Ischemic preconditioning and clinical scenarios

Molecular mechanism underlying the protective effects of ischemic preconditioning in total knee arthroplasty

PROPOSE

To investigate the molecular mechanisms underlying the protective effects of ischemic preconditioning (IPC) in patients undergoing total knee arthroplasty.

METHODS

GSE21164 was extracted from an online database, followed by an investigation of differentially expressed genes (DEGs) between IPC treatment samples at 2 time points (T0T and T1T). Function and pathway enrichment analyses were performed on the DEGs. A protein-protein interaction network was constructed to identify hub genes according to 5 different algorithms, followed by enrichment analysis. In addition, long noncoding RNAs (lncRNAs) were identified between the T0T and T1T samples. Furthermore, a competing endogenous RNA network was predicted based on the identified lncRNA-messenger RNA (mRNA), lncRNA-microRNA (miRNA), and mRNA-miRNA relationships revealed in this study. Finally, a drug-gene network was investigated. Statistical analyses were performed using GraphPad Prism 8.0. Differences between groups were determined using an unpaired t-test. p < 0.05 was considered significant.

RESULTS

A total of 343 DEGs at T0 and 10 DEGs at T1 were identified and compared with their respective control groups, followed by 100 DEGs between T0T and T1T. Based on these 100 DEGs, protein-protein interaction network analysis revealed 9 hub genes, mainly with mitochondria-related functions and the carbon metabolism pathway. Six differentially expressed lncRNAs were investigated between T0T and T1T. A competing endogenous RNA network was constructed using 259 lncRNA-miRNA-mRNA interactions, including alpha-2-macroglobulin antisense RNA 1-miR-7161-5p-iron-sulfur cluster scaffold. Finally, 13 chemical drugs associated with the hub genes were explored.

CONCLUSION

Iron-sulfur cluster scaffold may promote IPC-induced ischemic tolerance mediated by alpha-2-macroglobulin antisense RNA 1-miR-7161-5p axis. Moreover, IPC may induce a protective response after total knee arthroplasty via mitochondria-related functions and the carbon metabolism pathway, which should be further validated in the near future.

Differential Cytoprotective Effect of Resveratrol and Its Derivatives: Focus on Antioxidant and Autophagy-Inducing Effects

Numerous beneficial effects of resveratrol were reported; however, its pharmacological profile is contradictious. Previously, we have demonstrated that resveratrol has a dose-dependent cytoprotective effect and the essential role of autophagy induction was demonstrated. Resveratrol suffers from unfavorable pharmacokinetics, hindering its clinical use. Our aim was to study the cytoprotective effect of resveratrol derivatives to better understand structure-activity relationships that may facilitate the development of compounds with better druglike characteristics. Serum-deprivation-induced caspase activation, free radical generation, mitochondrial membrane depolarization and autophagy were detected in the presence of resveratrol analogs with different oxidation states on mouse embryonal fibroblasts. Distinct cytoprotective mechanisms of the examined compounds were revealed. Monomethyl resveratrol had similar potency to resveratrol (EC50: 85.3 vs. 84.2 μM); however, autophagy induction was not essential for its cytoprotective effect. Oxyresveratrol was found to be a strong antioxidant that can induce direct cytoprotection rather than autophagy. Trimethyl-resveratrol, lacking free hydroxyl groups, induced damage that was too significant and hardly compensated by the activation of cytoprotective machineries, and caspase activation was reduced by only 24.5%. Based on our results, methylation of resveratrol reduces its antioxidant activity, while autophagy induction can still contribute to its cytoprotective effect. The introduction of an additional hydroxyl group, however, augments the antioxidant properties, inducing cytoprotection without autophagy induction.

Resveratrol Preconditioning Downregulates PARP1 Protein to Alleviate PARP1-Mediated Cell Death Following Cerebral Ischemia

Stroke remains a leading cause of mortality; however, available therapeutics are limited. The study of ischemic tolerance, in paradigms such as resveratrol preconditioning (RPC), provides promise for the development of novel prophylactic therapies. The heavily oxidative environment following stroke promotes poly-ADP-ribose polymerase 1 (PARP1)-overactivation and parthanatos, both of which are major contributors to neuronal injury. In this study, we tested the hypothesis that RPC instills ischemic tolerance through decreasing PARP1 overexpression and parthanatos following in vitro and in vivo cerebral ischemia. To test this hypothesis, we utilized rat primary neuronal cultures (PNCs) and middle cerebral artery occlusion (MCAO) in the rat as in vitro and in vivo models, respectively. RPC was administered 2 days preceding ischemic insults. RPC protected PNCs against oxygen and glucose deprivation (OGD)-induced neuronal loss, as well as increases in total PARP1 protein, implying protection against PARP1-overactivation. Twelve hours following OGD, we observed reductions in NAD+/NADH as well as an increase in AIF nuclear translocation, but RPC ameliorated NAD+/NADH loss and blocked AIF nuclear translocation. MCAO in the rat induced AIF nuclear translocation in the ischemic penumbra after 24 h, which was ameliorated with RPC. We tested the hypothesis that RPC's neuroprotection was instilled through long-term downregulation of nuclear PARP1 protein. RPC downregulated nuclear PARP1 protein for at least 6 days in PNCs, likely contributing to RPC's ischemic tolerance. This study describes a novel mechanism by which RPC instills prophylaxis against ischemia-induced PARP1 overexpression and parthanatos, through a long-term reduction of nuclear PARP1 protein.

Hypometabolism, Alzheimer's Disease, and Possible Therapeutic Targets: An Overview

The brain is a highly dynamic organ that requires a constant energy source to function normally. This energy is mostly supplied by glucose, a simple sugar that serves as the brain's principal fuel source. Glucose transport across the blood-brain barrier (BBB) is primarily controlled via sodium-independent facilitated glucose transport, such as by glucose transporter 1 (GLUT1) and 3 (GLUT3). However, other glucose transporters, including GLUT4 and the sodium-dependent transporters SGLT1 and SGLT6, have been reported in vitro and in vivo. When the BBB endothelial layer is crossed, neurons and astrocytes can absorb the glucose using their GLUT1 and GLUT3 transporters. Glucose then enters the glycolytic pathway and is metabolized into adenosine triphosphate (ATP), which supplies the energy to support cellular functions. The transport and metabolism of glucose in the brain are impacted by several medical conditions, which can cause neurological and neuropsychiatric symptoms. Alzheimer's disease (AD), Parkinson's disease (PD), epilepsy, traumatic brain injury (TBI), schizophrenia, etc., are a few of the most prevalent disorders, characterized by a decline in brain metabolism or hypometabolism early in the course of the disease. Indeed, AD is considered a metabolic disorder related to decreased brain glucose metabolism, involving brain insulin resistance and age-dependent mitochondrial dysfunction. Although the conventional view is that reduced cerebral metabolism is an effect of neuronal loss and consequent brain atrophy, a growing body of evidence points to the opposite, where hypometabolism is prodromal or at least precedes the onset of brain atrophy and the manifestation of clinical symptoms. The underlying processes responsible for these glucose transport and metabolic abnormalities are complicated and remain poorly understood. This review article provides a comprehensive overview of the current understanding of hypometabolism in AD and potential therapeutic targets.

Madder (Rubia cordifolia L.) Alleviates Myocardial Ischemia-Reperfusion Injury by Protecting Endothelial Cells from Apoptosis and Inflammation

Objective

Ischemia-reperfusion injury often occurs in organ transplantation, coronary heart disease, ischemic heart disease, and other diseases, which greatly reduces clinical efficacy. This study examined the effectiveness of madder as a medicine to treat ischemia-reperfusion injury.

Methods

The efficacy of madder was evaluated by measuring myocardial infarction size, coronary outflow volume, myocardial contraction rate, activation of inflammatory factors, autophagy factors, apoptosis factors, and related pathway genes in mice.

Results

The results indicated that treatment with madder can effectively reduce the area of myocardial infarction and restore arterial blood flow velocity and myocardial contractility in mice. Additionally, madder treatment inhibited the expression of inflammatory factors, autophagy factors, and apoptosis factors in mice and reduced the degree of myocardial cell injury. Studies have also shown that madder treatment can alleviate myocardial ischemia-reperfusion injury in mice and inhibit the occurrence of inflammatory response by inhibiting the activity of the NF-κB pathway.

Conclusion

The results showed that madder was effective against ischemia-reperfusion injury, thus showing potential as a clinical drug for treating ischemia-reperfusion injury.

