Remote ischemic post-conditioning reduced brain damage in experimental ischemia/reperfusion injury

The potential mechanism and clinical application value of remote ischemic conditioning in stroke

Some studies have confirmed the neuroprotective effect of remote ischemic conditioning against stroke. Although numerous animal researches have shown that the neuroprotective effect of remote ischemic conditioning may be related to neuroinflammation, cellular immunity, apoptosis, and autophagy, the exact underlying molecular mechanisms are unclear. This review summarizes the current status of different types of remote ischemic conditioning methods in animal and clinical studies and analyzes their commonalities and differences in neuroprotective mechanisms and signaling pathways. Remote ischemic conditioning has emerged as a potential therapeutic approach for improving stroke-induced brain injury owing to its simplicity, non-invasiveness, safety, and patient tolerability. Different forms of remote ischemic conditioning exhibit distinct intervention patterns, timing, and application range. Mechanistically, remote ischemic conditioning can exert neuroprotective effects by activating the Notch1/phosphatidylinositol 3-kinase/Akt signaling pathway, improving cerebral perfusion, suppressing neuroinflammation, inhibiting cell apoptosis, activating autophagy, and promoting neural regeneration. While remote ischemic conditioning has shown potential in improving stroke outcomes, its full clinical translation has not yet been achieved.

MOTS-c mimics remote ischemic preconditioning in protecting against lung ischemia-reperfusion injury by alleviating endothelial barrier dysfunction

Remote ischemic preconditioning (RIPC) induces the expression of unidentified protective cytokines that mitigate lung ischemia-reperfusion injury (LIRI). This study hypothesizes that MOTS-c, a mitokine with potent protective effects against mitochondrial damage, contributes to RIPC-mediated protection by alleviating endothelial barrier dysfunction. In human lung transplantation patients, serum levels of MOTS-c significantly decreased following IR injury but were markedly increased when RIPC was performed prior to transplantation. Similarly, in a mouse model of LIRI, RIPC restored serum MOTS-c levels and improved lung injury outcomes. Intravenous administration of MOTS-c in mice replicated the protective effects observed with RIPC. Mechanistic studies demonstrated that repeated hypoxia in human primary skeletal muscle immortalized cells (HPSMIC) led to the secretion of conditioned media that protected HUVECs from OGD/R-induced injury; silencing MOTS-c abolished these protective effects. Further investigations using nuclear factor erythroid 2-related factor 2 (Nrf2) knockout mice and the Nrf2 inhibitor ML385 revealed that MOTS-c exerts its protective function by increasing Nrf2 protein levels, thereby maintaining endothelial barrier integrity. In conclusion, this study identifies MOTS-c as a novel mediator of RIPC's protective effects against LIRI and highlights its potential as a therapeutic alternative for preventing lung injury and preserving vascular endothelial function.

Beyond Pharmacology: The Biological Mechanisms of Remote Ischemic Conditioning in Cerebrovascular Disease

Cerebrovascular diseases (CVDs), comprising predominantly ischemic stroke and chronic cerebral hypoperfusion (CCH), are a significant threat to global health, often leading to disability and mortality. Remote ischemic conditioning (RIC) has emerged as a promising, non-pharmacological strategy to combat CVDs by leveraging the body's innate defense mechanisms. This review delves into the neuroprotective mechanisms of RIC, categorizing its effects during the acute and chronic phases of stroke recovery. It also explores the synergistic potential of RIC when combined with other therapeutic strategies, such as pharmacological treatments and physical exercise. Additionally, this review discusses the pathways through which peripheral transmission can confer central neuroprotection. This review concludes by addressing the challenges regarding and future directions for RIC, emphasizing the need for standardized protocols, biomarker identification, and expanded clinical trials to fully realize its therapeutic potential.

Remote ischemic post-conditioning for neonatal encephalopathy: a safety and feasibility trial

BACKGROUND

Despite implementation of therapeutic hypothermia (TH) for infants with neonatal encephalopathy (NE), a significant proportion of infants suffer neurodevelopmental impairment (NDI). Remote ischemic conditioning (RIC) is a proposed neuroprotective maneuver that has been studied in adults with brain injury, but it has not been previously investigated in infants with NE.

METHODS

We performed a prospective, randomized, safety and dose escalation study in 32 neonates with NE. Four cohorts of consecutive patients were randomized to RIC therapy, including four cycles of limb ischemia and reperfusion on progressive days of TH, or sham. Clinical, biochemical, and safety outcomes were monitored in both groups.

RESULTS

All patients received the designated RIC therapy without interruption or delay. RIC was not associated with increased pain, vascular, cutaneous, muscular, or neural safety events. There was no difference in the incidence of seizures, brain injury, or mortality between the two groups with the escalation of RIC dose and frequency.

CONCLUSIONS

We found that RIC is a safe and feasible adjunctive therapy for neonates with NE undergoing TH.

IMPACT

This pilot study establishes critical safety and feasibility data that are necessary for the design of future studies to investigate the potential efficacy of RIC to reduce NDI.

IMPACT

Remote ischemic conditioning (RIC) is a possible neuroprotective intervention in infants with hypoxic-ischemic encephalopathy (HIE). RIC can be administered concurrently with therapeutic hypothermia without any notable adverse events. Future studies will need to address potential efficacy of RIC to improve neurodevelopmental outcomes, as well as consider the ideal temporal window and dose for RIC in this patient population.

Remote ischemic conditioning slows blood-retinal barrier damage in type 1 diabetic rats

Diabetic retinopathy (DR) is one of the major complications of diabetes and can cause severe visual impairment. Blood-retina barrier (BRB) destruction resulted from chronic hyperglycemia underlines its major pathological process. However, current treatments have limited efficacy and may even cause serious complications. Remote ischemic conditioning (RIC), through repeated transient mechanical occlusion of limb blood vessels, has been confirmed to promote blood-brain barrier integrity after stroke, but its role in BRB disruption has not been elucidated. This study aimed to investigate the protective effects of RIC on the BRB in diabetic rats and its potential mechanisms. 48 Sprague-Dawley rats were randomly assigned to the Sham group, Sham + RIC group, diabetes mellitus (DM) group and DM+RIC group. The diabetic model was successfully induced by intraperitoneal injection of streptozotocin. RIC treatment was administered daily and lasted for 9 weeks. In functional analysis, RIC improved the retinal function based on electroretinogram data and reduced the leakage of BRB in diabetic rats. In proteomic analysis, tight junction pathway was enriched after RIC treatment, in which Patj gene was significantly increased. We also found that RIC increased mRNA levels of Patj, claudin-1 and zonula occludens (ZO)-1, protein expression of claudin-1 when compared with diabetic models. In conclusion, RIC slowed BRB damage in diabetic rats, which may be related to the preservation of tight junction proteins. RIC may be a promising protective strategy for the treatment of DR.

Neuroprotective effect of ischemic postconditioning against hyperperfusion and its mechanisms of neuroprotection

Background

In recent years, stroke and ischemia-reperfusion injury has motivated researchers to find new ways to reduce the complications. Although reperfusion is essential for brain survival, it is like a double-edged sword that may cause further damage to the brain. Ischemic postconditioning (IPostC) refers to the control of blood flow in postischemia-reperfusion that can reduce ischemia-reperfusion injuries.

Materials and Methods

Articles were collected by searching for the terms: Ischemic postconditioning and neuroprotective and ischemic postconditioning and hyperperfusion. Suitable articles were collected from electronic databases, including ISI Web of Knowledge, Medline/PubMed, ScienceDirect, Embase, Scopus, Biological Abstract, Chemical Abstract, and Google Scholar.

Results

New investigations show that IPostC has protection against hyperperfusion by reducing the amount of blood flow during reperfusion and thus reducing infarction volume, preventing the blood-brain barrier damage, and reducing the rate of apoptosis through the activation of innate protective systems. Numerous mechanisms have been suggested for IPostC, which include reduction of free radical production, apoptosis, inflammatory factors, and activation of endogenous protective pathways.

Conclusion

It seems that postconditioning can prevent damage to the brain by reducing the flow and blood pressure caused by hyperperfusion. It can protect the brain against damages such as stroke and hyperperfusion by activating various endogenous protection systems. In the present review article, we tried to evaluate both useful aspects of IPostC, neuroprotective effects, and fight against hyperperfusion.

