Ischaemic postconditioning rescues brain injury caused by focal ischaemia/reperfusion via attenuation of protein oxidization

Ischemic post-conditioning in acute ischemic stroke thrombectomy: A phase-I duration escalation study

Background

Previous experimental studies have found that ischemic post-conditioning exhibits neuroprotective effects by alleviating ischemia-reperfusion injury in an acute ischemic stroke model, and its efficacy is thought to be related to the duration of ischemic post-conditioning. However, ischemic post-conditioning has not been used in patients with acute ischemic stroke. This study aims to determine the safety, tolerability, and maximum tolerable duration of ischemic post-conditioning in patients with acute ischemic stroke receiving mechanical thrombectomy.

Methods

Patients with acute ischemic stroke with unilateral middle cerebral artery M1 segment occlusion eligible for mechanical thrombectomy will be enrolled. We adopt a 3 + 3 dose-escalation design with a duration escalation schedule of 0, 1, 2, 3, 4, and 5 min × 4 cycles for the ischemic post-conditioning study. After successful reperfusion following mechanical thrombectomy, the balloon for ischemic post-conditioning will be inflated at the site proximal to the culprit lesion four times for 0–5 min with low-pressure (3–4 atmospheres) inflations, each separated by 0–5 min of reflow. We pre-defined the major responses (vessel perforation or rupture, reocclusion of the culprit vessel after ischemic post-conditioning, vessel dissection, severe vasospasm, ischemic post-conditioning related thrombotic events, and rupture of the balloon used for ischemic post-conditioning) as the stopping rules. Each patient will undergo a rigorous evaluation to determine the safety, tolerability, and maximum tolerable duration of ischemic post-conditioning.

Discussion

This will be the first clinical study to ascertain the safety and tolerability of ischemic post-conditioning in patients with acute ischemic stroke receiving mechanical thrombectomy. The maximum tolerable duration obtained in this study will also serve as a starting point for future studies on the efficacy of ischemic post-conditioning.

Clinical trial registration

[https://clinicaltrials.gov], identifier [NCT05153655].

The Role of Ubiquitin-Proteasome Pathway and Autophagy-Lysosome Pathway in Cerebral Ischemia

The ubiquitin-proteasome pathway and autophagy-lysosome pathway are two major routes for clearance of aberrant cellular components to maintain protein homeostasis and normal cellular functions. Accumulating evidence shows that these two pathways are impaired during cerebral ischemia, which contributes to ischemic-induced neuronal necrosis and apoptosis. This review aims to critically discuss current knowledge and controversies on these two pathways in response to cerebral ischemic stress. We also discuss molecular mechanisms underlying the impairments of these protein degradation pathways and how such impairments lead to neuronal damage after cerebral ischemia. Further, we review the recent advance on the understanding of the involvement of these two pathways in the pathological process during many therapeutic approaches against cerebral ischemia. Despite recent advances, the exact role and molecular mechanisms of these two pathways following cerebral ischemia are complex and not completely understood, of which better understanding will provide avenues to develop novel therapeutic strategies for ischemic stroke.

Ischemic postconditioning prevents surge of presynaptic glutamate release by activating mitochondrial ATP-dependent potassium channels in the mouse hippocampus

