Neuroprotection mediated by remote preconditioning is associated with a decrease in systemic oxidative stress and changes in brain and blood glutamate concentration

New alternative approaches to stroke treatment: the blood cell-derived secretome shows promise in individuals with obesity

Ischaemic tolerance induced by remote ischaemic conditioning (RIC) has been extensively demonstrated in several preclinical models of cerebral ischaemia. However, animals with common stroke-related comorbidities do not benefit from the recent advances of RIC. Therefore, we investigated two alternative approaches for obese animals with stroke: (1) the efficacy of an additional round of the standard RIC protocol, and (2) the paracrine potential of the blood cell-derived secretome derived from RIC-induced healthy young rats. We found that a second round of remote ischaemic postconditioning (RIPostC) stimulus reduced neurodegeneration and exerted antioxidant effects but failed to decrease the infarct volume and alter glutamate homeostasis. However, when obese rats were administered the secretome from healthy, young RIC-stimulated rats, they exhibited improved neurological post-stroke outcomes. Intravenous administration of the tolerant secretome activated several endogenous mechanisms, including a reduction in the infarct volume and neurodegeneration in the penumbra. Furthermore, the blood cell-derived secretome accelerated brain-to-blood glutamate efflux in obese rats, and demonstrated antioxidant properties that may have contributed to the induction of tolerance in obese rats with stroke. These findings indicate that the blood cell-derived secretome has unique abilities and represents a new potential treatment for individuals with obesity and ischaemic stroke.

Effectiveness of remote ischaemic conditioning is not affected by hyper-inflammation in a rat model of stroke

The inflammation and coagulopathy during coronavirus disease (COVID-19) impairs the efficiency of the current stroke treatments. Remote ischaemic conditioning (RIC) has shown potential in recent years to protect the brain and other organs against pathological conditions. This study aimed to evaluate the efficiency of RIC in brain infarct size using TTC staining and lung injury reduction by H&E staining during the hyper-inflammatory response in rats. The inflammation and coagulopathy were assessed by sedimentation rate, haematocrit, systemic oxidative stress and clotting time. Moreover, we observed changes in the cytokine profile. The results of the first part of the experiment showed that the inflammation and lung injury are fully developed after 24 h of intratracheal LPS administration. At this time, we induced focal brain ischaemia and examined the effect of RIC pre- and post-treatment. Our results showed that RIPre-C reduced the infarct size by about 23%, while RIPost-C by about 30%. The lung injury was also reduced following both treatments. Moreover, RIC modulated systemic inflammation. The level of chemokines CINC-1, LIX and RANTES decreased after 24 h of post-ischaemic reperfusion in treated animals compared to non-treated. The RIC-mediated decrease of inflammation was reflected in improved sedimentation rate and hematocrit, as well as reduced systemic oxidative stress. The results of this work showed neuroprotective and lung protective effects of RIC with a decrease in inflammation response. On the basis of our results, we assume that immunomodulation through the chemokines CINC-1, LIX, and RANTES play a role in RIC-mediated protection.

Obesity as a Limiting Factor for Remote Ischemic Postconditioning-Mediated Neuroprotection after Stroke

Background

Remote ischemic postconditioning (RIPostC) may protect the brain from ischemia/reperfusion (I/R) injury. The association between RIPostC and obesity has not yet been extensively studied.

Methods

Twelve-week-old male Zucker diabetic fatty (ZDF; n=68) and Zucker diabetic lean (ZDL; n=51) rats were subjected to focal cerebral ischemia for 90 minutes, followed by 24 hours of reperfusion. RIPostC was performed with 5-minute I/R cycles using a tourniquet on the right hind limb.

Results

The results showed a negative association between obesity and neurological impairment in ischemic animals. We observed a 70% greater infarct size in ZDF rats compared with their lean counterparts, as evaluated by 2,3,5-triphenyltetrazolium chloride staining. To measure the total fragmented DNA in peripheral lymphocytes, comet assay was performed. Obese rats exhibited higher levels of DNA damage (by approximately 135%) in peripheral blood lymphocytes even before the induction of stroke. RIPostC did not attenuate oxidative stress in the blood in obese rats subjected to ischemia. Focal cerebral ischemia increased core and penumbra tissue glutamate release in the brain and decreased it in the blood of ischemic ZDL rats, and these changes improved following RIPostC treatment. However, changes in blood and tissue glutamate content were not detected in ischemic ZDF rats or after RIPostC intervention.