Neuroprotective effects of long noncoding RNAs involved in ischemic postconditioning after ischemic stroke

During acute reperfusion, the expression profiles of long noncoding RNAs in adult rats with focal cerebral ischemia undergo broad changes. However, whether long noncoding RNAs are involved in neuroprotective effects following focal ischemic stroke in rats remains unclear. In this study, RNA isolation and library preparation was performed for long noncoding RNA sequencing, followed by determining the coding potential of identified long noncoding RNAs and target gene prediction. Differential expression analysis, long noncoding RNA functional enrichment analysis, and co-expression network analysis were performed comparing ischemic rats with and without ischemic postconditioning rats. Rats were subjected to ischemic postconditioning via the brief and repeated occlusion of the middle cerebral artery or femoral artery. Quantitative real-time reverse transcription-polymerase chain reaction was used to detect the expression levels of differentially expressed long noncoding RNAs after ischemic postconditioning in a rat model of ischemic stroke. The results showed that ischemic postconditioning greatly affected the expression profile of long noncoding RNAs and mRNAs in the brains of rats that underwent ischemic stroke. The predicted target genes of some of the identified long noncoding RNAs (cis targets) were related to the cellular response to ischemia and stress, cytokine signal transduction, inflammation, and apoptosis signal transduction pathways. In addition, 15 significantly differentially expressed long noncoding RNAs were identified in the brains of rats subjected to ischemic postconditioning. Nine candidate long noncoding RNAs that may be related to ischemic postconditioning were identified by a long noncoding RNA expression profile and long noncoding RNA-mRNA co-expression network analysis. Expression levels were verified by quantitative real-time reverse transcription-polymerase chain reaction. These results suggested that the identified long noncoding RNAs may be involved in the neuroprotective effects associated with ischemic postconditioning following ischemic stroke. The experimental animal procedures were approved by the Animal Experiment Ethics Committee of Kunming Medical University (approval No. KMMU2018018) in January 2018.

Beneficial postoperative micro-rheological effects of intraoperative administration of diclophenac or ischemic preconditioning in patients with lower extremity operations -Preliminary data

BACKGROUND

Ischemia-reperfusion (I/R) may worsen blood rheology that has been demonstrated by clinical and experimental data. It is also known that anti-inflammatory agents and preconditioning methods may reduce I/R injury.

OBJECTIVE

We aimed to analyze hemorheological alterations in elective knee operations and the effects of intraoperative nonsteroidal anti-inflammatory drug (NSAID) administration and application of ischemic preconditioning.

METHODS

Hemorheological variables of 17 patients with total knee replacement or anterior crucial ligament replacement were analyzed. The ischemic (tourniquet) time was 92±15 minutes. Seven patients did not receive NSAID (Control group), 5 patients got i.v. sodium-diclophenac 10 minutes before and 6 hours after reperfusion. Five patients had ischemic preconditioning (3×15 minutes). Blood samples were collected before the ischemia, 10 minutes after reperfusion, on the 1st and 2nd p.o. day.

RESULTS

Whole blood viscosity didn't show notable inter-group differences, except for a slight decrease in the preconditioning group. RBC deformability decreased, erythrocyte aggregation enhanced by the 1st and 2nd p.o. days in Control group. In NSAID and preconditioning groups the changes were moderate, aggregation values significantly lowered compared to the Control group.

CONCLUSION

Intraoperatively administered diclophenac or ischemic preconditioning could moderate the deterioration in micro-rheological parameters caused by I/R in patients.

Elevated cerebral perfusion and preserved cognition in elite Brazilian Jiu-Jitsu athletes: Evidence for neuroprotection

Brazilian Jiu-Jitsu (BJJ) is a popular martial art that exposes participants to recurrent intermittent asphyxiation due to controlled application of neck chokes. To what extent the sport impacts the regulation of cerebral blood flow (CBF) and cognition has not been examined. This study compared eleven elite Brazilian Jiu-Jitsu athletes (aged 30 ± 8 y) who trained 12 ± 6 hours/week for 8 ± 4 years against eleven cardiorespiratory fitness (CRF)- and age-matched controls. Internal carotid (ICA) and vertebral artery (VA) blood flow were measured via duplex ultrasound to determine global cerebral blood flow (gCBF). Mild cognitive impairment and sub-domains of memory, attention/concentration/visual motor coordination, and executive function were determined by psychometric testing. There was no evidence of mild cognitive impairment in the athletes, and cognitive function was comparable between groups (all p > 0.05). In contrast, resting gCBF was selectively elevated in the athletes (741 ± 186 mL∙min^-1 vs. 573 ± 166 mL∙min^-1 , p = 0.037) due to combined differences in ICA (+65 mL∙min^-1 , p = 0.079) and VA (+19 mL∙min^-1 , p = 0.277) flow. In conclusion, the sustained elevation in resting cerebral perfusion provides preliminary evidence for adaptive neuroprotection that is independent of CRF and likely mediated by choke-induced cerebral preconditioning and/or lifelong exposure to BJJ-specific high-intensity interval training.

The involvement of nuclear factor-κB in astroprotection against ischemia-reperfusion injury by ischemia-preconditioned neurons

Ischemic preconditioned (IP) neurons protect astrocytes against ischemia/reperfusion (I/R)-induced injury by inhibiting oxidative stress. However, the relevant mechanisms are unknown. Based on the role of nuclear factor-κB (NF-κB) in cell survival and adaption to oxidative stress, we hypothesized that NF-κB might be associated with astroprotection induced by IP neurons via upregulation of antioxidant enzymes. Here, we investigated the effects of IP neurons on NF-κB activation, cell viability, reactive oxygen species (ROS), expression of antioxidant enzymes, erythropoietin (EPO), and tumor necrosis factor α (TNF-α), in the presence or absence of BAY11-7082 (an NF-κB inhibitor), anti-EPO, and anti-TNF-α antibodies, in astrocytes treated with or without I/R. We found that IP neurons could keep NF-κB activation at a relatively higher but beneficial level, and in turn, upregulated the activity of antioxidant enzymes and hence enhanced cell viability and reduced ROS in I/R treated astrocytes. The results collectively indicated that IP neurons are able to significantly inhibit the I/R-induced NF-κB overactivation, probably via EPO and TNF-α, being essential for IP neuron-induced astroprotection under the conditions of I/R. We concluded that NF-κB-mediated antioxidative stress is one of the mechanisms by which IP neurons protect astrocytes against I/R injury.

Inflammatory Response of Ischemic Tolerance in Circulating Plasma: Preconditioning-Induced by Transient Ischemic Attack (TIA) Phenomena in Acute Ischemia Patients (AIS)

Introduction: Ischemic tolerance (IT) refers to a state where cells are resistant to the damaging effects caused by periods of ischemia. In a clinical scenario, the IT phenomenon would be activated by a recent transient ischemic attack (TIA) before an ischemic stroke (IS). The characterization of inflammatory protein expression patterns will contribute to improved understanding of IT.

Methods: A total of 477 IS patients from nine hospitals, recruited between January 2011 and January 2016, were included in the current study and divided in three groups: 438 (91.9%) patients without previous TIA (group 1), 22 (4.6%) patients who suffered TIA 24 h before IS (group 2), and 17 (3.5%) patients who suffered TIA between 24 h and 7 days prior to IS (group 3). An inflammatory biomarker panel (IL-6, NT-proBNP, hsCRP, hs-Troponin, NSE, and S-100b) on plasma and a cytokine antibody array was performed to achieve the preconditioning signature potentially induced by TIA phenomena. Primary outcome was modified rankin scale (mRs) score at 90 days.

Results: Recent previous TIA was associated with better clinical outcome at 90 days (median mRS of group 1: 2.0 [1.0–4.0]; group 2: 2.0 [0.0–3.0]; group 3: 1.0 [0–2.5]; p = 0.086) and smaller brain lesion (group 1: 3.7 [0.7–18.3]; group 2: 0.8 [0.3–8.9]; group 3: 0.6 [0.1–5.5] mL; p = 0.006). All inflammation biomarkers were down regulated in the groups of recent TIA prior to IS compared to those who did not suffer a TIA events. Moreover, a cytokine antibody array revealed 30 differentially expressed proteins between the three groups. Among them, HRG1-alpha (Fold change 74.4 between group 1 and 2; 74.2 between group 1 and 3) and MAC-1 (Fold change 0.05 between group 1 and 2; 0.06 between group 1 and 3) expression levels would better stratify patients with TIA 7 days before IS. These two proteins showed an earlier inflammation profile that was not detectable by the biomarker panel.

Conclusion: Inflammatory pathways were activated by transient ischemic attack, however the period of time between this event and a further ischemic stroke could be determined by a protein signature that would contribute to define the role of ischemic tolerance induced by TIA.