Remote Ischemic Conditioning With Medical Management or Reperfusion Therapy for Acute Ischemic Stroke: A Systematic Review and Meta-Analysis

BACKGROUND AND OBJECTIVES

Remote ischemic conditioning (RIC) is a low-cost, accessible, and noninvasive neuroprotective treatment strategy, but its efficacy and safety in acute ischemic stroke are controversial. With the publication of several randomized controlled trials (RCTs) and the recent results of the RESIST trial, it may be possible to identify the patient population that may (or may not) benefit from RIC. This systematic review and meta-analysis aims to evaluate the effectiveness and safety of RIC in patients with ischemic stroke receiving different treatments by pooling data of all randomized controlled studies to date.

METHODS

We searched the PubMed, Embase, Cochrane, Elsevier, and Web of Science databases to obtain articles in all languages from inception until May 25, 2023. The primary outcome was the modified Rankin Scale (mRS) score at the specified endpoint time in the trial. The secondary outcomes were change in NIH Stroke Scale (NIHSS) and recurrence of stroke events. The safety outcomes were cardiovascular events, cerebral hemorrhage, and mortality. The quality of articles was evaluated through the Cochrane risk assessment tool. This study was registered in PROSPERO (CRD42023430073).

RESULTS

There were 7,657 patients from 22 RCTs included. Compared with the control group, patients who received RIC did not have improved mRS functional outcomes, regardless of whether they received medical management, reperfusion therapy with intravenous thrombolysis (IVT), or mechanical thrombectomy (MT). In the medical management group, patients who received RIC had decreased incidence of stroke recurrence (risk ratio 0.63, 95% CI 0.43-0.92, p = 0.02) and lower follow-up NIHSS score by 1.72 points compared with the control group (p < 0.00001). There was no increased risk of adverse events including death or cerebral hemorrhage in the IVT or medical management group.

DISCUSSION

In patients with ischemic stroke who are not eligible for reperfusion therapy, RIC did not affect mRS functional outcomes but significantly improved the NIHSS score at the follow-up endpoint and reduced stroke recurrence, without increasing the risk of cerebral hemorrhage or death. In patients who received IVT or MT, the benefit of RIC was not observed.

Combination of Atractylenolide I, Atractylenolide III, and Paeoniflorin promotes angiogenesis and improves neurological recovery in a mouse model of ischemic Stroke

BACKGROUND

Prognosis is critically important in stroke cases, with angiogenesis playing a key role in determining outcomes. This study aimed to investigate the potential protective effects of Atractylenolide I (Atr I), Atractylenolide III (Atr III), and Paeoniflorin (Pae) in promoting angiogenesis following cerebral ischemia.

METHODS

The bEnd.3 cell line was used to evaluate the effects of these three compounds on vascular endothelial cell proliferation, migration, and tube formation. Male C57BL/6 mice underwent transient middle cerebral artery occlusion (MCAO), followed by daily intragastric administration of the Chinese medicine compounds to assess their impact on brain protection and angiogenesis. In vivo experiments included measuring infarct size and assessing neurological function. Immunofluorescence staining and an angiogenesis antibody array were used to evaluate angiogenesis in ischemic brain tissue. Functional enrichment analysis was performed to further investigate the pathways involved in the protective effects of the compounds. Molecular docking analysis explored the potential binding affinity of the compounds to insulin-like growth factor 2 (IGF-2), and Western blotting was used to measure levels of angiogenesis-related proteins.

RESULTS

In vitro, the combination of Atr I, Atr III, and Pae enhanced cell proliferation, promoted migration, and stimulated tube formation. In vivo, the combined treatment significantly facilitated neurological function recovery and angiogenesis by day 14. The treatment also increased levels of angiogenesis-related proteins, including IGF-2. Pearson correlation analysis revealed a strong positive association between IGF-2 levels in ischemic brain tissue and angiogenesis, suggesting a good affinity of the compounds for the IGF-2 binding site, as supported by molecular docking analysis.

CONCLUSION

The administration of Atr I, Atr III, and Pae has shown significant enhancements in long-term stroke recovery in mice, likely due to the promotion of angiogenesis via increased activation of the IGF-2 pathway in ischemic brain tissue.

A multi-laboratory preclinical trial in rodents to assess treatment candidates for acute ischemic stroke

Human diseases may be modeled in animals to allow preclinical assessment of putative new clinical interventions. Recent, highly publicized failures of large clinical trials called into question the rigor, design, and value of preclinical assessment. We established the Stroke Preclinical Assessment Network (SPAN) to design and implement a randomized, controlled, blinded, multi-laboratory trial for the rigorous assessment of candidate stroke treatments combined with intravascular thrombectomy. Efficacy and futility boundaries in a multi-arm multi-stage statistical design aimed to exclude from further study highly effective or futile interventions after each of four sequential stages. Six independent research laboratories performed a standard focal cerebral ischemic insult in five animal models that included equal numbers of males and females: young mice, young rats, aging mice, mice with diet-induced obesity, and spontaneously hypertensive rats. The laboratories adhered to a common protocol and efficiently enrolled 2615 animals with full data completion and comprehensive animal tracking. SPAN successfully implemented treatment masking, randomization, prerandomization inclusion and exclusion criteria, and blinded assessment of outcomes. The SPAN design and infrastructure provide an effective approach that could be used in similar preclinical, multi-laboratory studies in other disease areas and should help improve reproducibility in translational science.

Time from Onset to Remote Ischemic Conditioning and Clinical Outcome After Acute Moderate Ischemic Stroke

OBJECTIVE

We conducted a post hoc exploratory analysis of Remote Ischemic Conditioning for Acute Moderate Ischemic Stroke (RICAMIS) to determine whether early remote ischemic conditioning (RIC) initiation after stroke onset was associated with clinical outcome in patients with acute moderate ischemic stroke.

METHODS

In RICAMIS, patients receiving RIC treatment in the intention-to-treat analysis were divided into 2 groups based on onset-to-treatment time (OTT): early RIC group (OTT ≤ 24 hours) and late RIC group (OTT 24-48 hours). Patients receiving usual care without RIC treatment from intention-to-treat analysis were assigned as the control group. The primary outcome was excellent functional outcome at 90 days.

RESULTS

Among 1,776 patients from intention-to-treat analysis, 387 were in the early RIC group, 476 in the late RIC group, and 913 in the control group. In the post hoc exploratory analysis, a higher proportion of excellent functional outcome was found in the early RIC versus control group (adjusted absolute difference = 8.1%, 95% confidence interval [CI] = 2.5%-13.8%, p = 0.005), but no difference in outcomes was detected in the late RIC versus control group (adjusted absolute difference = 3.3%, 95% CI = -2.1% to 8.6%, p = 0.23), or in the early RIC versus late RIC group (adjusted absolute difference = 5.0%, 95% CI = -1.3% to 11.2%, p = 0.12). Similar results were found in the per-protocol analysis.

INTERPRETATION

Among patients with acute moderate ischemic stroke who are not candidates for intravenous thrombolysis or endovascular therapy, early RIC initiation within 24 hours of onset may be associated with higher likelihood of excellent clinical outcome. ANN NEUROL 2023;94:561-571.

The 2023 Taiwan Stroke Society Guidelines for the management of patients with intracranial atherosclerotic disease

Intracranial atherosclerotic disease (ICAD) is a major cause of ischemic stroke, especially in Asian populations, which has a high risk of recurrent stroke and cardiovascular comorbidities. The present guidelines aim to provide updated evidence-based recommendations for diagnosis and management of patients with ICAD. Taiwan Stroke Society guideline consensus group developed recommendations for management of patients with ICAD via consensus meetings based on updated evidences. Each proposed class of recommendation and level of evidence was approved by all members of the group. The guidelines cover six topics, including (1) epidemiology and diagnostic evaluation of ICAD, (2) nonpharmacological management of ICAD, (3) medical therapy for symptomatic ICAD, (4) endovascular thrombectomy and rescue therapy for acute ischemic stroke with underlying ICAD, (5) endovascular interventional therapy for postacute symptomatic intracranial arterial stenosis, and (6) surgical treatment of chronic symptomatic intracranial arterial stenosis. Intensive medical treatment including antiplatelet therapy, risk factor control, and life style modification are essential for patients with ICAD.

