A feasible strategy for focal cerebral ischemia-reperfusion injury: remote ischemic postconditioning

Research progress on the mechanism of action and clinical application of remote ischemic post-conditioning for acute ischemic stroke

Remote ischemic post-conditioning (RIPostC) can reduce cerebral ischemia reperfusion injury (IRI) by inducing endogenous protective effects, the distal limb ischemia post-treatment and in situ ischemia post-treatment were classified according to the site of intervention. And in the process of clinical application distal limb ischemia post-treatment is more widely used and more conducive to clinical translation. Therefore, in this paper, we review the mechanism of action and clinical application of RIPostC in cerebral ischemia, hoping to provide reference help for future experimental directions and clinical translation.

Cooling Down Inflammation in the Cardiovascular System via the Nicotinic Acetylcholine Receptor

ABSTRACT

Inflammation is a major player in many cardiovascular diseases including hypertension, atherosclerosis, myocardial infarction, and heart failure. In many individuals, these conditions coexist and mutually exacerbate each other's progression. The pathophysiology of these diseases entails the active involvement of both innate and adaptive immune cells. Immune cells that possess the α7 subunit of the nicotinic acetylcholine receptor on their surface have the potential to be targeted through both pharmacological and electrical stimulation of the cholinergic system. The cholinergic system regulates the inflammatory response to various stressors in different organ systems by systematically suppressing spleen-derived monocytes and chemokines and locally improving immune cell function. Research on the cardiovascular system has demonstrated the potential for atheroma plaque stabilization and regression as favorable outcomes. Smaller infarct size and reduced fibrosis have been associated with improved cardiac function and a decrease in adverse cardiac remodeling. Furthermore, enhanced electrical stability of the myocardium can lead to a reduction in the incidence of ventricular tachyarrhythmia. In addition, improving mitochondrial dysfunction and decreasing oxidative stress can result in less myocardial tissue damage caused by reperfusion injury. Restoring baroreflex activity and reduction in renal damage can promote blood pressure regulation and help counteract hypertension. Thus, the present review highlights the potential of nicotinic acetylcholine receptor activation as a natural approach to alleviate the adverse consequences of inflammation in the cardiovascular system.

Preclinical evidence of remote ischemic conditioning in ischemic stroke, a metanalysis update

Remote ischemic conditioning (RIC) is a promising therapeutic approach for ischemic stroke patients. It has been proven that RIC reduces infarct size and improves functional outcomes. RIC can be applied either before ischemia (pre-conditioning; RIPreC), during ischemia (per-conditioning; RIPerC) or after ischemia (post-conditioning; RIPostC). Our aim was to systematically determine the efficacy of RIC in reducing infarct volumes and define the cellular pathways involved in preclinical animal models of ischemic stroke. A systematic search in three databases yielded 50 peer-review articles. Data were analyzed using random effects models and results expressed as percentage of reduction in infarct size (95% CI). A meta-regression was also performed to evaluate the effects of covariates on the pooled effect-size. 95.3% of analyzed experiments were carried out in rodents. Thirty-nine out of the 64 experiments studied RIPostC (61%), sixteen examined RIPreC (25%) and nine tested RIPerC (14%). In all studies, RIC was shown to reduce infarct volume (- 38.36%; CI - 42.09 to - 34.62%) when compared to controls. There was a significant interaction caused by species. Short cycles in mice significantly reduces infarct volume while in rats the opposite occurs. RIPreC was shown to be the most effective strategy in mice. The present meta-analysis suggests that RIC is more efficient in transient ischemia, using a smaller number of RIC cycles, applying larger length of limb occlusion, and employing barbiturates anesthetics. There is a preclinical evidence for RIC, it is safe and effective. However, the exact cellular pathways and underlying mechanisms are still not fully determined, and its definition will be crucial for the understanding of RIC mechanism of action.