A mild ischemic load applied after a lethal ischemic insult reduces the subsequent ischemia–reperfusion injury, and is called ischemic postconditioning (PostC). We studied the effect of ischemic PostC on synaptic glutamate release using a whole-cell patch-clamp technique. We recorded spontaneous excitatory post-synaptic currents (sEPSCs) from CA1 pyramidal cells in mouse hippocampal slices. The ischemic load was perfusion of artificial cerebrospinal fluid (ACSF) equilibrated with mixed gas (95% N₂ and 5% CO₂). The ischemic load was applied for 7.5 min, followed by ischemic PostC 30 s later, consisting of three cycles of 15 s of reperfusion and 15 s of re-ischemia. We found that a surging increase in sEPSCs frequency occurred during the immediate-early reperfusion period after the ischemic insult. We found a significant positive correlation between cumulative sEPSCs and the number of dead CA1 neurons (r = 0.70; p = 0.02). Ischemic PostC significantly suppressed this surge of sEPSCs. The mitochondrial K_ATP (mito-K_ATP) channel opener, diazoxide, also suppressed the surge of sEPSCs when applied for 15 min immediately after the ischemic load. The mito-K_ATP channel blocker, 5-hydroxydecanoate (5-HD), significantly attenuated the suppressive effect of both ischemic PostC and diazoxide application on the surge of sEPSCs. These results suggest that the opening of mito-K_ATP channels is involved in the suppressive effect of ischemic PostC on synaptic glutamate release and protection against neuronal death. We hypothesize that activation of mito-K_ATP channels prevents mitochondrial malfunction and breaks mutual facilitatory coupling between glutamate release and Ca²⁺ entry at presynaptic sites.

Neuroprotective Mechanism of Hypoxic Post-conditioning Involves HIF1-Associated Regulation of the Pentose Phosphate Pathway in Rat Brain

Post-conditioning is exposure of an injured organism to the same harmful factors but of milder intensity which mobilizes endogenous protective mechanisms. Recently, we have developed a novel noninvasive post-conditioning (PostC) protocol involving three sequential episodes of mild hypobaric hypoxia which exerts pronounced neuroprotective action. In particular, it prevents development of pathological cascades caused by severe hypobaric hypoxia (SH) such as cellular loss, lipid peroxidation, abnormal neuroendocrine responses and behavioural deficit in experimental animals. Development of these post-hypoxic pathological effects has been associated with the delayed reduction of hypoxia-inducible factor 1 (HIF1) regulatory α-subunit levels in rat hippocampus, whereas PostC up-regulated it. The present study has been aimed at experimental examination of the hypothesis that intrinsic mechanisms underlying the neuroprotective and antioxidant effects of PostC involves HIF1-dependent stimulation of the pentose phosphate pathway (PPP). We have observed that SH leads to a decrease of glucose-6-phosphate dehydrogenase (G6PD) activity in the hippocampus and neocortex of rats as well as to a reduction in NADPH and total glutathione levels. This depletion of the antioxidant defense system together with excessive lipid peroxidation during the reoxygenation phase resulted in increased oxidative stress and massive cellular death observed after SH. In contrast, PostC led to normalization of G6PD activity, stabilization of the NADPH and total glutathione levels and thereby resulted in recovery of the cellular redox state and prevention of neuronal death. Our data suggest that stabilization of the antioxidant system via HIF1-associated PPP regulation represents an important neuroprotective mechanism enabled by PostC.

Sodium hydrosulfide attenuates cerebral ischemia/reperfusion injury by suppressing overactivated autophagy in rats

Ischemic stroke is a leading cause of death and disability worldwide, and autophagy may be involved in the pathological process of cerebral ischemia/reperfusion injury. Hydrogen sulfide (H₂S) is an endogenous gasotransmitter with protective effects against multiple diseases. Here, we tested the effect of H₂S on cerebral ischemia/reperfusion injury in rats. Sodium hydrosulfide (NaHS), an H₂S donor, improved neurological function and reduced the size of the infarcts induced by transient middle cerebral artery occlusion (MCAO) followed by reperfusion in rats. NaHS treatment reduced the lactate dehydrogenase (LDH) activity in the serum (a marker of cellular membrane integrity) and the expression of cleaved caspase-3 (a marker for apoptosis) in the brains of MCAO rats. We also found that autophagy was overactivated in the brains of MCAO rats, as indicated by an increased ratio of LC3 II to I, decreased expression of p62, and transmission electron microscope detection. NaHS treatment significantly inhibited the autophagic activity in the brains of MCAO rats. Furthermore, PC12 cells were subjected to oxygen-glucose deprivation/reoxygenation (OGD/R) to mimic MCAO in vitro. We found that NaHS treatment reduced cellular injury and suppressed overactivated autophagy induced by OGD/R in PC12 cells. An autophagy stimulator (rapamycin) eliminated the protective effect of NaHS against LDH release and caspase-3 activity induced by OGD/R in PC12 cells. An autophagy inhibitor (3-methyladenine, 3-MA) also reduced the cellular injury induced by OGD/R in PC12 cells. In conclusion, the results indicate that overactivated autophagy accelerates cellular injury after MCAO in rats and that exogenous H₂S attenuates cerebral ischemia/reperfusion injury via suppressing overactivated autophagy in rats.

