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.

Ischemic Conditioning-Mediated Myocardial Protection in Relation to Duration of Coronary Occlusion

Background: Myocardial ischemia is a dynamic process whereby a cascade of events is initiated to stimulate transition from reversible to irreversible cellular injury. Non-pharmacologic approaches to cellular protection, such as ischemic conditioning, delay onset of cellular injury in most organs in a host of animal species;however the degree of protection is limited to rather short durations of ischemia. In the present study, we examined whether protection afforded by ischemic conditioning could be extended beyond currently established limits of coronary occlusion in an in situ animal model. Methods: Rabbits (n = 106) were exposed to 30-, 60-, 120-, 180-, 240-, or 360-min coronary occlusion followed by 180-min coronary reperfusion (i.e. non-conditioned control groups). Ischemic conditioned rabbits were pre-treated by ischemic conditioning (i.e. 2-cycles of 5-min coronary occlusion and 5-min reperfusion) prior to a prolonged period of ischemia as described above. Area at risk (AR; by fluorescent microparticles) and area of necrosis (AN;by tetrazolium staining) were quantified by planimetry. Serum troponin I levels were assessed at baseline (i.e. before experimental protocol) and at the end of the experiment. Results: Changes in heart rate and hemodyamic indices were similar for all groups regardless of duration of ischemia and regardless of treatment (i.e. non-conditioned vs. ischemic conditioned). Infarcts (as percent AR) were markedly smaller (~35%) in ischemic conditioned rabbits (vs. controls) for the 30-min coronary occlusion group. With longer durations of coronary occlusion (60-, 120-, 180-, 240-min) infarcts were smaller (~20%) in ischemic conditioned groups but protection afforded was not statistically significant. With 360-min coronary occlusion, infarct size was the same for both treatment groups. Serum troponin I levels were greater in relation to infarct size as expected but no differences were detected between treatments regardless of ischemic duration. Conclusions: Ischemic conditioning limits infarct development;however, protection is limited when the duration of ischemia is extended beyond 4 hours. These findings provide further support for the concept that ischemic conditioning can delay, but does not limit myocyte necrosis. Underlying mechanisms for cellular protection remain to be established.

The Influence of Remote Ischemic Conditioning on Focal Brain Ischemia in Rats

Despite obvious progress in the treatment of acute forms of ischemic stroke, the risk of this condition remains unacceptably high. Brain infarction in the middle cerebral artery basin occurs in patients with atherosclerosis. The onset of the brain infarction is facilitated by the cessation of circulation (embolism) in conditions of insufficient collateral circulation. The extent of the infarct zone is determined by neuronal death and impaired microcirculation. The development of new methods for effective targeted restorative stroke therapy is crucial for restorative treatment and reducing the risk of mortality after stroke. Remote ischemic conditioning (RIC) is an approach to limiting reperfusion injury in the ischemic region of the brain after focal ischemia. One of the most commonly used in vivo models in stroke studies is the filament model of Middle Cerebral Artery Occlusion (MCAO) in rats. In our experiment, it was performed for 30 min (J. Koizumi) with subsequent 48-hour reperfusion. Within the first 24 hours after the start of reperfusion several short episodes of ischemia in low limbs were induced. After 48 hours of reperfusion the brains were harvested and stained with TTC. Then we evaluated the effect of RIC within 24 hours ex vivo in rats’ brains, as well as syndecan-1 plasma concentration. Infarct area was assessed by means of Image-Pro program with statistical analysis. Infarct volumes in the model group (31.97% ± 2.5%) were significantly higher compared to the values in the RIC group 48 hours after ischemia-reperfusion (13.6% ± 1.3%) (*P < 0.05). A significant reduction in the area of infarction after RIC is likely due to the effect on the regulation of collateral blood flow in the ischemia area. On the second day after ischemia-reperfusion, tissue swelling was reduced in the RIC group compared to the model group. Analysis of the average concentration of Syndecan-1 revealed the difference between model and RIC groups. Syndecan-1, endothelial glycocalyx protein, might be the regulator which performs vascular control of the interaction with inflammatory cell and is responsible for mediate effect of remote ischemic conditioning on the restriction of ischemic-reperfusion injury.