Conclusion

Our findings suggest that obese animals respond more severely to ischemia-reperfusion brain injury. However, obese animals did not achieve neuroprotective benefits of RIPostC treatment.

Changes in excitatory amino acid transporters in response to remote ischaemic preconditioning and glutamate excitotoxicity

The successful implementation of remote ischaemic conditioning as a clinical neuroprotective strategy requires a thorough understanding of its basic principles, which can be modified for each patient. The mechanisms of glutamate homeostasis appear to be a key component. In the current study, we focused on the brain-to-blood glutamate shift mediated by glutamate transporters (excitatory amino acid transports [EAATs]) and the effect of remote ischaemic preconditioning (RIPC) as a mediator of ischaemic tolerance. We used model mimicking ischaemia-mediated excitotoxicity (intracerebroventricular administration of glutamate) to avoid the indirect effect of ischaemia-triggered mechanisms. We found quantitative changes in EAAT2 and EAAT3 and altered membrane trafficking of EAAT1 on the cells of the choroid plexus. These changes could underlie the beneficial effects of ischaemic tolerance. There was reduced oxidative stress and increased glutathione level after RIPC treatment. Moreover, we determined the stimulus-specific response on EAATs. While glutamate overdose stimulated EAAT2 and EAAT3 overexpression, RIPC induced membrane trafficking of EAAT1 and EAAT2 rather than a change in their expression. Taken together, mechanisms related to glutamate homeostasis, especially EAAT-mediated transport, represents a powerful tool of ischaemic tolerance and allow a certain amount of flexibility based on the stimulus used.

Remote Ischaemic Preconditioning Accelerates Brain to Blood Glutamate Efflux via EAATs-mediated Transport

Remote ischaemic conditioning (RIC) becomes an attractive strategy for the endogenous stimulation of mechanisms protecting neurons against ischaemia. Although the processes underlying the RIC are not clearly understood, the homeostasis of glutamate seems to play an important role. The present study is focused on the investigation of the brain to blood efflux of glutamate in a condition mimicking ischaemia-mediated excitotoxicity and remote ischaemic preconditioning (RIPC). The animals were pre-treated with a hind-limb tourniquet one hour before the intraventricular administration of glutamate and its release was monitored as the concentration of glutamate/glutathione in blood and liquor for up to 1 h. The transport mediated by excitatory amino acid transporters (EAATs) was verified by their inhibition with Evans Blue intraventricular co-administration. RIPC mediated the efflux of glutamate exceeding from CSF to blood in the very early stage of intoxication. As a consequence, the blood level of glutamate rose in a moment. EAATs inhibition confirmed the active role of glutamate transporters in this process. In the blood, elevated levels of glutamate served as a relevant source of antioxidant glutathione for circulating cells in RIPC-treated individuals. All of those RIPC-mediated recoveries in processes of glutamate homeostasis reflect the improvement of oxidative stress, suggesting glutamate-accelerated detoxication to be one of the key mechanisms of RIPC-mediated neuroprotection.

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.

Neuroprotective effects and mechanisms of ischemic/hypoxic preconditioning on neurological diseases

As the organ with the highest demand for oxygen, the brain has a poor tolerance to ischemia and hypoxia. Despite severe ischemia/hypoxia induces the occurrence and development of various central nervous system (CNS) diseases, sublethal insult may induce strong protection against subsequent fatal injuries by improving tolerance. Searching for potential measures to improve brain ischemic/hypoxic is of great significance for treatment of ischemia/hypoxia related CNS diseases. Ischemic/hypoxic preconditioning (I/HPC) refers to the approach to give the body a short period of mild ischemic/hypoxic stimulus which can significantly improve the body's tolerance to subsequent more severe ischemia/hypoxia event. It has been extensively studied and been considered as an effective therapeutic strategy in CNS diseases. Its protective mechanisms involved multiple processes, such as activation of hypoxia signaling pathways, anti-inflammation, antioxidant stress, and autophagy induction, etc. As a strategy to induce endogenous neuroprotection, I/HPC has attracted extensive attention and become one of the research frontiers and hotspots in the field of neurotherapy. In this review, we discuss the basic and clinical research progress of I/HPC on CNS diseases, and summarize its mechanisms. Furthermore, we highlight the limitations and challenges of their translation from basic research to clinical application.