Remote ischemic conditioning in the treatment of acute cerebral infarction: A case control study

OBJECTIVE

This paired case-control study aimed to evaluate the efficacy and safety of remote ischemic conditioning (RIC) in patients with acute cerebral infarction (CI) and explore potential serological markers of RIC.

METHODS

Patients with acute CI (<72 h) were matched 1:1 according to age, sex, and CI conditions and were divided into the RIC group and the control group. The RIC group received RIC intervention for 7 days on top of routine treatment, while the control group received a sham RIC. The curative effects and adverse reactions were observed.

RESULT

A total of 66 patients (mean age 60.00 ± 11.37 years; mean time of acute CI onset 32.91 ± 17.94 h) completed the study. The National Institute of Health stroke scale score on day 7, modified Rankin Scale scores on day 7 and day 90 were significantly lower than the baseline in the RIC group (P < 0.001, P = 0.003, P = 0.004, respectively) but not in the control group (P = 0.056, P = 0.169, P = 0.058, respectively). RIC was well-tolerated, and no adverse events were reported. Both plasma hypoxia-inducible factor-1α (HIF-1α) and vascular endothelial growth factor increased in the RIC group from day 0 to day 7, while they decreased in the control group. The changes in plasma HIF-1α in the RIC group were statistically different from those in the control group (P = 0.006).

CONCLUSION

Early and short-term RIC treatment was well-tolerated and effective in improving the prognosis in acute CI. HIF-1α can be recognized as a biomarker for evaluating the efficacy of RIC treatment.

A review of remote ischemic conditioning as a potential strategy for neural repair poststroke

Ischemic stroke is one of the major disabling health-care problem and multiple different approaches are needed to enhance rehabilitation, in which neural repair is the structural basement. Remote ischemic conditioning (RIC) is a strategy to trigger endogenous protect. RIC has been reported to play neuroprotective role in acute stage of stroke, but the effect of RIC on repair process remaining unclear. Several studies have discovered some overlapped mechanisms RIC and neural repair performs. This review provides a hypothesis that RIC is a potential therapeutic strategy on stroke rehabilitation by evaluating the existing evidence and puts forward some remaining questions to clarify and future researches to be performed in the field.

The Stroke Preclinical Assessment Network: Rationale, Design, Feasibility, and Stage 1 Results

Cerebral ischemia and reperfusion initiate cellular events in brain that lead to neurological disability. Investigating these cellular events provides ample targets for developing new treatments. Despite considerable work, no such therapy has translated into successful stroke treatment. Among other issues-such as incomplete mechanistic knowledge and faulty clinical trial design-a key contributor to prior translational failures may be insufficient scientific rigor during preclinical assessment: nonblinded outcome assessment; missing randomization; inappropriate sample sizes; and preclinical assessments in young male animals that ignore relevant biological variables, such as age, sex, and relevant comorbid diseases. Promising results are rarely replicated in multiple laboratories. We sought to address some of these issues with rigorous assessment of candidate treatments across 6 independent research laboratories. The Stroke Preclinical Assessment Network (SPAN) implements state-of-the-art experimental design to test the hypothesis that rigorous preclinical assessment can successfully reduce or eliminate common sources of bias in choosing treatments for evaluation in clinical studies. SPAN is a randomized, placebo-controlled, blinded, multilaboratory trial using a multi-arm multi-stage protocol to select one or more putative stroke treatments with an implied high likelihood of success in human clinical stroke trials. The first stage of SPAN implemented procedural standardization and experimental rigor. All participating research laboratories performed middle cerebral artery occlusion surgery adhering to a common protocol and rapidly enrolled 913 mice in the first of 4 planned stages with excellent protocol adherence, remarkable data completion and low rates of subject loss. SPAN stage 1 successfully implemented treatment masking, randomization, prerandomization inclusion/exclusion criteria, and blinded assessment to exclude bias. Our data suggest that a large, multilaboratory, preclinical assessment effort to reduce known sources of bias is feasible and practical. Subsequent SPAN stages will evaluate candidate treatments for potential success in future stroke clinical trials using aged animals and animals with comorbid conditions.

The Current Status of Neuroprotection in Congenital Heart Disease

Neurological deficits are a serious and common sequelae of congenital heart disease (CHD). While their underlying mechanisms have not been fully characterized, their manifestations are well-known and understood to persist through adulthood. Development of therapies to address or prevent these deficits are critical to attenuate future morbidity and improve quality of life. In this review, we aim to summarize the current status of neuroprotective therapy in CHD. Through an exploration of present research in the pre-operative, intra-operative, and post-operative phases of patient management, we will describe existing clinical and bench efforts as well as current endeavors underway within this research area.

Exosomes from Human Umbilical Vein Endothelial Cells Ameliorate Ischemic Injuries by Suppressing the RNA Component of Mitochondrial RNA-processing Endoribonuclease via the Induction of miR-206/miR-1-3p Levels

Exosomes might mediate the effects of remote ischemic post-conditioning (RIPostC) treatment on vital organs. The present study aimed to explore the role of RNA component of mitochondrial RNA-processing endoribonuclease (RMRP) in the effects of human umbilical vein endothelial cell (HUVEC)-derived exosomes on ischemic injuries in vitro and in vivo. HUVECs were subjected to oxygen-glucose deprivation (OGD) treatment and exosomes were collected OGD-treated human neural cells were incubated with HUVEC-derived exosomes. Changes in cell viability, apoptosis, and RMRP-mediated PI3K/Akt/mTOR pathway activity were detected. The role of RMRP inhibition in the anti-OGD effects of exosomes was further determined by upregulating RMRP expression in human neural cells. The potential RMRP inhibitory factors in exosomes were explored using microarray detection. The effects of exosomes were validated with MCAO mouse models. In OGD neurons incubated with the exosomes, cell viability was improved and cell apoptosis was suppressed. At molecular level, exosomes on downregulated RMRP, p-PI3K, p-Akt, and p-mTOR, while induced eNOS. After the overexpression of RMRP, the cell protective effects of exosomes were counteracted, which was associated with the re-activation of PI3K/Akt/mTOR pathway. Based on the detection of microarray, the induced levels of miR-206 and miR-1-3p by OGD in HVUECs contributed to the RMPR inhibition. Additionally, injection of exosomes restricted infarction area and suppressed RMRP in MCAO mice. Collectively, exosomes from OGD HUVECs could protect neurons against ischemia-induced injuries, and the effects were associated with the suppression of RMRP in neurons via distance transfer of miR-206 and miR-1-3p.

The effect of head cooling and remote ischemic conditioning on patients with traumatic brain injury

Cerebral impairment caused by an external force to the head is known as traumatic brain injury (TBI). The aim of this study was to determine the role of local hypothermia and remote ischemic conditioning (RIC) on oxidative stress, inflammatory response after TBI, and other involved variables. The present study is a clinical trial on 84 patients with TBI who were divided into 4 groups. The head cooling for 1.5 to 6 hr was performed in the first three days after TBI. RIC intervention was performed within the golden time after TBI in the form of four 5-min cycles with full cuff and 5 min of emptying of cuff. The group receiving the head cooling technique recovered better than the group receiving the RIC technique. Generally, combination of the two interventions of head cooling and RIC techniques is more effective on the improvement of clinical status of patients than each separate technique.

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The effect of the head cooling method in controlling secondary injury in patients with TBI.

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The effect of the RIC method in controlling secondary injury in patients with TBI.

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Comparison of two interventions of head cooling and RIC.

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Evaluation of clinical and paraclinical parameters.

