a subsequent activation of the DNA repair response with activation of a secretory phenotype whereby profibrotic factors are released. This insight introduces a number of potential new targets for therapeutic intervention to prevent and/or arrest CKD progression.

Acute kidney injury: Can remote ischaemic preconditioning prevent AKI?

A randomized multicentre controlled study of 240 cardiac surgery patients at high risk of acute kidney injury (AKI) has demonstrated that remote ischaemic preconditioning can reduce the rate of AKI and requirement for renal replacement therapy. These findings suggest this procedure could be a promising therapeutic option for this high-risk patient group.

Meclizine Preconditioning Protects the Kidney Against Ischemia-Reperfusion Injury

Global or local ischemia contributes to the pathogenesis of acute kidney injury (AKI). Currently there are no specific therapies to prevent AKI. Potentiation of glycolytic metabolism and attenuation of mitochondrial respiration may decrease cell injury and reduce reactive oxygen species generation from the mitochondria. Meclizine, an over-the-counter anti-nausea and -dizziness drug, was identified in a 'nutrient-sensitized' chemical screen. Pretreatment with 100 mg/kg of meclizine, 17 h prior to ischemia protected mice from IRI. Serum creatinine levels at 24 h after IRI were 0.13 ± 0.06 mg/dl (sham, n = 3), 1.59 ± 0.10 mg/dl (vehicle, n = 8) and 0.89 ± 0.11 mg/dl (meclizine, n = 8). Kidney injury was significantly decreased in meclizine treated mice compared with vehicle group (p < 0.001). Protection was also seen when meclizine was administered 24 h prior to ischemia. Meclizine reduced inflammation, mitochondrial oxygen consumption, oxidative stress, mitochondrial fragmentation, and tubular injury. Meclizine preconditioned kidney tubular epithelial cells, exposed to blockade of glycolytic and oxidative metabolism with 2-deoxyglucose and NaCN, had reduced LDH and cytochrome c release. Meclizine upregulated glycolysis in glucose-containing media and reduced cellular ATP levels in galactose-containing media. Meclizine inhibited the Kennedy pathway and caused rapid accumulation of phosphoethanolamine. Phosphoethanolamine recapitulated meclizine-induced protection both in vitro and in vivo.

Research Progress on Regulatory T Cells in Acute Kidney Injury

Immune inflammation is crucial in mediating acute kidney injury (AKI). Immune cells of both the innate and adaptive immune systems substantially contribute to overall renal damage in AKI. Regulatory T cells (Tregs) are key regulator of immunological function and have been demonstrated to ameliorate injury in several murine experimental models of renal inflammation. Recent studies have illuminated the renal-protective function of Tregs in AKI. Tregs appear to exert beneficial effects in both the acute injury phase and the recovery phase of AKI. Additionally, Tregs-based immunotherapy may represent a promising approach to ameliorate AKI and promote recovery from AKI. This review will highlight the recent insights into the role of Tregs and their therapeutic potential in AKI.

Elevation of miR-21, through targeting MKK3, may be involved in ischemia pretreatment protection from ischemia-reperfusion induced kidney injury

BACKGROUND

Ischemia-reperfusion (IR) causes acute kidney injury (AKI), and ischemia pretreatment may exert protection. Mitogen-activated protein kinase kinase 3 (MKK3), which is involved in the signal transduction pathway in IR-induced injury, is a potential target of miR-21. We aimed to verify the targeting regulation of miR-21 on MKK3 and to explore the effects of miR-21-mediated MKK3 expression changes in AKI.

METHODS

Vectors containing the MKK3 3'UTR and mutated MKK3-3U-M were constructed and co-transfected with nonsense miR, miR-21-5p mimics or inhibitor in HEK293 cells. Gene expressions were detected by dual luciferase reporter assay. The effects of miR-21 on mRNA and protein of MKK3 were investigated in HK-2 cells. Male C57BL/6J mice were treated with ischemic preconditioning (IPC) and IR. Kidney functions were assessed through monitoring serum creatinine (Scr) and blood urea nitrogen (BUN). Pathological changes were observed and scored with histological samples of kidney. Expression levels of miR-21, MKK3, interleukin (IL)-6, tumor necrosis factor (TNF)-α before and after IPC and IR were examined by real-time polymerase chain reaction and/or immunohistochemistry.

RESULTS

miR-21 regulated the expression of MKK3 via 3'UTR. Following IR, MKK3, IL-6 and TNF-α levels were increased. Scr, BUN and pathological injuries were aggravated, and miR-21 expression was increased. IPC increased miR-21 levels ahead of IR and inhibited the increases in MKK3, IL-6 and TNF-α levels and the aggravation of Scr, BUN and pathological injuries.