Adaptive preconditioning in neurological diseases - therapeutic insights from proteostatic perturbations

In neurological disorders, both acute and chronic neural stress can disrupt cellular proteostasis, resulting in the generation of pathological protein. However in most cases, neurons adapt to these proteostatic perturbations by activating a range of cellular protective and repair responses, thus maintaining cell function. These interconnected adaptive mechanisms comprise a 'proteostasis network' and include the unfolded protein response, the ubiquitin proteasome system and autophagy. Interestingly, several recent studies have shown that these adaptive responses can be stimulated by preconditioning treatments, which confer resistance to a subsequent toxic challenge - the phenomenon known as hormesis. In this review we discuss the impact of adaptive stress responses stimulated in diverse human neuropathologies including Parkinson׳s disease, Wolfram syndrome, brain ischemia, and brain cancer. Further, we examine how these responses and the molecular pathways they recruit might be exploited for therapeutic gain. This article is part of a Special Issue entitled SI:ER stress.

Neuroprotective effect of Shenqi Fuzheng injection pretreatment in aged rats with cerebral ischemia/reperfusion injury

Shenqi Fuzheng injection is extracted from the Chinese herbs Radix Astragali and Radix Codonopsis. The aim of the present study was to investigate the neuroprotective effects of Shenqi Fuzheng injection in cerebral ischemia and reperfusion. Aged rats (20–22 months) were divided into three groups: sham, model, and treatment. Shenqi Fuzheng injection or saline (40 mL/kg) was injected into the tail vein daily for 1 week, after which a cerebral ischemia/reperfusion injury model was established. Compared with model rats that received saline, rats in the treatment group had smaller infarct volumes, lower brain water and malondialdehyde content, lower brain Ca²⁺ levels, lower activities of serum lactate dehydrogenase and creatine kinase, and higher superoxide dismutase activity. In addition, the treatment group showed less damage to the brain tissue ultrastructure and better neurological function. Our findings indicate that Shenqi Fuzheng injection exerts neuroprotective effects in aged rats with cerebral ischemia/reperfusion injury, and that the underlying mechanism relies on oxygen free radical scavenging and inhibition of brain Ca²⁺ accumulation.

Neuroprotective effects of rutaecarpine on cerebral ischemia reperfusion injury

Rutaecarpine, an active component of the traditional Chinese medicine Tetradium ruticarpum, has been shown to improve myocardial ischemia reperfusion injury. Because both cardiovascular and cerebrovascular diseases are forms of ischemic vascular disease, they are closely related. We hypothesized that rutaecarpine also has neuroprotective effects on cerebral ischemia reperfusion injury. A cerebral ischemia reperfusion model was established after 84, 252 and 504 μg/kg carpine were given to mice via intraperitoneal injection, daily for 7 days. Results of the step through test, 2,3,5-triphenyl tetrazolium chloride dyeing and oxidative stress indicators showed that rutaecarpine could improve learning and memory ability, neurological symptoms and reduce infarction volume and cerebral water content in mice with cerebral ischemia reperfusion injury. Rutaecarpine could significantly decrease the malondialdehyde content and increase the activities of superoxide dismutase and glutathione peroxidase in mouse brain. Therefore, rutaecarpine could improve neurological function following injury induced by cerebral ischemia reperfusion, and the mechanism of this improvement may be associated with oxidative stress. These results verify that rutaecarpine has neuroprotective effects on cerebral ischemia reperfusion in mice.