Remote Ischemic Postconditioning Inhibited Mitophagy to Achieve Neuroprotective Effects in the Rat Model of Cardiac Arrest

Remote ischemic postconditioning (RI-postC) is an effective measure to improve nerve function after cardiac arrest. However, the brain protective mechanism of RI-postC has not been fully elucidated, and whether it is related to mitophagy is unclear. In this study, we used the rat model of cardiac arrest to study the effect of RI-postC on mitophagy and explore its possible signaling pathways. Rats were randomly divided into Sham group, CA/CPR group, Mdivi-1 group and RI-postC group. The animal model of cardiac arrest was established by asphyxia. RI-postC was performed by clamping and loosening the left femoral artery. Mdivi-1 was treated with a single intravenous injection. Levels of TOMM20, TIM23, Mfn1, PINK1 and parkin were detected by western blots. Mitochondrial membrane potential was measured by flow cytometry. Real-time PCR was used to detect relative mitochondrial DNA levels. The apoptosis of hippocampal neurons was detected by flow and TUNEL. In addition, Histopathological tests were performed. The results showed that RI-postC was similar to the mitophagy inhibitor Mdivi-1, which could inhibit the decrease of mitophagy-related protein level, improve mitochondrial membrane potential and up-regulate the ratio of mt-Atp6/Rpl13 after cardiopulmonary resuscitation (CPR). Furthermore, RI-postC could also reduce the rate of hippocampal nerve apoptosis and the damage of hippocampal neurons after CPR. Moreover, RI-postC and Mdivi-1 could reduce the protein levels of PINK1 and parkin in mitochondria after CPR, while increasing PINK1 levels in the cytoplasm. These findings suggested that RI-postC could inhibit the overactivation mitophagy through the PINK1/parkin signaling pathway, thus providing neuroprotective effects.

Hypoxia-Inducible Factor 1α and 2α Have Beneficial Effects in Remote Ischemic Preconditioning Against Stroke by Modulating Inflammatory Responses in Aged Rats

Limb remote ischemic preconditioning (RIPC) has been proven to alleviate stroke injury in young rats, but its protective effect and its mechanism in aged rats are still unclear. Hypoxia-inducible factor (HIF) is one of the important markers of stroke, and its high expression plays an important role in the pathogenesis of stroke. In this study, we tested the hypothesis that RIPC could regulate the expression of HIF, leading to reduced inflammatory responses in aged rats. Stroke was induced by transient middle cerebral artery occlusion (MCAo) in aged rats, and RIPC was conducted in both hind limbs. The HIF-1α and HIF-2α mRNA and protein were examined by real-time RT-PCR and western blotting (WB). Inflammatory cytokines in the peripheral blood and brain were measured using AimPlex multiplex immunoassays. The protein levels of p-Akt, Akt, p-ERK, and ERK were examined by WB. We investigated that RIPC reduced the infarct size, improved neurological functions, and decreased the expression of HIF-1α and HIF-2α in the ischemic brain. RIPC reduced the levels of IL-1β, IL-6 and IFN-γ in the peripheral blood and the levels of IL-1β and IFN-γ in the ischemic brain 48 h post-stroke. Moreover, intraperitoneal injection of the HIF inhibitor, acriflavine hydrochloride (ACF), abolished the protection of RIPC with respect to infarct size and neurological functions and neutralized the downregulation of pro-inflammatory IL-1β, IL-6 and IFN-γ. ACF also reversed the activation of the Akt signaling pathway induced by RIPC following stroke. HIF may play a key role in RIPC, which was likely mediated by the Akt signaling pathway and systemic modulation of the inflammatory response in aged rats.

Exosomal miR-199a-5p derived from endothelial cells attenuates apoptosis and inflammation in neural cells by inhibiting endoplasmic reticulum stress

Remote ischemic post-conditioning (RIPostC) is a technique that can protect vital organs in an indirect manner, the effects of which are exerted by the long-distance exosome-mediated transfer of functional factors. In the current study, the possible mechanism driving the function of RIPostC was explored using an in vitro system by focusing on miR-199a-5p and its downstream effectors involved in endoplasmic reticulum (ER) stress. Human umbilical vein endothelial cells (HUVECs) were administrated with hypoxia/re-oxygenation (H/R) process and exosomes were collected from the H/R-treated HUVECs. The levels of miR-199a-5p in HUVECs and exosomes were detected. Afterwards, H/R-treated SH-SY5Y neural cells was incubated with H/R HUVEC-derived exosomes, and the effect on cell apoptosis, inflammation, and miR-199a-5p-mediated ER stress was assessed. Furthermore, the key role of miR-199a-5p suppression in the protection effect of HUVEC-derived exosomes was validated by transfecting neural cells with specific inhibitor. The results showed that H/R administration increased miR-199a-5p levels both in HUVECs and exosomes. The incubation of neural cells with exosomes suppressed cell apoptosis and inflammation, and induced the level of miR-199a-5p, which led to suppressed ER stress. Moreover, the transfection of miR-199a-5p inhibitor blocked the anti-H/R function of exosomes. Taken together, the findings outlined in the current study showed that the protection effect of HUVEC derived miR-199a-5p on neural cells was exerted via exosome transfer, which then suppressed the ER stress-induced apoptosis and inflammation by targeting BIP.

Immediate remote ischemic postconditioning reduces cerebral damage in ischemic stroke mice by enhancing leptomeningeal collateral circulation

Remote ischemic postconditioning (RIPC) is a promising neuroprotective strategy for ischemic stroke. Here, we employed a focal ischemic stroke mouse model to test the hypothesis that poststroke collateral circulation as a potent mechanism of action underlying the therapeutic effects of immediate RIPC. During reperfusion of cerebral ischemia, the mice were randomly assigned to receive RIPC, granulocyte colony‐stimulating factor (G‐CSF) as a positive control, or no treatment. At 24 hr, we found RIPC and G‐CSF increased monocytes/macrophages in the dorsal brain surface and in the spleen, coupled with enhanced leptomeningeal collateral flow compared with nontreatment group. Blood monocytes depletion by 5‐fluorouracil (5‐FU) significantly limited the neuroprotection of RIPC or G‐CSF treatment. The protein expression of proangiogenic factors such as Ang‐2 was increased by ischemia, but treatment with either RIPC or G‐CSF showed no further upregulation. Thus, immediate RIPC confers neuroprotection, in part, by enhancing leptomeningeal collateral circulation in a mouse model of ischemic stroke.

Remote Ischemic Conditioning Protects Diabetic Retinopathy in Streptozotocin-induced Diabetic Rats via Anti-Inflammation and Antioxidation

Ischemic conditioning inhibits oxidative stress and inflammatory response in diabetes. However, whether limb remote ischemic conditioning (LRIC) has beneficial effects on diabetic retinopathy (DR) remains unknown. This study aims to investigate the protective effects of LRIC in retinal ganglion cell in streptozotocin (STZ) induced Type 1 diabetic rats. A total of 48 healthy male Sprague-Dawley (200-220g) rats were randomly assigned to the normal group, normal+LRIC group, diabetes mellitus (DM) group and DM+LRIC group. Streptozotocin (STZ, 60 mg/kg) was intraperitoneally injected into the rats to establish the diabetic model. LRIC was conducted by tightening a tourniquet around the upper thigh and releasing for three cycles daily (10 mins x 3 cycles). Retinas were harvested after 12 weeks of LRIC treatment for histopathologic, Western blot and ELISA analysis. Plasma were collected at the same time for ELISA analysis. LRIC alleviated diabetic retinopathy symptoms as evidenced by the increased number of retinal ganglion cells (P<0.01) and decreased glial fibrillary acidic protein (GFAP) expression level (P<0.01) in the rat retina. LRIC in DM rats exhibited anti-inflammatory and antioxidative effects as confirmed by the down-regulation of pro-inflammatory cytokine: interleukin-6 (IL-6), and the up-regulation of antioxidants: superoxide dismutase (SOD), and glutathione (GSH)/oxidized glutathione (GSSG). Furthermore, LRIC significantly downregulated VEGF protein expression in the retina (P<0.01). These results suggest that the antioxidative and anti-inflammatory activities of LRIC may be important mechanisms involved in the protective effect of LRIC in STZ-induced diabetic rats.