α7 Nicotinic Acetylcholine Receptor Mediates the Neuroprotection of Remote Ischemic Postconditioning in a Rat Model of Asphyxial Cardiac Arrest

BACKGROUND

Remote ischemic postconditioning (RIPost) has been shown to reduce the ischemia-reperfusion injury of the heart and brain. However, the protection mechanisms have not yet been fully elucidated. We have observed that RIPost could alleviate the brain injury after cardiac arrest (CA). The aim of this study was to explore whether α7 nicotinic acetylcholine receptor (α7nAChR) mediates the neuroprotection of RIPost in a rat model of asphyxial CA.

MATERIALS AND METHODS

Asphyxial CA model was induced by occlusion of the tracheal tube for 8 min and resuscitated later. RIPost produced by three cycles of 15-min occlusion and 15-min release of the right hind limb by a tourniquet was performed respectively at the moment and the third hour after restoration of spontaneous circulation. The α7nAChR agonist PHA-543613 and the antagonist methyllycaconitine (MLA) were used to investigate the role of α7nAChR in mediating neuroprotective effects.

RESULTS

Results showed that α7nAChR was decreased in hippocampus and cortex after resuscitation, whereas RIPost could attenuate the reduction. The use of PHA-543613 provided neuroprotective effects against cerebral injury after CA. Furthermore, RIPost decreased the levels of neuron-specific enolase, inflammatory mediators, the number of apoptotic cells, and phosphorylation of nuclear factor-κB while increased the phosphorylation of signal transducer and activator of transcription-3. However, the above effects of RIPost were attenuated by α7nAChR antagonist methyllycaconitine.

CONCLUSIONS

Neuroprotection of RIPost was related with the activation of α7nAChR, which could suppress nuclear factor-κB and activate signal transducer and activator of transcription-3 in a rat asphyxial CA model.

Modes of Calcium Regulation in Ischemic Neuron

Calcium (Ca2+) dysregulation is a major catalytic event. Ca2+ dysregulation leads to neuronal cell death and brain damage result in cerebral ischemia. Neurons are unable in maintaining calcium homeostasis. Ca2+ homeostasis imbalance results in increased calcium influx and impaired calcium extrusion across the plasma membrane. Ca2+ dysregulation is mediated by different cellular and biochemical mechanism, which leads to neuronal loss resulting stroke/cerebral ischemia. A better understanding of the Ca2+ dysregulation might help in the development of new treatments in order to reduce ischemic brain injury. An optimal concentration of Ca2+ does not lead to neurotoxicity in the ischemic neuron. Intracellular Ca2+ act as a trigger for acute neurotoxicity and this cause induction of long-lasting processes leading to necrotic and/or apoptotic post-ischemic delayed neuronal death or of compensatory, neuroprotective mechanisms has increased considerably. Moreover, routes of ischemic Ca2+ influx to neurons, involvement of intracellular Ca2+ stores and Ca2+ buffers, spatial and temporal relations between ischemia-induced increases in intracellular Ca2+ concentration and neurotoxicity will further increase our understanding about underlying mechanism and they can act as a target for the development of drugs. Here, in our article we are trying to provide a brief overview of various Ca2+ influx pathways involve in ischemic neuron and how ischemic neuron attempts to counterbalance this calcium overload.

Gene expression profiling analysis to investigate the role of remote ischemic postconditioning in ischemia-reperfusion injury in rats

Background

Blood flow restoration is a definitive therapy for salvaging the myocardium following ischemic injury. Nevertheless, the sudden restoration of blood flow to the ischemic myocardium can induce ischemia-reperfusion injury (IRI).