Ischemic postconditioning relieves cerebral ischemia and reperfusion injury through activating T-LAK cell-originated protein kinase/protein kinase B pathway in rats

BACKGROUND AND PURPOSE

Ischemic postconditioning (IPostC) protects against ischemic brain injury. To date, no study has examined the role of T-LAK-cell-originated protein kinase (TOPK) in IPostC-afforded neuroprotection. We explored the molecular mechanism related with TOPK in antioxidant effect of IPostC against ischemia/reperfusion.

METHODS

Focal ischemia was induced in rats by transient middle cerebral artery occlusion. Reactive oxygen species production in the peri-infarct cortex was detected using dihydroethidium. Malondialdehyde, as a marker of lipid peroxidation, and 3-nitrotyrosine, as a marker of protein oxidation, were detected by ELISA. The expression or location of antioxidant proteins and signal molecules TOPK, phosphatase, and tensin homolog, and Akt was analyzed by Western blotting and immunofluorescence.

RESULTS

Our results revealed that IPostC relieved transient middle cerebral artery occlusion-induced oxidative damage by reducing reactive oxygen species, malondialdehyde, and 3-nitrotyrosine accumulation in the peri-infarct cortex and raised levels of antioxidants perioxiredoxin-1, peroxiredoxin-2, and thioredoxin-1. In addition, IPostC increased p-AKT and p-TOPK levels, which colocalized in neural cells. In vitro TOPK knockdown by small interfering RNA decreased the levels of antioxidants peroxiredoxin-1, thioredoxin, and manganese superoxide dismutase activity in PC12 cells. In vivo intracerebroventricular injection of TOPK small interfering RNA reversed IPostC-induced neuroprotection by increasing infarct volume and nitric oxide content and reducing manganese superoxide dismutase activity. Moreover, IPostC-evoked Akt activation was blocked by TOPK small interfering RNA in vivo, but the decreased phosphorylated phosphatase and tensin homolog level in ischemia/reperfusion was not influenced by IPostC or by TOPK small interfering RNA treatment.

CONCLUSIONS

Our results suggest that the antioxidative effects of TOPK/Akt might contribute to the neuroprotection of IPostC treatment against transient middle cerebral artery occlusion.

Advances in research of the neuroprotective mechanisms of cerebral ischemic postconditioning

Ischemic postconditioning refers to controlling reperfusion blood flow during reperfusion after ischemia, which can induce an endogenous neuroprotective effect and reduce ischemia-reperfusion injury. Activation of endogenous neuroprotective mechanisms plays a key role in protecting against brain ischemia-reperfusion injury. The mechanisms of cerebral ischemic postconditioning are not completely clear, and the following aspects may be involved: downregulation of oxidative stress, attenuating mitochondrial dysfunction, attenuating endoplasmic reticulum stress, accelerating the elimination of glutamate, increasing rCBF, inhibiting apoptosis, inhibiting autophagy, and regulating signal transduction.

Protection of ischemic postconditioning against neuronal apoptosis induced by transient focal ischemia is associated with attenuation of NF-κB/p65 activation

Background and Purpose

Accumulating evidences have demonstrated that nuclear factor κB/p65 plays a protective role in the protection of ischemic preconditioning and detrimental role in lethal ischemia-induced programmed cell death including apoptosis and autophagic death. However, its role in the protection of ischemic postconditioning is still unclear.

Methods

Rat MCAO model was used to produce transient focal ischemia. The procedure of ischemic postconditioning consisted of three cycles of 30 seconds reperfusion/reocclusion of MCA. The volume of cerebral infarction was measured by TTC staining and neuronal apoptosis was detected by TUNEL staining. Western blotting was used to analyze the changes in protein levels of Caspase-3, NF-κB/p65, phosphor- NF-κB/p65, IκBα, phosphor- IκBα, Noxa, Bim and Bax between rats treated with and without ischemic postconditioning. Laser scanning confocal microscopy was used to examine the distribution of NF-κB/p65 and Noxa.