Intracranial atherosclerotic disease

Intracranial atherosclerosis (ICAS) is a progressive pathological process that causes progressive stenosis and cerebral hypoperfusion and is a major cause of stroke occurrence and recurrence around the world. Multiple factors contribute to the development of ICAS. Angiography imaging techniques can improve the diagnosis of and the selection of appropriate treatment regimens for ICAS. Neither aggressive medication nor endovascular interventions can eradicate stroke recurrence in patients with ICAS. Non-pharmacological therapies such as remote ischemic conditioning and hypothermia are emerging. Comprehensive therapy with medication in combination with endovascular intervention and/or non-pharmacological treatment may be a potential strategy for ICAS treatment in the future. We summarized the epidemiology, pathophysiological mechanisms, risk factors, biomarkers, imaging and management of ICAS.

Very Delayed Remote Ischemic Post-conditioning Induces Sustained Neurological Recovery by Mechanisms Involving Enhanced Angioneurogenesis and Peripheral Immunosuppression Reversal

Ischemic conditioning is defined as a transient and subcritical period of ischemia integrated in an experimental paradigm that involves a stimulus of injurious ischemia, activating endogenous tissue repair mechanisms that lead to cellular protection under pathological conditions like stroke. Whereas ischemic pre-conditioning is irrelevant for stroke treatment, ischemic post-conditioning, and especially non-invasive remote ischemic post-conditioning (rPostC) is an innovative and potential strategy for stroke treatment. Although rPostC has been shown to induce neuroprotection in stroke models before, resulting in some clinical trials on the way, fundamental questions with regard to its therapeutic time frame and its underlying mechanisms remain elusive. Hence, we herein used a model of non-invasive rPostC of hind limbs after cerebral ischemia in male C57BL6 mice, studying the optimal timing for the application of rPostC and its underlying mechanisms for up to 3 months. Mice undergoing rPostC underwent three different paradigms, starting with the first cycle of rPostC 12 h, 24 h, or 5 days after stroke induction, which is a very delayed time point of rPostC that has not been studied elsewhere. rPostC as applied within 24 h post-stroke induces reduction of infarct volume on day three. On the contrary, very delayed rPostC does not yield reduction of infarct volume on day seven when first applied on day five, albeit long-term brain injury is significantly reduced. Likewise, very delayed rPostC yields sustained neurological recovery, whereas early rPostC (i.e., <24 h) results in transient neuroprotection only. The latter is mediated via heat shock protein 70 that is a well-known signaling protein involved in the pathophysiological cellular cascade of cerebral ischemia, leading to decreased proteasomal activity and decreased post-stroke inflammation. Very delayed rPostC on day five, however, induces a pleiotropic effect, among which a stimulation of angioneurogenesis, a modulation of the ischemic extracellular milieu, and a reversal of the stroke-induced immunosuppression occur. As such, very delayed rPostC appears to be an attractive tool for future adjuvant stroke treatment that deserves further preclinical attention before large clinical trials are in order, which so far have predominantly focused on early rPostC only.

Muscle-derived autologous mitochondrial transplantation: A novel strategy for treating cerebral ischemic injury

The available evidence showed that mitochondrial transfer by releasing the extracellular vesicles containing mitochondria from astrocytes to neurons exerted a neuroprotective effect after stroke. Whether extracellular mitochondrial replenishment could rescue the tissues from cerebral ischemic injury still needs to be explored completely. It was hypothesized that the augmentation of mitochondrial damage after cerebral ischemia could be resolved by timely replenishment of exogenous mitochondria. A stroke model of middle cerebral artery occlusion (MCAO) was used in this study to verify this hypothesis. This study found that the number of extracellular mitochondria increased in rat cerebrospinal fluid after MCAO, and a higher proportion of mitochondria were associated with good neurological outcomes. Following 90-min ischemia, autologously derived mitochondria (isolated from autologous pectoralis major) or vehicle alone was infused directly into the lateral ventricles, and the rats were allowed to recover for 4 weeks. A plenty of infused mitochondria were found to be distributed in the boundary and ischemic penumbra areas. Furthermore, the transplantation of mitochondria reduced cellular oxidative stress and apoptosis, attenuated reactive astrogliosis, and promoted neurogenesis after stroke. Moreover, the transplantation of mitochondria decreased brain infarct volume and reversed neurological deficits. The findings suggested that the delivery of mitochondria through the lateral ventricles resulted in their widespread distribution throughout the brain and exerted a neuroprotective effect after ischemia-reperfusion injury.

Hypoxia, hibernation and Neuroprotection: An Experimental Study in Mice

Hibernation is a unique physiological state that evolved to survive periods of food shortages. It is characterized by profound decreases in metabolic rate, body temperature and physiological functions. Studies have shown that animals in hibernation can resist neurological damage. Here, we aimed to study whether hypoxia can induce a hibernation-like state in a traditionally non-hibernating animal and whether it is neuroprotective. All procedures were conducted according to international guidelines on laboratory animal safety. Mice C57BL/6 (19-21g) were placed into a 125 mL jar with fresh air and the jar was sealed with a rubber plug. For each run, the tolerance limit was judged by the animals' appearance for "air hunger". The animal was removed from the jar as soon as its first gasping breath appeared and was moved to another fresh-air-containing jar of similar volume. This procedure was performed in four runs. The hypoxia exposure significantly decreased oxygen (O2) consumption, carbon dioxide (CO2) production, respiratory rate and heart rate. Meanwhile, rectal temperature reached a minimum of 12.7±2.56°C, which is lower than a wide range of ambient temperatures. The mimicked hibernation decreased the infarct size in a focal cerebral ischemia mouse model. Our findings suggest the possibility of inducing suspended animation-like hibernation states for medical applications post injury.

Remote ischemic conditioning for acute stroke patients treated with thrombectomy

Objective

Remote ischemic conditioning (RIC) has been demonstrated to be safe and feasible for patients with acute ischemic stroke (AIS), as well as for those receiving intravenous thrombolysis. We assessed the safety and feasibility of RIC for AIS patients undergoing endovascular treatment (ET).

Methods

We conducted a pilot study with patients with AIS who were suspected of having an emergent large‐vessel occlusion in the anterior circulation and who were scheduled for ET within 6 hours of ictus. Four cycles of RIC were performed before recanalization, immediately following recanalization, and once daily for the subsequent 7 days. The primary outcome was any serious RIC‐related adverse events.

Results

Twenty subjects, aged 66.1 ± 12.1 years, were recruited. No subject experienced serious RIC‐related adverse events. The intracranial pressure, cranial perfusion pressure, mean arterial pressure, heart rate, middle cerebral artery peak systolic flow velocity, and pulsatility index did not change significantly before, during, or after the limb ischemia (P > 0.1 for all). Of 80 cycles, 71 (89%) were completed before recanalization and 80 (100%) were completed immediately after recanalization; 444 of 560 cycles (78%) were completed within 7 days posttreatment. No patients had to stop RIC because it affected routine clinical managements. Six subjects (30%) experienced intracerebral hemorrhage, which was symptomatic in one case (5%). At the 3‐month follow‐up, 11 subjects (55%) had achieved functional independence, and two subjects (10%) died.

Interpretation

RIC appears to be safe and feasible for patients with AIS undergoing ET. Investigations are urgently needed to determine the efficacy of RIC in this patient population.

Splenic responses play an important role in remote ischemic preconditioning-mediated neuroprotection against stroke

Background

Remote ischemic preconditioning (RIPC) of a limb has been reported to protect against ischemic stroke. Our previous results demonstrated that the RIPC-mediated neuroprotection is associated with alterations in circulating immune cell populations. Here, we evaluated the effect of the spleen, the largest reservoir of immune cells, on RIPC-mediated neuroprotection against stroke.

Methods

Noninvasive RIPC was achieved by four repeated cycles of 5-min blood flow constriction in the hindlimbs using a tourniquet. The blood and spleens were collected before and 1 h and 3 days after preconditioning to analyze the effect of RIPC on the spleen and the correlation between splenic and peripheral lymphocytes. Moreover, spleen weight and splenic lymphocytes were compared in stroke rats with or without RIPC. Finally, splenectomy was made 1 day or 2 weeks before RIPC and 90-min middle cerebral artery occlusion (MCAO). The infarct areas and deficits were assessed. Blood was collected 1 h after RIPC and 3 days after MCAO to explore the impact of splenectomy on RIPC-induced neuroprotection and immune changes. The contralateral and ipsilateral hemispheres were collected 3 days after MCAO to detect the infiltration of immune cells after RIPC and splenectomy.