Electroacupuncture Pretreatment Elicits Tolerance to Cerebral Ischemia/Reperfusion through Inhibition of the GluN2B/m-Calpain/p38 MAPK Proapoptotic Pathway

Background

As one of the first steps in the pathology of cerebral ischemia, glutamate-induced excitotoxicity progresses too fast to be the target of postischemic intervention. However, ischemic preconditioning including electroacupuncture (EA) might elicit cerebral ischemic tolerance through ameliorating excitotoxicity.

Objective

To investigate whether EA pretreatment based on TCM theory could elicit cerebral tolerance against ischemia/reperfusion (I/R) injury, and explore its potential excitotoxicity inhibition mechanism from regulating proapoptotic pathway of the NMDA subtype of glutamate receptor (GluN2B).

Methods

The experimental procedure included 5 consecutive days of pretreatment stage and the subsequent modeling stage for one day. All rats were evenly randomized into three groups: sham MCAO/R, MCAO/R, and EA+MCAO/R. During pretreatment procedure, only rats in the EA+MCAO/R group received EA intervention on GV20, SP6, and PC6 once a day for 5 days. Model preparation for MCAO/R or sham MCAO/R started 2 hours after the last pretreatment. 24 hours after model preparation, the Garcia neurobehavioral scoring criteria was used for the evaluation of neurological deficits, TTC for the measurement of infarct volume, TUNEL staining for determination of neural cell apoptosis at hippocampal CA1 area, and WB and double immunofluorescence staining for expression and the cellular localization of GluN2B and m-calpain and p38 MAPK.

Results

This EA pretreatment regime could improve neurofunction, decrease cerebral infarction volume, and reduce neuronal apoptosis 24 hours after cerebral I/R injury. And EA pretreatment might inhibit the excessive activation of GluN2B receptor, the GluN2B downstream proapoptotic mediator m-calpain, and the phosphorylation of its transcription factor p38 MAPK in the hippocampal neurons after cerebral I/R injury.

Conclusion

The EA regime might induce tolerance against I/R injury partially through the regulation of the proapoptotic GluN2B/m-calpain/p38 MAPK pathway of glutamate.

Possible involvement of D2/D3 receptor activation in ischemic preconditioning mediated protection of the brain

Ischemic stroke is a medical condition that arises because of poor blood supply to the brain. Reperfusion being salvage to the brain further causes, exacerbation of tissue injury, known as reperfusion injury. Ischemic preconditioning (IPC) has been known to provide benefits against ischemia reperfusion (I/R) injury. Dopamine D2/D3 receptor mediated several pathways are also reported as mediators in the IPC mediated neuroprotection. This study investigates the possible involvement of D2/D3 receptor activation in IPC mediated neuroprotection in the I/R brain. Global cerebral ischemia/reperfusion (GCI/R) injury in swiss albino mice was induced by occluding the common carotid arteries for 17 min, followed by 24 h reperfusion. IPC was provided by giving 3 episodes of I/R prior to Ischemia (17 min). Morris water maze (MWM) was used to assess the spatial learning, memory and Rota rod, lateral push test as well as inclined beam test were conducted to assess the motor functions in animals. Cerebral oxidative markers (thiobarbituric acid reactive species-TBARS, reduced glutathione-GSH, superoxide dismutase-SOD, and catalase-CAT), inflammatory markers (IL-6, IL-10, TNF-α, and myeloperoxidase-MPO), acetylcholinesterase activity-AChE, infarct size (% weight and % volume), and histopathological changes were also assessed. Haloperidol (0.05 mg/kg, i.p) was used to antagonize the effects of D2/D3 receptor activation. I/R animals showed reduction in memory, motor function, increase in cerebral oxidative stress, inflammation, AChE activity, infarct size and histopathological changes. Episodes of IPC prior to ischemia, attenuated the deleterious effects of I/R injury. Administration of haloperidol abolished the protective effects of IPC. Hence, it may be concluded that IPC mediated neuroprotection may involves dopamine D2/D3 receptor activation in mice.

Differential mechanisms of tolerance induced by NMDA and 3,5-dihydroxyphenylglycine (DHPG) preconditioning

We investigated the molecular events triggered by NMDA and 3,5-dihydroxyphenylglycine (DHPG) preconditioning, that lead to neuroprotection against excitotoxic insults (AMPA or oxygen and glucose deprivation) in rat organotypic hippocampal slices, with particular attention on glutamate receptors and on cannabinoid system. We firstly evaluated the protein expression of NMDA and AMPA receptor subunits after preconditioning using western blot analysis performed in post-synaptic densities. We observed that following NMDA, but not DHPG preconditioning, the expression of GluA1 was significantly reduced and this reduction appeared to be associated with the internalization of AMPA receptors. Whole-cell voltage clamp recordings on CA1 pyramidal neurons of organotypic slices show that 24 hr after exposure to NMDA and DHPG preconditioning, AMPA-induced currents were significantly reduced. To clarify the mechanisms induced by DHPG preconditioning, we then investigated the involvement of the endocannabinoid system. Exposure of slices to the CB1 antagonist AM251 prevented the development of tolerance to AMPA toxicity induced by DHPG but not NMDA. Accordingly, the MAG-lipase inhibitor URB602, that increases arachidonoylglycerol (2-AG) content, but not the FAAH inhibitor URB597, that limits the degradation of anandamide, was also able to induce tolerance versus AMPA and OGD toxicity, suggesting that 2-AG is responsible for the DHPG-induced tolerance. In conclusion, preconditioning with NMDA or DHPG promotes differential neuroprotective mechanisms: NMDA by internalization of GluA1-AMPA receptors, DHPG by producing the endocannabinoid 2-AG.

Refocusing the Brain: New Approaches in Neuroprotection Against Ischemic Injury

A new era for neuroprotective strategies is emerging in ischemia/reperfusion. This has forced to review the studies existing to date based in neuroprotection against oxidative stress, which have undoubtedly contributed to clarify the brain endogenous mechanisms, as well as to identify possible therapeutic targets or biomarkers in stroke and other neurological diseases. The efficacy of exogenous administration of neuroprotective compounds has been shown in different studies so far. However, something must be missing to get these treatments successfully applied in the clinical environment. Here, the mechanisms involved in neuronal protection against physiological level of ROS and the main neuroprotective signaling pathways induced by excitotoxic and ischemic stimuli are reviewed. Also, the endogenous ischemic tolerance in terms of brain self-protection mechanisms against subsequent cerebral ischemia is revisited to highlight how the preconditioning has emerged as a powerful tool to understand these phenomena. A better understanding of endogenous defense against exacerbated ROS and metabolism in nervous cells will therefore aid to design pharmacological antioxidants targeted specifically against oxidative damage induced by ischemic injury, but also might be very valuable for translational medicine.

Ischemic preconditioning provides long-lasting neuroprotection against ischemic stroke: The role of Nrf2

BACKGROUND AND PURPOSE

A major gap in the field of ischemic preconditioning (IPC) is whether or not long-lasting neuroprotection can be achieved. Moreover, the specific mechanisms underlying IPC and how they can be translated into the clinic remain uncertain. To fill these gaps, we tested the hypothesis that IPC exerts long-lasting structural and functional neuroprotection against ischemic stroke through the master gatekeeper of antioxidant defenses, nuclear factor erythroid 2-related factor 2 (Nrf2). We also tested whether the brain could be pharmaceutically preconditioned with a potent and blood-brain barrier-permeable Nrf2 activator, 2-cyano-3,12-dioxo-oleana-1,9(11)-dien-28-trifluoethyl amide (CDDO-TFEA).

METHODS

IPC was induced by transient middle cerebral artery occlusion (MCAO) for 12 min, and ischemic stroke was generated by MCAO for 60 min in wild-type (WT) or Nrf2 knockout (KO) mice. Sensorimotor function, learning/memory skills, and brain tissue loss were measured up to 35 days after stroke. Primary rodent cortical neurons from wildtype (WT) and Nrf2 KO mice were subjected to lethal oxygen-glucose deprivation (OGD) or a brief OGD episode as a preconditioning (PC) stimulus before OGD. Cell viability/death, lipid electrophile generation, and Nrf2 activation were measured. CDDO-TFEA or its vehicle was administered in vivo for three consecutive days before MCAO. Tissue loss and neurological tests were performed 35 days after stroke.

RESULTS

IPC significantly reduced sensorimotor deficits, post-stroke cognitive impairments, and brain tissue loss, 35 days after MCAO in WT mice. These enduring protective effects of IPC were inhibited in Nrf2 KO mice. In neuronal cultures, PC also endowed primary neurons with ischemic tolerance against OGD-induced cell death, an effect that was abolished by loss of Nrf2 expression in KO neurons. PC induced the generation of low levels of lipid electrophiles and led to activation of the Nrf2 pathway. The mechanism underlying IPC may be translatable, as exogenous administration of the Nrf2 activator CDDO-TFEA significantly reduced neurological dysfunction and ischemic brain damage after MCAO.