Results

Ischemic postconditioning made transient focal ischemia-induced infarct volume decrease obviously from 38.6%±5.8% to 23.5%±4.3%, and apoptosis rate reduce significantly from 46.5%±6.2 to 29.6%±5.3% at reperfusion 24 h following 2 h focal cerebral ischemia. Western blotting analysis showed that ischemic postconditioning suppressed markedly the reduction of NF-κB/p65 in cytoplasm, but elevated its content in nucleus either at reperfusion 6 h or 24 h. Moreover, the decrease of IκBα and the increase of phosphorylated IκBα and phosphorylated NF-κB/p65 at indicated reperfusion time were reversed by ischemic postconditioning. Correspondingly, proapoptotic proteins Caspase-3, cleaved Caspase-3, Noxa, Bim and Bax were all mitigated significantly by ischemic postconditioning. Confocal microscopy revealed that ischemic postconditioning not only attenuated ischemia-induced translocation of NF-κB/p65 from neuronal cytoplasm to nucleus, but also inhibited the abnormal expression of proapoptotic protein Noxa within neurons.

Conclusions

We demonstrated in this study that the protection of ischemic postconditioning on neuronal apoptosis caused by transient focal ischemia is associated with attenuation of the activation of NF-κB/p65 in neurons.

Ischemic postconditioning protects the neurovascular unit after focal cerebral ischemia/reperfusion injury

Recently, cerebral ischemic postconditioning (Postcond) has been shown to reduce infarction volume in cerebral ischemia/reperfusion (I/R) injury. However, it is unclear if ischemic Postcond offers more extensive neuroprotection than current therapies. The aim of this study was to investigate the neuroprotective effects of ischemic Postcond on the neurovascular unit (NVU). A middle cerebral artery occlusion rat model was used; cerebral infarct volumes, neurologic scores, and transmission electron microscopy were evaluated 24 h after reperfusion. We used Evans blue extravasation, immunohistochemistry, and Western blot analyses to evaluate the integrity of the blood brain barrier (BBB) and the distribution and expression of the tight junction (TJ)-associated proteins of claudin-5 and occludin in brain microvessel endothelium. The Postcond group showed significantly reduced infarct volumes and decreased neurologic impairment scores compared to the I/R group. Also, injuries to the cerebral microvascular endothelial cells, astrocytes, and neurons were minimized in the Postcond group. The permeability of the BBB increased in both the I/R and Postcond groups, but the Postcond group showed a significant decrease in permeability than the I/R group. Expression of both claudin-5 and occludin were higher in the Postcond groups compared to the I/R group, but expression of both proteins decreased in the I/R and Postcond groups compared to the sham group. The results of our study suggest that ischemic Postcond is an effective way to reduce injury to neurons, astrocytes, and endothelial cells, to increase protein expressions of TJ-associated proteins, and to improve BBB intergrity affected by focal I/R. Ischemic Postcond could protect the NVU from I/R injury.

Role of the ubiquitin-proteasome system in brain ischemia: friend or foe?