Results

Flow cytometry analysis demonstrated that the RIPC promptly increased the percentages of CD3⁺CD8⁺ cytotoxic T (Tc) cells in the spleen with a relatively delayed elevation in CD3⁺CD161⁺ natural killer T (NKT) and CD3⁻CD45RA⁺ B lymphocytes. The percentages of circulating lymphocytes are positively correlated with the percentages of splenic lymphocytes in normal rats. Interestingly, RIPC resulted in negative correlations between the percentages of splenic and circulating T lymphocytes, while the correlation between splenic and circulating B lymphocytes remained positive. For animals subjected to RIPC followed by MCAO, RIPC increased splenic volume with an expansion of splenic lymphocytes 3 days after MCAO. Furthermore, the removal of the spleen 1 day or 2 weeks before RIPC and MCAO reduced the protective effect of RIPC on ischemic brain injury and reversed the effects of RIPC on circulating immune cell composition. RIPC significantly reduced brain infiltration of Tc and NKT cells. Prior splenectomy showed no effect on immune cell infiltration after RIPC and stroke.

Conclusion

These results reveal an immunomodulatory effect of the spleen, effecting mainly the spleen-derived lymphocytes, during RIPC-afforded neuroprotection against cerebral ischemia.

Electronic supplementary material

The online version of this article (10.1186/s12974-018-1190-9) contains supplementary material, which is available to authorized users.

Hypoxia Inducible Factor 1α Plays a Key Role in Remote Ischemic Preconditioning Against Stroke by Modulating Inflammatory Responses in Rats

Background

Limb remote ischemic preconditioning (RIPC) protects against brain injury induced by stroke, but the underlying protective mechanisms remain unknown. As hypoxia inducible factor 1α (HIF‐1α) is neuroprotective in stroke and mediates neuroinflammation, we tested the hypothesis that HIF‐1α is a key factor of RIPC against stroke by mediating inflammation.

Methods and Results

Stroke was induced by transient middle cerebral artery occlusion in rats, and RIPC was conducted in both hind limbs. The HIF‐1α mRNA was examined by quantitative reverse transcription polymerase chain reaction after RIPC. In addition, inflammatory cytokines in the peripheral blood and brain were measured using the AimPlex multiplex immunoassays. Data showed that RIPC reduced the infarct size, improved neurological functions, and increased HIF‐1α mRNA levels, interleukin (IL)‐4, and IL‐10 protein levels in the peripheral blood. Intraperitoneal injection of the HIF activator, dimethyloxaloylglycine, reduced the infarct size and inhibited interferon‐γ protein levels, while promoting IL‐4 and IL‐10 protein levels, while decreasing interferon‐γ protein levels in both the peripheral blood and ischemic brain. In addition, injection of dimethyloxaloylglycine had a synergistic effect with RIPC on reducing infarction and improving neurological functions, as well as decreasing interferon‐γ in the peripheral blood and ischemic brain. In contrast, injection of the HIF inhibitor, acriflavine hydrochloride, abolished the protective effects of RIPC on infarction, and reduced IL‐4 and IL‐10 protein levels in both the peripheral blood and ischemic brain.

Conclusions

We conclude that HIF‐1α plays a key role in RIPC, likely mediated by a systemic modulation of the inflammatory response.

Remote ischemic conditioning for acute ischemic stroke: dawn in the darkness

Stroke is a leading cause of disability with high morbidity and mortality worldwide. Of all strokes, 87% are ischemic. The only approved treatments for acute ischemic stroke are intravenous thrombolysis with alteplase within 4.5 h and thrombectomy within 8 h after symptom onset, which can be applied to just a few patients. During the past decades, ischemic preconditioning has been widely studied to confirm its neuroprotection against subsequent ischemia/reperfusion injury in the brain, including preconditioning in situ or in a remote organ (such as a limb) before onset of brain ischemia, the latter of which is termed as remote ischemic preconditioning. Because acute stroke is unpredicted, ischemic preconditioning is actually not suitable for clinical application. So remote ischemic conditioning performed during or after the ischemic duration of the brain was then designed to study its neuroprotection alone or in combination with alteplase in animals and patients, which is named as remote ischemic perconditioning or remote ischemic postconditioning. As expected, animal experiments and clinical trials both showed exciting results, indicating that an evolution in the treatment for acute ischemic stroke may not be far away. However, some problems or disputes still exist. This review summarizes the research progress and unresolved issues of remote ischemic conditioning (pre-, per-, and post-conditioning) in treating acute ischemic stroke, with the hope of advancing our understanding of this promising neuroprotective strategy for ischemic stroke in the near future.

Limb remote ischemic postconditioning protects integrity of the blood-brain barrier after stroke

Integrity of the blood-brain barrier structure is essential for maintaining the internal environment of the brain. Development of cerebral infarction and brain edema is strongly associated with blood-brain barrier leakage. Therefore, studies have suggested that protecting the blood-brain barrier may be an effective method for treating acute stroke. To examine this possibility, stroke model rats were established by middle cerebral artery occlusion and reperfusion. Remote ischemic postconditioning was immediately induced by three cycles of 10-minute ischemia/10-minute reperfusion of bilateral hind limbs at the beginning of middle cerebral artery occlusion reperfusion. Neurological function of rat models was evaluated using Zea Longa’s method. Permeability of the blood-brain barrier was assessed by Evans blue leakage. Infarct volume and brain edema were evaluated using 2,3,5-triphenyltetrazolium chloride staining. Expression of matrix metalloproteinase-9 and claudin-5 mRNA was determined by real-time quantitative reverse transcription-polymerase chain reaction. Expression of matrix metalloproteinase-9 and claudin-5 protein was measured by western blot assay. The number of matrix metalloproteinase-9- and claudin-5-positive cells was analyzed using immunohistochemistry. Our results showed that remote ischemic postconditioning alleviated disruption of the blood-brain barrier, reduced infarct volume and edema, decreased expression of matrix metalloproteinase-9 mRNA and protein and the number of positive cells, increased expression of claudin-5 mRNA and protein and the number of positive cells, and remarkably improved neurological function. These findings confirm that by suppressing expression of matrix metalloproteinase-9 and claudin-5 induced by acute ischemia/reperfusion, remote ischemic postconditioning reduces blood-brain barrier injury, mitigates ischemic injury, and exerts protective effects on the brain.

Remote Limb Ischemic Preconditioning Protects Rats Against Cerebral Ischemia via HIF-1α/AMPK/HSP70 Pathway

Remote limb ischemic preconditioning (RIPC) is a clinically feasible strategy to protect against ischemia/reperfusion injury, but the knowledge concerning the mechanism underlying RIPC is scarce. This study was performed to examine the effect of RIPC on brain tissue suffering from ischemia challenge and explore its underlying mechanism in a rat model. The animals were divided into four groups: Sham, middle cerebral artery occlusion (MCAO), RIPC, and MCAO+RIPC. We found that previous exposure to RIPC significantly attenuated neurological dysfunction and lessened brain edema in MCAO+RIPC group. Moreover, other important events were observed in MCAO+RIPC group, including substantial decrements in the concentrations of oxidative response indicators [malondialdehyde (MDA), 8-hydroxy-2-deoxyguanosine (8-OHdG), and protein carbonyl], significant reductions in levels of inflammation mediators [myeloperoxidase (MPO), tumor necrosis factor-a (TNF-a), interleukin-1β (IL-1β), and IL-6], and significant decline in neuronal apoptosis revealed by a smaller number of TUNEL-positive cells. Interestingly, both MCAO and RIPC groups exhibited meaningful elevations in the levels of HIF-1a, HSP70, and AMP-activated protein kinase (AMPK) compared to Sham group, and previous exposure to RIPC further elevated the levels of HIF-1a, HSP70, and AMPK in MCAO+RIPC group. Furthermore, the administration of YC-1 (HIF-1 inhibitor), 8-bAMP (AMPK inhibitor), and Quercetin (HSP70 inhibitor) to MCAO+RIPC rats demonstrated that HIF-1α/AMPK/HSP70 was involved in RIPC-mediated protection against cerebral ischemia.