CONCLUSIONS

IPC provides long-lasting neuroprotection against ischemic brain injury and post-stroke cognitive dysfunction. Nrf2 activation plays a key role in this beneficial outcome and is a promising therapeutic target for the attenuation of ischemic brain injury.

Estrogen preconditioning: A promising strategy to reduce inflammation in the ischemic brain

During the premenopausal phase of a woman's life, estrogen naturally protects against ischemic brain damage and its debilitating consequence of cognitive decline. However, the decline in estrogen at menopause exponentially increases a women's risk for cerebral ischemia and its severity. Supplementation of estrogen during menopause is the most logical solution to abate this increased risk for cerebral ischemia; however, continuous therapy has proven to be contraindicative. Studies from our laboratory over the past decade have shown that a single bolus or long-term periodic 17β-estradiol treatment(s) two days prior to ischemia mimics ischemic preconditioning-conferred protection of the brain in ovariectomized or reproductively senescent female rats. These studies also demonstrated that 17β-estradiol-induced preconditioning (EPC) requires estrogen receptor (ER)-subtype beta (ER-β) activation. ER-β is expressed throughout the brain, including in the hippocampus, which plays a key role in learning and memory. Because periodic activation of ER-β mitigates post-ischemic cognitive decline in ovariectomized female rats, it can be surmised that EPC has the potential to reduce post-ischemic damage and cognitive decline in females. Estrogens are key anti-inflammatory agents; therefore this review discusses the effects of EPC on the inflammasome. Furthermore, as we now clearly know, the brain acts differently in males and females. Indeed, neurodegenerative diseases, including cerebral ischemia, and pharmacological drugs affect males and females in different ways. Thus, inasmuch as the National Institutes of Health and the Stroke Treatment Academic Industry Roundtable (STAIR) consortium mandate inclusion of female experimental animals, this review also discusses the need to close the gap in our knowledge in future studies of EPC in female animal models of cerebral ischemia.

Emerging therapeutic strategies for transplantation-induced acute kidney injury: protecting the organelles and the vascular bed

INTRODUCTION

Renal ischemia-reperfusion injury (IRI) is a significant clinical challenge faced by clinicians in a broad variety of clinical settings such as perioperative and intensive care. Renal IRI induced acute kidney injury (AKI) is a global public health concern associated with high morbidity, mortality, and health-care costs. Areas covered: This paper focuses on the pathophysiology of transplantation-related AKI and recent findings on cellular stress responses at the intersection of 1. The Unfolded protein response; 2. Mitochondrial dysfunction; 3. The benefits of mineralocorticoid receptor antagonists. Lastly, perspectives are offered to the readers. Expert opinion: Renal IRI is caused by a sudden and temporary impairment of blood flow to the organ. Defining the underlying cellular cascades involved in IRI will assist us in the identification of novel interventional targets to attenuate IRI with the potential to improve transplantation outcomes. Targeting mitochondrial function and cellular bioenergetics upstream of cellular damage may offer several advantages compared to targeting downstream inflammatory and fibrosis processes. An improved understanding of the cellular pathophysiological mechanisms leading to kidney injury will hopefully offer improved targeted therapies to prevent and treat the injury in the future.

Exosome-shuttled miR-92b-3p from ischemic preconditioned astrocytes protects neurons against oxygen and glucose deprivation

Ischemic preconditioning (IPC) exerts protective effects against ischemic cerebral injury. In the present study, an in vitro model of cerebral ischemia (oxygen and glucose deprivation, OGD) was established to investigate the neuroprotective mechanism of IPC. We found that conditioned medium (C.M.) from astrocytes rather than neurons nor microglia cell line BV2 exerted neuroprotection. Moreover, exosomes derived from OGD preconditioned astrocytes can be taken up by neurons and attenuated OGD-induced neuron death and apoptosis. High-throughput microRNA (miRNA) sequencing revealed that miR-92b-3p levels in exosomes released from preconditioned astrocytes were increased. Overexpression of miR-92b-3p in neurons with miR-92b-3p mimic achieved the same protective effects as C.M. from astrocytes. Thus, we propose that the mechanism of IPC may associate with astrocytes, and that exosome-mediated miR-92b-3p shuttle from preconditioned astrocytes to neurons participate in these process.

Effect of remote ischemic preconditioning on cerebral vasospasm and biomarkers of cerebral ischemia in aneurysmal subarachnoid hemorrhage (ERVAS): A protocol for a randomized, controlled pilot trial

INTRODUCTION:

Cerebral vasospasm is a dreaded complication of aneurysmal subarachnoid hemorrhage (aSAH) predisposing to delayed cerebral ischemia. We intend to study the cerebroprotective effects of remote ischemic preconditioning (RIPC) in patients with aSAH.

MATERIALS AND METHODS:

This is a single-center, prospective, parallel group, randomized, pilot trial, approved by the Institutional Ethics Committee. Patients with aSAH admitted to our hospital for surgical clipping; fulfilling the trial inclusion criteria will be randomized to true RIPC (n = 12) (inflating upper extremity blood pressure cuff thrice for 5 min to 30 mmHg above systolic blood pressure) or sham RIPC (n = 12) (inflating blood pressure cuff thrice for 5 min to 30 mmHg) in 1:1 allocation ratio using a computerized random allocation sequence and block randomization.

RESULTS:

Our primary outcome measure is vasospasm on cerebral angiography and transcranial Doppler study, and concentration of serum S100B and neuron-specific enolase at 24 h after RIPC and on day 7 of ictus. Our secondary outcomes are safety of RIPC, cerebral oxygen saturation, and Glasgow coma score, and extended Glasgow outcome scale scores at discharge and at 1, 3, and 6 months following discharge. Outcome measures will be assessed by an observer blinded to the study intervention.

CONCLUSION:

If our preliminary results demonstrate a beneficial effect of RIPC, this would serve as a clinically applicable and safe preemptive method of protection against cerebral ischemia.

Barriers and Advances in Kidney Preservation

Despite the fact that a significant fraction of kidney graft dysfunctions observed after transplantation is due to ischemia-reperfusion injuries, there is still no clear consensus regarding optimal kidney preservation strategy. This stems directly from the fact that as of yet, the mechanisms underlying ischemia-reperfusion injury are poorly defined, and the role of each preservation parameter is not clearly outlined. In the meantime, as donor demography changes, organ quality is decreasing which directly increases the rate of poor outcome. This situation has an impact on clinical guidelines and impedes their possible harmonization in the transplant community, which has to move towards changing organ preservation paradigms: new concepts must emerge and the definition of a new range of adapted preservation method is of paramount importance. This review presents existing barriers in transplantation (e.g., temperature adjustment and adequate protocol, interest for oxygen addition during preservation, and clear procedure for organ perfusion during machine preservation), discusses the development of novel strategies to overcome them, and exposes the importance of identifying reliable biomarkers to monitor graft quality and predict short and long-term outcomes. Finally, perspectives in therapeutic strategies will also be presented, such as those based on stem cells and their derivatives and innovative models on which they would need to be properly tested.

Effect of Combined Treatment of Ketorolac and Remote Ischemic Preconditioning on Renal Ischemia-Reperfusion Injury in Patients Undergoing Partial Nephrectomy: Pilot Study

We evaluated postoperative renal function in patients with/without combined therapy of ketorolac and remote ischemic preconditioning during partial nephrectomy. Sixteen patients were randomly allocated to either the ketorolac combined with RIPC group (KI, n = 8) or control group (n = 8). The KI group received both remote ischemic preconditioning before surgery and intravenous ketorolac of 1 mg/kg before renal artery clamping. Renal parameters were measured before induction, after anesthesia induction, and 2, 12, 24, 48, and 72 h after renal artery declamping. Acute kidney injury was assessed by Acute Kidney Injury Network criteria. The estimated glomerular filtration rate decreased in both groups, but then increased significantly at 48 h and 72 h after declamping only in the KI group compared to 24 h (p = 0.001 and p = 0.016). Additionally, it was higher at 48 h and 72 h after declamping in the KI group compared to the control group (p = 0.025 and p = 0.044). The incidence of acute kidney injury was significantly reduced in the KI group (13%) compared to the control group (83%) (p = 0.026). FE_Na was markedly increased at 2 h after declamping, and recovered in both groups, but it was more significant at 12 h after declamping in the KI group (p = 0.022). Urinary N-acetyl-1-β-D-glucosoaminidase and serum neutrophil gelatinase-associated lipocalin were similar (p = 0.291 and p = 0.818). There is a possibility that combined therapy of ketorolac and remote ischemic preconditioning prior to ischemia may alleviate renal dysfunction and reduce the incidence of acute kidney injury in patients undergoing partial nephrectomy.