CONCLUSIONS

miR-21 targets MKK3 in vivo and in vitro, inhibiting the downstream factors IL-6 and TNF-α. Therefore, miR-21 might be involved in protection of IPC against IR of the kidney.

Renalase contributes to the renal protection of delayed ischaemic preconditioning via the regulation of hypoxia-inducible factor-1α

Ischaemic preconditioning (IPC) attenuates acute kidney injury (AKI) from renal ischaemia reperfusion. Renalase, an amine oxidase secreted by the proximal tubule, not only degrades circulating catecholamines but also protects against renal ischaemia reperfusion injury. Here, it has been suggested that the renoprotective effect of renal IPC is partly mediated by renalase. In a model of brief intermittent renal IPC, the increased cortex renalase expression was found to last for 48 hrs. IPC significantly reduced renal tubular inflammation, necrosis and oxidative stress following renal ischaemia reperfusion injury. Such effects were attenuated by blocking renalase with an anti-renalase monoclonal antibody. We further demonstrated that renalase expression was up-regulated by hypoxia in vitro via an hypoxia-inducible factor (HIF)-1α mechanism. The IPC-induced up-regulation of renalase in vivo was also reduced by pre-treatment with an HIF-1α inhibitor, 3-(5′-Hydroxymethyl-2′-furyl)-1-benzyl indazole. In summary, the renoprotective effect of IPC is partly dependent on the renalase expression, which may be triggered by hypoxia via an HIF-1α mechanism. Endogenous renalase shows potential as a therapeutic agent for the prevention and treatment of AKI.

Liver protection strategies in liver transplantation

BACKGROUND

Liver transplantation is the therapy of choice for patients with end-stage liver diseases. However, the gap between the low availability of organs and high demand is continuously increasing. Innovative strategies for organ protection are necessary to expand donor pool and to achieve better outcomes for liver transplantation. The present review analyzed and compared various strategies of liver protection.

DATA SOURCES

Databases such as PubMed, Embase and Ovid were searched for the literature related to donor liver protection strategies using following key words: "ischemia reperfusion injury", "graft preservation", "liver transplantation", "machine perfusion" and "conditioning". Of the 146 studies identified, only those with cutting edge strategies were analyzed.

RESULTS

A variety of therapeutic approaches were proposed to alleviate graft ischemia/reperfusion injury, which included static cold storage, machine perfusion (hypothermic, normothermic and subnormothermic), manual conditioning (pre, post and remote), and pharmacological conditioning. Evidences from animal experiments and clinical trials suggested that all these strategies could potentially protect liver graft; however, their clinical applications are limited partially due to their own disadvantages.

CONCLUSIONS

There are a plenty of methods suggested to decrease the degree of donor liver transplantation-related injury. However, none of these approaches is perfect in clinical practice. More translational researches (molecular and clinical studies) are needed to improve the techniques in liver graft protection.

Etiology and outcomes of anuria in acute kidney injury: a single center study

BACKGROUND

It was previously known that anuric acute kidney injury (AKI) is uncommon and its occurrence suggests complete ureteral obstruction, shock, or a major vascular event. As the epidemiology of AKI has significantly changed over the past decade, it is possible that the incidence, etiology, or clinical characteristics of anuric AKI have also changed.

METHODS

A prospective cohort study was conducted that included all patients undergoing renal replacement therapy (RRT) for AKI during a 2-year period in a tertiary hospital. Patients were classified as having anuric, oliguric, or nonoliguric AKI based on their volume of urine when RRT started using the modified Acute Kidney Injury Network criteria.

RESULTS

Of the 203 patients included in the study, 21.2% met the criteria for anuric AKI. Septic and postoperative AKI were the main causes of anuric AKI, with 60.5% of incidences occurring in hospital. Anuric AKI was associated with a younger age, a lower prevalence of pre-morbid chronic kidney disease and diabetes, more frequent continuous RRT requirement, and multi-organ dysfunction. In addition, patients with anuric AKI had a higher rate of in-hospital mortality and long-term dependence on RRT than patients with nonanuric AKI.

CONCLUSION

Anuric AKI is common, with sepsis as the main etiological insult, and is associated with adverse outcomes among patients with AKI who require RRT.

Recent advances in the understanding of acute kidney injury

Acute kidney injury (AKI) is a common clinical entity associated with high morbidity and mortality and clinical costs. The pathophysiology is multifaceted and involves inflammation, tubular injury, and vascular damage. Recently identified components include necroptosis, a special form of cell death, and autophagy. Most of the pathophysiological knowledge is obtained from animal models but these do not directly reflect the reality of the clinical situation. Tubular cells have a remarkable capacity to regenerate, and the role of stem/progenitor cells is discussed. Acute kidney injury is frequently associated with chronic kidney disease, and the implications are widespread.