Prevention of the collapse of pial collaterals by remote ischemic perconditioning during acute ischemic stroke

Collateral circulation is a key variable determining prognosis and response to recanalization therapy during acute ischemic stroke. Remote ischemic perconditioning (RIPerC) involves inducing peripheral ischemia (typically in the limbs) during stroke and may reduce perfusion deficits and brain damage due to cerebral ischemia. In this study, we directly investigated pial collateral flow augmentation due to RIPerC during distal middle cerebral artery occlusion (MCAo) in rats. Blood flow through pial collaterals between the anterior cerebral artery (ACA) and the MCA was assessed in male Sprague Dawley rats using in vivo laser speckle contrast imaging (LSCI) and two photon laser scanning microscopy (TPLSM) during distal MCAo. LSCI and TPLSM revealed that RIPerC augmented collateral flow into distal MCA segments. Notably, while control rats exhibited an initial dilation followed by a progressive narrowing of pial arterioles 60 to 150-min post-MCAo (constricting to 80-90% of post-MCAo peak diameter), this constriction was prevented or reversed by RIPerC (such that vessel diameters increased to 105-110% of post-MCAo, pre-RIPerC diameter). RIPerC significantly reduced early ischemic damage measured 6 h after stroke onset. Thus, prevention of collateral collapse via RIPerC is neuroprotective and may facilitate other protective or recanalization therapies by improving blood flow in penumbral tissue.

The role of glycogen synthase kinase 3 beta in brain injury induced by myocardial ischemia/reperfusion injury in a rat model of diabetes mellitus

Myocardial ischemia/reperfusion injury can lead to severe brain injury. Glycogen synthase kinase 3 beta is known to be involved in myo-cardial ischemia/reperfusion injury and diabetes mellitus. However, the precise role of glycogen synthase kinase 3 beta in myocardial ischemia/reperfusion injury-induced brain injury is unclear. In this study, we observed the effects of glycogen synthase kinase 3 beta on brain injury induced by myocardial ischemia/reperfusion injury in diabetic rats. Rat models of diabetes mellitus were generated via intraperitoneal injection of streptozotocin. Models of myocardial ischemia/reperfusion injury were generated by occluding the anterior descending branch of the left coronary artery. Post-conditioning comprised three cycles of ischemia/reperfusion. Immunohistochemical staining and western blot assays demonstrated that after 48 hours of reperfusion, the structure of the brain was seriously damaged in the experimental rats compared with normal controls. Expression of Bax, interleukin-6, interleukin-8, terminal deoxynucleotidyl transferase dUTP nick end labeling, and cleaved caspase-3 in the brain was significantly increased, while expression of Bcl-2, interleukin-10, and phospho-glycogen synthase kinase 3 beta was decreased. Diabetes mellitus can aggravate inflammatory reactions and apoptosis. Ischemic post-conditioning with glycogen synthase kinase 3 beta inhibitor lithium chloride can effectively reverse these changes. Our results showed that myocardial ischemic post-conditioning attenuated myocardial ischemia/reperfusion injury-induced brain injury by activating glyco-gen synthase kinase 3 beta. According to these results, glycogen synthase kinase 3 beta appears to be an important factor in brain injury induced by myocardial ischemia/reperfusion injury.

Ischemic Post-Conditioning Induces Post-Stroke Neuroprotection via Hsp70-Mediated Proteasome Inhibition and Facilitates Neural Progenitor Cell Transplantation

In view of the failure of pharmacological therapies, alternative strategies promoting post-stroke brain repair are needed. Post-conditioning is a potentially promising therapeutic strategy, which induces acute neuroprotection against ischemic injury. To elucidate longer lasting actions of ischemic post-conditioning, mice were exposed to a 60-min stroke and post-conditioning by an additional 10-min stroke that was induced 10 min after reperfusion onset. Animals were sacrificed 24 h or 28 days post-stroke. Post-conditioning reduced infarct volume and neurological deficits 24 h post-stroke, enhancing blood-brain barrier integrity, reducing brain leukocyte infiltration, and reducing oxidative stress. On the molecular level, post-conditioning yielded increased Hsp70 expression, whereas nuclear factor (NF)-κB and proteasome activities were decreased. Reduced infarct volume and proteasome inhibition were reversed by Hsp70 knockdown, suggesting a critical role of the Hsp70 proteasome pathway in ischemic post-conditioning. The survival-promoting effects of ischemic post-conditioning, however, were not sustainable as neuroprotection and neurological recovery were lost 28 days post-stroke. Although angioneurogenesis was not increased by post-conditioning, the favorable extracellular milieu facilitated intracerebral transplantation of neural progenitor cells 6 h post-stroke, resulting in persisted neuroprotection and neurological recovery. Thus, post-conditioning might support brain repair processes, but in view of its transient, neuroprotection is unlikely useful as stroke therapy in its current form.

Limb remote ischemic per-conditioning in combination with post-conditioning reduces brain damage and promotes neuroglobin expression in the rat brain after ischemic stroke

Purpose: Limb remote ischemic per-conditioning or post-conditioning has been shown to be neuroprotective after cerebral ischemic stroke. However, the effect of combining remote per-conditioning with post-conditioning on ischemic/reperfusion injury as well as the underlying mechanisms are largely unexplored.

Methods: Here, adult male Sprague Dawley rats were subjected to middle cerebral artery occlusion (MCAO). The limb ischemic stimulus was immediately applied after onset of focal ischemia (per-conditioning), followed by repeated short episodes of remote ischemia 24 hr after reperfusion (post-conditioning). The infarct volume, motor function, and the expression of neuroglobin (Ngb) were measured at different durations after reperfusion.

Results: We found that a single episode of limb remote per-conditioning afforded short-term protection, but combining repeated remote post-conditioning during the 14 days after reperfusion significantly ameliorated cerebral ischemia/reperfusion injury. Interestingly, we also found that ischemic per- and post-conditioning significantly increased expression of Ngb, an oxygen-binding globin protein that has been demonstrated to be neuroprotective against stroke, at peri-infarct regions from day 1 to day 14 following ischemia/reperfusion.

Conclusion: Our results suggest that the conventional per-conditioning combined with post-conditioning may be used as a novel neuroprotective strategy against ischemia-reperfusion injury, and Ngb seems to be one of the important players in limb remote ischemia-mediated neuroprotection.

Ischemia-reperfusion Injury in the Brain: Mechanisms and Potential Therapeutic Strategies

Ischemia-reperfusion injury is a common feature of ischemic stroke, which occurs when blood supply is restored after a period of ischemia. Reperfusion can be achieved either by thrombolysis using thrombolytic reagents such as tissue plasminogen activator (tPA), or through mechanical removal of thrombi. Spontaneous reperfusion also occurs after ischemic stroke. However, despite the beneficial effect of restored oxygen supply by reperfusion, it also causes deleterious effect compared with permanent ischemia. With the recent advancement in endovascular therapy including thrombectomy and thrombus disruption, reperfusion-injury has become an increasingly critical challenge in stroke treatment. It is therefore of extreme importance to understand the mechanisms of ischemia-reperfusion injury in the brain in order to develop effective therapeutics. Accumulating experimental evidence have suggested that the mechanisms of ischemia-reperfusion injury include oxidative stress, leukocyte infiltration, platelet adhesion and aggregation, complement activation, mitochondrial mediated mechanisms, and blood-brain-barrier (BBB) disruption, which altogether ultimately lead to edema or hemorrhagic transformation (HT) in the brain. Potential therapeutic strategies against ischemia-reperfusion injury may be developed targeting these mechanisms. In this review, we briefly discuss the pathophysiology and cellular and molecular mechanisms of cerebral ischemia-reperfusion injury, and potential therapeutic strategies.