Resveratrol Preconditioning Induces Genomic and Metabolic Adaptations within the Long-Term Window of Cerebral Ischemic Tolerance Leading to Bioenergetic Efficiency

Neuroprotective agents administered post-cerebral ischemia have failed so far in the clinic to promote significant recovery. Thus, numerous efforts were redirected toward prophylactic approaches such as preconditioning as an alternative therapeutic strategy. Our laboratory has revealed a novel long-term window of cerebral ischemic tolerance mediated by resveratrol preconditioning (RPC) that lasts for 2 weeks in mice. To identify its mediators, we conducted an RNA-seq experiment on the cortex of mice 2 weeks post-RPC, which revealed 136 differentially expressed genes. The majority of genes (116/136) were downregulated upon RPC and clustered into biological processes involved in transcription, synaptic signaling, and neurotransmission. The downregulation in these processes was reminiscent of metabolic depression, an adaptation used by hibernating animals to survive severe ischemic states by downregulating energy-consuming pathways. Thus, to assess metabolism, we used a neuronal-astrocytic co-culture model and measured the cellular respiration rate at the long-term window post-RPC. Remarkably, we observed an increase in glycolysis and mitochondrial respiration efficiency upon RPC. We also observed an increase in the expression of genes involved in pyruvate uptake, TCA cycle, and oxidative phosphorylation, all of which indicated an increased reliance on energy-producing pathways. We then revealed that these nuclear and mitochondrial adaptations, which reduce the reliance on energy-consuming pathways and increase the reliance on energy-producing pathways, are epigenetically coupled through acetyl-CoA metabolism and ultimately increase baseline ATP levels. This increase in ATP would then allow the brain, a highly metabolic organ, to endure prolonged durations of energy deprivation encountered during cerebral ischemia.

Brain ischemic preconditioning protects against ischemic injury and preserves the blood-brain barrier via oxidative signaling and Nrf2 activation

Brain ischemic preconditioning (IPC) with mild ischemic episodes is well known to protect the brain against subsequent ischemic challenges. However, the underlying mechanisms are poorly understood. Here we demonstrate the critical role of the master redox transcription factor, nuclear factor (erythroid-derived 2)-like 2 (Nrf2), in IPC-mediated neuroprotection and blood-brain barrier (BBB) preservation. We report that IPC causes generation of endogenous lipid electrophiles, including 4-hydroxy-2-nonenal (4-HNE), which release Nrf2 from inhibition by Keap1 (via Keap1-C288) and inhibition by glycogen synthase kinase 3β (via GSK3β-C199). Nrf2 then induces expression of its target genes, including a new target, cadherin 5, a key component of adherens junctions of the BBB. These effects culminate in mitigation of BBB leakage and of neurological deficits after stroke. Collectively, these studies are the first to demonstrate that IPC protects the BBB against ischemic injury by generation of endogenous electrophiles and activation of the Nrf2 pathway through inhibition of Keap1- and GSK3β-dependent Nrf2 degradation.

The Neuronal Ischemic Tolerance Is Conditioned by the Tp53 Arg72Pro Polymorphism

Cerebral preconditioning (PC) confers endogenous brain protection after stroke. Ischemic stroke patients with a prior transient ischemic attack (TIA) may potentially be in a preconditioned state. Although PC has been associated with the activation of pro-survival signals, the mechanism by which preconditioning confers neuroprotection is not yet fully clarified. Recently, we have described that PC-mediated neuroprotection against ischemic insult is promoted by p53 destabilization, which is mediated by its main regulator MDM2. Moreover, we have previously described that the human Tp53 Arg72Pro single nucleotide polymorphism (SNP) controls susceptibility to ischemia-induced neuronal apoptosis and governs the functional outcome of patients after stroke. Here, we studied the contribution of the human Tp53 Arg72Pro SNP on PC-induced neuroprotection after ischemia. Our results showed that cortical neurons expressing the Pro72-p53 variant exhibited higher PC-mediated neuroprotection as compared with Arg72-p53 neurons. PC prevented ischemia-induced nuclear and cytosolic p53 stabilization in Pro72-p53 neurons. However, PC failed to prevent mitochondrial p53 stabilization, which occurs in Arg72-p53 neurons after ischemia. Furthermore, PC promoted neuroprotection against ischemia by controlling the p53/active caspase-3 pathway in Pro72-p53, but not in Arg72-p53 neurons. Finally, we found that good prognosis associated to TIA within 1 month prior to ischemic stroke was restricted to patients harboring the Pro72 allele. Our findings demonstrate that the Tp53 Arg72Pro SNP controls PC-promoted neuroprotection against a subsequent ischemic insult by modulating mitochondrial p53 stabilization and then modulates TIA-induced ischemic tolerance.

Rationale and Study Design for a Single-Arm Phase IIa Study Investigating Feasibility of Preventing Ischemic Cerebrovascular Events in High-Risk Patients with Acute Non-disabling Ischemic Cerebrovascular Events Using Remote Ischemic Conditioning

Background:

Acute minor ischemic stroke (AMIS) or transient ischemic attack (TIA) is a common cerebrovascular event with a considerable high recurrence. Prior research demonstrated the effectiveness of regular long-term remote ischemic conditioning (RIC) in secondary stroke prevention in patients with intracranial stenosis. We hypothesized that RIC can serve as an effective adjunctive therapy to pharmacotherapy in preventing ischemic events in patients with AMIS/TIA. This study aimed to investigate the feasibility, safety, and preliminary efficacy of daily RIC in inhibiting cerebrovascular/cardiovascular events after AMIS/TIA.

Methods:

This is a single-arm, open-label, multicenter Phase IIa futility study with a sample size of 165. Patients with AMIS/TIA receive RIC as an additional therapy to secondary stroke prevention regimen. RIC consists of five cycles of 5-min inflation (200 mmHg) and 5-min deflation of cuffs on bilateral upper limbs twice a day for 90 days. The antiplatelet strategy is based on individual physician's best practice: aspirin alone, clopidogrel alone, or combination of aspirin and clopidogrel. We will assess the recurrence rate of ischemic stroke/TIA within 3 months as the primary outcomes.

Conclusions:

The data gathered from the study will be used to determine whether a further large-scale, multicenter randomized controlled Phase II trial is warranted in patients with AMIS/TIA.

Trial Registration:

ClinicalTrials.gov, NCT03004820; https://www.clinicaltrials.gov/ct2/show/NCT03004820.

Focusing on claudin-5: A promising candidate in the regulation of BBB to treat ischemic stroke

Claudin-5 is a tight junction (TJ) protein in the blood-brain barrier (BBB) that has recently attracted increased attention. Numerous studies have demonstrated that claudin-5 regulates the integrity and permeability of the BBB. Increased claudin-5 expression plays a neuroprotective role in neurological diseases, particularly in cerebral ischemic stroke. Moreover, claudin-5 might be a potential marker for early hemorrhagic transformation detection in ischemic stroke. In light of the distinctive effects of claudin-5 on the nervous system, we present the elaborate network of roles that claudin-5 plays in ischemic stroke. In this review, we first introduce basic knowledge regarding the BBB and the claudin family, the characterization and regulation of claudin-5, and association between claudin-5 and other TJ proteins. Subsequently, we describe BBB dysfunction and neuron-specific drivers of pathogenesis of ischemic stroke, including inflammatory disequilibrium and oxidative stress. Furthermore, we summarize promising ischemic stroke treatments that target the BBB via claudin-5, including modified rt-PA therapy, pharmacotherapy, hormone treatment, receptor-targeted therapy, gene therapy, and physical therapy. This review highlights recent advances and provides a comprehensive summary of claudin-5 in the regulation of the BBB and may be helpful for drug design and clinical therapy for treatment of ischemic stroke.

Bi-directionally protective communication between neurons and astrocytes under ischemia

The extensive existing knowledge on bi-directional communication between astrocytes and neurons led us to hypothesize that not only ischemia-preconditioned (IP) astrocytes can protect neurons but also IP neurons protect astrocytes from lethal ischemic injury. Here, we demonstrated for the first time that neurons have a significant role in protecting astrocytes from ischemic injury. The cultured medium from IP neurons (IPcNCM) induced a remarkable reduction in LDH and an increase in cell viability in ischemic astrocytes in vitro. Selective neuronal loss by kainic acid injection induced a significant increase in apoptotic astrocyte numbers in the brain of ischemic rats in vivo. Furthermore, TUNEL analysis, DNA ladder assay, and the measurements of ROS, GSH, pro- and anti-apoptotic factors, anti-oxidant enzymes and signal molecules in vitro and/or in vivo demonstrated that IP neurons protect astrocytes by an EPO-mediated inhibition of pro-apoptotic signals, activation of anti-apoptotic proteins via the P13K/ERK/STAT5 pathways and activation of anti-oxidant proteins via up-regulation of anti-oxidant enzymes. We demonstrated the existence of astro-protection by IP neurons under ischemia and proposed that the bi-directionally protective communications between cells might be a common activity in the brain or peripheral organs under most if not all pathological conditions.