Angiotensin II removes kidney resistance conferred by ischemic preconditioning

Ischemic preconditioning (IPC) by ischemia/reperfusion (I/R) renders resistance to the kidney. Strong IPC triggers kidney fibrosis, which is involved in angiotensin II (AngII) and its type 1 receptor (AT1R) signaling. Here, we investigated the role of AngII/AT1R signal pathway in the resistance of IPC kidneys to subsequent I/R injury. IPC of kidneys was generated by 30 minutes of bilateral renal ischemia and 8 days of reperfusion. Sham-operation was performed to generate control (non-IPC) mice. To examine the roles of AngII and AT1R in IPC kidneys to subsequent I/R, IPC kidneys were subjected to either 30 minutes of bilateral kidney ischemia or sham-operation following treatment with AngII, losartan (AT1R blocker), or AngII plus losartan. IPC kidneys showed fibrotic changes, decreased AngII, and increased AT1R expression. I/R dramatically increased plasma creatinine concentrations in non-IPC mice, but not in IPC mice. AngII treatment in IPC mice resulted in enhanced morphological damage, oxidative stress, and inflammatory responses, with functional impairment, whereas losartan treatment reversed these effects. However, AngII treatment in non-IPC mice did not change I/R-induced injury. AngII abolished the resistance of IPC kidneys to subsequent I/R via the enhancement of oxidative stress and inflammatory responses, suggesting that the AngII/AT1R signaling pathway is associated with outcome in injury-experienced kidney.

miR-21 in ischemia/reperfusion injury: a double-edged sword?

MicroRNAs (miRNAs or miRs) are endogenous, small RNA molecules that suppress expression of targeted mRNA. miR-21, one of the most extensively studied miRNAs, is importantly involved in divergent pathophysiological processes relating to ischemia/reperfusion (I/R) injury, such as inflammation and angiogenesis. The role of miR-21 in renal I/R is complex, with both protective and pathological pathways being regulated by miR-21. Preconditioning-induced upregulation of miR-21 contributes to the protection against subsequent renal I/R injury through the targeting of genes such as the proapoptotic gene programmed cell death 4 and interactions between miR-21 and hypoxia-inducible factor. Conversely, long-term elevation of miR-21 may be detrimental to the organ by promoting the development of renal interstitial fibrosis following I/R injury. miR-21 is importantly involved in several pathophysiological processes related to I/R injury including inflammation and angiogenesis as well as the biology of stem cells that could be used to treat I/R injury; however, the effect of miR-21 on these processes in renal I/R injury remains to be studied.

Dexmedetomidine preconditioning ameliorates kidney ischemia-reperfusion injury

Kidney ischemia-reperfusion (I/R) injury is a common cause of acute kidney injury. We tested whether dexmedetomidine (Dex), an alpha2 adrenoceptor (α2-AR) agonist, protects against kidney I/R injury. Sprague-Dawley rats were divided into four groups: (1) Sham-operated group; (2) I/R group (40 min ischemia followed by 24 h reperfusion); (3) I/R group + Dex (1 μg/kg i.v. 60 min before the surgery), (4) I/R group + Dex (10 μg/kg). The effects of Dex postconditiong (Dex 1 or 10 μg/kg i.v. after reperfusion) as well as the effects of peripheral α2-AR agonism with fadolmidine were also examined. Hemodynamic effects were monitored, renal function measured, and acute tubular damage along with monocyte/macrophage infiltration scored. Kidney protein kinase B, toll like receptor 4, light chain 3B, p38 mitogen-activated protein kinase (p38 MAPK), sirtuin 1, adenosine monophosphate kinase (AMPK), and endothelial nitric oxide synthase (eNOS) expressions were measured, and kidney transciptome profiles analyzed. Dex preconditioning, but not postconditioning, attenuated I/R injury-induced renal dysfunction, acute tubular necrosis and inflammatory response. Neither pre- nor postconditioning with fadolmidine protected kidneys. Dex decreased blood pressure more than fadolmidine, ameliorated I/R-induced impairment of autophagy and increased renal p38 and eNOS expressions. Dex downregulated 245 and upregulated 61 genes representing 17 enriched Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways, in particular, integrin pathway and CD44. Ingenuity analysis revealed inhibition of Rac and nuclear factor (erythroid-derived 2)-like 2 pathways, whereas aryl hydrocarbon receptor (AHR) pathway was activated. Dex preconditioning ameliorates kidney I/R injury and inflammatory response, at least in part, through p38-CD44-pathway and possibly also through ischemic preconditioning.