The ubiquitin-proteasome system (UPS) is a catalytic machinery that targets numerous cellular proteins for degradation, thus being essential to control a wide range of basic cellular processes and cell survival. Degradation of intracellular proteins via the UPS is a tightly regulated process initiated by tagging a target protein with a specific ubiquitin chain. Neurons are particularly vulnerable to any change in protein composition, and therefore the UPS is a key regulator of neuronal physiology. Alterations in UPS activity may induce pathological responses, ultimately leading to neuronal cell death. Brain ischemia triggers a complex series of biochemical and molecular mechanisms, such as an inflammatory response, an exacerbated production of misfolded and oxidized proteins, due to oxidative stress, and the breakdown of cellular integrity mainly mediated by excitotoxic glutamatergic signaling. Brain ischemia also damages protein degradation pathways which, together with the overproduction of damaged proteins and consequent upregulation of ubiquitin-conjugated proteins, contribute to the accumulation of ubiquitin-containing proteinaceous deposits. Despite recent advances, the factors leading to deposition of such aggregates after cerebral ischemic injury remain poorly understood. This review discusses the current knowledge on the role of the UPS in brain function and the molecular mechanisms contributing to UPS dysfunction in brain ischemia with consequent accumulation of ubiquitin-containing proteins. Chemical inhibitors of the proteasome and small molecule inhibitors of deubiquitinating enzymes, which promote the degradation of proteins by the proteasome, were both shown to provide neuroprotection in brain ischemia, and this apparent contradiction is also discussed in this review.

Role of mitochondrial function in the protective effects of ischaemic postconditioning on ischaemia/reperfusion cerebral damage

Objective

To investigate the effects of ischaemic postconditioning on brain injury and mitochondria in focal ischaemia and reperfusion, in rats.

Methods

Adult male Wistar rats ( n = 15 per group) underwent sham surgery, ischaemia (2-h middle cerebral artery occlusion), or ischaemia followed by ischaemic postconditioning (three cycles of 30 s reperfusion/30 s reocclusion). Brain infarction size, neurological function, mitochondrial reactive oxygen species (ROS) production, mitochondrial membrane potential and mitochondrial swelling were evaluated 24 h postsurgery.

Results

Infarct size was significantly smaller, and neurological function was significantly better, in the ischaemic postconditioning group than in the ischaemia group. Ischaemia resulted in significant increases in mitochondrial ROS production and swelling, and a reduction in mitochondrial membrane potential, all of which were significantly reversed by postconditioning.

Conclusions

The protective role of ischaemic postconditioning in focal ischaemia/reperfusion may be due to decreased mitochondrial ROS production, reduced mitochondrial membrane potential and suppressed mitochondria swelling. Mitochondria are potential targets for new therapies to prevent brain damage caused by ischaemia and reperfusion.

Ischemic postconditioning decreases cerebral edema and brain blood barrier disruption caused by relief of carotid stenosis in a rat model of cerebral hypoperfusion

Background and Purpose

Complications due to brain edema and breakdown of blood brain barrier are an important factor affecting the treatment effects of patients with severe carotid stenosis. In this study, we investigated the protective effects of ischemic postconditioning on brain edema and disruption of blood brain barrier via establishing rat model of hypoperfusion due to severe carotid stenosis.

Methods

Wistar rat model of hypoperfusion due to severe carotid stenosis was established by binding a stainless microtube to both carotid arteries. Ischemic postconditioning procedure consisted of three cycles of 30 seconds ischemia and 30 seconds reperfusion. Brain edema was evaluated by measuring cerebral water content, and blood brain barrier permeability was assayed by examining cerebral concentration of Evans' Blue (EB) and fluorescein sodium (NaF). ELISA was used to analyze the expression of MMP-9, claudin-5 and occludin. The activity and location of MMP-9 was analyzed by gelatin zymography and in situ zymography, respectively. The distribution of tight junction proteins claudin-5 and occludin was observed by immunohistochemistry.

Results

The increased brain water content and cerebral concentration of EB and NaF were suppressed by administration of ischemic postconditioning prior to relief of carotid stenosis. Zymographic studies showed that MMP-9 was mainly located in the cortex and its activity was significantly improved by relief of carotid stenosis and, but the elevated MMP-9 activity was inhibited markedly by ischemic postconditioning. Immunohistochemistry revealed that ischemic postconditioning improved the discontinuous distribution of claudin-5 and occludin. ELISA detected that the expression of up-regulated MMP-9 and down-regulated claudin-5 and occludin caused by carotid relief were all attenuated by ischemic postconditioning.

Conclusions

Ischemic postconditioning is an effective method to prevent brain edema and improve BBB permeability and could be used during relief of severe carotid stenosis.