Ischemic Preconditioning in the Intensive Care Unit

OPINION STATEMENT

Preconditioning is the premise that controlled preemptive exposure to sub-lethal doses of a stressor and can condition an organism or organ to later withstand a lethal dose. This process relies on marshaling endogenous survival resources that have evolved as part of an organism's evolutionary struggle to overcome at times harsh environmental conditions. This preconditioning response occurs through activation of myriad complex mechanisms that run the gamut from alterations in gene expression to the de novo synthesis and post-translational modification of proteins, and it may occur across exposure to a wide variety of stressors (i.e., ischemia, hypoxia, hypothermia, drugs). This review will focus on preconditioning in relation to an ischemic stressor (ischemic preconditioning) and how this process may be harnessed as a protective method to ameliorate targeted acute neurologic diseases especially. There has been considerable eagerness to translate ischemic preconditioning to the bedside, and to that end there have been recent trials examining its efficacy in various clinical settings. However, some of these trials have reached diverging conclusions with a protective effect seen in studies targeting acute kidney injury solely while no benefit was seen in larger trials targeting combined endpoints including cardio-, neuro-, and renoprotection in a cohort of patients undergoing cardiac surgery. While an extensive body of pre-clinical research offers ischemic preconditioning as a robust and highly faithful protective phenomenon, its clinical utility remains unproven. This current state may be due to persisting gaps in our understanding of how best to harness its power. This review will provide an overview of the biological mechanisms proposed to underlie ischemic preconditioning, explore initial disease targets, examine the challenges we must overcome to optimally engage this system, and report findings of recent clinical trials.

Tackling issues in the path toward clinical translation in brain conditioning: Potential offered by nutraceuticals

Brief periods of ischemia have been shown in many experimental setups to provide tolerance against ischemia in multiple organs including the brain, when administered before (preconditioning) or even after (postconditioning) the normally lethal ischemia. In addition to these so-called ischemic conditionings, many pharmacological and natural agents (e.g., chemicals and nutraceuticals) can also act as potent pre- and post-conditioners. Deriving from the original concept of ischemic preconditioning, these various conditioning paradigms may be promising as clinical-stage therapies for prevention of ischemic-related injury, especially stroke. As no proven experimentally identified strategy has translated into clinical success, the experimental induction of neuroprotection using these various conditioning paradigms has raised several questions, even before considering translation to clinical studies in humans. The first aim of the review is to consider key questions on preclinical studies of pre- or post-conditioning modalities including those induced by chemical or nutraceuticals. Second, we make the argument that several key issues can be addressed by a novel concept, nutraceutical preconditioning. Specifically, α-linolenic acid (alpha-linolenic acid [ALA] an omega-3 polyunsaturated fatty acid), contained in plant-derived edible products, is essential in the daily diet, and a body of work has identified ALA as a pre- and post-conditioner of the brain. Nutritional intervention and functional food development are an emerging direction for preventing stroke damage, offering the potential to improving clinical outcomes through activation of the endogenous protective mechanisms known collectively as conditioning.

Effects of Remote Ischemic Preconditioning on Heme Oxygenase-1 Expression and Cutaneous Wound Repair

Skin wounds may lead to scar formation and impaired functionality. Remote ischemic preconditioning (RIPC) can induce the anti-inflammatory enzyme heme oxygenase-1 (HO-1) and protect against tissue injury. We aim to improve cutaneous wound repair by RIPC treatment via induction of HO-1. RIPC was applied to HO-1-luc transgenic mice and HO-1 promoter activity and mRNA expression in skin and several other organs were determined in real-time. In parallel, RIPC was applied directly or 24h prior to excisional wounding in mice to investigate the early and late protective effects of RIPC on cutaneous wound repair, respectively. HO-1 promoter activity was significantly induced on the dorsal side and locally in the kidneys following RIPC treatment. Next, we investigated the origin of this RIPC-induced HO-1 promoter activity and demonstrated increased mRNA in the ligated muscle, heart and kidneys, but not in the skin. RIPC did not change HO-1 mRNA and protein levels in the wound 7 days after cutaneous injury. Both early and late RIPC did not accelerate wound closure nor affect collagen deposition. RIPC induces HO-1 expression in several organs, but not the skin, and did not improve excisional wound repair, suggesting that the skin is insensitive to RIPC-mediated protection.

Remote Ischemic Preconditioning Enhances the Expression of Genes Encoding Antioxidant Enzymes and Endoplasmic Reticulum Stress-Related Proteins in Rat Skeletal Muscle

Purpose:

Ischemic preconditioning (IPC), including remote IPC (rIPC) and direct IPC (dIPC), is a promising method to decrease ischemia-reperfusion (IR) injury. This study tested the effect of both rIPC and dIPC on the genes for antioxidant enzymes and endoplasmic reticulum (ER) stress-related proteins.

Materials and Methods:

Twenty rats were randomly divided into the control and study groups. In the control group (n=10), the right hind limb was sham-operated. The left hind limb (IscR) of the control group underwent IR injury without IPC. In the study group (n=10), the right hind limb received IR injury after 3 cycles of rIPC. The IscR received IR injury after 3 cycles of dIPC. Gene expression was analyzed by Quantitative real-time polymerase chain reaction from the anterior tibialis muscle.

Results:

The expression of the antioxidant enzyme genes including glutathione peroxidase (GPx), superoxide dismutase (SOD) 1 and catalase (CAT) were significantly reduced in IscR compared with sham treatment. In comparison with IscR, rIPC enhanced the expression of GPx, SOD2, and CAT genes. dIPC enhanced the expression of SOD2 and CAT genes. The expression of SOD2 genes was consistently higher in rIPC than in dIPC, but the difference was only significant for SOD2. The expression of genes for ER stress-related proteins tended to be reduced in IscR in comparison with sham treatment. However, the difference was only significant for C/EBP homologous protein (CHOP). In comparison with IscR, rIPC significantly up-regulated activating transcription factor 4 and CHOP, whereas dIPC up-regulated CHOP.

Conclusion:

Both rIPC and dIPC enhanced expression of genes for antioxidant enzymes and ER stress-related proteins.

Low-Dose Ethanol Preconditioning Protects Against Oxygen-Glucose Deprivation/Reoxygenation-Induced Neuronal Injury By Activating Large Conductance, Ca2+-Activated K+ Channels In Vitro

Increasing evidence suggests that low to moderate ethanol ingestion protects against the deleterious effects of subsequent ischemia/reperfusion; however, the underlying mechanism has not been elucidated. In the present study, we showed that expression of the neuronal large-conductance, Ca²⁺-activated K⁺ channel (BK_Ca) α-subunit was upregulated in cultured neurons exposed to oxygen-glucose deprivation/reoxygenation (OGD/R) compared with controls. Preconditioning with low-dose ethanol (10 mmol/L) increased cell survival rate in neurons subjected to OGD/R, attenuated the OGD/R-induced elevation of cytosolic Ca²⁺ levels, and reduced the number of apoptotic neurons. Western blots revealed that ethanol preconditioning upregulated expression of the anti-apoptotic protein Bcl-2 and downregulated the pro-apoptotic protein Bax. The protective effect of ethanol preconditioning was antagonized by a BK_Ca channel inhibitor, paxilline. Inside-out patches in primary neurons also demonstrated the direct activation of the BK_Ca channel by 10 mmol/L ethanol. The above results indicated that low-dose ethanol preconditioning exerts its neuroprotective effects by attenuating the elevation of cytosolic Ca²⁺ and preventing neuronal apoptosis, and this is mediated by BK_Ca channel activation.

Ischemic preconditioning inhibits over-expression of arginyl-tRNA synthetase gene Rars in ischemia-injured neurons

The expression changes of Rars gene in ischemia-injured neurons were investigated by detecting its translational product arginyl-tRNA synthetase (ArgRS), and the inhibitory effects of ischemic preconditioning (IPC) on Rars gene were explored. Both IPC model and prolonged ischemia (PI) model were established by using the classic oxygen glucose deprivation (OGD) method. The primary cultured neurons were assigned into the following groups: the experimental group (IPC+PI group), undergoing PI after a short period of IPC; the conditional control group (PI control group), subjected to PI without IPC; blank control group, the normally cultured neurons. The Rars transcriptional activities and ArgRS expression levels were measured at different time points after re-oxygenation (3 h/6 h/12 h/24 h). Data were collected and statistically analyzed. Compared to the blank control group, the Rars activities and ArgRS levels were significantly increased in PI control group, peaking at the time point of 6 h after re-oxygenation. Rars activities and ArgRS levels were significantly lower in the experimental group than in the PI control group at different time points after re-oxygenation. PI insult can induce an escalating activity of Rars and lead to ArgRS over-expression in primary cultured neurons. IPC can inhibit the increased Rars activity and down-regulate ArgRS expression of ischemia-insulted neurons. This mechanism may confer ischemic tolerance on neurons.