Remote ischemic conditioning prevents ischemic cerebrovascular events in children with moyamoya disease:a randomized controlled trial

Background Moyamoya disease(MMD)is a significant cause of childhood stroke and transient ischemic attacks(TIAs).This study aimed to assess the safety and efficacy of remote ischemic conditioning(RIC)in children with MMD.Methods In a single-center pilot study,46 MMD patients aged 4 to 14 years,with no history of reconstructive surgery,were randomly assigned to receive either RIC or sham RIC treatment twice daily for a year.The primary outcome measured was the cumulative incidence of major adverse cerebrovascular events(MACEs).Secondary outcomes included ischemic stroke,recurrent TIA,hemorrhagic stroke,revascularization rates,and clinical improvement assessed using the patient global impression of change(PGIC)scale during follow-up.RIC-related adverse events were also recorded,and cerebral hemodynamics were evaluated using transcranial Doppler.Results All 46 patients completed the final follow-up(23 each in the RIC and sham RIC groups).No severe adverse events associated with RIC were observed.Kaplan-Meier analysis indicated a significant reduction in MACEs frequency after RIC treatment[log-rank test(Mantel-Cox),P=0.021].At 3-year follow-up,two(4.35%)patients had an ischemic stroke,four(8.70%)experienced TIAs,and two(4.35%)underwent revascularization as the qualifying MACEs.The clinical improvement rate in the RIC group was higher than the sham RIC group on the PGIC scale(65.2%vs.26.1%,P<0.01).No statistical difference in cerebral hemodynamics post-treatment was observed.Conclusions RIC is a safe and effective adjunct therapy for asymptomatic children with MMD.This was largely due to the reduced incidence of ischemic cerebrovascular events.

Remote ischemic conditioning-induced hyperacute and acute responses of plasma proteome in healthy young male adults:a quantitative proteomic analysis

Background: Long-term remote ischemic conditioning (RIC) has been proven to be beneficial in multiple diseases, such as cerebral and cardiovascular diseases. However, the hyperacute and acute effects of a single RIC stimulus are still not clear. Quantitative proteomic analyses of plasma proteins following RIC application have been conducted in preclinical and clinical studies but exhibit high heterogeneity in results due to wide variations in experimental setups and sampling procedures. Hence, this study aimed to explore the immediate effects of RIC on plasma proteome in healthy young adults to exclude confounding factors of disease entity, such as medications and gender. Methods: Young healthy male participants were enrolled after a systematic physical examination and 6-month lifestyle observation. Individual RIC sessions included five cycles of alternative ischemia and reperfusion, each lasting for 5 min in bilateral forearms. Blood samples were collected at baseline, 5 min after RIC, and 2 h after RIC, and then samples were processed for proteomic analysis using liquid chromatography-tandem mass spectrometry method. Results: Proteins related to lipid metabolism (e.g., Apolipoprotein F), coagulation factors (hepatocyte growth factor activator preproprotein), members of complement cascades (mannan-binding lectin serine protease 1 isoform 2 precursor), and inflammatory responses (carboxypeptidase N catalytic chain precursor) were differentially altered at their serum levels following the RIC intervention. The most enriched pathways were protein glycosylation and complement/coagulation cascades. Conclusions: One-time RIC stimulus may induce instant cellular responses like anti-inflammation, coagulation, and fibrinolysis balancing, and lipid metabolism regulation which are protective in different perspectives. Protective effects of single RIC in hyperacute and acute phases may be exploited in clinical emergency settings due to apparently beneficial alterations in plasma proteome profile. Furthermore, the beneficial effects of long-term (repeated) RIC interventions in preventing chronic cardiovascular diseases among general populations can also be expected based on our study findings.

Interactions between remote ischemic conditioning and post-stroke sleep regulation

Sleep disturbances are common in patients with stroke,and sleep quality has a critical role in the onset and outcome of stroke.Poor sleep exacerbates neurological injury,impedes nerve regeneration,and elicits serious complications.Thus,exploring a therapy suitable for patients with stroke and sleep disturbances is imperative.As a multi-targeted nonpharmacological intervention,remote ischemic conditioning can reduce the ischemic size of the brain,improve the functional outcome of stroke,and increase sleep duration.Preclinical/clinical evidence showed that this method can inhibit the inflammatory response,mediate the signal transductions of adenosine,activate the efferents of the vagal nerve,and reset the circadian clocks,all of which are involved in sleep regulation.In particular,cytokines tumor necrosis factorα(TNFα)and adenosine are sleep factors,and electrical vagal nerve stimulation can improve insomnia.On the basis of the common mechanisms of remote ischemic conditioning and sleep regulation,a causal relationship was proposed between remote ischemic conditioning and post-stroke sleep quality.