Results

Herein, we investigated the cardioprotective effect of remote ischemic postconditioning (RPostC) through our in vivo rat model of myocardial IRI. The study included three groups: the control group, the IRI group, and the IRI + RPostC group. Ischemia-reperfusion treatment led to an increase in the myocardial infarction area, which was inhibited by RPostC. In contrast to that in the control group, the myocardial apoptosis level was enhanced in the IRI group, whereas RPostC treatment decreased IRI-induced cellular apoptosis. Affymetrix Rat Gene 2.0 ST chip data identified a total of 265 upregulated genes and 267 downregulated genes between the IRI and IRI + RPostC groups. A group of differentially expressed noncoding RNAs (ncRNAs), such as MTA_TC0600002772.mm, MTA_TC1300002394.mm, U7 small nuclear RNA (Rnu7) and RGD7543256_1, were identified. Gene Ontology (GO) enrichment analysis indicated that the positive regulation of some molecular functions, such as GTPase activity, GTP binding, cyclic-nucleotide phosphodiesterase activity and cytokine activity, may contribute to the cardioprotective role of RPostC. Moreover, pathway enrichment analysis using the Kyoto Encyclopedia of Genes and Genomes (KEGG) suggested the potential implication of the TNF signaling pathway and Toll-like receptor signaling pathway. Global signal transduction network analysis, co-expression network analysis and quantitative real-time polymerase chain reaction analysis further identified several core genes, including Pdgfra, Stat1, Lifr and Stfa3.

Conclusion

Remote ischemic postconditioning treatment can decrease IRI-mediated myocardial apoptosis by regulating multiple processes and pathways, such as GTPase activity, cytokine activity, and the TNF and Toll-like receptor signaling pathways. The potential role of the above ncRNAs and core genes in IRI-induced cardiac damage merits further study as well.

Electronic supplementary material

The online version of this article (10.1186/s12864-019-5743-9) contains supplementary material, which is available to authorized users.

Limb Remote Ischemic Conditioning: Mechanisms, Anesthetics, and the Potential for Expanding Therapeutic Options

Novel and innovative approaches are essential in developing new treatments and improving clinical outcomes in patients with ischemic stroke. Remote ischemic conditioning (RIC) is a series of mechanical interruptions in blood flow of a distal organ, following end organ reperfusion, shown to significantly reduce infarct size through inhibition of oxidation and inflammation. Ischemia/reperfusion (I/R) is what ultimately leads to the irreversible brain damage and clinical picture seen in stroke patients. There have been several reports and reviews about the potential of RIC in acute ischemic stroke; however, the focus here is a comprehensive look at the differences in the three types of RIC (remote pre-, per-, and postconditioning). There are some limited uses of preconditioning in acute ischemic stroke due to the unpredictability of the ischemic event; however, it does provide the identification of biomarkers for clinical studies. Remote limb per- and postconditioning offer a more promising treatment during patient care as they can be harnessed during or after the initial ischemic insult. Though further research is needed, it is imperative to discuss the importance of preclinical data in understanding the methods and mechanisms involved in RIC. This understanding will facilitate translation to a clinically feasible paradigm for use in the hospital setting.

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 Postconditioning Alone and Combined with Hypothermia Improved Postresuscitation Cardiac and Neurological Outcomes in Swine

Objective. Previously, we demonstrated that remote ischemic postconditioning (RIpostC) improved postresuscitation myocardial and cerebral functions in rat. Here, we investigated the effects of RIpostC alone and combined with therapeutic hypothermia (TH) on cardiac and neurological outcomes after CPR in swine. Methods. Twenty-one pigs were subjected to 10 mins of VF and then 5 mins of CPR. The animals were randomized to receive RIpostC alone, or its combination with TH, or sham control. RIpostC was induced by 4 cycles of limb ischemia followed by reperfusion. TH was implemented by surface cooling to reach a temperature of 32–34°C. Results. During 72 hrs after resuscitation, lower level of cardiac troponin I and greater stroke volume and global ejection fraction were observed in animals that received RIpostC when compared to the control. RIpostC also decreased serum levels of neuron-specific enolase and S100B and increased neurologic alertness score after resuscitation. The combination of RIpostC and TH resulted in greater improvement in cardiac and neurological outcomes than RIpostC alone. Conclusion. RIpostC was conducive to improving postresuscitation myocardial and cerebral functions and reducing their organ injuries. Its combination with TH further enhanced its protective effects.