Repeat remote ischaemic pre-conditioning for improved cardiovascular function in humans: A systematic review

BACKGROUND

Single exposure to remote ischaemic pre-conditioning (RIPC) has been shown to be effective in reducing major adverse events during cardiac surgery. We evaluated the efficacy of repeated exposure RIPC to elicit improvements in cardiovascular function.

METHODS

A systematic search was conducted up until May 1st, 2015, using the following databases: EMBASE, PubMed (Medline), Web of Science and the Cochrane Central Registry of Controlled Trials (CENTRAL). Data was extracted and synthesized from published studies of repeat RIPC.

RESULTS

Data from seven studies showed evidence of improvements in vascular function and anti-hypertensive effects of systolic, diastolic and mean arterial blood pressure following repeat RIPC. Currently existing work justifies a systematic review but not data pooling of individual study data. Repeat RIPC has also produced evidence of improvements in endothelial dependent vasodilation, but not non-endothelial dependent vasodilation, cutaneous vascular conductance or cardiorespiratory fitness.

CONCLUSION

Repeated RIPC exposure has produced evidence of improvements in endothelial dependent vasodilation, ulcer healing and blood pressure but no benefit in non-endothelial dependent vasodilation, cutaneous vascular conductance or cardiorespiratory fitness. The optimal delivery of RIPC remains unclear, but at least 3 or preferably 4, 5 min exposures appears to be most beneficial, at least for reducing blood pressure. Aside from those undertaking cardiac surgery, other study populations with endothelial dysfunction may benefit from repeat exposure to RIPC.

Paradoxical Motor Recovery From a First Stroke After Induction of a Second Stroke: Reopening a Postischemic Sensitive Period

BACKGROUND AND OBJECTIVE

Prior studies have suggested that after stroke there is a time-limited period of increased responsiveness to training as a result of heightened plasticity-a sensitive period thought to be induced by ischemia itself. Using a mouse model, we have previously shown that most training-associated recovery after a caudal forelimb area (CFA) stroke occurs in the first week and is attributable to reorganization in a medial premotor area (AGm). The existence of a stroke-induced sensitive period leads to the counterintuitive prediction that a second stroke should reopen this window and promote full recovery from the first stroke. To test this prediction, we induced a second stroke in the AGm of mice with incomplete recovery after a first stroke in CFA.

METHODS

Mice were trained to perform a skilled prehension (reach-to-grasp) task to an asymptotic level of performance, after which they underwent photocoagulation-induced stroke in CFA. After a 7-day poststroke delay, the mice were then retrained to asymptote. We then induced a second stroke in the AGm, and after only a 1-day delay, retrained the mice.

RESULTS

Recovery of prehension was incomplete when training was started after a 7-day poststroke delay and continued for 19 days. However, a second focal stroke in the AGm led to a dramatic response to 9 days of training, with full recovery to normal levels of performance.

CONCLUSIONS

New ischemia can reopen a sensitive period of heightened responsiveness to training and mediate full recovery from a previous stroke.

Remote ischemic preconditioning in the prevention of ischemic brain damage during intracranial aneurysm treatment (RIPAT): study protocol for a randomized controlled trial

BACKGROUND

The treatment of intracranial aneurysms may be associated with cerebral ischemia. We hypothesize that pre-interventional remote ischemic preconditioning (RIPC) reduces ischemic cerebral tissue damage in patients undergoing elective intracranial aneurysm treatment.

METHODS/DESIGN

This study is a single-center, prospective, randomized, double-blind explorative trial. Patients with an unruptured intracranial aneurysm admitted to Innsbruck Medical University Hospital for coiling or clipping will be consecutively randomized to either the intervention group (= RIPC by inflating an upper extremity blood-pressure cuff for 3 x 5 min to 200 mmHg) or the control group after induction of anesthesia. Participants will be randomized 1:1 to either the preconditioning group or the sham group using a random allocation sequence and block randomization. The precalculated sample size is n = 24 per group. The primary endpoint is the area-under-the-curve concentration of serum biomarkers (S100B, NSE, GFAP, MMP9, MBP, and cellular microparticles) in the first five days after treatment. Secondary endpoints are the number and volume of new ischemic lesions in magnetic resonance imaging and clinical outcome evaluated with the National Institutes of Health Stroke Scale, the modified Rankin Scale, and neuropsychological tests at six and twelve months. All outcome variables will be determined by observers blinded to group allocation. This study was approved by the local institutional Ethics Committee (UN5164), version 3.0 of the study protocol, dated 20 October 2013.

DISCUSSION

This study uses the elective treatment of intracranial aneurysms as a paradigmatic situation to explore the neuroprotective effects of RIPC. If effects are demonstrable in this pilot trial, a larger, prospective phase III trial will be considered.

MicroRNAs in Kidney Transplantation: Living up to Their Expectations?

Since the discovery of microRNAs, ample research has been conducted to elucidate their involvement in an array of (patho)physiological conditions. Ischemia reperfusion injury is a major problem in kidney transplantation and its mechanism is still not fully known, nor is there an effective therapy. Furthermore, no biomarker is available to specifically measure (ischemic) damage after kidney transplantation or predict transplantation outcome. In this review, we summarize studies conducted on microRNAs in renal ischemia reperfusion injury and kidney transplantation. Although the number of publications on miRNAs in different areas of nephrology is increasing every year, only a limited number of reports that address the role of miRNAs in relation to ischemia reperfusion injury or kidney transplantation are available. All reports up to June 2014 on microRNAs in renal IRI, kidney transplantation, and renal allograft status were included. Design of the studies was highly variable and there was limited overlap between microRNAs found in these reports. No single microRNA expression pattern could be found, although multiple microRNAs involved in the immune response seem to be altered after ischemia reperfusion injury and kidney transplantation. Although there is a growing interest in microRNA research in kidney transplantation aiming to identify biomarkers and therapeutical targets, to date, no specific microRNA has been demonstrated to be applicable as either one, mostly because of lack of specificity. More systematical research is needed to determine whether microRNAs can be applied as biomarker, therapeutic target, or therapeutic agent in kidney transplantation.

Ischemic conditioning-induced endogenous brain protection: Applications pre-, per- or post-stroke

In the area of brain injury and neurodegenerative diseases, a plethora of experimental and clinical evidence strongly indicates the promise of therapeutically exploiting the endogenous adaptive system at various levels like triggers, mediators and the end-effectors to stimulate and mobilize intrinsic protective capacities against brain injuries. It is believed that ischemic pre-conditioning and post-conditioning are actually the strongest known interventions to stimulate the innate neuroprotective mechanism to prevent or reverse neurodegenerative diseases including stroke and traumatic brain injury. Recently, studies showed the effectiveness of ischemic per-conditioning in some organs. Therefore the term ischemic conditioning, including all interventions applied pre-, per- and post-ischemia, which spans therapeutic windows in 3 time periods, has recently been broadly accepted by scientific communities. In addition, it is extensively acknowledged that ischemia-mediated protection not only affects the neurons but also all the components of the neurovascular network (consisting of neurons, glial cells, vascular endothelial cells, pericytes, smooth muscle cells, and venule/veins). The concept of cerebroprotection has been widely used in place of neuroprotection. Intensive studies on the cellular signaling pathways involved in ischemic conditioning have improved the mechanistic understanding of tolerance to cerebral ischemia. This has added impetus to exploration for potential pharmacologic mimetics, which could possibly induce and maximize inherent protective capacities. However, most of these studies were performed in rodents, and the efficacy of these mimetics remains to be evaluated in human patients. Several classical signaling pathways involving apoptosis, inflammation, or oxidation have been elaborated in the past decades. Newly characterized mechanisms are emerging with the advances in biotechnology and conceptual renewal. In this review we are going to focus on those recently reported methodological and mechanistic discoveries in the realm of ischemic conditioning. Due to the varied time differences of ischemic conditioning in different animal models and clinical trials, it is important to define optimal timing to achieve the best conditioning induced neuroprotection. This brings not only an opportunity in the treatment of stroke, but challenges as well, as data is just becoming available and the procedures are not yet optimized. The purpose of this review is to shed light on exploiting these ischemic conditioning modalities to protect the cerebrovascular system against diverse injuries and neurodegenerative disorders.