Protective limb remote ischemic post-conditioning against high-intraocular-pressure-induced retinal injury in mice

AIM: To determine whether limb remote ischemic postconditioning(LRIC) protects against high-intraocularpressure(IOP)-induced retinal injur y, and to identify underlying molecular mechanisms. METHODS: In mice, IOP was increased to 110 mm Hg for 50 min and LRIC applied to the unilateral leg for three occlusion cycles(5 min/release). Three animal groups(control, high IOP, and high IOP+LRIC) were arranged in this study. Plasma was collected from LRIC treated mice. Retinal histology, oxidative stress were determined by histological section staining and chemical kit. C/EBP homologous protein(CHOP), and Iba-1 parameters were evaluated by immunofluorescent staining and Western blot. RESULTS: The data showed that LRIC treatment alleviated the retinal histological disorganization and ganglion cell loss induced by high IOP. The CHOP, Iba-1 expression and oxidative stress marker also were inhibited by LRIC treatment. To further explore underlying mechanisms, plasma from LRIC treated animals was intravenously transfused into high-IOP animals. The results showed plasma injection decreased caspase 9 expression and DHE staining signals compared with that in high IOP retinas. CONCLUSION: These data suggest that LRIC treatments exert retinal protective effects against high-IOP injury.Endogenous humoral factors release into the circulation by LRIC may contribute to homeostatic protection by reducing monocyte infiltration and/or microglia activation.

Neuroprotective effects of ischemic adaptation on cognitive dysfunction in mice with cerebral ischemia-reperfusion injury

Objective: To observe the effects of remote ischemia on cognitive function and neuronal pathological damage in rats with cognitive impairment induced by bilateral common carotid artery occlusion(BCAO).Methods:Male SD rats were selected to establish the cognitive impairment model induced by cerebral ischemia reperfusion caused by BCAO.The tests included three groups of rats:a sham group,a model group with vascular cognitive impairment (VCI) , and a remote ischemic conditioning (RIC) group (VCI + RIC group). From 24 h after operation, both hind limbs of rats in VCI + RIC group were treated with RIC. After 28 d, Morris water maze test and HE staining was used to observe the pathological changes of white matter and hippocampus in each group.Results: After 3 d mice in VCI group began to improve gradually. The recovery of rats in the VCI + RIC group was relatively slow,but they started to recover rapidly 2 d after the operation.Morris water maze test showed that the escape latency of rats in VCI group and VCI+RIC group was longer than that in the sham group, and the score of VCI+RIC group was better than that of the VCI group, but there was a significant difference between the two groups(P<0.05).The space exploration experiment was performed at 7 d and 28 d after the operation;the VCI+RIC group outperformed the VCI group in both trials;the difference between the two groups was statistically significant (P<0.05).In the target quadrant exploration time, the difference between the VCI group (33.5±11.3 s) and the VCI+RIC group (41.2±9.7 s) was statistically significant (P<0.05).Results from the hematoxylin and eosin(HE)staining showed that compared with VCI group, cortical cells in VCI + RIC group had loose stroma, thinner nerve fibers, fewer broken cells, and slightly shrunken cells. Compared with VCI group, neurons in VCI + RIC group had a little vacuolar degenera-tion and slightly shrunken cell volume.Conclusion:Cerebral ischemia-reperfusion injury can cause learning and memory impairment in rats, leading to VCI. RIC can significantly improve VCI and play a neuroprotective role.

Induction of ischemic tolerance as a promising treatment against diabetic retinopathy

Diabetic retinopathy is a leading cause of acquired blindness, and it is the most common ischemic disorder of the retina. Available treatments are not very effective. Efforts to inhibit diabetic reti- nopathy have focused either on highly specific therapeutic approaches for pharmacologic targets or using genetic approaches to change expression of certain enzymes. However, it might be wise to choose innovative treatment modalities that act by multiple potential mechanisms. The resis- tance to ischemic injury, or ischemic tolerance, can be transiently induced by prior exposure to a non-injurious preconditioning stimulus. A complete functional and histologic protection against retinal ischemic damage can be achieved by previous preconditioning with non-damaging isch- emia. In this review, we will discuss evidence that supports that ischemic conditioning could help avert the dreaded consequences that results from retinal diabetic damage.

Novel adjunctive treatments of myocardial infarction

Myocardial infarction is a major cause of death and disability worldwide and myocardial infarct size is a major determinant of prognosis. Early and successful restoration of myocardial reperfusion following an ischemic event is the most effective strategy to reduce final infarct size and improve clinical outcome,but reperfusion may induce further myocardial damage itself. Development of adjunctive therapies to limit myocardial reperfusion injury beyond opening of the coronary artery gains increasing attention. A vast number of experimental studies have shown cardioprotective effects of ischemic and pharmacological conditioning,but despite decades of research,the translation into clinical effects has been challenging. Recently published clinical studies,however,prompt optimism as novel techniques allow for improved clinical applicability. Cyclosporine A,the GLP-1 analogue exenatide and rapid cooling by endovascular infusion of cold saline all reduce infarct size and may confer clinical benefit for patients admitted with acute myocardial infarcts. Equally promising,three follow-up studies of the effect of remote ischemic conditioning(RIC) show clinical prognostic benefit in patients undergoing coronary surgery and percutaneous coronary intervention. The discovery that RIC canbe performed noninvasively using a blood pressure cuff on the upper arm to induce brief episodes of limb ischemia and reperfusion has facilitated the translation of RIC into the clinical arena. This review focus on novel advances in adjunctive therapies in relation to acute and elective coronary procedures.