Ischemic postconditioning alleviates neuronal injury caused by relief of carotid stenosis in a rat model of cerebral hypoperfusion

The effects of early relief of heavy bilateral carotid stenosis and ischemic postconditioning on hippocampus CA1 neurons are still unclear. In this study, we used a rat model to imitate severe bilateral carotid stenosis in humans. The rats were divided into sham group, carotid stenosis group, stenosis relief group and ischemic postconditioning group. Ischemic postconditioning consisted of three cycles of 30 s ischemia and 30 s reperfusion. The cerebral blood flow was measured with a laser Doppler flowmeter. Neuronal death in the CA1 region was observed by hematoxylin-eosin staining, and the number of live neurons was assessed by cell counting under a light microscope. The levels of oxidative products MDA and 8-iso-PGF2α, inflammatory factors IL-1β and TNF-α, and the activities of anti-oxidative enzymes SOD and CAT were assayed by specific enzyme-linked immunosorbent assay (ELISA) kits, respectively. We found that relief of carotid stenosis and ischemic postconditioning could increase cerebral blood flow. When stenosis was relieved, the percentage of live neurons was 66.6% ± 6.2% on day 3 and 62.3% ± 9.8% on day 27, which was significantly higher than 55.5% ± 4.8% in stenosis group. Ischemic postconditioning markedly improved the live neurons to 92.5% ± 6.7% on day 3 and 88.6% ± 9.1% on day 27. Further study showed that, neuronal death caused by relief of stenosis is associated with increased oxidative stress and enhanced inflammatory response, and the protection of ischemic postconditioning is related to inhibition of oxidative stress and suppression of inflammatory response.

Ischemic postconditioning protects neuronal death caused by cerebral ischemia and reperfusion via attenuating protein aggregation

OBJECTIVE

To investigate the effect of ischemic postconditioning on protein aggregation caused by transient ischemia and reperfusion and to clarify its underlying mechanism.

METHODS

Two-vessel-occluded transient global ischemia rat model was used. The rats in ischemic postconditioning group were subjected to three cycles of 30-s/30-s reperfusion/clamping after 15 min of ischemia. Neuronal death in the CA1 region was observed by hematoxylin-eosin staining, and number of live neurons was assessed by cell counting under a light microscope. Succinyl-LLVY-AMC was used as substrate to assay proteasome activity in vitro. Protein carbonyl content was spectrophotometrically measured to analyze protein oxidization. Immunochemistry and laser scanning confocal microscopy were used to observe the distribution of ubiquitin in the CA1 neurons. Western blotting was used to analyze the quantitative alterations of protein aggregates, proteasome, hsp70 and hsp40 in cellular fractions under different ischemic conditions.

RESULTS

Histological examination showed that the percentage of live neurons in the CA1 region was elevated from 5.21% ± 1.21% to 55.32% ± 5.34% after administration of ischemic postconditioning (P = 0.0087). Western blotting analysis showed that the protein aggregates in the ischemia group was 32.12 ± 4.87, 41.86 ± 4.71 and 34.51 ± 5.18 times higher than that in the sham group at reperfusion 12h, 24h and 48h, respectively. However, protein aggregates were alleviated significantly by ischemic postconditioning to 2.84 ± 0.97, 13.72 ± 2.13 and 14.37 ± 2.42 times at each indicated time point (P = 0.000032, 0.0000051 and 0.0000082). Laser scanning confocal images showed ubiquitin labeled protein aggregates could not be discerned in the ischemic postconditioning group. Further study showed that ischemic postconditioning suppressed the production of carbonyl derivatives, elevated proteasome activity that was damaged by ischemia and reperfusion, increased the expression of chaperone hsp70, and maintained the quantity of chaperone hsp40.

CONCLUSION

Ischemic postconditioning could rescue significantly neuronal death in the CA1 region caused by transient ischemia and reperfusion, which is closely associated with suppressing the formation of protein aggregation.