Mesenchymal stromal cell therapy in conditions of renal ischaemia/reperfusion

Acute kidney injury (AKI) represents a worldwide public health issue of increasing incidence, with a significant morbi-mortality. AKI treatment mostly relies on supportive manoeuvres in the absence of specific target-oriented therapy. The pathophysiology of AKI commonly involves ischaemia/reperfusion (I/R) events, which cause both immune and metabolic consequences in renal tissue. Similarly, at the time of kidney transplantation (KT), I/R is an unavoidable event which contributes to early graft dysfunction and enhanced graft immunogenicity. Mesenchymal stromal cells (MSCs) represent a heterogeneous population of adult, fibroblast-like multi-potent cells characterized by their ability to differentiate into tissues of mesodermal lineages. Because MSC have demonstrated immunomodulatory, anti-inflammatory and tissue repair properties, MSC administration at the time of I/R and/or at later times has been hypothesized to attenuate AKI severity and to accelerate the regeneration process. Furthermore, MSC in KT could help prevent both I/R injury and acute rejection, thereby increasing graft function and survival. In this review, summarizing the encouraging observations in animal models and in pilot clinical trials, we outline the benefit of MSC therapy in AKI and KT, and envisage their putative role in renal ischaemic conditioning.

Moving beyond supportive care--current status of specific therapies in pediatric acute kidney injury

Acute kidney injury (AKI) remains a significant challenge, leading to increased morbidity, mortality, and medical costs. Therapy for AKI to this point has largely been supportive; specific interventions to treat established AKI have had minimal effect. Review of the pathogenesis of AKI reveals complex, interacting mechanisms, including changes in microcirculation, the immune system, and inflammation, and cell death from both necrosis and apoptosis. Past definitions of AKI have been imprecise; newer methods for AKI identification and classification, including novel biomarkers and improved criteria for defining AKI, may permit earlier intervention with greater potential for success. With improved understanding of pathophysiology and the opportunity for intervention before AKI is fully established, clinicians may be able to move beyond supportive care and improve outcomes.

[Role of AMP-activated protein kinase in renal ischemic preconditioning]

Kidney transplantation represents the best treatment of end-stage renal disease. In addition to the degree of human leukocyte antigen matching, long-term graft survival is influenced by the quality of the graft before its transplantation. Quality criteria include the level of ischemic damage caused by the transplantation per se. Renal ischemic preconditioning (IP) consists of different approaches to prevent ischemia/reperfusion (I/R) damage induced by the interruption and recovery of renal circulation, as observed during transplantation. Distinct animal models show promising results regarding the efficiency of PCI to preserve kidney structure and function in I/R conditions. Characterizing the cellular cascades involved in I/R led to the identification of putative targets of renal IP, including the adenosine monophosphate-activated protein kinase (AMPK). AMPK is a ubiquitous energy sensor, which has been implicated in the maintenance of epithelial cell polarization under energy deprivation. Among others, the anti-diabetic drug, metformin, is a potent activator of AMPK. Here, we summarize the in vitro and in vivo data about the role of AMPK in renal IP. Defining the pharmacological conditions of IP would help to improve the quality of the renal graft before its transplantation, thereby increasing its long-term survival.

Preconditioning with recombinant high-mobility group box 1 protein protects the kidney against ischemia-reperfusion injury in mice

A preconditioning effect occurs when exposure to a nonharmful quantity of a mediator of injury provides protection against injury upon subsequent reexposure. High-mobility group box 1 (HMGB1) protein, an endogenous ligand for Toll-like receptor (TLR) 4, is a TLR4-dependent mediator of kidney ischemia-reperfusion injury. Here we determined whether preconditioning with recombinant HMGB1 can block kidney ischemia-reperfusion injury, whether this effect is TLR4 dependent and, if so, how preconditioning downregulates TLR signaling. Wild-type mice pretreated with rHMGB1 before ischemia were protected against kidney ischemia-reperfusion injury, indicated by lower serum creatinine, less tubular damage, less tubulointerstitial neutrophil and macrophage infiltration, and less tubular epithelial cell apoptosis versus control mice. Gene expression of TLR-downstream cytokines and chemokines in ischemia-reperfusion injury kidney were also significantly reduced. While TLR4 and TLR2 knockout mice were protected against kidney ischemia-reperfusion injury, HMGB1 preconditioning provided additional protection to TLR2 but not TLR4 knockout mice. The protective effect of rHMGB1 preconditioning involved Siglec-G upregulation, a negative regulator of HMGB1-mediated TLR4 pathway activation. Thus, preconditioning with rHMGB1 affords significant protection from TLR4-dependent kidney ischemia-reperfusion injury, indicating therapeutic potential.