Influence of cardiac nerve status on cardiovascular regulation and cardioprotection

Neural elements of the intrinsic cardiac nervous system transduce sensory inputs from the heart, blood vessels and other organs to ensure adequate cardiac function on a beat-to-beat basis. This inter-organ crosstalk is critical for normal function of the heart and other organs; derangements within the nervous system hierarchy contribute to pathogenesis of organ dysfunction. The role of intact cardiac nerves in development of, as well as protection against, ischemic injury is of current interest since it may involve recruitment of intrinsic cardiac ganglia. For instance, ischemic conditioning, a novel protection strategy against organ injury, and in particular remote conditioning, is likely mediated by activation of neural pathways or by endogenous cytoprotective bloodborne substances that stimulate different signalling pathways. This discovery reinforces the concept that inter-organ communication, and maintenance thereof, is key. As such, greater understanding of mechanisms and elucidation of treatment strategies is imperative to improve clinical outcomes particularly in patients with comorbidities. For instance, autonomic imbalance between sympathetic and parasympathetic nervous system regulation can initiate cardiovascular autonomic neuropathy that compromises cardiac stability and function. Neuromodulation therapies that directly target the intrinsic cardiac nervous system or other elements of the nervous system hierarchy are currently being investigated for treatment of different maladies in animal and human studies.

Contribution of Myocyte Apoptosis to Myocardial Injury in an in Vivo Rabbit Preparation of Ischemia-Reperfusion

Objective: Exposure of the heart to repeated, brief episodes of coronary occlusion/reperfusion prevents lethal myocyte injury. Necrosis and apoptosis, two seemingly distinct mechanisms of cell death caused by ischemia could contribute independently to progressive loss of myocardium. Studies suggest that ischemic conditioning (IC) lessens myocyte injury by decreasing apoptosis. The goal of this study was to examine cell death in rabbit hearts subject to ischemia-reperfusion injury without (nIC) or with pretreatment by IC. Methods: In the control study, anesthetized, male rabbits (n = 4/group) underwent 30-min regional coronary occlusion (CO) and either 3, 6 or 24h reperfusion (REP). In the IC study, rabbits were pretreated by IC (2 cycles of 5-min CO and 10-min REP) before 30-min CO and subsequent REP. Additional groups were evaluated with 60, or 120-min CO followed by up to 96 h REP. Agarose electrophoresis was used to detect DNA laddering and poly (ADP-ribose) polymerase (PARP;chromatin bound nuclear DNA repair enzyme) was assessed in myocardial biopsies. Results: Genomic DNA from nIC and IC hearts showed no oligonucleosomal fragmentation. In addition, we did not detect any cleavage of PARP;however, myocardial PARP levels decreased when CO and REP durations were prolonged. Conclusion:Absence of genomic DNA fragmentation or PARP cleavage in an in vivo preparation of ischemia-reperfusion injury does not support the view that apoptosis contributes markedly to post-ischemic tissue necrosis.

Impact of Acute Ischemia-Reperfusion Injury on Left Ventricular Pressure-Volume Relations in Dogs

Objective: Ischemic conditioning (IC) limits myocyte necrosis after acute myocardial ischemia-reperfusion;however, controversy persists regarding its potential to attenuate LV contractile dysfunction. Pressure-volume (P-V) loop analysis, via the load-insensitive conductance catheter method, was used to evaluate LV contractility, diastolic function, and ventriculo-arterial coupling. The goal of this study was to evaluate the ability of IC to improve post-ischemic recovery of LV contractile function. Methods: Twelve anesthetized dogs were randomly distributed to either the IC or the non-IC group;all dogs were subject to 60-min acute coronary occlusion followed by 180-min reperfusion. IC consisted of 4 repeated cycles of 5-min occlusion and 5-min reperfusion of the left main coronary artery. LV P-V relations were constructed under steady-state conditions (by inferior vena cava occlusion) at the beginning and end of the experiments;P-V loops were acquired at different time points before and during ischemia-reperfusion. Results: During ischemia and reperfusion, dP/dtmax decreased significantly compared to baseline in both groups;dP/dtmin, an indicator of the rate of LV relaxation rate was not affected for either group. Significant changes in several parameters of LV function including LVEF, SW, tPFR, ESV, and EDV caused by ischemia were also identified;none of these negative effects were resorbed, even in part, during reperfusion. Conclusions: Diminished LV contractile efficiency during systole and diastole produced by ischemia-reperfusion did not improve with IC pre-treatment despite significant endogenous protection against tissue necrosis.