Targeting the blood-spinal cord barrier: A therapeutic approach to spinal cord protection against ischemia-reperfusion injury

One of the principal functions of physical barriers between the blood and central nervous system protects system (i.e., blood brain barrier and blood-spinal cord barrier) is the protection from toxic and pathogenic agents in the blood. Disruption of blood-spinal cord barrier (BSCB) plays a key role in spinal cord ischemia-reperfusion injury (SCIRI). Following SCIRI, the permeability of the BSCB increases. Maintaining the integrity of the BSCB alleviates the spinal cord injury after spinal cord ischemia. This review summarizes current knowledge of the structure and function of the BSCB and its changes following SCIRI, as well as the prevention and cure of SCIRI and the role of the BSCB.

Advance in spinal cord ischemia reperfusion injury: Blood-spinal cord barrier and remote ischemic preconditioning

The blood-spinal cord barrier (BSCB) is the physiological and metabolic substance diffusion barrier between blood circulation and spinal cord tissues. This barrier plays a vital role in maintaining the microenvironment stability of the spinal cord. When the spinal cord is subjected to ischemia/reperfusion (I/R) injury, the structure and function of the BSCB is disrupted, further destroying the spinal cord homeostasis and ultimately leading to neurological deficit. Remote ischemic preconditioning (RIPC) is an approach in which interspersed cycles of preconditioning ischemia is followed by reperfusion to tissues/organs to protect the distant target tissues/organs against subsequent lethal ischemic injuries. RIPC is an innovation of the treatment strategies that protect the organ from I/R injury. In this study, we review the morphological structure and function of the BSCB, the injury mechanism of BSCB resulting from spinal cord I/R, and the effect of RIPC on it.

Limb remote ischemic postconditioning protects cerebral ischemia from injury associated with expression of HIF-1α in rats

Background

Limb remote ischemic postconditioning (LRIP) can ameliorate cerebral ischemia–reperfusion injury (IRI), while the underlying mechanism remains elusive. Hypoxia-inducible factor 1α (HIF-1α) is an important transcription factor during cerebral ischemia damage. However, whether the neuroprotective effect of LRIP could be associated with HIF-1α is somewhat unclear. Here we tested the hypothesis that Limb remote ischemic postconditioning (LRIP) protecting brain from injury in middle cerebral artery occlusion (MCAO) rat model was associated with HIF-1α expression.

Results

LRIP was conducted with 3 cycles of 10 min occlusion/10 min reperfusion at the beginning of reperfusion. The analysis of neurobehavioral function and triphenyltetrazolium chloride (TTC) staining showed the neurological deficit, brain infarct and cerebral edema, caused by ischemia–reperfusion injury (IRI), were dramatically ameliorated in LRIP administrated animals. Meanwhile, the result of Q-PCR and western blot revealed that the overexpression of HIF-1α induced by IRI could be notably suppressed by LRIP treatment.

Conclusions

LRIP exhibits a protective effect against cerebral ischemia/reperfusion and the possible mechanism is associated with the suppression of HIF-1α in stroke rats.

Limb Ischemic Perconditioning Attenuates Blood-Brain Barrier Disruption by Inhibiting Activity of MMP-9 and Occludin Degradation after Focal Cerebral Ischemia

Remote ischemic perconditioning (PerC) has been proved to have neuroprotective effects on cerebral ischemia, however, the effect of PerC on the BBB disruption and underlying mechanisms remains largely unknown. To address these issues, total 90 adult male Sprague Dawley (SD) rats were used. The rats underwent 90-min middle cerebral artery occlusion (MCAO), and the limb remote ischemic PerC was immediately applied after the onset of MCAO. We found that limb remote PerC protected BBB breakdown and brain edema, in parallel with reduced infarct volume and improved neurological deficits, after MCAO. Immunofluorescence studies revealed that MCAO resulted in disrupted continuity of claudin-5 staining in the cerebral endothelial cells with significant gap formation, which was significantly improved after PerC. Western blot analysis demonstrated that expression of tight junction (TJ) protein occludin was significantly increased, but other elements of TJ proteins, claudin-5 and ZO-1, in the BBB endothelial cells were not altered at 48 h after PerC, compared to MCAO group. The expression of matrix metalloproteinase (MMP-9), which was involved in TJ protein degradation, was decreased after PerC. Interestingly, phosphorylated extracellular signal-regulated kinase 1/2 (pERK1/2), an upstream of MMP-9 signaling, was significantly reduced in the PerC group. Our data suggest that PerC inhibits MMP-9-mediated occludin degradation, which could lead to decreased BBB disruption and brain edema after ischemic stroke.

AKT/GSK3β-dependent autophagy contributes to the neuroprotection of limb remote ischemic postconditioning in the transient cerebral ischemic rat model

BACKGROUND

Limb remote ischemic postconditioning (RIPostC) has been recognized as an applicable strategy in protecting against cerebral ischemic injury. However, the time window for application of limb RIPostC and the mechanisms behind RIPostC are still unclear.

AIMS

In this study, we investigated the protective efficacy and the role of autophagy in limb RIPostC using a transient middle cerebral artery occlusion rat model.

RESULTS

Limb RIPostC applied in the early phase of reperfusion reduced infarct size and improved neurological function. Autophagy levels in penumbral tissues were elevated in neurons of limb RIPostC rats, with an increase in the phosphorylation of AKT and glycogen synthase kinase 3β (GSK3β). Blocking the AKT/GSK3β pathway via the AKT inhibitor LY294002 prior to limb RIPostC suppressed the RIPostC-induced autophagy and resulted in the activation of caspase-3 in RIPostC rats, suggesting a critical role for AKT/GSK3β-dependent autophagy in reducing cell death after cerebral ischemia.

CONCLUSIONS

These results aid optimization of the time window for RIPostC use and offer novel insight into, and a better understanding of, the protective mechanism of autophagy in limb RIPostC.

Remote Ischemic Preconditioning-Mediated Neuroprotection against Stroke is Associated with Significant Alterations in Peripheral Immune Responses

AIMS

Remote ischemic preconditioning (RIPC) of a limb is a clinically feasible strategy to protect against ischemia-reperfusion injury after stroke. However, the mechanism underlying RIPC remains elusive.

METHODS

We generated a rat model of noninvasive RIPC by four repeated cycles of brief blood flow constriction (5 min) in the hindlimbs using a tourniquet. Blood was collected 1 h after preconditioning and 3 days after brain reperfusion. The impact of RIPC on immune cell and cytokine profiles prior to and after transient middle cerebral artery occlusion (MCAO) was assessed.

RESULTS

Remote ischemic preconditioning protects against focal ischemia and preserves neurological functions 3 days after stroke. Flow cytometry analysis demonstrated that RIPC ameliorates the post-MCAO reduction of CD3(+)CD8(+) T cells and abolishes the reduction of CD3(+)/CD161a(+) NKT cells in the blood. In addition, RIPC robustly elevates the percentage of B cells in peripheral blood, thereby reversing the reduction in the B-cell population after stroke. RIPC also markedly elevates the percentage of CD43(+)/CD172a(+) noninflammatory resident monocytes, without any impact on the percentage of CD43(-)/CD172a(+) inflammatory monocytes. Finally, RIPC induces IL-6 expression and enhances the elevation of TNF-α after stroke.

CONCLUSION

Our results reveal dramatic immune changes during RIPC-afforded neuroprotection against cerebral ischemia.

Remote Limb Ischemic Preconditioning: A Neuroprotective Technique in Rodents

Sublethal ischemia protects tissues against subsequent, more severe ischemia through the upregulation of endogenous mechanisms in the affected tissue. Sublethal ischemia has also been shown to upregulate protective mechanisms in remote tissues. A brief period of ischemia (5-10 min) in the hind limb of mammals induces self-protective responses in the brain, lung, heart and retina. The effect is known as remote ischemic preconditioning (RIP). It is a therapeutically promising way of protecting vital organs, and is already under clinical trials for heart and brain injuries. This publication demonstrates a controlled, minimally invasive method of making a limb - specifically the hind limb of a rat - ischemic. A blood pressure cuff developed for use in human neonates is connected to a manual sphygmomanometer and used to apply 160 mmHg pressure around the upper part of the hind limb. A probe designed to detect skin temperature is used to verify the ischemia, by recording the drop in skin temperature caused by pressure-induced occlusion of the leg arteries, and the rise in temperature which follows release of the cuff. This method of RIP affords protection to the rat retina against bright light-induced damage and degeneration.