Blood as the carrier of ischemic tolerance in rat brain

This study provides clear evidence that the factor inducing tolerance to ischemia is transmitted via the circulating blood. By using the remote ischemia and the cross-circulation model, the tolerance to ischemia was transmitted from donor to recipient. For this study, the following experimental groups were designed: I, sham control group; II, group of tolerant hindlimb tourniquet-treated rats; III, positive control group; IV, control for cross-circulation influence; preconditioned animals: V, tolerant animals subjected to middle cerebral artery occlusion (MCAO); VI, tolerant animals cross-circulated with SHC, followed by MCAO; VII, SHC animals cross-circulated with tolerant animals and subsequently subjected to MCAO; VIII, tolerant animals cross-circulated with ischemic rats, followed by MCAO; IX, SHC animals cross-circulated with ischemic animals and subjected to MCAO; postconditioned animals: X, ischemic animals treated with a remote limb tourniquet; XI, ischemic animals cross-circulated with SHC control rats; and XII, ischemic animals cross-circulated with tolerant rats. Results confirmed that remote ischemia induced reduction of infarct volume in the preconditioned (V, 60%) as well as in the postconditioned group (X, 52%). Significant diminution was also observed in group XII (56.6%). In the preconditioned group, decreased infarct volume was detected in groups VI and VII (about 65%) and in group IX (about 50%). The greatest infarct reduction (84%) was induced by the presence of ischemic blood in a tolerant rat before ischemia induction. In summary, the factor inducing tolerance to ischemia is generated by remote ischemia and by ischemia itself; from the site of origin to the rest of the body, it is transported by the systemic blood circulation and can be transferred from animal to animal. The effect of conditioning with two different ischemic events (brain and hindlimb ischemia) led to a cumulative, stronger tolerance response.

Remote ischemic preconditioning delays the onset of acute mountain sickness in normobaric hypoxia

Acute mountain sickness (AMS) is a neurological disorder occurring when ascending too fast, too high. Remote ischemic preconditioning (RIPC) is a noninvasive intervention protecting remote organs from subsequent hypoxic damage. We hypothesized that RIPC protects against AMS and that this effect is related to reduced oxidative stress. Fourteen subjects were exposed to 18 hours of normoxia (21% oxygen) and 18 h of normobaric hypoxia (12% oxygen, equivalent to 4500 m) on different days in a blinded, randomized order. RIPC consisted of four cycles of lower limb ischemia (5 min) and 5 min of reperfusion, and was performed immediately before the study room was entered. A control group was exposed to hypoxia (12% oxygen, n = 14) without RIPC. AMS was evaluated by the Lake Louise score (LLS) and the AMS-C score of the Environmental Symptom Questionnaire. Plasma concentrations of ascorbate radicals, oxidized sulfhydryl (SH) groups, and electron paramagnetic resonance (EPR) signal intensity were measured as biomarkers of oxidative stress. RIPC reduced AMS scores (LLS: 1.9 ± 0.4 vs. 3.2 ± 0.5; AMS-C score: 0.4 ± 0.1 vs. 0.8 ± 0.2), ascorbate radicals (27 ± 7 vs. 65 ± 18 nmol/L), oxidized SH groups (3.9 ± 1.4 vs. 14.3 ± 4.6 μmol/L), and EPR signal intensity (0.6 ± 0.2 vs. 1.5 ± 0.4 × 10(6)) after 5 h in hypoxia (all P < 0.05). After 18 hours in hypoxia there was no difference in AMS and oxidative stress between RIPC and control. AMS and plasma markers of oxidative stress did not correlate. This study demonstrates that RIPC transiently reduces symptoms of AMS and that this effect is not associated with reduced plasma levels of reactive oxygen species.

Impact of remote ischemic preconditioning preceding coronary artery bypass grafting on inducing neuroprotection (RIPCAGE): study protocol for a randomized controlled trial

BACKGROUND

Neurological complications after cardiac surgery have a profound impact on postoperative survival and quality of life. The increasing importance of strategies designed to improve neurological outcomes mirrors the growing risk burden of the contemporary cardiac surgical population. Remote ischemic preconditioning (RIPC) reduces adverse sequelae of ischemia in vulnerable organs by subjecting tissues with high ischemic tolerance to brief periods of hypoperfusion. This trial will evaluate the neuroprotective effect of RIPC in the cardiac surgical arena, by employing magnetic resonance imaging (MRI) and neurocognitive testing.

METHODS

Patients scheduled for elective coronary artery bypass grafting with the use of cardiopulmonary bypass will be screened for the study. Eligible patients will be randomized to undergo either a validated RIPC protocol or a sham procedure. The RIPC will be induced by inflation of a blood pressure cuff to 200 mmHg for 5 minutes, followed by a 5-minute reperfusion period. Three sequences of interchanging cuff inflations and deflations will be employed. Neurocognitive testing and MRI imaging will be performed preoperatively and on postoperative day 7. Paired pre- and postoperative neurocognitive and neuroimaging data will then be compared. The primary composite outcome measure will consist of new ischemic lesions on brain MRI, postprocedural impairment in brain connectivity on resting-state functional MRI (rs-fMRI), and significant new declines in neurocognitive performance. The secondary endpoint measures will be the individual components of the primary endpoint measures, expressed as continuous variables, troponin T release on postoperative day 1 and the incidence of major adverse cardiovascular events at 3 months postoperatively. Major adverse cardiovascular events, including accumulating cardiovascular mortality, stroke, nonfatal myocardial infarction, and rehospitalization for ischemia, will form a composite endpoint measure.

DISCUSSION

This trial will aim to assess whether RIPC in patients subjected to surgical myocardial revascularization employing cardiopulmonary bypass initiates a neuroprotective response. Should the results of this trial indicate that RIPC is effective in reducing the incidence of adverse neurological events in patients undergoing coronary artery bypass grafting, it could impact on the current standard of care.

TRIAL REGISTRATION

ClinicalTrials.gov NCT02177981.

Pre-conditioning with low-level laser (light) therapy: light before the storm

Pre-conditioning by ischemia, hyperthermia, hypothermia, hyperbaric oxygen (and numerous other modalities) is a rapidly growing area of investigation that is used in pathological conditions where tissue damage may be expected. The damage caused by surgery, heart attack, or stroke can be mitigated by pre-treating the local or distant tissue with low levels of a stress-inducing stimulus, that can induce a protective response against subsequent major damage. Low-level laser (light) therapy (LLLT) has been used for nearly 50 years to enhance tissue healing and to relieve pain, inflammation and swelling. The photons are absorbed in cytochrome(c) oxidase (unit four in the mitochondrial respiratory chain), and this enzyme activation increases electron transport, respiration, oxygen consumption and ATP production. A complex signaling cascade is initiated leading to activation of transcription factors and up- and down-regulation of numerous genes. Recently it has become apparent that LLLT can also be effective if delivered to normal cells or tissue before the actual insult or trauma, in a pre-conditioning mode. Muscles are protected, nerves feel less pain, and LLLT can protect against a subsequent heart attack. These examples point the way to wider use of LLLT as a pre-conditioning modality to prevent pain and increase healing after surgical/medical procedures and possibly to increase athletic performance.

3-Nitropropionic acid-induced ischemia tolerance in the rat brain is mediated by reduced metabolic activity and cerebral blood flow

Tissue tolerance to ischemia can be achieved by noxious stimuli that are below a threshold to cause irreversible damage ('preconditioning'). Understanding the mechanisms underlying preconditioning may lead to the identification of novel therapeutic targets for diseases such as stroke. We here used the oxidative chain inhibitor 3-nitropropionic acid (NPA) to induce ischemia tolerance in a rat middle cerebral artery occlusion (MCAO) stroke model. Cerebral blood flow (CBF) and structural integrity were characterized by longitudinal magnetic resonance imaging (MRI) in combination with behavioral, histologic, and biochemical assessment of NPA-preconditioned animals and controls. Using this approach we show that the ischemia-tolerant state is characterized by a lower energy charge potential and lower CBF, indicating a reduced baseline metabolic demand, and therefore a cellular mechanism of neural protection. Blood vessel density and structural integrity were not altered by NPA treatment. When subjected to MCAO, preconditioned animals had a characteristic MRI signature consisting of enhanced CBF maintenance within the ischemic territory and intraischemic reversal of the initial cytotoxic edema, resulting in reduced infarct volumes. Thus, our data show that tissue protection through preconditioning occurs early during ischemia and indicate that a reduced cellular metabolism is associated with tissue tolerance to ischemia.