Accelerated capacity of glutamate uptake via blood elements as a possible tool of rapid remote conditioning mediated tissue protection

Recently, the function of blood cells in remote ischemic conditioning (RIC) mediated neuroprotection was undoubtedly confirmed. In the present paper, we have focused on the role of blood elements in glutamate homeostasis. The blood of remote conditioned (tolerant) animals was incubated ex vivo with 100 μM glutamate, and the quantitative and qualitative changes of excitatory amino acid transporters (EAAT 1, 2, and 3) were determined. We confirmed RIC mediated accelerated sequestration of extracellular glutamate via EAATs and altered distribution of that amino acid between plasma and cell elements compared to non-tolerant counterparts. The activity of EAATs was elevated in erythrocytes and monocytes, while the density of transporters was not affected. Quantitative changes of EAAT1 density were detected solely in platelets where the forced scavenging was independent of EAATs inhibition. Surprisingly, the trafficking of immunovisualised EAAT2 and 3 raised at tolerant erythrocytes and monocytes. We have found that protein synthesis underlined this process. On the other hand, depletion of protein synthesis did not significantly affect the scavenging capacity of those cell populations. Our work has demonstrated that the elevated blood scavenging of glutamate overdose could be one of the potential mechanisms underlying RIC mediated tissue protection.

Remote ischemic preconditioning-induced neuroprotection in cerebral ischemia-reperfusion injury: Preclinical evidence and mechanisms

Remote ischemic preconditioning (RIPC) is an intrinsic protective phenomenon in which 3 to 4 interspersed cycles of non-fatal regional ischemia followed by reperfusion to the remote tissues protect the vital organs including brain, heart and kidney against sustained ischemia-reperfusion-induced injury. There is growing preclinical evidence supporting the usefulness of RIPC in eliciting neuroprotection against focal and global cerebral ischemia-reperfusion injury. Scientists have explored the involvement of HIF-1α, oxidative stress, apoptotic pathway, Lcn-2, platelets-derived microparticles, splenic response, adenosine A₁ receptors, adenosine monophosphate activated protein kinase and neurogenic pathway in mediating RIPC-induced neuroprotection. The present review discusses the early and late phases of neuroprotection induced by RIPC against cerebral ischemic injury in animals along with the various possible mechanisms.

Turning the Oxygen Dial: Balancing the Highs and Lows

Oxygen is both vital and toxic to life. Molecular oxygen is the most used substrate in the human body and is required for several hundred diverse biochemical reactions. The discovery of the PHD-HIF-pVHL system revolutionized our fundamental understanding of oxygen sensing and cellular adaptations to hypoxia. It deepened our knowledge of the biochemical underpinnings of numerous diseases, ranging from anemia to cancer. Cellular dysfunction and tissue pathology can result from a mismatch of oxygen supply and demand. Recent work has shown that mitochondrial disease models display tissue hyperoxia and that disease pathology can be reversed by normalization of excess oxygen, suggesting that certain disease states can potentially be treated by modulating oxygen levels. In this review, we describe cellular and organismal mechanisms of oxygen sensing and adaptation. We provide a revitalized framework for understanding pathologies of too little or too much oxygen.

P2X7 Receptors as a Therapeutic Target in Cerebrovascular Diseases

Shortage of oxygen and nutrients in the brain induces the release of glutamate and ATP that can cause excitotoxicity and contribute to neuronal and glial damage. Our understanding of the mechanisms of ATP release and toxicity in cerebrovascular diseases is incomplete. This review aims at summarizing current knowledge about the participation of key elements in the ATP-mediated deleterious effects in these pathologies. This includes pannexin-1 hemichannels, calcium homeostasis modulator-1 (CALHM1), purinergic P2X7 receptors, and other intermediaries of CNS injury downstream of ATP release. Available data together with recent pharmacological developments in purinergic signaling may constitute a new opportunity to translate preclinical findings into more effective therapies in cerebrovascular diseases.