Up-regulation of iNOS by hypoxic postconditioning inhibits H9c2 cardiomyocyte apoptosis induced by hypoxia/re-oxygenation

Apoptosis is a crucial mode of cell death induced by ischemia and reperfusion, and ischemic postconditioning (PostC) has been reported to inhibit cell apoptosis. Inducible nitric oxide synthase (iNOS) has been confirmed to play an important role in triggering and mediating the late cardio-protection against ischemia/hypoxia. In this study, we found that hypoxic PostC remarkably up-regulated the expression of iNOS and decreased cardiomyocyte apoptosis. Pre-treatment with 1400w (a highly selective inhibitor of iNOS) or iNOS siRNA weakened the anti-apoptotic effect of hypoxic PostC. These findings suggested that iNOS may be one of the key molecular mechanisms responsible for the inhibition of apoptosis by hypoxic PostC.

Remote ischemic post-conditioning improves neurological function by AQP4 down-regulation in astrocytes

Cerebral ischemia is a primary cause of human death and long-term disability. Previous studies have suggested that remote ischemic post-conditioning (RIPC) is a potential useful tool for cerebral ischemic treatment. However, the protective mechanism of RIPC is not very clear. This study verified the hypothesis that, in remote post-conditioning of cerebral ischemic rats, down-regulation of aquaporin 4 (AQP4), which is an important player for water hemostasis in astrocytes, could attenuate cerebral damage after transient middle cerebral artery occlusion (MCAO). In this study, RIPC model was established after MCAO. Each hind limb of rat was clamped by small rubber tubes for 10 min, and then the tubes were opened for 10 min. The clamping and opening were operated for a total of three cycles to block the hind limbs blood flow. The results showed that, RIPC could significantly improve neurological function, decrease the percentage of the infarct volume and edema, and elevate the integrity of blood-brain barrier (BBB). In addition, the numbers of AQP4 and glial fibrillary acidic protein (GFAP) positive cells were significantly lower in the RIPC group. Moreover, we found that AQP4 expression decreased in response to ischemia/reperfusion in the RIPC group. Our findings indicated that RIPC could attenuate focal cerebral ischemia/reperfusion injury, and the neuroprotective mechanism was related with the down-regulation of AQP4 in astrocytes.

Neuroprotection by peripheral nerve electrical stimulation and remote postconditioning against acute experimental ischaemic stroke

OBJECTIVE

Local electrical stimulation (ES) was reported to protect the brain during ischaemic injury, while the protective effect of limb remote ischaemic postconditioning (RIPostC) was confirmed. The aim of this study was to explore whether remote peripheral nerve ES exerted neuroprotection and whether this procedure shared the same neuroprotective mechanism underlying RIPostC.

METHODS

Stroke in Sprague-Dawley rats was induced by distal middle cerebral artery occlusion (dMCAO). Rats were divided into five groups: dMCAO, RIPostC, ES, nerve resection (NR) + ES and RIPostC+ES. Twenty-four hours after reperfusion, rats were examined for neurobehavioural function, including forelimb fault placing test, Ludmila Belayev 12 score test, and infarct volume. The expression of Bcl-2 and cleaved-caspase-3 in ischaemic cortex was assessed by Western blot.

RESULTS

In forelimb fault placing test, as compared to the highest score in the stroke-only group, RIPostC, ES and RIPostC+ES groups showed a significantly (P < 0.01) lower score. The results were similar for the Ludmila Belayev 12 score test. The infarct volume of the treatment groups also exhibited significant (P < 0.01) reduction as compared to the stroke-only group. The volume of infarct tissue in the combination of RIPostC+ES was significantly less than RIPostC and ES alone (P < 0.05). Furthermore, NR blocked the ES's protection (P < 0.05) as compared to the ES group by using above-mentioned methods. Bcl-2 was upregulated, while cleaved-caspase-3 was downregulated in the experimental groups as compared to the control group. No difference was found among the experimental groups.

DISCUSSION

Peripheral nerve ES appears to have a neuroprotective effect in a rat dMCAO model. This effect may indicate a neural protective mechanism underlying beneficial effect of RIPostC.